USF Libraries
USF Digital Collections

Relationship of waste characteristics to the formation of mineral deposits in leachate collection systems

MISSING IMAGE

Material Information

Title:
Relationship of waste characteristics to the formation of mineral deposits in leachate collection systems
Physical Description:
Book
Language:
English
Creator:
Cardoso, Antonio J
Publisher:
University of South Florida
Place of Publication:
Tampa, Fla.
Publication Date:

Subjects

Subjects / Keywords:
Clogging
Co-disposal
Leachate collection systems
Lysimeter
Municipal solid waste
Wte combustion residues
Precipitates
Waste-to-energy
Dissertations, Academic -- Environmental Engineering -- Masters -- USF   ( lcsh )
Genre:
government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
ABSTRACT: Landfill leachate is generated as a result of reactions between water percolating through the landfill and wastes. Under normal conditions leachate is found at the bottom of landfills and from there, its movement can be controlled with collection systems to be treated, discharged, or recirculated. Landfill leachate collection systems are positioned above the liner and are designed to collect liquid under gravitational flow for the entire active, closure, and post-closure periods. Clogging of any portion of the system can lead to higher hydraulic heads and increase the potential for leakage through the liner. To reduce the quantity of municipal solid wastes (MSW) requiring landfilling, many municipalities have adopted waste-to-energy (WTE) facilities that yield energy in the form of combustible gases and noncombustible residues.Disposal practices for WTE residuals include landfilling in monofills or co-disposal with MSW and other materials such as residues from water and wastewater treatment facilities. There has been concern about co-disposal practices, because the impacts on leachate quality and waste interactions are not well known yet. This research was conducted to evaluate clogging of leachate collection systems due to co-disposal of MSW and combustion residues from WTE facilities. The use of laboratory lysimeters in conjunction with batch tests to predict short-term and long-term leaching characteristics of noncombustible residues from WTE facilities was also evaluated. Laboratory lysimeters were used to simulate monofills (WTE residues and MSW) and co-disposal practices. Relationships between waste composition and leachate quality were evaluated over a seven month period.
Thesis:
Thesis (M.S.E.E.)--University of South Florida, 2005.
Bibliography:
Includes bibliographical references.
System Details:
System requirements: World Wide Web browser and PDF reader.
System Details:
Mode of access: World Wide Web.
Statement of Responsibility:
by Antonio J. Cardoso.
General Note:
Title from PDF of title page.
General Note:
Document formatted into pages; contains 114 pages.

Record Information

Source Institution:
University of South Florida Library
Holding Location:
University of South Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 001670393
oclc - 62333241
usfldc doi - E14-SFE0001266
usfldc handle - e14.1266
System ID:
SFS0025587:00001


This item is only available as the following downloads:


Full Text
xml version 1.0 encoding UTF-8 standalone no
record xmlns http:www.loc.govMARC21slim xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.loc.govstandardsmarcxmlschemaMARC21slim.xsd
leader nam Ka
controlfield tag 001 001670393
003 fts
005 20051216093347.0
006 m||||e|||d||||||||
007 cr mnu|||uuuuu
008 051123s2005 flu sbm s000 0 eng d
datafield ind1 8 ind2 024
subfield code a E14-SFE0001266
035
(OCoLC)62333241
SFE0001266
040
FHM
c FHM
049
FHMM
090
TA170 (Online)
1 100
Cardoso, Antonio J.
0 245
Relationship of waste characteristics to the formation of mineral deposits in leachate collection systems
h [electronic resource] /
by Antonio J. Cardoso.
260
[Tampa, Fla.] :
b University of South Florida,
2005.
502
Thesis (M.S.E.E.)--University of South Florida, 2005.
504
Includes bibliographical references.
516
Text (Electronic thesis) in PDF format.
538
System requirements: World Wide Web browser and PDF reader.
Mode of access: World Wide Web.
500
Title from PDF of title page.
Document formatted into pages; contains 114 pages.
520
ABSTRACT: Landfill leachate is generated as a result of reactions between water percolating through the landfill and wastes. Under normal conditions leachate is found at the bottom of landfills and from there, its movement can be controlled with collection systems to be treated, discharged, or recirculated. Landfill leachate collection systems are positioned above the liner and are designed to collect liquid under gravitational flow for the entire active, closure, and post-closure periods. Clogging of any portion of the system can lead to higher hydraulic heads and increase the potential for leakage through the liner. To reduce the quantity of municipal solid wastes (MSW) requiring landfilling, many municipalities have adopted waste-to-energy (WTE) facilities that yield energy in the form of combustible gases and noncombustible residues.Disposal practices for WTE residuals include landfilling in monofills or co-disposal with MSW and other materials such as residues from water and wastewater treatment facilities. There has been concern about co-disposal practices, because the impacts on leachate quality and waste interactions are not well known yet. This research was conducted to evaluate clogging of leachate collection systems due to co-disposal of MSW and combustion residues from WTE facilities. The use of laboratory lysimeters in conjunction with batch tests to predict short-term and long-term leaching characteristics of noncombustible residues from WTE facilities was also evaluated. Laboratory lysimeters were used to simulate monofills (WTE residues and MSW) and co-disposal practices. Relationships between waste composition and leachate quality were evaluated over a seven month period.
590
Adviser: Audrey D. Levine, Ph.D.
653
Clogging.
Co-disposal.
Leachate collection systems.
Lysimeter.
Municipal solid waste.
Wte combustion residues.
Precipitates.
Waste-to-energy.
690
Dissertations, Academic
z USF
x Environmental Engineering
Masters.
773
t USF Electronic Theses and Dissertations.
4 856
u http://digital.lib.usf.edu/?e14.1266



PAGE 1

Relationship of Waste Characte ristics to the Formation of Mineral Deposits in Leachate Collection Systems by Antonio J. Cardoso A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Environmental Engineering Department of Civil and Environmental Engineering College of Engineering University of South Florida Major Professor: Audrey D. Levine, Ph.D. Valerie J. Harwood, Ph.D. Robert P. Carnahan, Ph.D. Date of Approval: July 14, 2005 Keywords: clogging, co-disposal, leachate, lysi meter, precipitates, waste-to-energy Copyright 2005 Antonio J. Cardoso

PAGE 2

Dedication I would like to dedicate this thesis to my family. No matter the distance, they have been one of the most important parts of this journey.

PAGE 3

Acknowledgements I would like to start by thanking my major professor, Dr. Audrey D. Levine. Her guidance, help, and support thr oughout the past two years made this possible. I am very grateful for all the learning oppor tunities we shared, both in life and professional growth. The help provided by Dr. Valerie J. Harw ood on this thesis is highly appreciated. Her leadership on the microbiological aspe cts of this project is treasured. I would also like to thank Dr. Robert P. Carnahan for being part of this quest, both as a committee member and as a professor in the classroom. I feel honored for the opportunity to work with Lisa R. Rhea on this project. Thank you not only for providing the necessary da ta on the batch tests, but also for being a friend. I am also thankful for having Bina Na yak as part of this research team. Thanks for all the hard work and the informa tion on the microbiological analyses. Thanks to all people who made life possibl e in the laboratory, especially Barbara M. Dodge, Mindy L. Decker, Cecilia M. Cla udio, George Dzama, and Lawrence Jones. I also appreciate the support of all my friends who, in one way or another, helped me and guided me through this process. I would like to recognize the Florida Center for Solid and Hazardous Waste, Camp, Dresser & McKee (CDM), and the So lid Waste Authority of Palm Beach County (SWA) for funding the main project, Assessmen t of Biogeochemical Deposits in Landfill Leachate Drainage Systems.

PAGE 4

i Table of Contents List of Tables................................................................................................................. ....iii List of Figures................................................................................................................ .....v Abstract....................................................................................................................... ......vii Introduction................................................................................................................... ......1 Objectives..................................................................................................................... ......4 Literature Review.............................................................................................................. ..5 Engineered Landfills...............................................................................................5 Landfill Leachate....................................................................................................7 Leachate Characteristics.............................................................................7 Factors Affecting Leachate Composition.................................................10 Regulatory Requirements for La ndfill Leachate Management.............................12 Leachate Collection Systems....................................................................12 Clogging of Leachate Collection Systems................................................15 Lysimeter Studies..................................................................................................20 Waste-to-Energy Residuals...................................................................................26 Ash Management and Disposal................................................................28 Leachate from WTE Combustion Residues..............................................29 Article 1: Lysimeter Comparison of the Role of Waste Characteristics in the Formation of Mineral Deposits in Leachate Drainage Systems..............................................32 Article 2: Assessment of Leachates Deri ved from Landfilling of Waste-to-Energy Residues: Implications for L eachate Collection Systems..................................59 Conclusions.................................................................................................................... ...80 Engineering Implications..................................................................................................82 Additional Research..........................................................................................................84

PAGE 5

iiReferences..................................................................................................................... ....86 Appendices..................................................................................................................... ...93 Appendix A: Chemical Ch aracterization Tests..................................................94 Appendix B: Lysimeter St ar-up and Operation.................................................96 Appendix C: Summary of Leachate Characterstics from Laboratory LysimeterTests Conducted from May 5 through November 29, 2004..............98

PAGE 6

iii List of Tables Table 1: Summary of Relevant Aspects to be Considered in Landfill Design...................6 Table 2: Representative Data on the Characteristics of Landfill Leachates.......................9 Table 3: Summary of Factors A ffecting Leachate Composition......................................10 Table 4: Landfill Leachate Collection Sy stem Components Shown in Figure 1..............14 Table 5: Potential Clogging Mechanisms and Leachate Characteristics of Concern.......16 Table 6: Comparison of Composition of Material Precipitated in Landfill Leachate Collection Systems (Values Reported in Percentages).......................19 Table 7: Comparison of Types of Test s Used to Evaluate Waste Leaching Potentials............................................................................................................20 Table 8: Design Parameters Us ed in Lysimeter Studies...................................................22 Table 9: Operational Aspects of Lysimeter Studies.........................................................23 Table 10: Summary of Different Types of Ash Residues from a WTE Facility..............27 Table 11: Comparison of Leachate Quality from Ash Monofills.....................................30 Table 12: Representative Data on the Characteristics of Landfill Lachate......................35 Table 13: Design Parameters Us ed in Lysimeters Studies...............................................37 Table 14: Composition and Distribution of Waste Sources in the Lysimeters (by Mass)..................................................................................................................40 Table 15: Field Capacity of Each Type of Lysimeter.......................................................41 Table 16: Summary of the Chemical Test Performed on the Leachate Samples..............43 Table 17: Summary of Different Types of Ash Residues from a WTE Facility..............62 Table 18: Comparison of Leachate Quality from Ash Monofills.....................................63 Table 19: Tests Used to Characterize the Leaching Potential of Landfill Materials........64 Table 20: Summary of the Chemical Test s Performed on the Leachate Samples............69 Table 21: Summary of pH and Alkalinity for Lysimeter and Batch Tests Leachates............................................................................................................71

PAGE 7

iv Table 22: Summary of Concentrations (mg/ L) of Main Ions Present in Leachate Samples...............................................................................................................74 Table A-1: Conditions from Analyti cal Methods for Atomic Absorption Spectrometry, 2000. Perkin Elmer.....................................................................95 Table C-1: Lysimeter Leachate Monitoring Summary. Ash 1: 80% Bottom Ash, 20% Fly Ash.......................................................................................................99 Table C-2: Lysimeter Leachate Monitoring Summary. Ash 2: 80% Bottom Ash, 20% Fly Ash.....................................................................................................100 Table C-3: Lysimeter Leachate Mon itoring Summary. MSW: 100% MSW.................101 Table C-4: Lysimeter Leachate Monito ring Summary. Mix 1: 60% MSW, 30% WTE Ash, 10% Treatment Residuals...............................................................102 Table C-5: Lysimeter Leachate Monito ring Summary. Mix 2: 60% MSW, 30% WTE Ash, 10% Treatment Residuals...............................................................103

PAGE 8

v List of Figures Figure 1: Diagram of the Leachate Collec tion System of Engineered Landfills. Adapted from Rhea (2004).................................................................................13 Figure 2: Schematic of Lysimeter Design Used in this Study..........................................39 Figure 3: Leachate Application System Consisting of Inverted Funnel and Perforated Plate..................................................................................................39 Figure 4: Comparison of the pH and Alkalinity in Leachates from Lysimeters Containing Monofills or Co-disposal.................................................................45 Figure 5: Comparison of the Concentration of Total Volatile and Dissolved Solids in Leachates from Lysimeters Containing Monofills or Co-disposal................46 Figure 6: Comparison of Volatile Acid s and Microbial Concentrations in Leachates from Lysimeters Containing Monofills or Co-disposal.....................48 Figure 7: Comparison of the Calcium Concentrations in Leachates from Lysimeters Containing Monofills or Co-disposal.............................................49 Figure 8: Comparison of the Calcium/Al kalinity and Calcium/TDS Ratios in Leachates from Lysimeters Containing Monofills or Co-disposal.....................51 Figure 9: Photograph of Deposits in L eachate Collection Tubing from a.) MSW Monofill Lysimeter, and b.) Co-disposal Lysimeters. Tubing has an ID of 8 mm and OD of 10 mm................................................................................52 Figure 10: Scanning Electron Micrographs a nd Dominant Elements of Deposits in Leachate Collection Tubing from a.) MSW Monofill Lysimeter, and b.) Co-disposal Lysimeters......................................................................................53 Figure 11: Comparison of pH, Alkalinity, a nd the Calcium to TDS and Calcium to Alkalinity Ratios from Monitoring Data for Landfill (4 Years) and Lysimeters Leachates (7 Months)......................................................................55 Figure 12: Schematic of Lysimeter Design Used in this Study........................................66 Figure 13: Overview of Contact Time a nd Sequential Extractions Batch Tests..............68 Figure 14: Comparison of TDS Concen trations Leached from Combustion Residues in a.) Lysimeters; b.) C ontact Time Tests; c.) Sequential Extraction Tests; and d.) mg TDS/g Ash in Sequential Extraction Tests..........72

PAGE 9

viFigure 15: Comparison of Calcium Leach ed from Combustion Residues in a.) Lysimeters; b.) Contact Time Tests; c.) Ca/TDS Percent in Sequential Extraction Tests; and d.) mg Ca/g As h in Sequential Extraction Tests..............75 Figure 16: Comparison of Saturation Indi ces for Calcite (Left) and Gypsum (Right) from CT Batch Tests..............................................................................76 Figure 17: SEM/EDS Analysis of Precipi tates Formed from the Addition of Sulfuric Acid to Leachates from CT Tests at a L/S Mass Ratio of 10; a.) Bottom Ash, and b.) Fly Ash..............................................................................77

PAGE 10

vii Relationship of Waste Characteristics to the Formation of Mineral Deposits in Leachate Collection Systems Antonio J. Cardoso ABSTRACT Landfill leachate is generated as a result of reactions between water percolating through the landfill and wastes. Under normal c onditions leachate is found at the bottom of landfills and from there, its movement can be controlled with collection systems to be treated, discharged, or recirculated. Landf ill leachate collection systems are positioned above the liner and are designed to collect liquid under gravitational flow for the entire active, closure, and post-closure periods. Cloggi ng of any portion of the system can lead to higher hydraulic heads a nd increase the potential fo r leakage through the liner. To reduce the quantity of municipal so lid wastes (MSW) requiring landfilling, many municipalities have adopted waste-to-ene rgy (WTE) facilities th at yield energy in

PAGE 11

viii the form of combustible gases and noncombus tible residues. Disposal practices for WTE residuals include landfilling in monofills or co-disposal with MSW and other materials such as residues from water and wastewater treatment facilities. There has been concern about co-disposal practices, because th e impacts on leachate quality and waste interactions are not well known yet. This research was conducted to evaluate clogging of leachate collection systems due to co-disposal of MSW and combustion residues from WTE fac ilities. The use of laboratory lysimeters in conjunction with batc h tests to predict short-term and long-term leaching characteristics of noncombustible residues from WTE facilities was also evaluated. Laboratory lysimeters were used to simulate monofills (WTE residues and MSW) and co-disposal practices. Relationships be tween waste composition and leachate quality were evaluated over a seven month period. In addition, two different types of batch tests were used to analyze the leaching behavior of combustion residues from three different WTE facilities in Florida. Data from this research produced a bette r understanding of the implication of codisposal of MSW and WTE re siduals in the production of precipitates in leachate collection systems. Lysimeter and batch tests proved to be useful tools for simulation of field conditions and predicting the degree to which WTE residuals contribute inorganic constituents to the leachate matrix.

PAGE 12

1 Introduction Land disposal of solid waste has been practiced for centuries. In the past, constituents leached from solid waste were considered to be attenuated by soil and groundwater. However, since the 1950s a nd due to increasing concerns for the environment, landfills have come under scru tiny and waste dumps have been transformed into engineered landfills (Bagchi, 19 90). In addition, many municipalities have implemented the use of Waste-to-Energy (WTE) facilities with the goal of reducing the net volume and mass of wastes prior to la ndfilling while producing energy through mass burn or Refuse Derived Fuel (RDF) practices (FDEP, 2000). Byproducts of thermal processing of solid waste include combustion gases, bottom and fly ash residues, a nd recoverable materials such as ferrous and nonferrous metals. Management approaches for ashes fr om WTE facilities in clude disposal in monofills, co-disposal with non-combusted Muni cipal Solid Waste (MSW) in landfills, or incorporation with ot her materials for various construc tion applications (Hjelmar, 1996). Typically, MSW landfills are permitted to receive a combination of MSW, fly and bottom ash from combustion processes, residua ls from waste and wastewater treatment facilities, construction wastes, and other materials (USEPA, 2004). In landfills, leachate is generated as a result of hydrological and biogeochemical reactions between water percolating thr ough the landfill and wastes. Leachate is composed of the liquid that enters the landf ill from external sources, such as surface drainage, rainfall, groundwater, and water from underground springs, liquid associate

PAGE 13

2 with the deposited wastes, and liquid produced from waste decomposition. Leachate composition changes as wastes degrade infl uencing microbial activity, solubility, and partitioning of many constituents (J ohnson et al., 1999; Kylefors, 2003). Leachate collection systems play an impor tant role in landfill management to control the build up of leachate within the landfill and limit the advective flow of leachate through the liner system. Properly functioni ng, leachate collection systems serve to reduce potential for groundw ater contamination and c ontrol the mass loading of contaminants available to pass through th e barrier system (Rowe et al., 2002). The current design concept for engineered la ndfills consists of constructing a low permeability liner below the landfill to restrict leachate percolation, a nd a perforated pipe system within a granular drainage blanke t to collect leachate generated within the landfills (USEPA, 1993). A potential difficulty in landfill leachate co llection systems is that solid material may deposit and accumulate in the pore spaces of drainage materials and in the perforated collection pipes, leading to clogging (Reinhardt and Town send, 1998; Maliva et al., 2000; Rowe et al., 2002). Factors that have been implicated in promoting clogging of leachate collection systems include sedi mentation and deposition of fi nes, biological activity, and biogeochemical precipitation (Paksy et at., 1998). In this thesis, a lysimeter study on the formation of biogeochemical deposits in leachate collection systems is presented. Inst ead of the traditional Results and Discussion section, two articles are used to illustrate so me of the factors aff ecting the formation of precipitates in leachate collection systems. The relationship of waste composition and leachate quality is presented in the first article, in which th e clogging of leachate collection systems due to co-disposal of MSW, WTE combustion residues, and byproducts from water and wastewater treatment is evaluated. The second article deals with the leaching behavior a nd the role of combustion resi dues from WTE facilities for

PAGE 14

3 providing calcium and other minerals, influencin g the formation of precipitates that may cause malfunction of leac hate collection systems. Limited information is available on th e specific mechanisms of clogging and the factors that influence reaction ra tes. From an engineering perspective, it is important to ensure that leachate collection systems re main operational throughout the lifespan and post-closure periods of landfills. Improve d understanding of biological and mineral clogging is needed to develop strategies fo r preventing clogging and reducing the failure potential of the landfill ba rriers (Bennett et al., 2000).

PAGE 15

4 Objectives This project was conducted to investigate the impact of co-dis posal of municipal solid waste (MSW), waste-to-energy (WTE) combustion residues, and residuals from water and wastewater treatment, and associ ated characteristics of leachate on the development of mineral precipitates that lead to clogging of leachate collection systems. The specific objectives are: 1. Use of laboratory lysimeter tests to co mpare leachate characteristics from monofills of MSW or WTE combustion resi dues to leachates generated by codisposal of MSW, WTE combustion resi dues, and residuals from water and wastewater treatment. 2. Assess the use of laboratory lysimeters in conjunction with batch tests to predict short-term and long-term leaching charac teristics of combustion residues from WTE facilities. 3. Identify dominant chemical and biological factors that influence the formation of deposits in leachate collection systems.

PAGE 16

5 Literature Review A major issue associated with the disposal of municipal solid wastes in landfills is the management of leachates generated fr om reactions between waste materials and rainfall or other sources of moisture. In this section, the compos ition and formation of landfill leachates are discussed and relevant State and Federal regulatory requirements for landfill leachate management are presented. An area of concern in the operation of engineered landfill is the potential for clogg ing of the leachate collection systems and therefore, a review of prev ious research on the development of biogeochemical deposits in landfill leachate drainage systems is pres ented. A comparison of field and laboratory studies that used lysimeters to determine the effect of different factors on leachate composition and clog development is also prov ided. Finally, the literature review is concluded with a discussion on waste-to -energy (WTE) comb ustion residuals. Engineered Landfills Landfilling or land disposal is the most commonly used method for disposal of municipal solid wastes around the world. The planning, design, and operation of landfills involve the application of scientific, engine ering, and economic principles (Bagchi, 1990; Tchobanoglous et al., 1993). The construction an d design of landfills is influenced by the topography, the hydrology, and pot ential environmental constraints associated with management of the landfill site.

