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 00000nas 2200000Ka 4500
controlfield tag 008 s2002 xx |||| |||||| eng
datafield ind1 7 ind2 024
subfield code a M36-00486-ML-1094
Sustainable Futures 2002.
Estudio de viabilidad de las opciones sostenibles del saneamiento para Santa Elena en la zona de Monteverde.
Feasibility study of sustainable sanitation options for Santa Elena in the zone of Monteverde.
g agosto 2002/August 2002.
Books / Reports / Directories
Santa Elena -- Monteverde
Scanned by Monteverde Institute.
The State of Water in Monteverde, Costa Rica: A Resource Inventory.
3.a.5, e Feasibility Study of Sustainable Sanitation Options for Santa Elena in the zone of Monteverde Sustainable Futures 2002 August 2002
Table of Contents 1. Introduction 1 1.1 Latin America 3 1.2 Sustainability as a Water Management Objective ...... 3 2.0. Available Wastewater Treatment Technologies for Santa Elena 5 2.1. On-Site Technology 5 2.1.1. Composting Toilets 8 2.2.2. Septic Tanks 8 2.2.3. Improved On-Site Treatment Units 8 188.8.131.52. Inverted Trench 8 184.108.40.206. Aerobic Treatment Unit 9 2.3. Off-Site Treatment Technologies 9 2.3.1 Aquatic Systems ... 9 220.127.116.11. Lagoons 9 18.104.22.168. Constructed Wetlands 11 22.214.171.124. Aquaculture 11 126.96.36.199. Sand Filters 11 2.4. Terrestrial Systems 11 2.4.1.Slow Rate Systems 12 2.4.2. Rapid Infiltration 12 2.4.3. Subsurface Infiltration 12 2.5. Mechanical Systems 12 2.6. Treatment Performance 12 2.7. Treatment Systems Impact on Sustainable Development 14 2.8. Site Limitations 15 2.9. Collection (Sewerage )Systems 16 2.10. Sludge Treatment 17 2.10.1. Vermistabilization 18 2.10.2 Composting 18 3. Santa Elena Study 19 3.1 Climate 19 3.2. Soils 19 3.3. Current Wastewater Conditions 20 3.3.1. Greywater 20 3.3.2. Blackwater 21 3.4. Research into Water Quality 21 3.5. Data Collection 21 3.5.1 Water Survey 21 3.5.2. Mapping 22 3.5.3. Catchments 22
3.6. Summary 22 4. Recommendations 24 5. The Future 26 5.1 Future Studies 26 5.2 Community Education 26 5.3 Summary 27 Works Referenced 28 Appendix 1. Physical-Chemical Data 30 Appendix 3. Design Philosophy 34 Appendix 3. Water Survey 36 Appendix 4. Catchments 39
Feasibility study of sustainable sanitation options for Santa Elena, Monteverde 1. Introduction Costa Rica is part of