PAGE 17

6 Landfills are engineered to prevent a nd control risks to human health and minimize the potential for negative effects on the environment associated with solid waste disposal. Landfill practice is dynamic in that it will change with both advances in technology and changes in regulations (E PA Ireland, 2000). A summ ary of relevant aspects to be considered in the design of engineered landfills is presented in Table 1. Table 1. Summary of Relevant Aspects to be Considered in Landfill Design. Aspect Consideration Nature and quantity of wastes The waste types accepted at the landfill dictates the control measures required. Quantities and rate of waste input determine the life of the site. Water control To reduce leachate generation, control measures are required to minimize the quantity of water contacting the landfill waste. Protection of soil and water A liner must be provided to prevent leachate migration to soil, groundwater, and surface water. The liner must meet prescribed requirements. Leachate management Leachate collection systems must be provided to ensure that leachate accumu lation at the base of the landfill is kept to a minimum. Gas control The accumulation and migration of landfill gas must be controlled. Environmental nuisances Provisions must be incorporated to minimize and control nuisances such as odors, fires, noise, and dust. Stability The sub-grade and basal liner should be sufficiently stable to prevent excessive settlement. The method of waste emplacement should ensure stability of the waste mass against sliding and rotational failure. Adapted from EPA publication EPA625-R-01-012, Florida Administrative Code 62701.40000(4)(b), and EPA Ireland (2000). MSW landfills are permitted to receive a combination of MSW, bottom and fly ash from combustion processes, residuals from water and wastewater treatment facilities, construction wastes, and other material s (USEPA, 1993). Regulatory requirements stipulate that MSW landfills must have liner s and leachate collection systems to prevent the migration of leachate into groundwate r systems (USEPA, 1993). To better understand the potential for clogging of leachate collection systems, it is important to evaluate the

PAGE 18

7 composition and formation of landfill leachate, as well as current design and operating leachate management practices. Landfill Leachate Leachate is generated as a result of reactions betw een water percolating through the landfill and wastes. It results from a complex interplay between hydrological and biogeochemical processes. Leachate is composed of the liquid that enters the landfill from external sources, such as surface dr ainage, rainfall, groundw ater, and water from underground springs, liquid asso ciated with the deposited wastes, and liquid produced from waste decomposition. While hydrological processes determine the extent of leaching, biogeochemical processes of the matrix components determine the major solution variables (Bagchi, 1990; Johnson et al., 1999). Leachate generation from landfilled wastes occurs over time spans ranging from decades to centuries, depending on the si ze and depth of the landfill, precipitation patterns, and leachate management practices. Waste consolidation and pressure differentials promote the migration of leach ate through the landfill layers. Under normal conditions, leachate is found at the bottom of landfills and from there, although some lateral movement may also occur, its moveme nt can be controlled with collection systems to be treated, discharged, or recircul ated (Tchobanoglous and Kreith, 2002). Leachate Characteristics When water percolates through solid wa stes, biological materials and chemical constituents are mobilized into the liquid. Di ssolved and suspended materials in leachates are composed of varying concentrations of organic carbon, ammonia, chloride, iron,

PAGE 19

8 sodium, potassium, carbonates, and other cons tituents (Levine and Kroemer, 1989). The quality and quantity of leachate generate d in a landfill is influenced by waste characteristics, local precipitation pattern s, landfill age and lo cation, and other site specific variables (Peeling et at ., 1999; Johnson et al., 1999). The composition of the leachate is an i ndication of the state of the biological processes occurring within the waste matrix a nd the relative solubility of the chemical constituents. Movement of liquid through th e waste layers and collection systems can promote biological activity whic h, coupled with chemical reac tions, has the potential to produce mineral precipitates. Certain com pounds like sodium, potassium, and chloride are readily soluble and their concentrat ions do not change significantly during degradation processes, although an abundance of these ions does influence the ionic strength of the leachate (EPA Ireland, 2000; Rhea, 2004). Other ions such as calcium, iron, and magnesium are particularly important w ith respect to the precipitation of solids (Islam and Singhal, 2004; VanGulck et al., 2003 ; Rowe et al., 2002; Ma liva et al., 2000). As a landfill ages, changes in the quantity and quality of the leachate occur due to the establishment of microbial communities and the degradation and solubilization of constituents from the waste. Over the last th irty years, many factor s have contributed to changes in the composition of municipal solid waste and therefore, leachate (Rowe et al., 2002; Rhea, 2004). Representative data on the characteristics of landfill leachates are reported in Table 2.

PAGE 20

9Table 2. Representative Data on the Characteristics of Landfill Leachates. Parameter Units Bagchi (1990) Owen and Manning (1997) Kjeldsen et al. (2002) Levine et al. (2005) General pH pH units 3.7 8.9 6.3 8.1 4.5 9.0 5.8 7.8 Conductivity mS/cm n/a 1.1 29.3 2.5 35.0 5.0 20.7 Phosphorus, Total mg/L PO4 BDL 250 n/a 0.1 23.0 0.2 98.0 Solids, Total Dissolved mg/L TDS 584 55,000 1,558 91,057 n/a 3,202 14,975 Solids, Total Suspended mg/L TSS 2 140,900 n/a n/a n/a Biological Activity Indicators Alkalinity, Total mg/L as CaCO3 BDL 15,000 n/a n/a 350 9,500 Organic Carbon, Total mg/L TOC BDL 195,000 n/a 30 29,000 15 12,300 Volatile Acids mg/L as acetic acid n/a n/a n/a 8.3 1,950 Anions Chloride mg/L Cl 2 11,400 24 9,710 150 4,500 300 45,000 Sulphate mg/L SO4 BDL 1,900 5 1,720 8 7,750 BDL 1,000 Cations Calcium mg/L Ca 3 2,500 82 1,592 10 7,200 210 11,000 Iron mg/L Fe BDL 4,000 BDL 118.5 3.0 5,500 6.8 1,400 Magnesium mg/L Mg 4 780 41 1,290 30 15,000 0.01 377.5 Manganese mg/L Mn BDL 400 BDL 23.1 0.03 1,400 46 9,000 Potassium mg/L K BDL 3,200 11 1,450 50 3,700 66 67,000 Sodium mg/L Na 12 6,010 10 4,790 70 7,700 60 2,869 BDL = Below Detection Limits n/a = Not Available

PAGE 21

10 Factors Affecting Leachate Composition The variability of leachate character istics complicates design and operation practices for leachate management and tr eatment (Kjeldsen et al., 2002; Tchobanoglous et al., 1993). The quality and quantity of leachat e generated in a landfil l is influenced by waste characteristics, local precipitation patte rns, landfill age and location, and other site specific variables (Peeling et at. 1999; Johns on et al., 1999). A summary of the factors affecting leachate composition is presented in Table 3. Table 3. Summary of Factors A ffecting Leachate Composition. Factor Effect Comments Waste characteristics Determines the types of compounds that leach into solution. Controls the type and extent of biological activity within the landfill. Amount of water that can be absorbed depends on the type of waste and physical characteristics (size, surface area, porosity, etc.). WTE residues and water and wastewater treatment processes have different properties than MSW. Local precipitation patterns Determines frequency and the amount of water available for leachate generation. Impacts the dilution, concentration, solubilization, and/or precipitation of leachate components. Biogeochemical processes are moisture limited. Changes between seasons (dry wet) also play a role in dissolution/precipitation reactions. Landfill age and location Determines the degradation stage of the waste and the availability of certain compounds. Climatic factors and precipitation patterns are related to the location of the site. Location also determines the type of community served by the facility and therefore, the kinds of activities producing waste. Landfill operation Rate of waste input and practices such as co-disposal of residues and leachate recirculation affect leachate quality and quantity. Maintenance practices for collection system and gas control management are important too.

PAGE 22

11 Knowledge about leachate generation charac teristics of a landfill is a prerequisite to the planning of a leachate management strategy. The potential for the formation of leachate can be assessed by preparing a water balance that involves the amounts of water entering the landfill, the amounts of water c onsumed in biochemical reactions, and the quantity leaving as water vapor. The potential leachate quantity is the quantity of water in excess of the field capacity of the wa ste (Tchobanoglous and Kreith, 2002). There are four successive stages in the de gradation of waste which lead directly to leachate and gas production: (1) aerobic stage; (2) hydrolysis and fermentation stage; (3) anaerobic acetogenic stage; and (4) an aerobic methanogenic stage (USEPA, 2000; Kjeldsen et al., 2002). These processes are dynamic, each stage being dependent on the creation of a suitable environment by the pre ceding stage. In each stage a number of biologically mediated reactions take place, depending on the competing ability of the microbiological community to f unction within a changing chemical environment (Bagchi, 1990; Owen and Manning, 1997; EPA Ireland, 2 000). Biological activity influences redox potential, pH, and temperature, which can impact the rate and extent of biological degradation and chemical equilibrium so lubility affecting leachate composition. Landfill management approaches also affect leachate characteristics. Typically, MSW landfills are permitted to receive a combination of MSW, fly and bottom ash from combustion processes, residuals from wast e and wastewater treatment facilities, construction wastes, and other materials (U SEPA, 2004). All these residues have very different compositions, leaching potentials, a nd properties that have an impact in the leachate (Hjelmar, 1996). Interest in leachate recirculation and bi oreactor landfills is intensifying around the world, because waste decomposition and the time to stabilization are accelerated through these kinds of practices (Reinhart, 1996; Morris et al., 2003; USEPA, 2000). Leachate recirculation can enhance the degradation of MSW, as it provides an aqueous environment that facilitates the provision of nutrients a nd microbes within the landfill

PAGE 23

12 affecting leachate quality (Chan et al., 2002) Leachate quality changes occur as a result of a uniform distribution of moisture, higher quantities of inoculum, possible flushing and dilution of inhibitory products, and concentrat ion of metals due to biological activity. Regulatory Requirements for Landfill Leachate Management The safe and reliable long-term disposal of solid waste residues is an important component of integrated waste management There are many potential environmental problems associated with landfilling of solid wastes. In the past, many problems occurred as a result of non engineered facilities, poor management, and weak regulatory oversight. Regulations for waste management and landfill design have been established to protect public health and prevent envir onmental contamination. Design, operation, and closure practices for MSW landfills are ba sed on 40 CFR Part 258 of the Resource Conservation and Recovery Act (RCRA) Subtitle D requirements for control of leachates and gases generated during the life of th e landfill (USEPA, 2000) In this section, regulatory requirements for landfill design, landfill operation, and landfill leachate management are summarized. The Federal re gulations establish mi nimum standards and allow the States to make the necessary adju stment to compensate for local variations. Leachate Collection Systems The main purpose of leachate collecti on systems is to allow the removal of leachate from the landfill and to control the depth of the leachate above the liner (USEPA, 2000; Tchobanoglous and Kreith, 2002). Typically landfill leachate collection systems are positioned above the liner a nd are designed to collect liquid under

PAGE 24

13 gravitational flow for the entire active, cl osure, and post-closure periods. Clogging of any portion of the system can lead to higher hydraulic heads within the waste zone and increase the potential for leakage through the liner. A schematic of a leachate collection sy stem is shown in Figure 1 and design requirements specified by the USEPA are summarized in Table 4. As shown, the composite liner serves as the landfill base and consists of an impermeable layer with a hydraulic conductivity of less than 10-7 cm/sec (USEPA, 1993). Typi cally, clay is used to construct this relatively impermeable layer. The clay layer is overlain by a flexible membrane liner that provides an additional barrier protection in cas e cracking occurs in the underlying clay due to shifts in the soil. Figure 1. Diagram of the Leachate Collectio n System of Engineered Landfills. Adapted from Rhea (2004). Perforated Leachate Collection Pipe Composite Liner Drainage layer C Waste 30 c m A B D E Flow of leachate

PAGE 25

14Table 4. Landfill Leachate Collection System Components Shown in Figure 1. Parameter Section Material and Specifications Label in Figure 1 Base Soil with hydraulic conductivity less than 1 x 10-7 cm/sec. Slope > 2%. A Composite liner Liner Flexible membrane. B Drainage layer Placed directly over liner; material based on availability of granular material or geosynthetic net. Conductivity greater than 1 x 10 -2 cm/sec. Slope > 2% C Collection pipes Perforated; minimum 6 inch diameter; embedded within the drainage layer; strong enough to support waste and drainage layer. D Leachate collection system Filter layer Geotextile and/or sand. Protects drainage layer from physical clogging. E Adapted from Rhea (2004), EPA publication EPA530-R-93-017, and Florida Administrative Code 62-701.40000(4)(b). If the leachate develops su fficient head (depth), it has potential to penetrate the composite liner. The leachate head is a function of leachate generation, bottom slope, pipe spacing, and the hydraulic conductiv ity of the drainage layer. To prevent accumulation of leachate above the composite liner, leachate collection systems are designed to maintain the leachate depth be low 30 cm (Bagchi 1990; USEPA, 1993; EPA Ireland, 2000). However, during times of peak flow it is acceptable to exceed this value. The transport of leachate from waste matrices occurs through a series of perforated pipes embedded in a drainage layer. Regulatory requirements stipulate minimum requirements for perforated pipes to be at least 6-inch diameter plastic pipe capable of supporting the combin ed weight of the drainage layer and the waste at design capacity. If the pipes are not able to support this weight, the leachate collection system will fail. The conductivity of the drainage layer material must be at least 10-2 cm/sec, with a minimum slope of 2% so that the l eachate will flow towards the collection pipes (USEPA, 1993).

PAGE 26

15 To prevent physical clogging of the co llection pipes, the size of the drainage material must be larger than the perforations in the pipe. Another measure used to prevent physical clogging is the filter layer. This laye r of geotextile and sa nd is placed above the drainage blanket and prevents waste from traveling into the drainage layer and the collection pipes creating physical blockage s in the flow (USEPA, 1993). Leachate monitoring points and leachate collection sumps or a header pipe system may also be required for leachate control and removal. Biological and chemical clogs can occur in the leachate collection system pipes (Fleming et al., 1999; Jefferies and Ba th, 1999; Maliva et al., 2000; Missmer International, 2000; Paksy et al., 1998; Re inhardt and Townsend, 1998; Rittman et al., 1996; Rowe and Fleming, 1998; Rowe et al., 2000a, b, c; Rowe et al., 2002; USEPA, 1983). Within pipes, accumulation of deposits may be induced because of inadequate localized flows caused by areas of hydrauli c perturbation (EPA Ireland, 2000). To help control the formation of mine ral precipitates and biofilms, clean-out access ports are required in leachate collection systems. These por ts must be placed at locations that allow cleaning equipment and chemicals to access the whole syst em (USEPA, 1993). The suggested method for removal of minera l deposits is to flus h the system with a liquid that contains biocid es and cleaning agents. The cl eaning is intended to remove mineral precipitates and biofilm buildup in th e pipes, but does not prevent the formation of future clogs (USEPA, 1993). The clean ing frequency is determined by local regulations and landfill operating protocols. Clogging of Leachate Collection Systems Typically, the design life of landfills spans several decades, depending on the available space and the quantity of waste received (Fleming et al., 1999). A common

PAGE 27

16 reason for failure of leachate collection syst ems is clogging as a result of the growth of biofilms, accumulation of inorganic solids, a nd attachment of susp ended particles in pipes, drainage layers, and/or the filter la yer (VanGulck et al., 2003; Islam and Singhal, 2004; Manning and Robinson, 1999; Rowe et al ., 2002). The leachate characteristics which have an impact in the potential mechanisms related to the formation of deposits in leachate drainage systems are summarized in Table 5. Table 5. Potential Clogging Mechanisms a nd Leachate Characteristics of Concern. Potential Clogging Mechanism Leachate Characteristics of Concern Particulate pH and solids (TS, TDS, TSS). Biological pH, oxygen, organic content (COD, BOD, TOC), nutrients (total phosphorus and total nitrogen), oxidationreduction potential (ORP), temperature, and inhibitory metals (Zn, Cu, Fe, etc). Chemical Precipitate Formation pH, conductivity, alkalinity (CO3), calcium, chloride, magnesium, manganese, sodium, sulfate, and phosphorus. Biochemical pH, iron, manganese, partial pressure of CO2, redox potential, electron acceptors (sulfate, nitrate, oxygen), inhibitory metals (Zn, Cu, Fe, etc). Adapted from EPA Ireland (2000). In some cases, evidence of clogging has b een observed to occur within 4 years of landfill initiation (Rowe et al. 2002). Draina ge media have been implicated in the formation of clogs in landfill leachate coll ection systems (Rowe et al. 2000c; USEPA, 1991). While the initial hydrauli c conductivity and porosity of different media may be similar, there are differences in the size of the pores and the available surface area for different types of media. For a given volum e, smaller media provides a greater surface area, allowing for increased biofilm development that may influence the clogging rate (Koerner and Koerner, 1990; Rohde a nd Gribb, 1990; Rowe et al. 2000a). Regardless of the medium, the flow of th e leachate also affects the rate at which clogs form. Clogging has been found in both satu rated and unsaturated zones of leachate

PAGE 28

17 collection systems. In anaerobic environmen ts, unsaturated regions tend to have less clogging than saturated regions due to differences in available substrate for microbial activity. Microbial activity can influence e nvironmental conditions like redox potential and pH, which impact the rate and extent of biological degrad ation and chemical solubility (Kylefors et al. 2003). During times of high leachate flow rates, the increased activity of the microorganisms can lead to biofilm produc tion and the precipitation of insoluble minerals. In reality, the environment in the leachate collection system of a landfill cycles between saturated and unsaturated cond itions depending on preci pitation patterns. Unfortunately, deposition of precipitates is most pronounced in regions that experience changing flows, cycling between saturated and unsaturated conditions (Paksy et al., 1998; Rowe et al., 2000b). The clogging process appears to pass through a number of microbial mediated stages which include, but may not necessari ly be limited to, formation of surface biofilms, generation of slimes, and growth on interconnected mineral bio-concretions that gradually become denser and less pervious. Entrapment within these formations of recalcitrant particles (silt and sand particles or fines derived from the waste) may also accelerate clogging. The structural integr ity of the clog may be developed by precipitation of low-solubility sulfide a nd carbonate minerals (Fleming et al. 1999). Landfill leachates have been reported to contain significant numbers of microorganisms which are delivered to the drai nage system, attach to surfaces, and form biofilms (Huang et al., 2003; 2004). It is hypothesized that b acteria growing within the decomposing waste detach from the developing biofilms, flow with the leachate into the leachate collection system, and colonize the gr anular drainage material (Rowe et al. 2000a).

PAGE 29

18 The accumulation of clog material can be represented as being composed of a volatile and inorganic solid film (Cooke et al ., 2001; Rowe et al., 2002 ). The volatile film contains an active component where microorga nisms grow and substrate is utilized and an inactive component which consists of pr ecipitate material, inorganic solids, and entrapped inorganic suspende d particles (VanGulck and Rowe, 2004b). Unlike the active biofilm, the inactive film does not approach a steady state but continues to increase over time. Leachates have abundant potential to precipitate minerals (Owen and Manning, 1997). The most common precipitate is of cal cium carbonate, but others are manganese carbonate, manganese sulfides, and silicates (EPA Ireland, 2000). Geochemical modeling studies have reported calcite (CaCO3) and dolomite (CaMg(CO3)2) to be supersaturated in landfill leachates (Owen and Manning, 1997; Bennett et al., 2000; Johnson et al., 1999). Typically, leachates are also saturated with respect to FeCO3, MgCO3, and Ca5(PO4)3OH (Rowe et al., 2002). As leachate passes through the drainage material, depletion of calcium can be correlated with the loss of COD due to the fermentation of acetic acid and the consequent generation of carbon dioxide and formation of carbonic acid (Rittmann et al., 1996). The results are an increase in pH and carbonate concentration, both of which allow, or accelera te, the chemical precipitation of calcium carbonate and other compounds. It has also been suggested that the am ount of calcium carbonate in the precipitate can be estimated from the mass ratio of cal cium to carbonate in leachates (Rowe and Booker, 1998). If precipitation were the only mechanism for calcium accumulation within the clog material, and all calcium within the clog material were bound to carbonate, a mass balance consideration of calcium carbonate preci pitation (equation 1) requires the theoretical calcium to carbonate ratio to be 0.667 (40 g Ca2+/60 g CO3 2-). CO3 2+ Ca2+ CaCO3 (s) (equation 1)

PAGE 30

19 Calcium to carbonate mass ratios larger than 0.667 suggest that calcium may precipitate as compounds ot her than calcium carbonate, while ratios less than 0.667 suggest metals other than calcium may precip itate with carbonate (V anGulck et al., 2003; VanGulck and Rowe, 2004a, b). From this approach, it was determined that the availability of calcium rather than the carbonate limits the formation of the calcite in leachate drainage and collection systems (Rowe et al. 2002). Several field studies have reported the composition of the clog material found in landfill leachate collection systems. Brune et al. (1991) conducted studies in German landfills, while Fleming et al. (1999) repor ted organic and inorganic materials in a Toronto landfill. Maliva et al. (2000) detected a low magnesium form of calcite in clog scale obtained from a leachate collection pipe in a Florida landfill that received combustion residues from a WTE facility. Le vine et al. (2005) also reported the composition of clog materials collected at di fferent locations of the leachate collection system in the same Florida landfill. The resu lts of these studies are presented in Table 6. Table 6. Comparison of Composition of Material Precipitated in Landfill Leachate Collection Systems (Values Reported in Percentages). Material Brune et al. (1991) Fleming et al. (1999) Levine et al. (2005) Ca 21 20 75 85 CO3 34 30 n/a Si 16 21 1 5 Mg 1 5 <1 Fe 8 2 <1 n/a = Not Available Samples removed in these studies ranged from soft clog material containing solid sand-size particles, to hard solid material w ith the appearance and consistency of a weak concrete or rock. The precipitate is genera lly mixed with a biological slime, which is quite adherent and can block flow through the drainage system. Precipitates produced as a result of biochemical activity are generally quite different in form and structure from

PAGE 31

20 those resulting in chemical processes alone and may show a greater tendency to clogging. This clogging tendency is apparent in the case of adherence to plastic piping (EPA Ireland, 2000). Lysimeter Studies In addition to observations from active landfills, laboratory studies have been used to assess different aspects of landfilling practices. Various tests have been developed to determine the leaching behavi ors of materials (Hage and Mulder, 2003). Tests used to establish the leaching characteris tics of wastes include field tests, simulator (lysimeter) tests, and batch tests. A comp arison of these tests is given in Table 7. Table 7. Comparison of Types of Tests Used to Evaluate Waste Leaching Potentials. Category Description Advantages Disadvantages Field Monitors leachate characteristics produced by wastes in an established landfill. Establishment of microbial communities; heterogeneity of waste constituents. Can take several years; limited access to the reacting materials; inability to determine the contribution of waste constituents to leachate quality. Simulator Waste is placed in a column, commonly called a lysimeter, and allowed to react over several months. Establishment of microbial populations; mimics a landfill; controlled flow of leachant; access to the reacting materials in select locations. Can take months to complete; inability to determine the contribution of the individual waste constituents to the characteristics of the leachate. Batch Select wastes are placed in non-reactive containers with leachant for a specific length of time. Can be completed in weeks; identification of the contribution of waste constituents to leachate quality. Missing microbial activity; limited interaction among different types of waste. Adapted from Rhea (2004).

PAGE 32

21 Simulators or lysimeters tests require le ss time than field tests but can still take several months to be completed. Lysimeters can be used to simulate specific landfill conditions under a controlled environment, evaluated the relationships between waste composition and leachate quality, and provide an opportunity to observe the establishment of microbial communities in relation to leachate flow patterns. In these tests, wastes are placed in parallel reactors where temperature, moisture content, and the degree of leachate recircul ation can be controlled and gas production and leachate composition can be monitored. In addition, the composition of the wastes can be characterized more completely than in a landfill setting. In many ways lysimeters are black boxes, since the ability to determine a direct relationship between individual materials and leachate characterist ics is unknown (Rhea, 2004). The design, placement, and operation of the reactors depend on the purpose of the study and can influence the results. In a la boratory, the results may not correlate with field tests due to differences in temperature, time, and liquid to solid contact frequency (van der Sloot, 1998). Lysimeter design parame ters from published studies are compared in Table 8, while different lysimeter ope ration aspects are summarized in Table 9.

PAGE 33

22Table 8. Design Parameters Used in Lysimeter Studies. Reference Aspect Column Material Packing Material Blight et al. (1999) 3.12 m2 X 1.06 m deep Brick and concrete Liner: HDPE Drainage layer: 100 mm gravel MSW Chan et al. (2002) 150 mm diameter; 150 cm length Stainless steel MSW, sewage sludge, marine dredging Cooke et al. (2001) 51 mm diameter; 760 cm length PVC 6-mm diameter glass beads Fleming et al. (1999) 0.25 X 0.6 X 0.70 m PVC Drainage blanket: clear stone MSW: 5 10 yr old waste Geotextile Islam and Singhal (2004) 50 mm diameter; 500 mm length n/a Clean sand: 0.21 0.61 mm in size Karnchanawong et al. (1995) 1.9 m diameter; 6.14 m length Steel coated with coal tar resin Drainage layer: gravel Cover layer: soil MSW Paksy et al. (1998) 350 mm diameter; 900 mm length MDPE/HDPE Drainage layer: limestone and Thames gravel MSW: 4 5 yr old waste Peeling et al. (1999) 220 mm diameter; 910 mm length MDPE/HDPE Drainage layer: limestone and Thames gravel MSW: 4 5 yr old waste Rowe et al. (2000) 50 mm diameter; 700 mm length PVC Schedule 40 4, 6, 15 mm diameter glass beads. Sallam, M. (2002) 150 mm diameter; 122 cm length PVC Drainage layer: silica gravel MSW Geotextile San and Onay (2001) 35 cm diameter; 100 cm length PVC Drainage layer: gravel MSW: shredded and compacted synthetic solid waste. VanGulck and Rowe (2004) 51 mm diameter; 700 mm length PVC Schedule 40 6 mm diameter glass beads. n/a = Not Available

PAGE 34

23Table 9. Operational Aspects of Lysimeter Studies. Reference Liquid source and flow rate Time span and temperature Gas and leachate collection Blight et al. (1999) Rainfall 865 days 17 20 C Leachate: single base drainage orifice Chan et al. (2002) Distilled water (500 ml) added weekly; leachate recirculation 69 78 days 38 C Gas: gas-venting valve on the lid, connected to water-filled glass column Leachate: weekly samples from valve at the bottom Cooke et al. (2001) Liquid: landfill and synthetic leachate Flow rate: continuous, upward (1.12 L/d) 280 days 22 C Allowed escape of gas Islam and Singhal (2004) Liquid: landfill leachate Flow rate: continuous, upward (0.33 7.2 L/d) 58 126 days 18 30 C n/a Karnchanawong et al. (1995) Rainfall 853 days n/a Leachate samples collected weekly Paksy et at. (1998) Liquid: landfill and synthetic leachate Flow rate: continuous, vertically down (0.6 10 L/d) 800 days 18 37 C Gas outlet port in the lid Peeling et at. (1999) Liquid: synthetic leachate with recirculation Flow rate: continuous, vertically down (0.62, 1.30, 2.59 L/d) 350 500 days n/a Gas: flow meters; headspace gases sampled with syringes Rowe et al. (2000) Liquid: landfill and synthetic leachate Flow rate: continuous, upward (1, 2, 4 L/d) 121 422 days 26 37 C Gas: Tedlar gas collection bag; piezometer connection Leachate: valve above the top of the beads Sallam, M. (2002) Liquid: landfill and synthetic leachate with recirculation Flow rate: continuous, vertically down (0.04 L/d) 180 days 17 28 C Gas valve at the top San and Onay (2001) Liquid: tap water; leachate recirculation Flow rate: continuous, vertically down 275 days 34 C Gas: measured using the inverted cylinder technique Leachate: screen and tubing VanGulck and Rowe (2004) Liquid: landfill leachate Flow rate: continuous, upward (1.02 L/d) 245 days 21 C Gas: Tedlar gas collection bag; piezometer connection Leachate: valve above the top of the beads n/a = Not Available

PAGE 35

24 Lysimeter studies have been used for leachate characterization and modeling of MSW co-disposed with incinerated residuals Based on reported results from tests on leachate quality, co-disposal of MSW and incinerated residuals provides an efficient method of waste disposal, since the organic content of the leachate is lower than for leachates produced during the traditional di sposal method (Gau and Chow, 1998). It was also found that a shallower waste layer produces lower concentrations of pollutants in the leachate, although higher amounts of leachate volume and extracted substances per dry weight of waste may be produced (Karnchanawong et al., 1995). Identification of the effects of leach ate recirculation on biogas production and leachate quality has been subject of several lysi meter studies (Blight et al., 1999; Chan et al., 2002; San and Onay, 2001). The conclusions of these studies suggests that leachate recirculation could maximize the efficiency and waste volume reduction rate of landfill sites, with the additional be nefit of overall leachate lo ading reduction for treatment. Waste decomposition can be improved by an increas e in the moisture flow, as a result of increased flushing and dilution of the inhi bitory products, maintenance of favorable environmental conditions by uniform distribut ion of moisture, and addition of higher quantities of inoculums a nd nutrients (USEPA, 2000). Laboratory lysimeter studies have been us ed to assess the clogging process. Paksy et al. (1998) demonstrated th at the clogging rates in anae robic drainage systems are highly sensitive to the particle size of the drai nage material, and that drains subjected to alternating periods of saturation and unsatur ation may become more uniformly and more extensively clogged. These stud ies recommended that draina ge material consisting of sand or gravel with a nominal particle size less than 10 mm should be avoided, and that it is preferable to keep the whole system fully saturated. Cooke et al. (2001) used lysimeter te sts to compare calcium removal and COD consumption in landfill leachate drainage syst ems. They found that calcium removal goes through three stages: a lag period, a period of rapidly in creasing removal, and a steady-

PAGE 36

25 state period. Calcium removal paralleled changes in the COD. This correspondence underscores the importance of mi crobial reactions in stimul ating the precipitation of calcium carbonate. In addition, VanGulck and Rowe (2004a) and VanGulck et al. (2003) demonstrated through the use of column experi ments, that the anaer obic fermentation of volatile fatty acids (mainly acetate) is the primary driver of calcium carbonate precipitation in leachate dr ainage collection systems. Several physical, geochemical, and biologi cal interactions ha ve been reported from column studies (Peeli ng et al., 1999; Rowe et al ., 2002; VanGulck and Rowe, 2004b). Leachate transport in soils resulted in a reduction of its permeability, possibly due to impermeable barriers formed through stimulation of anaerobic activity at the base of landfills (Islam and Singhal, 2004). Experi mental observations suggested simultaneous reduction of manganese and iron accompan ied by sulfate degradation and methane production. From lysimeter studies, Rowe at al. (2000b) concluded that mass loading has a significant impact on the rate and extent of cl ogging in a granular medium. The increased mass of inorganic material available for pr ecipitation on the granular medium, coupled with the higher mass loading near the collection pipes tends to accelerate clogging. Reducing the distance between the leachate collection pipes can decrease the total volume of leachate collected by each pipe and reduce the ma ss loading and the rate of clogging around the pipe. The placement of a geotextile filter/separator between the unsaturated stone layer and the overlying waste was studied by McIsaac et al. (2000). In this study, the presence of a separator minimized the occlusion of the voids with waste materi al at the top of the unsaturated stone layer. The presence of a geotextile decreased the amount of fines and sand sized particles, resulted in less clog mate rial present in the drain material. Visually more clog material was observed in the draina ge system in lysimeters with no geotextile separator.

PAGE 37

26 The information obtained from lysimete r studies provides a means to understand the factors and identify environmental condi tions that influence the clogging process. From an engineering perspective, it is impor tant to ensure that landfill leachate collection systems remain operational throughout the lif espan and post-closure periods of landfills (Bennett et al. 2000). Therefore, improve d understanding of biological and mineral clogging is needed. Waste-To-Energy Residuals WTE combustion is an important technology th at can be a significant factor in an overall fully integrated solid waste manageme nt strategy. These technologies offer great opportunities for reducing the volume and mass of waste to be landfilled up to 90% and 75% respectively, as well as for generati ng heat and power (USEPA, 2004). The major constraints on WTE combustion f acilities are their cost, the le vel of sophistication needed to operate them safely, cont rol of air emissions, and the fact that the public lacks confidence in their safety (Tchobanoglous and Kreith, 2002). Byproducts of thermal processing of so lid waste include combustion gases, ash residues, and recoverable materials such as ferrous and nonferrous metals. Ash residues are produced and discharged at various locati ons in a WTE facility. Combustion residues vary in composition depending on the source of the combusted material, degree of preprocessing (mass-burn, RDF, material recove ry), the efficiency of the combustion process, the ash management practices, emi ssion control systems, and the methods of residue collection (Berenyi, 1996; Brereton, 1996; USEPA, 2004) Different types of ash and their characteristics ar e summarized in Table 10.

PAGE 38

27Table 10. Summary of Different Types of Ash Residues from a WTE Facility. Residue Location Characteristics Bottom ash Discharged from the bottom of the furnace, primarily the grate, after the waste has progressed down the stoker. Consists of inert residues, glass and metallic objects, and 2 to 10 percent carbon. It is usually quenched with water, although it can also be collected in a dry state. Stoker grate siftings Fall through clearances in the grates and are collected with bottom ash. May include unburned organic matter. Boiler ash Carried by combustion gases. It may fall onto the stoker into the bottom ash, or it may be collected in hoppers. Consists of flyi ng particles and condensable metal vapor which may attach to refractory and water-cooled walls. Fly ash Carried by combustion gases through the furnace, boiler, and scrubber. It is collected by the particulate control device. Reaction products of primarily calcium chlorides and un-reacted lime. Includes volatiles condensed during flue gas cooling. Scrubber reaction products Collected at the bottom of spray-dry or dry lime-injection acid gas scrubbers. Include fly ash and reacted or partially reacted alkaline reagent (such as lime) and some carbon. Mixed ash Various locations from the combustion and emission control equipment. May contain siftings, bottom ash, boiler deposits, scrubber residues, fly ash, and scrubber products. Adapted from Hasselriis (2002) and Wiles (1996). Disposal of ash residues imposes a subs tantial increment to the total cost of operation of a WTE facility. Since 1994, when the Supreme Court ruled that ash from MSW combustion must be treated as other hazardous wastes in City of Chicago vs. Environmental Defense Fund all WTE facilities have been required to test the ash using the Federal Resource Conservation and Recove ry Act testing requirements for hazardous waste, prior to disposal in lined landfills (FDEP, 2000). There are over 150 WTE plants in operation today in the United States and since they have be come an integral part of waste management around the country, more are either planned or under construction (Tchobanoglous and Kreith, 2002).

PAGE 39

28 Ash Management and Disposal Over the past several years there has b een significant controversy concerning the proper management of the residues fro m WTE facilities and their regulatory classification as hazardous or non-hazardous wa ste. This controversy and other factors, such as the lack of Fede ral guidance and heavy metal content, have resulted in inconsistent management requirements am ong several States and uncertainty about beneficial utilization of the residues (Wiles, 1996). Ash residues can be processe d at the WTE facility to re duce the rate of release of contaminants into the environment, facilitate disposal, improve the quality of the residues, remove valuable and useful materi als, and to prepare por tions of the ash for beneficial use (Hasselriis, 2002). Treatment op tions include processi ng to recover ferrous and nonferrous metals, compaction aging durin g storage, solidification/stabilization, vitrification, and chemical extraction. Major utilization options incl ude aggregate for road base, embankments, asphalt pavements, and aggregate in Portland cement for construction (Wiles, 1996). Utilization, how ever, must follow sound scientific and engineering principles and be conducted with appropriate measur es to assure that it is acceptable to the environment and to human health. Although there are options fo r using ash residues and for treating them prior to use or as a requirement for disposal, most of the WTE combustion residues generated in the United States are disposed either in monofills, or co-disposed with MSW and/or residuals from water and wast ewater treatment facilities (Hjelmar, 1996; Wiles, 1996; Levine et al., 2005). Placing ash residues in monofills has the advantage that a solid, relatively impervious mass is created, over whic h trucks can drive as soon as it is placed. Ash monofills can be so impervious to wate r that 90% or more of rainfall runs off, without leaching much of the soluble materi al in the ash (Hasselriis, 2002). There has

PAGE 40

29 been concern about co-disposal practices because the impacts on leachate quality and waste interactions are not well known yet. Due to the potential leaching of contaminants, landfilling of WTE combustion residues may have long-term consequences for the environment. It has been suggested that monofill or co-disposal of WTE com bustion residues and MSW may lead to suboptimal management solutions in terms of resource conservation and environmental safety (Hjelmar, 1996). Co-disposal of com bustion residues with MS W has the potential to introduce metals, minerals and other nonbiodegradable materials to the leachate matrix; the acids generated by decomposi ng MSW could increase concentrations of soluble toxic metals in the collected leach ate (Hasselriis, 2002). WTE ash would provide minerals while MSW would provide biomass, carbonate species, and alternative electron acceptors, resulting in clogging of leachat e collection systems due to mineral precipitation (Levine et al., 2005). Leachate from WTE Combustion Residues From a technical perspective, the devel opment of strategies for disposal of WTE combustion residues and management of the leachate should be based on extensive knowledge of leaching behaviors. The degree to which combustion residues contribute to landfill leachate characteristics is influen ced by the type of combustion residue, the disposal practices, the net volume of liquid th at percolates through the landfill, biological activity, the age of the landfill, and site-specific factors (Johnson et al., 1999). The potential for leaching of minerals from combustion residues has been evaluated by several re searchers (Abbas et al., 2003; Br uder-Hubscher et al., 2002; Hage and Mulder, 2003; Kim et al., 2003; Kim and Batchelor, 2001; Kylefors et al., 2003; Song et al., 2004; van der Sloot, 1998). In addition, differences in the properties of

PAGE 41

30 combustion residues from different types of processing have been identified (Brereton, 1996; Dijkstra et al., 2002; Song et al., 2004) WTE combustion residues show systematic leaching patterns, and the leaching behaviors ar e controlled by such factors as pH, redox potential, ionic strength, complexing inorga nic ions and organics and L/S ratios. The leachate from WTE residues usually contains roughly 50% of soluble salts resulting from the removal of acid gases by emission controls, and low organic contents. The major elements include Ca, Cl, Fe, K, Na, O, and SO4, while minor elements are Cr, Cu, Mg, Mn, Pb, and Zn (Wiles, 1996). A comp arison of leachate characteristics from ash monofills is given in Table 11. Table 11. Comparison of Leacha te Quality from Ash Monofills. Parameter Bagchi (1990) Cambotti and Roffman (1993) Hjelmar (1996) Lundtorp et al. (2003) pH (pH units) 8.47 9.94 5.7 7.5 8.7 10.5 11.19 11.20 Conductivity (mS/cm) 2.5 18.7 n/a 1,400 3,900 2.4 310 Aluminum (mg/L) 2.3 88.8 n/a n/a 0.230 0.420 Arsenic (mg/L) < 0.187 BDL 0.40 0.005 0.025 n/a Cadmium (mg/L) 0.004 0.300 BDL 0.60 BDL 0.001 BDL 3.50 Calcium (mg/L) n/a 1,300 16,000 32 1,000 450 4,500 Chloride (mg/L) 32.6 305.0 n/a 2,400 11,400 25 390,000 Chromium (mg/L) < 0.010 0.044 BDL 0.03 BDL 0.080 0.220 0.460 Copper (mg/L) 0.026 0.103 BDL 0.60 BDL 0.210 BDL 0.035 Iron (mg/L) < 0.01 0.10 BDL 32.0 < 0.010 0.760 0.020 0.054 Lead (mg/L) 0.15 0.60 BDL 0.14 BDL 0.040 0.008 1,600 Magnesium (mg/L) 0.006 0.057 n/a n/a n/a Mercury (mg/L) < 0.0002 BDL BDL 0.003 BDL 0.003 Nickel (mg/L) 0.01 0.03 n/a n/a 0.001 0.017 Potassium (mg/L) 3.66 79.80 520 6,900 600 4,300 98 85,000 Sodium (mg/L) 11.5 48.5 3,000 9,300 2,800 7,300 800 70,000 Sulfate (mg/L) 105 1,400 n/a 2,000 7,200 n/a Zinc (mg/L) 0.002 0.012 BDL 1.60 < 0.010 0.590 0.016 0.068 BDL = Below Detection Limits n/a = Not Available

PAGE 42

31 The concentrations of trace elements in the leachate are low due to the reducing environment (redox potential is low due to mi crobiological degradation of the residual organic material) and the favorable pH re gime. Aging or weathering of ash normally results in a decrease of le achate pH towards neutral. On e aging reaction results from uptake of CO2 and self-neutralization of the ash. Ot her aging reactions that promote metal immobilization include hydrolysis of oxides to hydroxides, and the oxidation of elemental metals to form oxyhydroxide su rface deposits. These changes result in decreased solubility of many elements and consequently decrease d release (Wiles, 1996; Hjelmar, 1996). Landfill practices have evolved from very basic beginnings to become a sophisticated activity, with careful planning to ensure containment of gases and leachate, and to ensure achievement of waste and la ndfill site stabilizati on. Knowledge about the relationship between waste composition and leachate quality, from the point of view of environmental protection, is needed to improve landfill management practices. As new waste treatment technologies are developed a nd society consumption habits are modified, the production and composition of the wast e, as well as the products of waste degradation, are also in constant chan ge. Understanding leaching behaviors of the different types of wastes could result in better landfill design, landfill operation, and improved leachate management practices.

PAGE 43

32 LYSIMETER COMPARISON OF THE RO LE OF WASTE CHARACTERISTICS IN THE FORMATION OF MINERAL DE POSITS IN LEACHATE DRAINAGE SYSTEMS Antonio Cardoso1; Audrey Levine1; Bina Nayak2; Valerie Harwood2 University of South Florida 1Department of Civil and Environmental Engineering 2Department of Biology 4202 East Fowler Ave.; Tampa, FL 33620 ajcardos@eng.usf.edu ; levine@eng.usf.edu ; bnayak@mail.usf.edu ; vharwood@cas.usf.edu Lisa R. Rhea Jones, Edmunds and Assoc., Inc. 324 S. Hyde Park Ave., Suite 250; Tampa, FL 33606 lrhea@jea.net Abstract: A common operational problem in leacha te collection systems is clogging due to deposits formation within pore spaces a nd collection pipes. This study was conducted to evaluate clogging of leachate collection syst ems due to co-disposal of Municipal Solid Waste (MSW) and combustion residues from Waste-to-Energy (WTE) facilities. Five parallel lysimeters were filled (monofills or mixtures) with combinations of MSW, WTE combustion residues, and water/wastewat er treatment byproducts. Each lysimeter received a regular applicati on of leachate to simulate flooding and drying conditions; chemical tests of the leachates were conducted over a seven month period. Waste composition and the presence/ absence of biological activ ity influenced leachate properties such as redox potential, pH, and alka linity, which impacted the rate and extent of biological degradation and chemical solu bility. Calcium carbonate was identified as

PAGE 44

33 one of the most abundant chemical precipitate s. Leachates from ash monofills had high levels of pH, calcium and other minerals su ch as potassium and sodium, while carbonate levels were limited due to the lack of biological activity. The MSW monofill generated leachates with high levels of biological activ ity, lower concentrations of calcium, and a rich carbonate system. The co-disposal of MSW, combustion and treatment process residues generated leachates not limited in either calcium or carbonate, creating ideal conditions for precipitates formation. Keywords: Clogging; Co-disposal; Leachate collect ion systems; Lysimeter; Municipal Solid Waste; WTE combustion residues 1. INTRODUCTION One of the principal considerations in the planning, design, and operation of engineered landfills is the management of leachate. Leachate collection systems consist of a series of perforated pipe s within a granular drainage bl anket to collect the leachate. Low permeability liners are installed below the leachate collection system to restrict leachate percolation. These systems are manage d to prevent build-up of leachate within the landfill and to reduce the mass loading of contaminants available to pass through the liner (Rowe et al. 2002). A common operational problem in leachate collection systems is clogging due to the formation of deposits in the pore spaces and collection pipes. In general, clogging of leachate management syst ems has been attributed to several factors including sedimentation and de position of fines, biological activity, and biogeochemical precipitation (Paksy et at. 1998). From an engineering perspective, it is important to ensure that leachate collection systems remain operational throughout the lif espan and post-closure periods of landfills; therefore, improved understanding of biol ogical and mineral clogging is needed. The objective of this paper is to evaluate the clogging of leachate collection systems due to

PAGE 45

34 co-disposal of Municipal Solid Waste (MSW ) and combustion residues from Waste-toEnergy (WTE) facilities. 2. BACKGROUND Safe and reliable long-term disposal of solid wastes in engineered landfills is widely practiced (Tchobanoglous et al. 1993), however due to limited availability of sites for new landfills, particularly in highly populat ed urbanized regions, municipalities are under increasing pressure to reduce the qua ntity of landfilled waste. WTE facilities provide a means to reduce waste volumes in landfills and to recover energy through mass burn or Refuse Derived Fuel (RDF) practices Byproducts of thermal processing of solid waste include combustion gases, bottom and fl y ash residues, and recoverable materials such as ferrous and nonferrous metals. Ma nagement approaches for ashes from WTE facilities include disposal in monofills, co-disposal with non-combusted MSW in landfills, or incorporation w ith other materials for various construction applications. Typically, MSW landfills are permitted to receive a combination of MSW, fly and bottom ash from combustion processes, residua ls from waste and wastewater treatment facilities, construction wastes, and other materials (USEPA, 2004). 2.1. Leachate characteristics Leachate is generated as a result of reactions betw een water percolating through the landfill and wastes. Waste consolidati on and pressure differentials promote the migration of leachate through the landfill laye rs. Dissolved and suspended materials in leachates are composed of varying concentr ations of organic carbon, ammonia, chloride, iron, sodium, potassium, carbonates, and othe r constituents (Levine and Kroemer, 1989; Tchobanoglous et al. 1993). The quality and quantity of leachate genera ted in a landfill is influenced by waste characteristics, local pr ecipitation patterns, landfill age and location,

PAGE 46

35 and other site specific variables (Peeling et at. 1999). Movement of liquid through the waste layers and collection systems can prom ote microbial activity which, coupled with chemical reactions, has the potential to produ ce mineral precipitates. Representative data on the characteristics of landfill le achates are reported in Table 12. Table 12. Representative Data on th e Characteristics of Landfill Leachate. Parameter Units Bagchi (1990) Tchobanoglous et al. (1993) Kjeldsen et al. (2002) Levine et al. (2005) General pH pH units 3.7 8.9 4.5 7.5 4.5 9.0 5.8 7.8 Phosphorus, Total mg/L PO4 BDL 234 5 100 0.1 23.0 n/a Solids, Total mg/L 586 195,900 n/a 2,000 60,000 1,200 88,000 Biological related Alkalinity, Total mg/L as CaCO3 BDL 15,050 1,000 10,000 n/a 350 9,500 Organic Carbon, Total mg/L TOC BDL 195,000 1,500 20,000 30 29,000 n/a Anions Chloride mg/L Cl 2 11,375 200 3,000 150 4,500 300 45,000 Sulfate mg/L SO4 BDL 1,850 50 1,000 8 7,750 BDL 1,000 Cations Calcium mg/L Ca 3 2,500 200 3,000 10 7,200 210 11,000 Copper mg/L Cu BDL 9.0 n/a 0.005 10.0 n/a Iron mg/L Fe BDL 4,000 50 1,200 3.0 5,500 1 900 Magnesium mg/L Mg 4 780 50 1,500 30 15,000 6.8 1,400 Manganese mg/L Mn BDL 400 n/a 0.03 1,400 n/a Potassium mg/L K BDL 3,200 200 1,000 50 3,700 46 9,000 Sodium mg/L Na 12 6,010 200 2,500 70 7,700 66 67,000 Zinc mg/L Zn BDL 731 n/a 0.03 1,000 n/a BDL = Below Detection Limit; n/a = not available Laboratory and field stud ies on clogging of leachate collection systems have identified calcium carbonate to be the dominan t component of the clog material (Rowe at

PAGE 47

36 al. 2000b; Cooke et al. 2001). It has been postulated that a mixed community of facultative anaerobes, iron-related bacteria, su lfate-reducing bacteria slime formers, and enterics may act as catalysts for calcite nucl eation and precipitate fo rmation (Rowe et al. 2000a; Maliva et al. 2000; Kylefors et al. 2003). The structural integrity of the clog material is influenced by pr ecipitation of low solubility ca rbonate and sulfate minerals (Fleming et al. 1999). Biological activity infl uence redox potential, pH, and temperature, which can impact the rate and extent of biological degradation and chemical equilibrium solubility. 2.2. Lysimeter studies In addition to observations from active la ndfills, laboratory lysimeter studies have been used to assess the clogging process. Lysi meters are reactors that can be used to simulate landfill reactions and to assess the variability of leachate composition under different controlled conditions. In these tests, wastes are placed in column reactors for an extended period of time allowing for direct co mparison of leachate properties. Lysimeter design parameters from published st udies are compared in Table 13. Lysimeter studies have reported that clogging rates under anae robic conditions are highly sensitive to the particle size of the drai nage material, and that drains subjected to alternating periods of saturation and unsatur ation tend to be clogged more extensively (Paksy et al. 1998). Based on these studies, it has been suggested to avoid drainage material consisting of sand or gravel with a nominal particle size less than 10 mm.

PAGE 48

37Table 13. Design Parameters Used in Lysimeters Studies. Lysimeter Geometry and Size Lysimeter Structure Packing Material Reference Column: Diameter: 50 mm Height: 700 mm PVC: Schedule 40 6-mm diameter glass beads Rowe et al. (2002) Box: Width: 250 mm Length: 600 mm Height: 700 mm PVC Drainage blanket: clear stone MSW: 5-10 yr old waste Geotextile: separating MSW from drainage blanket Fleming et al. (1999) Box: Width: 1760 mm Length: 1060 mm Height: 1760 mm Brick and Concrete Liner: HDPE Drainage layer: 100-mm gravel MSW Blight et al. (1999) Column: Diameter: 230 mm Height: 900 mm MDPE/HDPE Drainage layer: limestone/Thames gravel MSW: 4-5 yr old waste Paksy et al. (1998) Lysimeter tests have also been used to compare calcium removal and COD consumption in landfill leachate drainage systems (Cooke et al. 2001). They found that calcium levels paralleled COD removal, s uggesting that microbial reactions may be involved in precipitation of calcium carbonate. The rate and extent of clogging in drainage layers has also b een correlated to mass loadi ng rates (Rowe et al. 2000b). The placement of a geotextile filter/separator between the drainage layer and the overlying waste was reported to decrease the amount of fines and sand si zed particles and resulted in less clog material present in the drainage layer as compared to parallel lysimeters without geotextile separati on (McIsaac et al. 2000).

PAGE 49

38 3. MATERIALS AND METHODS In this project, laboratory lysimeters were used to assess the potential for development of mineral deposits in relation to waste composition and flow patterns. The lysimeter design, operation and monitoring methods are summarized in this section. 3.1. Lysimeter design The lysimeters were designed as cylindr ical reactors with a volume of 0.42 m3 and a surface area of 0.30 m2. Each of the five lysimeters was constructed using 1.4 m long, 30.5 cm diameter, schedule 40 PVC pipes. Leachate generated in the lysimeters was collected in 32 mm diameter PVC pipe with 9.5 mm diameter perforations, which were spaced at intervals of 15 cm with two staggered rows separated by 120 The materials surrounding the collection pipes were combina tions of gravel, sand, geotextiles, geonet, and liners. Peristaltic pumps and leachate rese rvoirs were attached to the lysimeters as shown in Figure 2. The leachate application system consisted of an inverted funnel and a perforated plate as shown in Figure 3. This system helped to limit excessive channeling of the water, and promoted exposure of the entire lysimete r contents to liquid on a regular basis.

PAGE 50

39 Figure 2. Schematic of Lysimeter Design Used in this Study. Figure 3. Leachate Application System Consisti ng of Inverted Funnel and Perforated Plate. 32 mm diameter PVC pipe To vent 5-6.4 cm gravel. 12.7 cm Geotextile Sampling ports Waste Gas collection and flow meter. Cholee sand. 12.7 cm layer 4 L leachate reservoir 30.5 cm diameter, 1.4 m long PVC pipe Water/leachate application system. Sand layer Appropriate liner, geonet, and geotextile 4 L leachate reservoir Pum p

PAGE 51

40 3.2. Composition and distribution of waste in the reactors The lysimeters included two ash mono fills, one MSW monofill (RDF process rejects), and 2 reactors to simulate co-d isposal of RDF proce ss rejects, combustion residues, and water and wastewater treat ment plant byproducts (chemical sludge and biosolids). The co-disposal reactors (Mixtu re 1 and Mixture 2) were started up by combining the materials in a 60 L container and manually mixing the contents prior to introduction into the lysimeters. The distribut ion of waste materials in each lysimeter is shown in Table 14. Table 14. Composition and Distribution of Waste Sources in the Lysimeters (by Mass). WTE ash Treatment plant residues Lysimeter MSW Fly ash Bottom ash Water treatment Wastewater treatment Monofills Ash MSW 0% 100% 20% 0% 80% 0% 0% 0% 0% 0% Co-disposal 60% 6% 24% 5% 5% All materials used for this study were obtained in April 2004 from the North County Resource Recovery Facility in Palm Beach County, FL. This facility started accepting wastes in 1989 and it was de signed with a footprint of 1.35 km2 (334 acres). The landfill accepts ash and residues from a WTE Plant that burns RDF, unprocessed MSW, wastewater and water treatment residua ls, dead animals, and other non-hazardous wastes as defined by their by Solid Wast e Authoritys Household Hazardous Waste Facility. After emplacement of the wastes, distille d water was applied to each lysimeter to saturate the wastes to field capacity. A measured quantity of water was slowly added to the top of each lysimeter until the wastes were completely submerged. The lysimeters

PAGE 52

41 were then covered and allowed to absorb the water for a 72 hour period. Following the absorption period, excess water was drained and the volume recovered was measured. The difference between the amount of distil led water added and the amount of water recovered was considered to be the net field ca pacity of each lysimete r, equal to the water absorbed by the wastes to reach saturation. Th e estimated liquid to solid ratios needed to reach field capacity for each type of lysimeter are shown in Table 15. Table 15. Field Capacity of Each Type of Lysimeter. Lysimeter Volume added (L) Volume recovered (L) Volume absorbed (L) Liquid/Solid ratio (g/g) Monofills Ash MSW 40 70 24 52 16 18 0.09 0.13 Co-disposal 50 33 17 0.11 3.3. Lysimeter operation and monitoring After reaching field capacity, an additiona l four liters of distilled water were applied to each lysimeter to generate leach ate and initiate waste degradation. Every 24 hours, three liters of leachate was pumped from the lower to the upper reservoir and applied to each lysimeter through the leachate application system, simulating a rain event of 15 to 20 minutes. This mode of operation wa s intended to provide a lternating cycles of flooding and draining within each lysimeter in an effort to accelerate the leaching reactions and provide adequate mo isture for biological activity. Leachate characteristics were monitored to identify dominant electron acceptors, redox conditions, dissolved mineral conten ts, and buffer capacities. Samples were collected routinely over a seven month period an d analyzed for the parameters listed in Table 16. The volume of leachate that wa s withdrawn for each sampling event was

PAGE 53

42 replaced with an equal amount of distilled wa ter to maintain a constant volume of liquid within the lysimeter. 3.4. Microbiological testing Microbiological testing involved monito ring the concentration of bacteria once per week using a staining technique. 10 mL of sample was obtained from each lysimeter and filtered. The filters were stained using the 4, 6-diamidino-2-phenylindole (DAPI) stain, which binds to the DNA of cells and ma kes them appear blue under a fluorescence microscope. This technique measures the tota l number of bacteria per unit volume, but does not indicate viability.

PAGE 54

43 Table 16. Summary of the Chemical Test Performed on the Leachate Samples. Test MethodA Instrument Detection Limits General ConductivityT 2510 B. Laboratory Method inoLab conductivity meter 1 S/cm ORPT 2580 B. Electrometric MethodHach ORP probe 1 mV pHT 4500-H+ B. Electrometric Method Fisher Scientific AR50 pH meter 0.01 Solids (TS, TVS)O 2540 B. Total Solids and 2540 E. Total Volatile Solids AG245 Mettler Toledo and Fisher Scientific Isotemp Muffle 6.0 mg/L TemperatureT 2550 B. Laboratory Method inoLab temperature probe 0.1 C NutrientsO Nitrogen, Total 4500-N C. Persulfate Method Hach DR/4000U Spectrophotometer 0.2 mg/L Phosphorus, Total 4500-P C. Vanadomolybdophosphoric Acid Colorimetric Method Hach DR/4000U Spectrophotometer 0.2 mg/L Biological related Alkalinity, TotalT 2320 B. Titration Method Burette 20 mg/L as CaCO3 Organic Carbon, TotalO 5310 C. Persulfate Ultraviolet Method Sievers 800 Portable TOC Analyzer 0.1 mg/L Volatile AcidsT DiLallo and Albertson (1961). Dual Titration Method Burette 10 mg/L as acetic acid AnionsO Chloride Sulfate 4140 B. Capillary Ion Electrophoresis with indirect UV Detection Beckman P/ACE System 5500 Capillary Electrophoresis 0.1 mg/L CationsO Calcium Iron Magnesium Potassium Sodium 3111 B. Direct Air-Acetylene Flame Method PerkinElmer AAnalyst 100 Atomic Absorption Spectrometer 0.01 mg/L A All methods from Standard Methods 20th edition (1998). T Twice per week sampling frequency. O Once per week sampling frequency 4. RESULTS AND DISCUSSION To facilitate comparison of all data, the lysimeters were categorized either as monofills or mixtures as defined in Tabl e 13. The monofills include the ash monofills

PAGE 55

44 (Ash 1 and Ash 2) and the MSW monofill (MSW); the mixtures include the lysimeters simulating co-disposal of MSW, ash, and treatment plant residues (Mixture 1 and Mixture 2). The focus of this paper is to compare factors that influence precipitate formation including pH, alkalini ty, the concentrations of dissolved minerals, carbonate, and the presence/absence of biological activity. 4.1. pH and Alkalinity The leachates generated from the ash monofill lysimeters were relatively clear and free of particles, biomass and were signif icantly different from the other leachates in terms of pH and alkalinity. As shown in Fi gure 4, the pH associated with the ash lysimeters was significantly higher (t-test p va lue of 0.62) than the pH of leachates from the MSW or the co-disposal lysimeters; the hi gh pH levels may have inhibited biological activity in the lysimeters containing WTE combustion residues. Alkalinity levels in leachates from ash dominated lysimeters were fairly consistent, whereas alkalinity levels decr eased with time in leachates from MSW dominated lysimeters at a rate of about 9 to 18 mg/L-day for the MSW monofill and 4 to 9 mg/L-day for leachates from lysimeters containing mixtures. All alkalinity levels converged at approximately 2000 mg/L as CaCO3 under steady-state conditions, but the composition of the alkalinity varied for each group of reactors. The carbonate alkalinity of the leachates from ash lysimeters was only 10% of the total alkalinity, whereas the carbonate fraction of the total alkalinity fo r the MSW monofill and mixtures leachates ranged from 75 to 95%.

PAGE 56

45 4 6 8 10 12 14 3-May22-Jun11-Aug30-Sep19-NovpH Ash 1 Ash 2 MSW 4 6 8 10 12 14 3-May22-Jun11-Aug30-Sep19-NovpH Mixture 1 Mixture 2 0 1000 2000 3000 4000 5000 3-May22-Jun11-Aug30-Sep19-NovTotal Alkalinity (mg/L CaCO3) Ash 1 Ash 2 MSW 0 1000 2000 3000 4000 5000 3-May22-Jun11-Aug30-Sep19-NovTotal Alkalinity (mg/L CaCO3) Mixture 1 Mixture 2 Figure 4. Comparison of the pH and Alkalinit y in Leachates from Lysimeters Containing Monofills or Co-disposal. 4.2. Total Volatile Solids and Total Dissolved Solids The Total Volatile Solids (TVS) can be us ed as an estimate of the organic content of the leachates, while the concentration of Total Dissolved Solids (TDS) provides an estimate of the amount of minerals available for formation of preci pitates and the ionic strength of the leachate. A comparison of the concentrations of total volatile and dissolved solids in leachates from the lysi meters is shown in Figure 5. As shown, the TVS content of the MSW monofill leachate wa s four to six times higher than the TVS

PAGE 57

46 content of the leachate from ash monofills, pa rticularly during the first few months of operation. The volatile fraction of the co-dispos al leachates tended to be higher than the MSW monofill fraction most likely due to c ontributions of the wastewater treatment byproducts. 0 2000 4000 6000 8000 3-May22-Jun11-Aug30-Sep19-NovTotal Volatile Solids (mg/L) Ash 1 Ash 2 MSW 0 2000 4000 6000 8000 3-May22-Jun11-Aug30-Sep19-NovTotal Volatile Solids (mg/L) Mixture 1 Mixture 2 0 4000 8000 12000 16000 3-May22-Jun11-Aug30-Sep19-NovTotal Dissolved Solids (mg/L) Ash 1 Ash 2 MSW 0 4000 8000 12000 16000 3-May22-Jun11-Aug30-Sep19-NovTotal Dissolved Solids (mg/L) Mixture 1 Mixture 2 Figure 5. Comparison of the Concentration of Total Volatile and Dissolved Solids in Leachates from Lysimeters Containi ng Monofills or Co-disposal. Conversely, the TDS content of leachate s derived from the ash monofills was two to three times higher than the TDS from th e MSW monofill leachate, due to the higher mineral content of the ashes. Typically, th e solids concentrations in the co-disposal

PAGE 58

47 leachates reflected the relative quantity of ash (30%) and MSW (60%) within each lysimeter. 4.3. Volatile Acids and Micr obial Concentrations The degradation of organic matter in la ndfills is a sequential process initiated by hydrolysis of complex organic matter into simple carbohydrates, amino acids, and fatty acids. The simple carbohydrates and acids provide energy for growth by fermenting bacteria, producing volatile acids and hydroge n. The volatile acids are then partially oxidized to produce additional hydrogen and ace tic acid, which are the main substrates used by methanogens to produce methane (Tc hobanoglous et al. 1993) The volatile acids concentration therefore can be used as a key indicator of microbial activity. Volatile acids and microbial concentrations are shown in Figure 6. The concentrations of volatile acid s in leachates from the MSW monofill lysimeter were significant higher than the con centrations associated with leachates from the co-disposal lysimeters, es pecially during the first few months of operation, when concentrations up to 1,000 mg/L as acetic acid were observed. The accumulation of volatile acids suggested that it took longer for the methanogenic population to develop in the MSW monofill than in the co-disposal lysi meters, which contained biosolids that may have provided a more diverse microbial popu lation. The volatile acids levels within leachates from the ash monofill lysimeters were almost negligible and constant during the entire experimental period, suggesting the lack of micr obial populations in that environment.

PAGE 59

48 0 400 800 1200 3-May22-Jun11-Aug30-Sep19-NovVA (mg/L as acetic acid) Ash 1 Ash 2 MSW 0 400 800 1200 3-May22-Jun11-Aug30-Sep19-NovVA (mg/L as acetic acid) Mixture 1 Mixture 2 0 1 2 3 4 3-May22-Jun11-Aug30-Sep19-NovCell number x 109/mL Ash 1 Ash 2 MSW 0 1 2 3 4 3-May22-Jun11-Aug30-Sep19-NovCell number x 109/mL Mixture 1 Mixture 2 Figure 6. Comparison of Volatile Acids and Microbial Concentrations in Leachates from Lysimeter Containing Mono fills or Co-disposal. The highest microbial concentrations in the lysimeter leachates were associated with the co-disposal of MSW, ash a nd treatment plant byproducts. Microbial concentrations in the leachates from the as h monofill lysimeters (Ash 1 and Ash 2) were below detection limits as determined by DAPI staining. During the first month of operation, the DAPI cell count in the leachates obtained from the other lysimeters increased consistently. After about a month, the cell numbers in these leachates started decreasing and then the counts appeared to st abilize suggesting the em ergence of a stable population of microorganisms as the readil y degradable material was consumed.

PAGE 60

49 4.3. Calcium, Calcium/Alkalinity Ratio, and Calcium/TDS Ratio. Because calcium carbonate has been repor ted to be the most common precipitate to form in leachate collection systems (Je fferies and Bath, 1999; Manning and Robinson, 1999; Reinhart and Townsend, 1998), examination of the ratio of calcium to alkalinity can provide some insight into the overall stab ility of the leachate. A relatively high ratio of calcium to alkalinity suggests that th e formation of precipitates is limited by the availability of carbonate. Leach ates with these characterist ics may be susceptible to forming precipitates under conditions that fa vor biological activity or promote exposure of the leachate to atmospheric carbon dioxide (Bagchi, 1990). A comparison of calcium concentrations of the leachates from the lysimeters is shown in Figure 7. Calcium levels ranged from about 350 to over 4,000 mg/L. There was a trend of decreasing calcium c oncentrations over time in each lysimeter at a rate ranging from 7 to 10 mg/L-day for the monofills (correlation coefficient, R2, 0.8 to 0.9) and 3 to 5 mg/L-d for the co-disposal. 0 1000 2000 3000 4000 5000 3-May22-Jun11-Aug30-Sep19-NovCalcium (mg/L) Ash 1 Ash 2 MSW 0 1000 2000 3000 4000 50003-May22-Jun11-Aug30-Sep19-NovCalcium (mg/L) Mixture 1 Mixture 2 Figure 7. Comparison of the Calcium Concentrations in Leachates from Lysimeters Containing Monofills or Co-disposal.

PAGE 61

50 A comparison of the relationship of calci um to total dissolved solids and calcium to alkalinity is shown in Figure 8. Calcium to TDS ratios tended to be higher for the leachates from lysimeters containing MSW (either monofill or co-disposal), whereas calcium to alkalinity ratios tended to be hi gher for the ash monofills than for lysimeters containing MSW. These ratios reflect the relative sources of carbonate in the ash dominated lysimeters as compared to the MS W dominated lysimeters. Also, the ratios of calcium to TDS tended to exhibit a more pronounced decrease over time in the ash dominated leachates as compared to the MS W dominated leachates from the co-disposal with the rate of decreas e about 0.05% per day (cor relation coefficient, R2, 0.9). Similar trends were observed for the calcium to alkalin ity ratios with the rate of decrease about 0.004 mg calcium per mg alkalinity per day. 4.4. Development of solid deposits. After about 4 months of lysimeter op eration, operational problems developed within the leachate management system due to the development of deposits within the leachate collection tubing of MSW dominated lysimeters (monofill and mixtures). No deposits developed in the ash dominated ly simeters. The tubing was replaced and the elemental composition of the deposits wa s analyzed. Deposits in the MSW monofill tubing tended to contain more biomass and less granular ma terial than did the deposits from the lysimeters containing mixtures of MSW, ash, and treatment plant residuals as shown in Figure 9.

PAGE 62

51 0.0 1.0 2.0 3.0 4.0 5.0 3-May22-Jun11-Aug30-Sep19-NovCalcium/Alkalinity Ratio Ash 1 Ash 2 MSW 0.0 1.0 2.0 3.0 4.0 5.0 3-May22-Jun11-Aug30-Sep19-NovCalcium/Alkalinity Ratio Mixture 1 Mixture 2 0 10 20 30 40 3-May22-Jun11-Aug30-Sep19-NovCalcium/TDS (%) Ash 1 Ash 2 MSW 0 10 20 30 40 3-May22-Jun11-Aug30-Sep19-NovCalcium/TDS (%) Mixture 1 Mixture 2 Figure 8. Comparison of the Calcium/Alkalin ity and Calcium/TDS Ratios in Leachates from Lysimeters Containing Monofills or Co-disposal.

PAGE 63

52 (a) (b) Figure 9. Photograph of Deposits in Leacha te Collection Tubing from a.) MSW Monofill Lysimeter, and b.) Co-disposal Lysimeters. T ubing has an ID of 8 mm and OD of 10 mm. To provide additional insight into the characteristics of the clogged material in the lysimeter tubing, Scanning Electron Micr oscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were used to analyze th e surface characteristics of the deposits. Deposits were preserved using 2.5% glutaraldehyde, dehydrated in ethanol, and sputter coated with carbon. Example electron micr ographs and distributions of dominant elements associated with the deposits from lysimeters containing MSW monofill or codisposal are shown in Figure 10.

PAGE 64

53 0 25 50 75 100 MgSiPSClKCaMnTiCrFePercentElemental analysis of solid deposits from Lysimeter Leachate Collection System MSW 1 (a) 0 25 50 75 100 MgSiPSClKCaMnTiCrFePercentElemental analysis of solid deposits from Lysimeter Leachate Collection System Mix 1 0 25 50 75 100 MgSiPSClKCaMnTiCrFePercentElemental analysis of solid deposits from Lysimeter Leachate Collection System Mix 2 (b) Figure 10. Scanning Electron Micrographs and Dominant Elements of Deposits in Leaching Collection Tubing from a.) MSW Monofill Lysimeter, and b.) Co-disposal Lysimeters.

PAGE 65

54 The dominant elements associated with the deposits included calcium, silica, phosphorus, sulfur, and iron. The deposit co mposition varied among the samples, but calcium levels tended to be higher in depos its formed in the lysimeters containing a combination of MSW, ash, and treatment plant residuals as would be expected from the leachate characteristics. There was evidence of bacteria in all of the deposits suggesting that microorganisms play a role in the deposition process. 4.5. Comparison of leachates from lysimeters and landfill leachates The co-disposal lysimeters in this study were designed to simulate conditions at the North County Resource Recovery Facility landfill in Palm Beach County, FL, and to identify factors that may contribute to the development of deposits within the leachate collection systems. Monitoring data for a four year period from Cell 6 at the Palm Beach landfill was used to compare the characteris tics of landfill leachates to laboratory generated leachates which reflected relativel y short-term waste degradation conditions. A comparison of pH, temperature, and the ratios of calcium to TDS and to alkalinity for the leachates from the Palm Beach landfill and leachates from the five lysimeters is shown in Figure 11 in a boxplot format. The boxes represent 50% of the data, the horizontal line represents the medi an value, and the lines extending above and below the boxes represent the 95% confidence intervals. The relative height of the boxes provides a measure of the degree of variab ility associated with each measurement. The pH levels of leachates from the MSW dominated lysimeters and the landfill were not significant different, while signifi cantly higher temperatures were associated with field conditions. The per cent of the TDS that consiste d of calcium was slightly higher in the lysimeters than the landfill leachates. The calcium to alkalinity ratios were highly variable in the landfill leachate, re flecting changes in biological activity; less

PAGE 66

55 variability was observed in the lysimeters, perhaps due to the relatively consistent application of moisture. Ce l l 6 Ash 1 As h 2 MSW Mixture 1 M i x tu re 2 4 6 8 10 12 14pH Cell 6 As h 1 A sh 2 MSW M ixt u r e 1 Mi xt u r e 2 15 20 25 30 35 40Temperature (oC) Cell 6 Ash 1 Ash 2 MSW Mi x t ur e 1 Mi x t ur e 2 0 10 20 30 40Ca/TDS (%) Ce l l 6 A s h 1 A s h 2 M SW Mixture 1 Mix t u r e 2 0 1 2 3 4 5 6Ca/Alkalinity Ratio Figure 11. Comparison of pH, Alkalinity, and the Calcium to TDS and Calcium to Alkalinity Ratios from Monitoring Data for Landfill (4 years) and Lysimeters Leachates (7 Months). 5. SUMMARY Based on operation of laboratory lysimeters for a period of seven months, several trends were observed. Leachates from ash dominated lysimeters tended to have high levels of pH, TDS, and calcium to alkalinity ratios than did MSW dominated leachates.

PAGE 67

56 The higher pH levels inhibited biological ac tivity and the producti on of volatile acids, while the potential for formation of solid precipitates was modulated by the relatively high ionic strength which can increase the solubility of minerals. MSW dominated leachates tended to contain higher alkalinity, volatile solids, and calcium to TDS ratios than ash dominated leachates. Leachates from the MSW monofill lysimeter had the lowest calcium to alkalin ity ratios, suggesting that the formation of precipitates was not limited by the availabi lity of carbonate but by the sources of available calcium and other minerals. The co -disposal of MSW, combustion residues, and treatment plant byproducts generated leachates with calcium to alkalinity ratios in a higher range than leachates associated with the MSW monofill, but a lower range than that observed in leachates from ash monof ill lysimeters. The results from this study suggest that, when MSW is co-disposed w ith residues from combustion processes and treatment plant byproducts, the contributions from each type of waste produce a more susceptible environment for formation of minera l precipitates, due to the relatively higher quantities of constituents that could co-precipitate. The chemical composition of leachates from lysimeter tests were within the range of reported values for landfill leachates (Table 1 and Figure 9). Although leachate compositions vary widely depending on moisture content, age of landfill, and the events preceding the time of sampling (Tchobanoglous et al. 1993), laboratory lysimeters provided an effective model system for study of the reactions that might impact clogging of leachate collection systems. It is important to evaluate the degree to which the lysimeter leachates simulate leachates produced in landfills. Besides the differences in the amount of moisture available for waste degradation and landf ill age, different temperature ranges are associated with biologically active landfill as compared to the laboratory environment. Landfill leachate temperatures have been reported to range from 15 to 38 oC (Figure 9). Laboratory lysimeters were operated at r oom temperature with typical leachate

PAGE 68

57 temperatures ranging from 21 to 30 oC. Temperature variations can impact mineral solubility, biological growth ra tes, and reaction kinetics. 6. CONCLUSIONS This study has provided an opportunity to investigate relationships among waste characteristics, leachate composition, and the potential for clogging. Based upon experimental results obtained during the inve stigation, the following conclusions can be drawn: 1. Leachates from lysimeters containing actively degrading MSW have higher levels of microbial activity and bi carbonate, but contain lower levels of calcium species than do ash dominated lysimeters. Calcium to alkalinity ratios in leachates from the MSW monofill lysimeter ranged from 0.8 to 0.4. 2. Leachates from ash monofill lysimeters ar e dominated by high concentrations of dissolved calcium and high pH levels, but contain relatively low levels of carbonates with calcium to alkalinity ratios ranging from 3.8 to 0.5. When the carbonate alkalinity is relate d to the concentration of calcium in the leachates, these ratios can range from 20 to 4.5. 3. The solids concentrations in leachates derived from the co-disposal lysimeters reflected the relative quantity of ash and MSW within each reactor. Although lysimeters containing MSW either alone or co-disposed with combustion residues generated leachates with hi gher calcium to TDS ratios, these ratios in leachates from lysimeters containing WTE ash e xhibited a more pronounced decrease over time.

PAGE 69

58 4. The use of monofills appears to lead to less clogging of leachate collection systems. For ash monofills, the lower degr ee of microbial activity in the leachate results in lower concentrations of carbonate species, thus restricting the extent of chemical precipitation, while leachates from MSW monofills contain adequate carbonate, but fewer sources of calci um and other insoluble minerals. 5. Landfills practicing co-disposal of WTE ash and MSW appear to be more susceptible to clogging due to the relative contributions of each waste stream. The WTE ash provides the minerals while the MSW provides biomass, carbonate species, and alternative electron acceptors Additional inputs of treatment plant residuals can introduce more minerals (water treatment) and more biomass sources (wastewater treatment), further exacerbating the problem. Acknowledgements The authors acknowledge the financial s upport provided by the Florida Center for Solid and Hazardous Waste Management (Gai nesville), the Solid Waste Authority of Palm Beach County, FL, and CDM. The authors would like to thank the Solid Waste Authorities of Palm Beach County, FL for the information and materials provided. The authors would also like to thank Ed Haller of the Department of Pathology at USF for his help with sample processing and analysis on SEM and EDS. The assistance of Barbara Dodge as the Environmental Engineering Labo ratory Manager at USF is appreciated. The assistance of Mindy Decker, George Dzama, and Lawrence Jones and the financial support of the Research Experience for Undergraduates (REU) program are also appreciated.

PAGE 70

59 ASSESSMENT OF LEACHATES DERIVED FROM LANDFILLING OF WASTETO-ENERGY RESIDUES: IMPLICATIONS FOR LEACHATE COLLECTION SYSTEM DESIGN Antonio J. Cardoso1; Lisa R. Rhea2, and Audrey D. Levine1 1Department of Civil and E nvironmental Engineering; University of South Florida. 4202 East Fowler Ave., Tampa, FL 33620 2Jones, Edmunds and Assoc., Inc. 324 S. Hyde Park Ave., Suite 250; Tampa, FL 33606 ajcardos@eng.usf.edu ; lrhea@jea.net ; Levine@eng.usf.edu Abstract: Laboratory lysimeters were used in co njunction with batch tests to predict shortand long-term leachi ng characteristics of un-combus ted residues from Waste-toEnergy (WTE) facilities. Two parallel laborato ry lysimeters were filled with refuse derived fuel (RDF) combustion residuals (fly ash and bottom ash) and saturated to field capacity using distilled water to simulate ra infall and generate leachate. Leachates were recirculated daily and solub ilization of inorganic constituents was assessed over a seven month period. In addition, ash samples obtained from three WTE facilities in Florida (two mass-burn and one RDF) were used in ba tch tests to assess le aching potential as a function of contact time and liquid to solid ra tios. Field leachates a nd laboratory leachates were similar in chemical composition, although field leachates had higher concentrations of TDS and more neutral pH levels. The tests proved to be useful tools for simulation of field conditions and predicting the degree to which WTE residuals contribute inorganic constituents to the leachate matrix. The role of inorganic constituents leached from WTE residuals in forming precipitates in l eachate collection systems is discussed. Keywords: Batch tests; Leachate collection sy stems; Lysimeters; WTE combustion residues

PAGE 71

60 1. INTRODUCTION To reduce the quantity of Municipal Solid Wastes (MSW) requiring landfilling, many municipalities have adopted Waste-to-Ene rgy (WTE) facilities th at yield energy in the form of combustible gases and noncom bustible residues (fly ash and bottom ash). There are options for using ash residues in different construction applications, but the most common practices for disposal of WTE re siduals include landfilling in monofills or co-disposal with MSW and other materials su ch as residues from water and wastewater treatment facilities (Tchobanoglous and Kreith, 2002; Wiles, 1996) Due to the potential leaching of contaminants, landfilling of WTE residues may have long-term consequences for the environm ent. Since properties of WTE residues are very different from those of un-combusted MSW, it is important to understand factors that influence leaching characte ristics of wastes for effec tive management of leachates generated in landfills (Hjelmar 1996). The purpose of this arti cle is to assess the use of laboratory lysimeters in conjunction with batc h tests to predict short-term and long-term leaching characteristics of noncombustib le residues from WTE facilities. 2. BACKGROUND From a technical perspective, the devel opment of strategies for disposal of WTE combustion residues and management of the leachate should be based on extensive knowledge of leaching behaviors. The relative contribution of solub ilized minerals from WTE residues in landfill leachates depends on the relative amount of residues that are entombed in landfills in conjunction with the net combustion efficiency, ash handling practices, the net volume of liquid that percol ates through the landfill, biological activity,

PAGE 72

61 the age of the landfill, whether ashes are disp osed in monofills or co-disposed with other material, along with site-speci fic factors (Kylefors et al., 2003 ). The shortand long-term leaching and release of contaminants c onstitute the most important potential environmental problems related to dispos al of WTE residues (Johnson et al., 1999). 2.1. Waste-to-Energy residues Ash residues are produced and discharged at various locations in a WTE facility. Combustion residues vary in composition de pending on the source of the combusted material, degree of pre-processing (mass-burn, re fuse derived fuel, material recovery), the efficiency of the combustion process, the ash management practices, emission control systems, and the methods of residue colle ction (Berenyi, 1996; Br ereton, 1996; USEPA, 2004). These residues differ in terms of water solubility and the potential of leaching and release of components, which are important properties in re lation to landfilling of the residues and management of leachates. In general, WTE residues have low organic contents and the major elements include Al, C, Ca, Cl, Fe, K, Na, and O, while minor elements are Cr, Cu, Mg, Mn, Pb, and Zn (Hjelmar, 1996; Wiles, 1996). Different types of ash and their characteristic s are summarized in Table 17. Over the past several years there has b een significant controversy concerning the proper management of the residues fro m WTE facilities and their regulatory classification as hazardous or non-hazardous wast e. It has been suggested that monofill or co-disposal of WTE com bustion residues and MSW may lead to sub-optimal management solutions in terms of resour ce conservation and environmental safety (Hjelmar, 1996). Co-disposal of combustion residues with MSW has the potential to introduce metals, minerals and other non-biodegr adable materials to the leachate matrix; the acids generated by decomposing MSW could increase concentrations of soluble toxic metals in the collected leachate (Hasselr iis, 2002). WTE ash woul d provide minerals

PAGE 73

62 while MSW would provide biomass, carbona te species, and alternative electron acceptors, resulting in clogging of leachat e collection systems due to mineral precipitation (Levine et al., 2005). Table 17. Summary of Different Types of Ash Residues from a WTE Facility. Residue Location Characteristics Bottom ash Material discharged from the bottom of the furnace, primarily the grate, after the waste has progress down the stoker. Consists of inert residues, glass and metallic objects, 2 to 10% carbon. It is usually quenched with water, although it can also be collected in a dry state. Stoker grate siftings Fall through clearances in the grates and are collected with bottom ash. May include unburned organic matter. Boiler ash Carried by combustion gases. It may fall onto the stoker into the bottom ash, or it may be collected in hoppers. Consists of flyi ng particles and condensable metal vapor which may attach to refractory and water-cooled walls. Fly ash Carried by combustion gases through the furnace, boiler, and scrubber. It is collected by the particulate control device. Reaction products of primarily calcium chlorides and un-reacted lime. Includes volatiles condensed during gas cooling. Scrubber reaction products Collected at the bottom of spray-dry or dry lime-injection acid gas scrubbers. Include fly ash and reacted or partially reacted alkaline reagent (such as lime) and some carbon. Mixed ash Various locations from the combustion and emission control equipment. May contain siftings, bottom ash, boiler and scrubber residues, fly ash, and scrubber products. 2.2. Leachates from Wast e-to-Energy residues Leachates are the longest lasting emissi on from landfills and the development of strategies for leachate management shoul d be based on knowledge of wastes leaching behavior. Leachate collection systems consist of a series of pipe s within a granular drainage blanket with low permeability line rs installed below to restrict leachate percolation. It has been reported that in so me landfills, solid preci pitates deposit in the collection system resulting in clogging and malfunctions of the drainage system. The

PAGE 74

63 formation of precipitates is linked to the chem ical and biological stability of the leachate generated within the landfill. A comparison of leachate characteristics from ash monofills is given in Table 18. Table 18. Comparison of Leacha te Quality from Ash Monofills. Parameter Bagchi (1990) Cambotti and Roffman (1993) Hjelmar (1996) Lundtorp et al. (2003) pH (pH units) 8.47 9.94 5.7 7.5 8.7 10.5 11.19 11.20 Conductivity (mS/cm) 2.5 18.7 n/a 1,400 3,900 2.4 310 Aluminum (mg/L) 2.3 88.8 n/a n/a 0.230 0.420 Arsenic (mg/L) < 0.187 BDL 0.40 0.005 0.025 n/a Cadmium (mg/L) 0.004 0.300 BDL 0.60 BDL 0.001 BDL 3.50 Calcium (mg/L) n/a 1,300 16,000 32 1,000 450 4,500 Chloride (mg/L) 32.6 305.0 n/a 2,400 11,400 25 390,000 Chromium (mg/L) < 0.010 0.044 BDL 0.03 BDL 0.080 0.220 0.460 Copper (mg/L) 0.026 0.103 BDL 0.60 BDL 0.210 BDL 0.035 Iron (mg/L) < 0.01 0.10 BDL 32.0 < 0.010 0.760 0.020 0.054 Lead (mg/L) 0.15 0.60 BDL 0.14 BDL 0.040 0.008 1,600 Magnesium (mg/L) 0.006 0.057 n/a n/a n/a Mercury (mg/L) < 0.0002 BDL BDL 0.003 BDL 0.003 Nickel (mg/L) 0.01 0.03 n/a n/a 0.001 0.017 Potassium (mg/L) 3.66 79.80 520 6,900 600 4,300 98 85,000 Sodium (mg/L) 11.5 48.5 3,000 9,300 2,800 7,300 800 70,000 Sulfate (mg/L) 105 1,400 n/a 2,000 7,200 n/a Zinc (mg/L) 0.002 0.012 BDL 1.60 < 0.010 0.590 0.016 0.068 BDL = Below Detection Limits n/a = Not Available WTE combustion residues show systema tic leaching patterns that have been evaluated by several re searchers (Abbas et al., 2003; Br uder-Hubscher et al., 2002; Hage and Mulder, 2003; Kim et al., 2003; Kim and Batchelor, 2001; Kylefors et al., 2003; Song et al., 2004; van der Sloot, 1998). The mo st significantly vari ables which impact solubility, leaching, and release potential of minerals in WTE residues are final pH of the solution, biological activity, redox conditions, ionic strength, complexing inorganic ions

PAGE 75

64 and organics, and the liquid-to-solid ratio. Th e major leachate constituents are salts and hydroxides, while the main salts constituents are chloride, sulfate, calcium, potassium, and sodium (Johnson et al, 1999). 2.3. Leaching tests Tests that can be used to evaluate th e leaching characteristics of WTE residues include field tests, simulator (lysimeter) tests, and batch tests. A co mparison of these tests is given in Table 19. The tests differ mainly in dur ation and the presence or absence of biological activity; the results from these tests can be used to help predict the shortand long-term leaching behavior of noncombustible residues from WTE facilities (Hage and Mulder, 2003). Table 19. Tests Used to Characterize the Leaching Potential of Landfill Materials. Category Description Advantages Disadvantages Field Monitors leachate characteristics produced by wastes in an established landfill. Established microbial communities; heterogeneity of waste constituents. Can take several years; limited access to the reacting materials; inability to determine the contribution of waste constituents to leachate quality. Simulator Waste is placed in a column, commonly called a lysimeter, and allowed to react over several months. Establishment of microbial populations; mimics a landfill; controlled flow of leachant; access to the reacting materials in select locations. Can take months to complete; inability to determine the contribution of the individual waste constituents to the characteristics of the leachate. Batch Select wastes are placed in non-reactive containers with leachant for a specific length of time. Can be completed in weeks; identification of the contribution of waste constituents to leachate quality. Missing microbial activity; limited interaction among different types of waste.

PAGE 76

65 In lysimeter tests, wastes are placed in parallel reactors where temperature, moisture content, and the degree of leachat e recirculation can be controlled and gas production and leachate composition can be mo nitored. In addition, the composition of the wastes can be characterized more comple tely than in a landfill setting. In many ways lysimeters are black boxes, since the ability to determine a direct relationship between individual materials and leachate charact eristics is unknown. To determine leaching characteristics of individual wastes, batch tests can be used having as main variables the liquid to solid mass ratio (L/S ), the leaching medium, temperature, contact time, and the separation technique. 3. MATERIAL AND METHODS Laboratory lysimeters and batch tests were used to assess the leaching potential of WTE combustion residues as a function of cont act time and liquid to solid ratios. Details on lysimeter design and operation, batch tests, and monitoring methods are summarized in this section. 3.1. Lysimeter design and operation Two lysimeters were designed as cylindr ical reactors with a volume of 0.42 m3 and a surface area of 0.30 m2. Each lysimeters was constructed using 1.4 m long, 30.5 cm diameter, schedule 40 PVC pipes. Leachate gene rated in the lysimeters was collected in 32 mm diameter PVC pipe with 9.5 mm diamet er perforations, which were spaced at intervals of 15 cm with two staggered rows separated by 120 Peristaltic pumps and leachate reservoirs were attached to the lysimeters as shown in Figure 12.

PAGE 77

66 Figure 12. Schematic of Lysimeter Design Used in this Study. A geonet was placed above the drainage layer and WTE residuals were introduced into each lysimeter above the geonet. Th e WTE residues were obtained from a Refuse Derived Fuel (RDF) WTE facility (Palm Beach County, FL.). The depth of the WTE layer was about 2.4 ft (0.73 m) and consis ted of a mixture of 159 kg (350.54 lbs) of bottom ash and 22 kg (48.5 lbs) of fly ash. The relative amounts of bottom ash (80%) and fly ash (20%) were intended to simulate conditions typical of WTE facilities. After compacting the WTE residues, the contents of each lysimeter were saturated to field capacity using distilled water. An additional four liters of distilled water was applied to each lysimeter to generate leachat e and the lysimeters were capped and sealed. On a daily basis, three liters of leachate was pumped to the upper reservoir and 32 mm diameter PVC pipe To vent 5-6.4 cm gravel. 12.7 cm Geotextile Sampling ports Waste Gas collection and flow meter. Cholee sand. 12.7 cm layer 4 L leachate reservoir 30.5 cm diameter, 1.4 m long PVC pipe Water/leachate application system. Sand layer Appropriate liner, geonet, and geotextile 4 L leachate reservoir Pum p

PAGE 78

67 distributed to the top of each lysimeter th rough a 12 inch horizontal perforated plate designed to simulate a rain event of 15 to 20 minutes. Leachate samples were collected over a seven month period and analyzed as depicted in Table 20. The volume of leachate that was withdrawn for each sampling event was replaced with an equal amount of distilled water to maintain a constant volume of liquid within the lysimeter. 3.2. Batch tests Two different types of batch tests were us ed in this project: contact time (CT) and sequential extraction (SE). The CT batch test was used to assess the rate at which different elements reach equilibrium while SE batch tests were developed to predict the net capacity of soluble material to be rele ased from combustion re sidues based on liquid to solid ratios spanning the range of conditions likely to be encountered over the lifespan of a landfill. Batch testing methodology was adapted from the Method for Accelerated Leaching of Solidified Waste (Department of Nuclear Energy, 1990) as shown in Figure 13. All tests were conducted using Nalgene amber high-density polyethylene (HDPE) wide mouth bottles. Distilled water was us ed as a leachant to mimic the chemical composition of rainwater. To simulate internal landfill temperatures, batch tests were incubated at 35C. Leachates from batch te sts were analyzed following the parameters described in Table 20.

PAGE 79

68 Figure 13. Overview of Contact Time and Sequential Extractions Batch Tests. The contact time batch test was designed to yield a static view of the interaction between the waste material and the leachant. To insure a broad view of the interaction between combustion residues and leachant, the tests were c onducted up to 21 days with three replicates per time inte rval. On the other hand, the se quential extracti on batch test was designed to provide a dynamic view of the interaction between WTE residuals and leachants. The time interval between extractions was set at 72 hours, to allow apparent equilibrium to be reached while providing adeq uate time to test each sequential step. The duration of the sequential extraction tests was determined by the L/S ratio, which started at 10 g/g and increased with each subsequent extraction until the cumu lative ratio reached 100 g/g. Weigh sample into tared HDPE bottle; record mass of sample Add distilled water to achieve an L/S ratio of 10, using 1g/mL as the density of water Place bottles with sample and water on the orbital shaker for 20 minutes Place bottles in a 35C incubator for the selected length of time Remove sample by filtration, run time sensitive tests and preserve for future analysis Place bottles in a 35C incubator for 72 hours Remove leachate sample Run analysis and preserve leachate samples Replace removed leachate with equal volume of distilled water Contact time Sequential extraction

PAGE 80

69 3.3. Analytical Methods and Equipment Water quality analyses were conducte d on the leachate samples to identify dominant electron acceptors, redox conditions, dissolved mineral content, and buffer capacity. Chemical characterization of the l eachates from lysimeters, CT, and SE tests were analyzed following the parameters listed in Table 20. Table 20. Summary of the Chemical Test Performed on the Leachate Samples. Test MethodA Instrument Detection Limits General Alkalinity, Total 2320 B. Titration Method Burette 20 mg/L as CaCO3 Conductivity 2510 B. Laboratory Method inoLab conductivity meter 1 S/cm Organic Carbon, Total 5310 C. Persulfate Ultraviolet Method Sievers 800 Portable TOC Analyzer 0.1 mg/L ORP 2580 B. Electrometric MethodHach ORP probe 1 mV pH 4500-H+ B. Electrometric Method Fisher Scientific AR50 pH meter 0.01 Solids (TS, TDS) 2540 B. Total Solids and 2540 C. Total Dissolved Solids AG245 Mettler Toledo and Fisher Scientific Isotemp Muffle 6.0 mg/L Temperature 2550 B. Laboratory Method inoLab temperature probe 0.1 C Anions Chloride Sulfate 4140 B. Capillary Ion Electrophoresis with indirect UV Detection Beckman P/ACE System 5500 Capillary Electrophoresis 0.1 mg/L Cations Calcium Iron Magnesium Potassium Sodium 3111 B. Direct Air-Acetylene Flame Method PerkinElmer AAnalyst 100 Atomic Absorption Spectrometer 0.01 mg/L A All methods from Standard Methods 20th edition (1998).

PAGE 81

70 4. RESULTS AND DISCUSSION A comparison of selected results from the Contact Time (CT) tests and the Sequential Extraction (SE) tests is provided a nd compared to characteristics of leachates from laboratory lysimeters (Ash 1 and Ash 2) and field samples. Key leachate variables include pH, alkalinity, concentrations of dissolved minerals, and concentrations of calcium in the systems. 4.1. pH and Alkalinity The leachates generated from lysimeters and batch tests were relatively clear and free of particles and biomass. All samples had re latively high levels of pH regardless of residue source or leachate ex traction method, probably due to the presence of Ca(OH)2 and alkali metal hydroxides. The pH associat ed with leachates from an ash monofill in Florida (mass burn) ranged from 7.0 to 11.0, suggesting that environmental factors and biological activity may have impacted leachate characteristics. Alkalinity levels in lysimeter leachates were fairly consistent, converging at approximately 2000 mg/L as CaCO3 after seven months of op eration. Only 10% of the total alkalinity in the lysimeter leachates was at tributed to carbonate alkalinity. Alkalinity levels in batch test leachates varied with the source of the ash. Al kalinity concentrations tended to decrease with increasi ng liquid to solid ratios in th e SE tests and during the first six extractions, alkalinity values decreased by 18% to 83%. After encountering a mass of water equal to 100 times the initi al mass of ash, the final alkalin ity values were similar to those of typical groundwater rangi ng from 60 to 110 mg/L as CaCO3. Alkalinity and pH levels for leachates from lysimeters a nd batch tests are summarized in Table 21.

PAGE 82

71Table 21. Summary of pH and Alkalinity fo r Lysimeter and Batch Tests Leachates. pH Alkalinity (mg/L as CaCO3) Test Mean Range Mean Range LysimeterA Ash 1 11.7 11.4 12.0 1,872 1,064 2,133 Ash 2 11.7 11.4 12.1 1,905 1,227 2,250 Contact Time (0 500 hours) Mass burn bottom and fly ash 1 11.7 11.6 12.0 1,407 1,057 1,590 Mass burn bottom and fly ash 2 11.8 11.7 12.0 1,292 850 1,557 Bottom ash from RDF 11.6 11.4 11.9 613 470 667 Fly ash from RDF 11.6 11.4 11.7 1,537 1,953 1323 Sequential Extraction Liquid to Solid Ratio 10 g liquid/g ash Mass burn bottom and fly ash 1 11.8 11.8 11.8 1,217 1,216 1,218 Mass burn bottom and fly ash 2 11.7 11.7 11.8 1,167 1,163 1,171 Bottom ash from RDF 12.1 12.0 12.1 637 635 639 Fly ash from RDF 11.2 11.1 11.2 1,303 1,302 1,304 Liquid to Solid Ratio 100 g liquid/g ash Mass burn bottom and fly ash 1 10.7 10.7 10.7 127 124 130 Mass burn bottom and fly ash 2 11.0 11.0 11.0 107 105 109 Bottom ash from RDF 11.2 11.2 11.2 113 110 116 Fly ash from RDF 11.5 11.5 11.6 390 388 393 A Seven months of continuous operation 4.2. Total Dissolved Solids Concentrations of Total Dissolved So lids (TDS) provide an estimate of the amount of minerals available for formation of precipitates and the ionic strength of the leachate. A comparison of the concentrations of TDS in the leachates from the batch tests and the lysimeters is shown in Figure 14. The TDS concentrations in the lysimeter leachates ranged from 10,000 to 15,000 mg/L, refl ecting the relative contributions of the bottom and fly ash in the reactors.

PAGE 83

72a) 0 5000 10000 15000 20000 3-May22-Jun11-Aug30-Sep19-NovTDS (mg/L ) Ash 1 Ash 2 0 5000 10000 15000 20000 0200400 Contact Time (hours)TDS (mg/L) BA/FA 1 BA/FA 2 BA FAb) c) 0 5000 10000 15000 200000306090120L/S RatioTDS (mg/L) BA/FA 1 BA/FA 2 BA FA 0 100 200 300 400 0306090120L/S Ratiomg TDS/g Ash BA/FA 1 BA/FA 2 BA FA d) Figure 14. Comparison of TDS Concentrations Leached from Combustion Residues in a) Lysimeters; b) Contact Time Tests; c) Sequential Extraction Tests; and d) mg TDS/g Ash in Sequential Extraction Tests. In the CT tests, the fly ash yielded about a three fold higher concentration of TDS than did the mixed combustion residues. During the SE test, the greatest decrease in TDS concentration for all samples occurred during the first three extractions, suggesting that the readily soluble ions were washed out of the ash quick ly, leaving behind less soluble constituents. Most of the samples had a decr ease greater than 80% from the initial TDS values after six or seven extractions. The mass of solids solubilized from the bottom ash and mixed ashes ranged from 0.35 to 0.55 g TDS/kg of ash per liter of liqui d, whereas about a fourfold higher mass of

PAGE 84

73 solids was leached from fly ash (about 1.30 g/kg pe r unit increase in L/S ratio). Even at L/S ratios of 100 g/g, dissolution of solids had not stabilized. The L/S mass ratio of the lysimeters after seven months of operati on was about 0.15 g/g. TDS concentrations in field leachate samples ranged from 20,000 to 25,000 mg/L, suggesting higher liquid to solid ratios than the ones attained in lysimeter tests. 4.3. Concentrations of Dissolved Minerals The dominant ions in the leachates from batch tests and lysimeters were calcium, potassium, sodium, chloride, and sulfate. Sodium, potassium, and chloride ions are readily soluble and not usually found in deposited materials. Since calcium can precipitate with several i ons including carbonate, sulfate, and hydroxide, it will be discussed in a different secti on. A summary of the concentration of the main ions present in leachates from lysimeters, CT, an d SE tests is presented in Table 22. The sodium, potassium and chloride ions are dominant constituents of the TDS in all leachate samples, influencing the ionic strength of the leachate and changing the activities of precipitate-forming ions. It is in teresting to note that the concentrations of potassium in leachates from the lysimeters increased at a rate of about 4 mg/L-d (correlation coefficient, R2, about 0.75). The rate of pot assium increase is about 0.25% of the rate of calcium decr ease (~0.1 meq/day for potassium and ~0.4 meq/d for calcium) suggesting some type of ion exchange occurri ng within the solid matr ix or the drainage layer. The results for the batch tests followe d the same patterns as seen above; the CT tests established equilibrium while the SE tests showed th e most important reduction in concentrations during the firs t six or seven extractions.

PAGE 85

74 Table 22. Summary of Concentrations (mg/L) of Main Ions Present in Leachate Samples. Cl SO4 K Na Test Mean Range Mean Range Mean Range Mean Range LysimeterA Ash 1 5,150 3,330 7,430 72 25 123 1,065 350 1,500 1,985 808 2,502 Ash 2 4,565 1,240 8,210 97 25 460 950 255 1,340 1,865 568 2,870 Contact TimeB Mass burn bottom and fly ash 1 2,080 1,805 2,615 266 168 334 171 150 200 404 330 456 Mass burn bottom and fly ash 2 1,546 1,230 1,856 324 190 577 143 110 205 265 212 342 Bottom ash (RDF) 76 36 120 11 4.2 18 22 19 26 50 43 58 Fly ash (RDF) 8,470 7,450 9,055 366 71 624 1,043 830 1,137 1,650 1,378 2,350 Sequential Extraction L/S Ratio 10 g liquid/g ash Mass burn bottom and fly ash 1 2,152 1,984 2,300 244 235 251 243 238 250 446 436 480 Mass burn bottom and fly ash 2 1,463 1,188 1,710 320 316 333 150 133 161 256 249 263 Bottom ash (RDF) 35 22 41 16 12 20 52 50 55 61 55 67 Fly ash (RDF) 7,652 7,590 7,900 512 505 520 1,164 995 1,210 1,834 1,750 1,990 L/S Ratio 100 g liquid/g ash Mass burn bottom and fly ash 1 3.0 2.6 3.5 40 37 44 3.2 2.9 3.4 1.6 0.9 2.2 Mass burn bottom and fly ash 2 2.0 1.9 2.2 35 30 37 0.1 0.1 0.2 0.7 0.2 1.5 Bottom ash (RDF) 0.4 0.3 0.5 30 28 33 0.2 0.1 0.2 0.5 0.1 1.1 Fly ash (RDF) 15 13 18 20 15 25 7.0 6.0 9.0 0.3 0.2 0.3 A Seven months of continuous operation. B 0 500 hours. 4.4. Calcium Concentrations Based on analysis of clogged materials from leachate collection systems and on previous studies (Manning and Robinson, 1999; Rowe et al., 2002; VanGulck et al.,

PAGE 86

75 2003; VanGulck and Rowe, 2004), it has been established that calcium plays an important role in the formation of precipita tes. A comparison of calcium levels observed in leachates from lysimeters and batch tests is shown in Figure 15. a) 0 1000 2000 3000 4000 5000 0100200300400500 Contact Time (hours)Calcium (mg/L ) BA/FA 1 BA/FA 2 BA FAb) c) 0 10 20 30 40 50 020406080100L/S RatioCa/TDS Percen t BA/FA 1 BA/FA 2 BA FA 0 30 60 90 120 0306090120L/S Ratiomg Ca/g Ash BA/FA 1 BA/FA 2 BA FAd) Figure 15. Comparison of Calcium Leached fr om Combustion Residues in a) Lysimeters; b) Contact Time Tests; c) Ca/TDS Percent in Sequential Extraction Tests; and d) mg Ca/g Ash in Sequential Extraction Tests. The relative amount of calcium, carbonate and sulfate in leachates can impact the potential for formation of precipitates; if the molar ratio of calcium to either carbonate or sulfate is greater than one to one, the soluti on is supersaturated. Fu rther insight into the 0 1000 2000 3000 4000 5000 3-May22-Jun11-Aug30-Sep19-NovCalcium (mg/L ) Ash 1 Ash 2

PAGE 87

76 predictive capability of the ba tch tests is shown in Figure 16 in terms of saturation indices for calcite and gypsum associated with each of the WTE combustion residues in the CT tests. As shown, the fly ash yields a highl y supersaturated solution for both calcite and gypsum, but the degree of supersaturation decreases with contact time for gypsum, perhaps due to the participation of sulfat e in other complexing reactions. Leachate derived from bottom ash was unsaturated for calcite and gypsum. These results suggest that further stabilization of fly ash or deve lopment of alternative disposal practices may help to reduce the extent of mineral pr ecipitation and clogging of landfill leachate collection systems. -2.E+05 0.E+00 2.E+05 4.E+05 6.E+05 0100200300400500Time (hours)Saturation index for calcit e Supersaturated Saturated Unsaturated FA BA/FA 1 BA/FA 2 BA -10 0 10 20 30 40 50 0100200300400500Time (hours)Saturation index for gypsumSupersaturated Saturated Unsaturated FA BA BA/FA 2 BA/FA 1 Figure 16. Comparison of Saturation Indices for Calcite (Left) and Gypsum (Right) from CT Batch Tests. 4.5. Formation of Precipitates Leachates associated with different types of WTE combustion residues can be supersaturated with respect to minerals that tend to precipitate. Some type of perturbation to the leachate chemistry such as modifi cation of the oxidatio n-reduction potential, stimulation of the growth of bacteria, or addition of various clean ing agents can induce

PAGE 88

77 deposit formation. One type of cleaning agent that is widely applied for clean-out of leachate collection systems is the use of aci d with the goal of solubilizing minerals. 0 25 50 75 100 MgSiPSClKCaMnTiCrFeNiCuZnPercentElemental analysis of solid deposits from Bottom Ash deposit SEM 4685 a) 0 25 50 75 100 MgSiPSClKCaMnTiCrFeNiCuZnPbPercentElemental analysis of solid deposits from Fly ash batch leaching SEM 4639 b) Figure 17. SEM/EDS Analysis of Precipitates Form ed from the Addition of Sulfuric Acid to Leachates from CT Tests at a L/S Mass Ratio of 10; a) Bottom Ash, and b) Fly Ash. In this study, acid was added to samples from lysimeters and batch testing as a preservative. However, precipitates form ed within the leachate solutions upon the addition of sulfuric acid. Examples of the precipitates that formed are shown in Figure 17 for samples of bottom ash batch test leachat es at a liquid to solid mass ratio of 10 and

PAGE 89

78 for fly ash batch leaching test samples. As discussed above, all of these samples were undersaturated for gypsum due to the relativel y low concentrations of sulfate. It is interesting to note that in addition to the plate-like gypsum material that formed, other calcium and magnesium dominated precipitate s were also present, perhaps due to changes in the oxidation-reduction conditions. It should also be noted that there was no evidence of microbial interactions in these r eactions, since the pH le vel in the leachates samples was an inhibitory factor. 5. CONCLUSIONS This study has provided the opportunity to evaluate the leaching behavior of different WTE combustion residues through th e use of lysimeters, contact time, and sequential extraction batch tests. Predictions of the contributions of the different WTE residuals and the potential for the formation of mineral precipitates were discussed. The major conclusions of this study are: 1. Lysimeter tests allowed for a detailed ev aluation of one-set of conditions over an extended time period allowing for examination of changes in leachate composition. The reactors were useful t ools to simulate landfill conditions in a laboratory environment. 2. Batch leaching tests provided a means to estimate the rate and extent of mineral leaching as a function of contact time and liquid to solid ratios. The contact time (CT) test provided insight into the do minant solubilizable components and the chemical stability of leachates genera ted by WTE combustion residues, while the sequential extraction (SE) test provided a means to quantify the leaching behavior resulting from sequential exposure to rain water as it percolates through a landfill.

PAGE 90

79 3. Comparisons between batch tests, lysimete r tests, and field samples suggest that laboratory solubilization studies may pr ovide useful tools for predicting the impacts of alternative ash management practices and various combinations of wastes on leachate composition and stability. 4. All leachates samples from lysimeter and batch tests contained high concentrations of calcium, potassium, sodium, chloride, and sulfate. Although sodium, potassium, and chloride were hi ghly soluble, these ions increased the ionic strength of the leacha te, thereby reducing the activity of the less soluble ions in the leachate. 5. The high degree of calcium solubilization associated with W TE residue leachates can impact the stability of landfill leachates, particularly when combustion residues are co-disposed with MSW. Re sults from leaching and solubilization studies can help to predict the pote ntial for formation of calcium-based precipitates in leachate collection systems and possibly lead to the development of improved leachate management practices. Acknowledgements The authors acknowledge the financial s upport provided by the Florida Center for Solid and Hazardous Waste Management (Gaine sville). The authors would like to thank the Solid Waste Authorities of Hillsborough, Palm Beach, and Pasco County, FL for the information and materials provided. The authors would also like to thank Ed Haller of the Department of Pathology at USF for his help with sample processing and analysis on SEM and EDS. The assistance of Barbara D odge is appreciated. The assistance of Mindy Decker, George Dzama, and Lawrence Jones and the financial support of the Research Experience for Undergraduates (REU) pr ogram at USF are also appreciated.

PAGE 91

80 Conclusions This study has provided an opportunity to investigate relationships among waste characteristics, leachate composition, and the potential for formation of precipitates. The goal was to provide a means for predicting the contributions of differe nt waste streams to potential clog formation in landfill leachat e collection systems. The major conclusions from this project are: 1. The use of monofills appears to lead to less clogging of leachate collection systems. For ash monofills, the lower degr ee of microbial activity in the leachate results in lower concentrations of carbonate species, thus restricting the extent of chemical precipitation, while leachates from MSW monofills contain adequate carbonate, but fewer sources of calci um and other insoluble minerals. 2. Landfills practicing co-disposal of WTE combustion residues and MSW appear to be more susceptible to clogging of leachat e collection system due to the relative contributions of each waste stream. The WTE ash provides the minerals while the MSW provides biomass, carbonate species and alternative electron acceptors. Additional inputs of treatment plant residua ls can introduce more minerals (water treatment) and more biomass sources (w astewater treatment), further exacerbating the problem. 3. Clogging seems to occur when the equilibrium of calcium species is disrupted by microbial activity, the additional leaching of minerals, and/or a change in oxidation conditions. Microbi al activity, as evidenced by volatile acids and

PAGE 92

81 monitoring of microbial concentrations, in fluenced the rate a nd extent of clogging that occurred in lysimeter tubing. 4. Batch leaching tests provided a means to estimate the rate and extent of mineral leaching as a function of contact time and liquid to solid ratios. The contact time (CT) test provided insight into the do minant solubilizable components and the chemical stability of leachates genera ted by WTE combustion residues, while the sequential extraction (SE) test provided a means to quantify the leaching behavior resulting from sequential exposure to rain water as it percolates through a landfill. The use of this test to screen ash st abilization methods may help to reduce the incidence of clogging in landfill leachate collection systems. 5. Comparisons between batch tests, lysimete r tests, and field samples suggest that laboratory solubilization studies may pr ovide useful tools for predicting the impacts of alternative ash management practices and co-disposal of different types of wastes on leachate composition and stability. All the tests correctly predicted the identities of the dominant i ons and the supersatur ated or unsaturated nature of the leachate. 6. The high degree of calcium solubilization associated with W TE residue leachates can impact the stability of landfill leachates, particularly when combustion residues are co-disposed with MSW. Re sults from leaching and solubilization studies can help to predict the pote ntial for formation of calcium-based precipitates in leachate collection systems and possibly lead to the development of improved leachate management practices.

PAGE 93

82 Engineering Implications Landfills are designed to prevent and contro l the migration of contaminants to the surrounding environment. Landfill leachate collec tion systems are integral components of landfill management. This research has provided an initial evaluation of the chemical and microbiological factors that ma y impact the formation of biogeochemical deposits in leachate collection systems. It is important to develop tools for preventing and correcting problems associated with clogging of landfill drainage material and collection pipes. Monofills appear to be a better dispos al option for WTE combustion residues, rather than co-disposal with MSW and byproduc ts from water and wastewater treatment. The monofill practice would prevent two leachates with different characteristics from interacting and producing preci pitates. WTE combustion resi dues leachate provides the minerals while the MSW leachate provides biomass, carbonate species, and alternative electron acceptors, creating ideal conditions fo r the formation of precipitates. Clogging of leachate collection systems allows for accu mulation of liquid within the landfill, increasing the failure potential of the liner. Routine monitoring of biologically relate d parameters such as volatile acids, chemical oxygen demand (COD) and biochemical oxygen demand (BOD) in landfill leachates may be instrumental in relating th e extent of biological activity with the potential for formation of biogeochemical de posits. Comparison of the time period of decreasing calcium to alkalinity ratios with th e time periods associated with leachate pipe clogging might provide insight into the potenti al use of this ratio as a diagnostic or predictive tool for control a nd establishment of maintenance frequencies for leachate collection system.

PAGE 94

83 Methods for prevention and control of clogging in leachate collection pipes should be evaluated taking into account leacha te characteristics and waste interactions. Detailed testing of the impacts of practices su ch as chemical augmentation with acids and chelating agents is needed to identify the optimum appro ach for clogging prevention. The equilibrium of supersaturated leachates ma y be easily disrupted with the addition of cleaning chemicals, increasing the potential for precipitates formation. The impacts of current combustion t echnologies and ash handling protocols on the leaching characteristics of residues fr om WTE combustion facilities may help to develop protocols for stabilization of residues prior to landfilling or beneficial reuse. Laboratory lysimeters and batch tests can provide useful information during the development of treatment alternatives and also in the selection of appropriate materials for construction of landfill leachate drainage systems.

PAGE 95

84 Additional Research Recommendations for further research of the impacts of co-disposal of MSW, WTE combustion residues, and byproducts of water and wastewater treatment are: 1. Evaluate leachate characte ristics through the us e of laboratory lysimeters without leachate recirculation. This approach would allow studying the interactions between different types of waste and l eachate quality, as new liquid is added every time and a better control on the li quid to solid ratio in the reactors is achieved. This operational mode would also mimics a landfill environment in which the moisture content is an importa nt factor affecting biological activity, redox conditions, and solubility of minerals. 2. Determine the role of increasing temperat ures on the formation of biogeochemical deposits. Landfill environments reach higher temperatures than the ones usually found in laboratories. Temperature affect s biological activity as well as redox conditions and solubility of minerals in the leachate. By running laboratory lysimeters and batch tests at different temperatures, a relationship between this factor and leachate characteristics can be established. 3. Examine the impact of co-disposal of MSW and byproducts of water and wastewater treatment. Since this type of residuals are also co-disposed in landfills, the use of laboratory lysimeter and batch te sts may help in the identification of the individual contributions to the biomass a nd mineral content of the leachate, due to the presence of biosolids and/or water treatment sludge.

PAGE 96

85 4. Evaluate the production and compositi on of the biogas during laboratory lysimeter tests. Analyses of the biogas will allow es tablishing stronger relationships among biological activity, degrad ation of wastes within the reactors, leachate quality, and formation of precipitates. 5. Develop a relationship to predict the formation of precip itates by studying the sources of carbonate and the depletion of calcium in the leachate. The generation and consumption of volatile acids affects the pH and the carbonate concentration of the leachate. Identification of the co mposition and behavior of volatile acids may help to identify chemical and biol ogical factors that play a role in the leachate chemical stability. 6. Study the impact of having an anaerobic versus aerobic environment on the clogging of leachate collection system. New landfill management practices include the aeration of landfilled waste to promote faster degradation. Biological activity, redox conditions, and solubility of minerals are affected by this practice and the implications on the formation of biogeochemical deposits are not well understood yet. 7. Perform a statistical analysis of waste di sposal practices and the incidences of leachate management problems related to the formation of biogeochemical deposits. This could be achieved by conduc ting a large scale survey of landfills and comparing the disposal practices (monofills versus co-disposal of MSW, WTE combustion residues, and residuals fr om water and wastewater treatment) and the formation of precipitates in leachate collection systems.

PAGE 97

86 References Abbas, Z., Moghaddam, A.P., and Steenari, B.M. (2003). Release of Salts from Municipal Solid Waste Combustion Residues. Waste Management 23, 291-305. APHA, AWWA, WEF (1998). Standard Methods for the Examination of Water and Wastewater, 20th Edition Baltimore, MD. Bagchi, A. (1990). Design, Construction and Monito ring of Sanitary Landfill New York: John Wiley and Sons. Bennett, P.J., Longstaffe, F.J. and Rowe, R.K. (2000). The Stability of Dolomite in Landfill Leachate Collection Systems. Canadian Geotechnical Journal 37 (No. 2), 371-378. Berenyi, Eileen B. (1996). The Status of Municipal Waste Combustion in the United States. Journal of Hazardous Materials 47, 1-17. Blight, G.E., Fourie, A.B., Shamrock, J., Mbande, C. and Morris, J.W.F. (1999). The Effect of Waste Composition on Leachat e and Gas Quality: A Study in South Africa. Waste Management & Research 17, 124-140. Brereton, Clive (1996). Municipal Solid Wast eIncineration, Air Pollution Control and Ash Management. Resources, Conservation and Recycling 16, 227-264. Bruder-Hubscher, V., Lagarde, F., Leroy, M.J.F., Coughanowr, C., and Enguehard, F. (2002). Application of a Sequential Extrac tion Procedure to Study the Release of Elements from Municipal Solid Waste Incineration Bottom Ash. Analytica Chimica Acta 451, 285-295. Brune, M., Ramke, H.G., Collins, H., and Hane rt, H.H. (1991). Incrustations Process in Drainage Systems of Sanitary Landfills. In: Proceedings 3rd International Landfill Symposium, Cagliari, Italy, pp 999-1035.

PAGE 98

87 Cambotti, R.K., and Roffman, H.K. (1993) Municipal Waste Combustion Ash and Leachate Characterization. Monofill Fifth Year Study, Woodburn Monofill Woodburn, Oregon. Report prepared by AWD Technologies, Pittsburgh, Pennsylvania. Chan, G.Y.S., Chu, L.M., and Wong, M.H. ( 2002). Effects of Leachate Recirculation on Biogas Production from Landfill Co-disposal of Municipal Solid Waste, Sewage Sludge and Marine Sediment. Environmental Pollution, 118, 393-399. Cooke, A.J., Rowe, R.K., Rittman, B.E., VanG ulck, J. and Millward, S. (2001). Biofilm Growth and Mineral Precipitation in Synthetic Leachate Columns. Journal of Geotechnical and Geoenvironmental Engineering 127 (No. 10), 849-856. Dijkstra, J.J., van der Sloot, H.A., and Coma ns, R.N.J. (2002). Pro cess Identification and Model Development of Contaminan t Transport in MSWI Bottom Ash. Waste Management 22, 531-541. DiLallo, R., and Albertson, O.E. (1961). Volatile Acids by Direct Titration. Journal of Water Pollution Control Federation 33, 4, 356-365. Environmental Protection Agency, Ireland. (2000).Landfill Manuals. Landfill Site Design EPA An Ghniomhaireacht um Chaomhnu Comhshaoil, Ireland. Fleming, I.R., Rowe, R.K. and Cullimore, D. R. (1999). Field Observations of Clogging in a Landfill Leachate Collection System. Canadian Geotechnical Journal 36 (No. 4), 685-707. Florida Department of Envi ronmental Protection (2000). Solid Waste Management in Florida. Bureau of Solid and Hazardous Waste, July, 2000. Tallahassee, FL. Gau, S.H., and Chow, J.D. (1998). Landfill L eachate Characteristics and Modeling of Municipal Solid Wastes Combined with Incinerated Residuals. Journal of Hazardous Materials 58, 249-259. Hage, J.L.T., and Mulder, E. (2003). Prelim inary Assessment of Three New European Leaching Tests. Waste Management 24, 165-172. Hasselriis, Floyd (2002). Waste-to-Energy Co mbustion. Part 13B: Ash Management and Disposal. Handbook of Solid Waste Management Second Edition. New York: McGraw Hill.

PAGE 99

88 Hjelmar, Ole (1996). Disposal Strategies for Municipal Solid Waste Incineration Residues. Journal of Hazardous Materials 47, 345-368. Huang, L.N., Chen, Y.Q., Zhou, H., Luo, S., Lan, C.Y., and Qu, L.H. (2003). Characterization of Methanogenic Archaea in the Leachate of a Closed Municipal Solid Waste Landfill. FEMS Microbiology Ecology 46, 171-177. Huang, L.N., Zhou, H., Zhu, S., and Qu, L.H. (2 004). Phylogenetic Diversity of Bacteria in the Leachate of a Full-Scale Recirculating Landfill. FEMS Microbiology Ecology 50, 175-183. Islam, Jahangir, and Singhal, Naresh. ( 2004). A Laboratory Study of Landfill-Leachate Transport in Soils. Water Research 38, 2035-2042. Jefferies, S. A., and Bath, A. (1999). Rati onalizing the Debate on Calcium Carbonate Clogging and Dissolution in La ndfill Drainage Materials. Proceedings Sardinia 99, Seventh International Waste Ma nagement and Landfill Symposium. Johnson, C.A., Kaeppeli, M., Brandenberger, S., Ulrich, A., and Baumann, W. (1999). Hydrological and Geochemical Factor s Affecting Leachate Composition in Municipal Solid Waste Incinerator Bottom Ash. Part II. The Geochemistry of Leachate from Landfill Lostorf, Switzerland. Journal of Contaminant Hydrology 40, 239-259. Karnchanawong, S., Ikeguchi, T., Karnchanawong, Seni, and Koottatep, S. (1995). Characteristics of Leachate Produced from Simulation of Landfill in a Tropical Country. Water Science and Technology 31 (No. 9), 119-127. Kim, A.G., Kazonich, G., and Dahlberg, M. ( 2003). Relative Solubility of Cations in Class F Fly Ash. Environmental Science and Technology 37, 4507-4511. Kim, I., Batchelor, B. (2001). Empirical Partitioning Leach Model for Solidified/Stabilized Wastes. Journal of Environmental Engineering 127 (No. 3) 188-195. Kjeldsen, P., Barlaz, M.A., Rooker, A.P., Baun, A., Ledin, A., and Christensen, T.H. (2002). Present and Long-Term Compos ition of MSW Landfill Leachate: A Review. Critical Reviews in Environmental Science and Technology 32, 3, 297336.

PAGE 100

89 Koerner, G. R., and Koerner R. M. (1990). Bi ological Activity and Potential Remediation involving Geotextile Landfill Leachate Fi lters. Geosynthetic Testing for Waste Containment Applications, ASTM STP 1081, R. M. Koerner. Ed., American Society for Testing and Materials Philadelphia. Kylefors, K., Andreas, L, and Lagerkvist, A. (2003). A Comparison of Small-Scale, Pilot-Scale and Large-Scale Tests for Pr edicting Leaching Behavior of Landfilled Wastes. Waste Management 23, 45-59. Levine, A. D. and Kroemer, L. R. (1989). A Critical Look at the Use of TOC and TOX as Indicator Parameters for Organic Contaminants in Landfill Leachates. Waste Management and Research 7, 337-349. Levine, A. D., Cardoso, A. J., Nayak, B., Rhea, L. R., Dodge, B. M., Harwood, V. J. (2005). Assessment of Biogeochemical De posits in Landfill Leachate Drainage Systems. Project Final Report Center for Solid and Hazardous Waste Management, Gainesville, FL. Lundtorp, K., Jensen, D.L., Sorensen, M.A., Mosbaek, H., and Christensen, T.H. (2003). On-Site Treatment and Landfilling of MSWI Air Pollution Control Residues. Journal of Hazardous Materials B97, 59-70. Maliva, R.G., Missimer, T.M., Leo, K.C., Statom, R.A., Dupraz, C., Lynn, M., and Dickson, J.A.D. (2000). Unusual calcite st romatolites and pisoids from a landfill leachate collection system, Geology 28,10, 931-934. Manning, K.C. and Robinson, N. (1999). Leach ate Mineral Reactions: Application for Drainage System Stability and Clogging Proceedings of the Seventh International Waste Manage ment and Landfill Symposium Cagliari, Italy, October, 99, 269-276. McIsaac, R. S., Rowe, R. K., Fleming, I. R., Armstrong, M. D. (2000). Leachate Collection System Design and Clog Development. 6th Environmental Engineering Specialty Conference of the CSCE and 2nd Spring Conference of the Geoenvironmental Division of the Canadian Geotechnical Society June: 66-73. Missmer International, CDM. (2000). L eachate Collection System Precipitate Characterization Solid Waste Authority of Palm Beach County Class I Landfill. Project Report

PAGE 101

90 Morris, J.W.F., Vasuki, N.C., Baker, J. A., and Pendleton, C.H. (2003). Finding from Long-Term Monitoring Studies at MSW La ndfill Facilities with Leachate Recirculation. Waste Management 23, 653-666. Owen, J.A. and Manning, D.A.C. (1997). Sili ca in Landfill Leachates : Implications for Clay Mineral Stabilities. Applied Geochemistry 12, 267-280. Paksy, A., Powrie, W., Robinson, J.P. and P eeling, L. (1998). A Laboratory Investigation of Anaerobic Microbial Clogging in Gr anular Landfill Drainage Media. Geotechnique 48 (No. 3), 389-401. Peeling, L., Paksy, A., Robinson, J. P., Powrie W. (1999). Removal of Volatile acids from Synthetic landfill Leachate by Anaer obic Biofilms on Drainage Aggregates: a Laboratory Study. Waste Management and Research, 17: 141-149. Reinhart, D., and Townsend, T. (1998). Assessment of Leachate Collection System Clogging at Florida Municipal Solid Waste Landfills. Florida Center for Solid and Hazardous Waste Management June. Rhea, L.R. (2004). Mineral Solubilization from Municipal Solid Waste Combustion Residues: Implications for Landfill Leach ate Collection Systems. M.S. Thesis, University of South Florida, Department of Civil and Environmental Engineering. Rittman, B. E., Fleming, I. R., and Rowe R. K. (1996). Leachate Chemistry: Its Implication for Clogging. Proceedings of the North American Water Congress Anaheim, California, June 22-28. Rohde, J. R., and Gribb, M. M. (1990). Biological and Particulate Clogging of Geotextile/Soil Filter Systems. Geosynt hetic Testing for Waste Containment Applications, ASTM STP 1081, Robert M. Koerner, Editor, American Society for Testing and Materials Philadelphia. Rowe, R.K. and Booker, J.R. (1998). Modeli ng Impacts Due to Multiple Landfill Cells and Clogging of Leachate Collection Systems. Canadian Geotechnical Journal 35 (No. 1), 1-14. Rowe, R.K. and Fleming, J.R. (1998). Estimating the Time for Clogging of Leachate Collection Systems, Proceedings of the 3rd International Congress on Environmental Geotechnics Lisbon, September, Vol. 1, pp.23-28.

PAGE 102

91 Rowe, R. K., Armstrong, M. D., Cullimore, D. R. (2000a). Partic le Size and Clogging of Granular Media Permeated with Leachate. Journal of Geotechnical and Geoenvironmental Engineering, September: 775-786. Rowe, R. K., Armstrong, M. D., Cullimore D. R. (2000b). Mass Loading and the Rate of Clogging due to Municipal Solid Waste Leachate. Canadian Geotechnical Journal, 37: 335-370. Rowe, R.K., Fleming, I.R., Rittman, B.R., Longstaffe, F.J., Cullimore, D.R., Moissac, R., Bennett, P., Cooke, A.J., Armstrong, M.D., and VanGulck, J. (2000c). Multidisciplinary Study of Cl ogging of Leachate Drains. 6th Environmental Engineering Specialty Conference of the CSCE London, Ontario, June. Rowe, R.K., VanGulck, J. and Millward, S. (2002). Biologically Induced Clogging of a Granular Medium Permeated with Synthetic Leachate. Canadian Journal of Environmental Engineering and Science 1, 135-156. Sallam, M. (2002). Treatability Study of M unicipal Solid Waste Landfills: Contaminated Leachate. M.S. Thesis, University of S outh Florida, Department of Civil and Environmental Engineering. San, Irem, and Onay, Turgut. (2001). Impact of Various Leachate Recirculation Regimes on Municipal Solid Waste Degradation. Journal of Hazardous Materials B87, 259-271. Song, G., Kim, H., Seo, Y., and Kim, S. (2004). Characteristic s of Ashes from Different Locations at the MSW Incinerator Equi pped with Various Air Pollution Control Devices. Waste Management 24, 99-106. Tchobanoglous, G., Theisen, H., Vigil, S. A. (1993). Integrated Solid Waste Management. Engineering Principles and Management Issues. McGraw Hill International Editions. Tchobanoglous, G., and Kreith, F. (2002). Handbook of Solid Waste Management Second Edition. New York: McGraw Hill. U.S. Environmental Protection Agency ( 1983). Potential Clogging of Landfill Drainage Systems, sponsored by Municipal E nvironmental Research Laboratory, Cincinnati, Ohio, EPA600/2-83-109, October.

PAGE 103

92 U.S. Department of Nuclear Energy (1990). Method for Accelerated Leaching of Solidified Waste BNL 52268. Upton, New York. U.S. Environmental Protection Agency (1991) Landfill Leachate Clogging of Geotextile (and Soil) Filters, EPA/600/2-91/025, July. U.S. Environmental Protection Agency (1993). Solid Waste Disposal Facility Criteria EPA530-R-93-017. Washington D.C. U.S. Environmental Protection Agency (2000) State of the Pract ice for Bioreactor Landfills. In: Workshop on Bioreactor Landfills. Arlington, Virginia. U.S. Environmental Protection Agen cy (2004). Municipal Solid Waste. http://www.epa.gov/epaoswer/non-hw/muncpl/disposal.htm Accessed September, 2004. van der Sloot, H.A. (1998). Quick Techniques for Evaluating the Leaching Properties of Waste Materials: Their Relation to D ecisions on Utilization and Disposal. Trends in Analytical Chemistry 17, (No. 5), 298-310. VanGulck, J.F., Rowe, R.K., Rittmann, B. E., and Cooke, A.J. (2003). Predicting Biogeochemical Precipitation in Landfill Leachate Collection Systems. Biodegradation 14, 331-346. VanGulck, J.F., and Rowe, R.K. (2004a). E volution of Clog Formation with Time in Columns Permeated with Synthetic Landfill Leachate. Journal of Contaminant Hydrology 75, 115-139. VanGulck, J.F., and Rowe R.K. (2004b). Influence of Landfill Leachate Suspended Solids on Clog (Biorock) Formation. Waste Management 24, 723-738. Wiles, Carlton (1996). Municipal Solid Wast e Combustion Ash: State-of-the-Knowledge. Journal of Hazardous Materials, 47, 325-344.

PAGE 104

93 Appendices

PAGE 105

94 Appendix A: Chemical Ch aracterization Tests Metals: Flame AA Calcium, Copper, Iron, Magnesium, Ma nganese, Potassium, Sodium, Zinc Source: Standard Methods for the Exami nation of Water and Wastewater 20th edition, 3111 B Direct Air-Acetylene Flame Method Equipment: PerkinElmer AAnalyst 100, Atomic Absorption Spectrometer Time Frame: 6 months with preservation, store at 4C. Preservation of Sample: Preserve by adding 5 mL of concentrated nitric acid to 1 L of sample and the sample can be stored for up to 6 months (EPA Method 3005). Preparation of Reference Standards: Make up at least three standards. The first should be below the expected concentra tion, the second should be near the expected concentration and the final standard should be above the expected concentration. The middle standard will be used to re-slope. Prepare by adding th e appropriate amount of reference standard to reagent grade water. Preparation of Sample: If th ere are large amounts of partic ulate matter the sample needs to be filtered. If not, ther e is no preparation required.

PAGE 106

95 Appendix A (continued) Table A-1: Conditions from Analytical Methods for Atomic Absorption Spectrometry, 2000. PerkinElmer Metal Wavelength (nm) Slit (nm) Relative Noise Characteristic Concentrations (mg/L) Characteristic concentration checks (mg/L) Linear Range (mg/L) Ca 422.7 0.7 1.00 0.092 4.00 5.0 Cu 324.8 0.7 1.00 0.077 4.00 5.0 Fe 248.3 0.2 1.00 0.110 6.00 6.0 Mg 285.2 0.7 1.00 0.008 0.30 0.5 766.5 0.7 1.00 0.043 2.00 2.0 K 769.9 0.7 1.40 0.083 4.00 20.0 Na 589.0 0.2 1.00 0.012 0.50 1.0 330.2 0.7 0.63 1.700 80.00 --Zn 213.9 0.7 1.00 0.018 1.00 1.0 Recommended Flame: Air-acetylene, oxidizing (lean, blue) Anions: Capillary Ion Electrophoresis Chloride, Bromide, Nitrate, Nitrit e, Sulfate, Fluoride, o-Phosphate Source: Standard Methods for the Exami nation of Water and Wastewater 20th edition, 4140 B: Capillary Ion Electrophoresi s with Indirect UV Detection Equipment: Beckman P/ACE 5000 Series Capillary Electroph oresis System eCap Capillary Tubing in cartridge : 375 m O.D., 75 m I.D., 50 cm L Preparation: The samples need to be filtered if it contains a high concentration of suspended solids. Once completed the sample may need to be diluted.

PAGE 107

96 Appendix B: Lysimeter Star-up and Operation Lysimeter Star-up Placement of the Waste and Field Capacity Test. Procedure: 1. Select the amount of each type of waste according to its weight and volume. For the co-disposal lysimeters, the wastes were mixed in 60-Liter containers prior to be placed in the reactor. 2. Place the waste in the reactors and close the outlet/sampling valve at the end of the leachate collection pipe. Add distilled water until the wastes are completely submerged. Record the amount of distil led water added to each reactor. 3. Leave the reactors in the submerge mode for 72 hours to allow the waste to absorb enough water to reach its saturation point. 4. Open the outlet/sampling valve and drain the reactors. Measure the amount of water/leachate recovered. Save samples for complete chemical and biological characterization. 5. The amount of water absorbed by the waste, considered to be th e field capacity, is going to be the difference between the am ount of water added and the amount of water/leachate recovered. 6. Cap the reactors and make sure there ar e no leaks. Connect the tubing from the top containers to the water/leachate distribution system. 7. Add four liters of distilled water to each lysimeter through the distribution systems to start the generation of leachate.

PAGE 108

97 Appendix B (continued) Lysimeter Operation Procedure: 1. After addition of four liters of distilled wa ter or recirculation of three liters of leachate, provide enough time to the liquid so it will travel through the reactor and generate leachate. 2. Once most of the four/three liters have been recovered in the bottom container, close the outlet/sampling valve to avoid ch anges of pressure inside the reactor. 3. Take samples for chemical and biological char acterization. 4. Replace the same amount of leachate taken during the sampling event with distilled water and open agai n the outlet/sampling valve. 5. The removed leachate needs to be promptly tested or preserved. 6. Set the timer for the pumps to start afte r the samples have been taken. Pumping time should be enough to transfer three liters of leachate from the bottom container to the upper one. 7. Recirculate three liters of leachate into each reactor by tipping the upper containers to simulate a rain event of 15 to 20 minutes. 8. Repeat steps 1 through 7 with a 24 hours time interval.

PAGE 109

98 Appendix C: Summary of Leachate Charac teristics from Laboratory Lysimeter Tests Conducted from May 5 through November 29, 2004

PAGE 110

99 Table C-1. Lysimeter Leachate Monitoring Sum mary. Ash 1: 80% Bottom Ash, 20% Fly Ash. Parameter Mean Median Minimum Maximum Standard Deviation Standard Error Skewness Kurtosis Sample Variance n pH 11.74 11.76 11.4 12.01 0.16 0.02 -0.28 -0.93 0.03 99 Conductivity (S/cm) 20.68 23.3 13.41 26.5 4.21 0.42 -0.44 -1.46 17.71 99 Temperature (C) 22.28 22.3 19.3 24.8 1.43 0.16 -0.34 -0.68 2.04 77 ORP (mV) -46.91 -44 -140 -0.2 28.09 3.20 -0.83 0.93 788.99 77 Turbidity (NTU) 0.98 0.74 0.15 5.07 0.89 0.09 2.06 5.92 0.79 99 Ammonia (mg/L NH3) 246.30 54.99 0.51 1,189 314.1 59.35 1.34 1.35 98,640 28 Total Alkalinity (mg/L as CaCO3) 1,872 1,866 1,064 2,133 160.9 18.97 -1.85 8.32 25,904 72 Volatile Acids (mg/L as Acetic Acid) 19.2 16.7 16.7 33.3 5.85 0.83 2.09 2.48 34.17 49 Total Solids (mg/L) 13,118 12,863 11,626 17,826 1,303 217.24 2.40 6.52 1.7E+06 36 Volatile Solids (mg/L) 1,367 916.65 726.7 4,873 932.3 155.39 2.23 5.19 869,253 36 Estimated TDS (mg/L) 11,973 11,999 8,803 14,975 1,547 257.95 -0.001 -0.35 2.4E+06 36 Total Nitrogen (mg/L as N) 8.60 9 < 0.2 20 5.48 0.91 0.44 0.45 29.99 36 Total Phosphorus (mg/L as PO4) 5.40 5.1 1.5 10.9 2.31 0.38 0.52 -0.21 5.34 36 Silica (mg/L as SiO2) 4.7 3.8 < 0.3 18.3 4.24 0.71 1.89 4.13 18.01 36 Bromide (mg/L) 172.71 171.6 66.5 305.43 52.92 9.36 -0.009 0.24 2,800.5 33 Chloride (mg/L) 5,148 4,989 3,325 7,431 964.3 167.86 0.49 0.21 929,882 36 Sulfate (mg/L) 71.73 71.4 23.97 122.8 30.97 6.76 -0.03 -1.27 958.95 21 Calcium (mg/L) 1,826 1,556 638.7 4,360 978.9 163.15 1.23 1.14 958,265 36 Magnesium (mg/L) 0.038 0.011 < 0.01 0.855 0.141 0.023 5.920 35.330 0.020 36 Copper (mg/L) 0.176 0.165 0.054 0.376 0.085 0.014 0.618 -0.238 0.007 36 Iron (mg/L) 0.180 0.187 0.073 0.296 0.058 0.010 0.218 -0.412 0.003 36 Manganese (mg/L) 0.023 0.021 < 0.01 0.088 0.022 0.004 1.448 2.147 0.001 36 Zinc (mg/L) 0.250 0.234 0.033 0.362 0.065 0.011 -0.581 2.296 0.004 36 Potassium (mg/L) 1,065 1,217 350.4 1,494 335.6 55.94 -0.691 -0.818 112,650 36 Sodium (mg/L) 1,984 1,974 808 502 730.2 121.71 1.785 7.74 533,240 36 Aluminum (mg/L) 0.099 0.055 < 0.002 0.65 0.121 0.020 2.950 11.627 0.015 36 A pp endix C ( continued )

PAGE 111

100 Table C-2. Lysimeter Leachate Monitoring Sum mary. Ash 2: 80% Bottom Ash, 20% Fly Ash. Parameter Mean Median Minimum Maximum Standard Deviation Standard Error Skewness Kurtosis Sample Variance n pH 11.73 11.77 11.4 12.05 0.17 0.02 -0.22 -1.06 0.03 99 Conductivity ( S/cm) 20.06 22.9 12.2 24.8 4.34 0.44 -0.67 -1.24 18.80 99 Temperature (C) 22.24 22 19.3 24.7 1.45 0.17 -0.18 -0.84 2.09 77 ORP (mV) -117 -122 -159 121 34.56 3.94 4.38 29.20 1,195 77 Turbidity (NTU) 1.13 0.62 0.13 8.57 1.61 0.16 2.87 8.36 2.58 99 Ammonia (mg/L NH3) 475.06 86.02 1.36 3,816 864.70 163.41 2.83 8.65 747,698 28 Total Alkalinity (mg/L as CaCO3) 1,904 1,900 1,226 2,250 179.48 21.15 -0.69 2.13 32,211 72 Volatile Acids (mg/L as Acetic Acid) 22.68 16.7 8.33 35.7 8.37 1.20 0.49 -1.63 70.12 49 Total Solids (mg/L) 12,104 11,993 10,700 15,873 1,066 177.66 1.65 3.86 1.1E+06 36 Volatile Solids (mg/L) 1,313 963.35 633.3 3,346 777.17 129.53 1.79 2.05 603,991 36 Estimated TDS (mg/L) 10,922 11,268 7,295 13,425 1,249 208.29 -0.77 1.11 1.5E+06 36 Total Nitrogen (mg/L as N) 7.20 8.5 < 0.2 20 4.41 0.74 -0.07 0.94 19.44 36 Total Phosphorus (mg/L as PO4) 4.71 4.15 0.9 16.5 2.90 0.48 1.94 6.71 8.40 36 Silica (mg/L as SiO2) 4.44 3 < 0.3 19.4 3.98 0.66 1.89 5.02 15.81 36 Bromide (mg/L) 178.01 162.7 43.1 777.08 111.42 18.57 4.59 25.21 12,414 36 Chloride (mg/L) 4,562 4,478 1,237 8,209 1,208 201.43 0.09 2.99 1.5E+06 36 Sulfate (mg/L) 96.57 57.96 24.49 460.24 108.07 26.21 2.63 8.19 11,679 17 Calcium (mg/L) 1,727 1,380 640.5 4,526 948.49 158.08 1.14 0.96 899,626 36 Magnesium (mg/L) 0.052 0.01 < 0.01 0.775 0.154 0.026 4.116 16.79 0.024 36 Copper (mg/L) 0.092 0.109 < 0.01 0.16 0.052 0.009 -0.680 -0.996 0.003 36 Iron (mg/L) 0.174 0.165 0.028 0.35 0.067 0.011 0.638 0.628 0.005 36 Manganese (mg/L) 0.023 0.023 < 0.01 0.073 0.021 0.004 1.022 0.498 0.001 36 Zinc (mg/L) 0.240 0.238 0.11 0.344 0.060 0.010 -0.009 -0.618 0.004 36 Potassium (mg/L) 944.5 1,057 254.2 1,340 308.38 51.40 -0.843 -0.486 95,099 36 Sodium (mg/L) 1,864 1,879 568 2,869 580.86 96.81 -0.467 -0.302 337,398 36 Aluminum (mg/L) 0.153 0.16 < 0.002 0.53 0.136 0.023 0.769 0.181 0.019 36 A pp endix C ( continued )

PAGE 112

101 Table C-3. Lysimeter Leachate Moni toring Summary. MSW: 100% MSW. Parameter Mean Median Minimum Maximum Standard Deviation Standard Error Skewness Kurtosis Sample Variance n pH 6.58 6.7 5.84 7.08 0.31 0.03 -0.87 -0.23 0.10 99 Conductivity ( S/cm) 5.01 5.42 1.80 7.64 1.61 0.16 -0.47 -0.79 2.61 99 Temperature (C) 22.17 22.1 19.3 24.6 1.45 0.17 -0.19 -0.94 2.10 77 ORP (mV) -87.38 -83 -137 -14 25.44 2.90 -0.09 -0.38 647.11 77 Turbidity (NTU) 208.54 205 60.1 377 85.79 8.62 0.16 -1.02 7,359 99 Ammonia (mg/LNH3) 1,029 78.2 0.51 8,715 1,984 374.98 2.74 8.24 4E+06 28 Total Alkalinity (mg/L as CaCO3) 3,177 3,083 2,066 4,600 680.8 80.23 0.28 -0.85 463,493 72 Volatile Acids (mg/L as Acetic Acid) 307.16 100 16.7 1,025 314.52 44.93 0.63 -0.93 98,922 49 Total Solids (mg/L) 6,785 7,272 2,940 10,686 2,699 449.85 -0.05 -1.53 7.3E+06 36 Volatile Solids (mg/L) 3,527 4,292 1,160 6,080 1,661 276.97 -0.10 -1.59 2.8E+06 36 Estimated TDS (mg/L) 5,006 4,963 3,201 7,490 1,237 206.23 0.43 -0.62 1.5E+06 36 Total Nitrogen (mg/L as N) 84.56 60 40 180 50.99 8.50 0.85 -1.06 2,600.37 36 Total Phosphorus (mg/L as PO4) 16.89 14.7 0.6 42 13.12 2.19 0.48 -1.01 172.19 36 Silica (mg/L as SiO2) 172.97 164.5 100 268 43.24 7.21 0.50 -0.44 1,869 36 Bromide (mg/L) 2.45 1.65 0.79 9.17 2.49 0.79 2.65 7.44 6.18 10 Chloride (mg/L) 107.67 96.78 39.39 191.69 35.97 5.99 0.93 0.50 1,293 36 Phosphate (mg/L) 417.77 466 17.03 826.71 347.33 96.33 -0.16 -1.92 120,640 13 Sulfate (mg/L) 82.94 36.43 10.85 222 88.10 29.37 0.80 -1.48 7,761 9 Calcium (mg/L) 1,128 1,194 423.7 1,899 452.15 75.36 0.11 -1.26 204,437 36 Magnesium (mg/L) 50.27 50.35 27 73.5 9.66 1.61 -0.12 0.32 93.35 36 Copper (mg/L) 0.045 0.053 < 0.01 0.089 0.033 0.006 -0.202 -1.556 0.001 36 Iron (mg/L) 15.19 13.16 0.829 49.08 13.84 2.307 0.602 -0.694 191.61 36 Manganese (mg/L) 2.996 3.116 0.086 7.65 2.52 0.420 0.375 -1.097 6.352 36 Potassium (mg/L) 102.90 94.85 27.3 165.3 40.42 6.74 -0.24 -0.71 1,633 36 Sodium (mg/L) 177.61 178 60 279 49.53 8.26 -0.31 0.58 2,453 36 Aluminum (mg/L) 0.644 0.685 0.12 0.99 0.215 0.036 -0.451 -0.535 0.046 36 A pp endix C ( continued )

PAGE 113

102 Table C-4. Lysimeter Leachate Monitoring Summary. Mix 1: 60% MSW, 30% WTE Ash, 10% Treatment Residuals. Parameter Mean Median Minimum Maximum Standard Deviation Standard Error Skewness Kurtosis Sample Variance n pH 6.45 6.56 5.82 6.79 0.25 0.03 -0.85 -0.48 0.06 99 Conductivity ( S/cm) 7.13 7.53 1.96 12.15 2.91 0.29 -0.41 -0.67 8.48 99 Temperature (C) 22.11 22 19.1 24.4 1.44 0.16 -0.28 -0.74 2.08 77 ORP (mV) -77.3 -83 -147 -7 30.88 3.52 0.42 -0.23 953.27 77 Turbidity (NTU) 144.54 139 51.7 430 53.43 5.37 1.94 7.84 2,854.98 99 Ammonia (mg/LNH3) 2,995 75.56 3.06 17,296 4,913 928.53 1.84 2.90 2.4E+07 28 Total Alkalinity (mg/L as CaCO3) 2,670 2,250 1,733 4,533 842.46 99.28 0.61 -1.18 709,734 72 Volatile Acids (mg/L as Acetic Acid) 132.69 33.3 16.7 875 189.86 27.12 1.93 3.88 36,047 49 Total Solids (mg/L) 7,719 5,520 4,526 14,940 3,390 565.02 0.98 -0.36 1.1E+07 36 Volatile Solids (mg/L) 3,307 2,210 1,720 7,593 1,739 289.91 1.11 0.03 3E+06 36 Estimated TDS (mg/L) 5,916 4,870 3,457 9,835 1,845 307.55 0.81 -0.52 3.4E+06 36 Total Nitrogen (mg/L as N) 82.78 61 30 240 55.78 9.30 1.89 2.46 3,110 36 Total Phosphorus (mg/L as PO4) 4.94 5 < 0.2 9.8 2.78 0.46 -0.16 -0.84 7.72 36 Silica (mg/L as SiO2) 170.75 145 103 327 57.65 9.61 1.04 0.18 3,323 36 Bromide (mg/L) 39.18 27.985 10.09 172.05 32.48 5.93 2.80 9.21 1,054.8 30 Chloride (mg/L) 1,084 1,052 243.86 1,890 291.12 50.68 0.17 2.60 84,748 36 Phosphate (mg/L) 744.86 659.25 16.13 1,705 665.99 200.81 0.11 -1.82 443,553 11 Sulfate (mg/L) 215.04 65.01 13.77 719 280.64 81.01 1.13 -0.50 78,758 12 Calcium (mg/L) 1,182 842.95 416.1 2,961 712.32 118.72 1.42 1.11 507,399 36 Magnesium (mg/L) 189.55 184.7 123.5 300.7 33.25 5.54 1.14 2.78 1,105.7 36 Copper (mg/L) 0.081 0.060 < 0.01 0.384 0.095 0.016 2.091 4.50 0.01 36 Iron (mg/L) 11.11 6.341 1.527 38.59 10.29 1.715 1.356 1.421 105.87 36 Manganese (mg/L) 1.191 0.414 < 0.01 4.679 1.524 0.254 1.348 0.380 2.322 36 Potassium (mg/L) 128.46 130.1 76.7 229.3 31.29 5.53 0.995 2.389 979.27 36 Sodium (mg/L) 389 377.15 219 520 58.15 9.97 -0.343 1.513 3,381 36 Aluminum (mg/L) 0.5 0.48 0.18 0.86 0.152 0.025 0.477 0.191 0.023 36 A pp endix C ( continued )

PAGE 114

103 Table C-5. Lysimeter Leachate Moni toring Summary. Mix 2: 60% MSW, 30% WTE Ash, 10% Treatment Residuals. Parameter Mean Median Minimum Maximum Standard Deviation Standard Error Skewness Kurtosis Sample Variance n pH 6.63 6.66 6.11 6.93 0.17 0.02 -0.80 0.59 0.03 99 Conductivity ( S/cm) 6.84 7.62 1.9 11.22 2.62 0.26 -0.72 -0.46 6.87 99 Temperature (C) 22.12 22 19 24.6 1.49 0.17 -0.21 -0.89 2.23 77 ORP (mV) -99.64 -102 -131 -57 16.44 1.87 0.51 -0.30 270.16 77 Turbidity (NTU) 187.92 171 71.5 331 62.97 6.33 0.43 -0.71 3,965 99 Ammonia (mg/L NH3) 3,590 101.32 3.4 15,031 5,309 1,003 1.20 0.02 2.8E+07 28 Total Alkalinity (mg/L as CaCO3) 2,896 2,866 1,666 4,800 690.29 81.35 0.45 -0.36 476,500 72 Volatile Acids (mg/L as Acetic Acid) 172.76 33.3 16.7 675 213.64 30.52 0.94 -0.73 45,640 49 Total Solids (mg/L) 7,009 5,950 4,353 13,540 2,514 419.15 1.18 0.65 6.3E+06 36 Volatile Solids (mg/L) 2,829 2,313 1,853 5,453 1,023 170.60 1.02 0.02 1.1E+06 36 Estimated TDS (mg/L) 5,846 5,696 3,831 9,246 1,472 245.43 0.64 -0.15 2.2E+06 36 Total Nitrogen (mg/L as N) 119.89 109 80 220 38.42 6.40 1.59 1.67 1,476.1 36 Total Phosphorus (mg/L as PO4) 8.11 8.5 < 0.2 20 4.87 0.81 0.26 -0.37 23.67 36 Silica (mg/L as SiO2) 160.81 128 55 424 81.01 13.50 1.52 2.22 6,563.2 36 Bromide (mg/L) 30.92 25.03 12.83 82.58 18.43 3.07 2.36 4.31 339.51 36 Chloride (mg/L) 900.01 882.91 427.88 1,323 233.73 38.96 -0.02 -0.49 54,628 36 Phosphate (mg/L) 1,241 1,302 496.56 1,715 385.47 128.49 -0.78 0.44 148,584 9 Sulfate (mg/L) 165.71 39.70 12.22 449 194.19 68.66 0.71 -1.92 37,707 8 Calcium (mg/L) 1,120 1,065 396.4 2,326 497.73 82.96 1.16 0.95 247,734 36 Magnesium (mg/L) 156.90 156 121.3 189.9 16.50 2.75 0.09 -0.41 272.31 36 Copper (mg/L) 0.067 0.068 < 0.01 0.34 0.069 0.011 1.904 5.906 0.005 36 Iron (mg/L) 8.699 3.376 0.801 28.95 9.130 1.522 0.948 -0.631 83.348 36 Manganese (mg/L) 0.819 0.477 < 0.01 3.381 0.899 0.150 1.497 1.587 0.808 36 Potassium (mg/L) 115.76 118.55 75.8 146.5 16.72 2.79 -0.53 0.041 279.53 36 Sodium (mg/L) 306.99 301.25 240 407 34.65 5.78 0.76 1.25 1,200.9 36 Aluminum (mg/L) 0.481 0.485 0.1 0.86 0.189 0.032 -0.180 -0.542 0.036 36 A pp endix C ( continued )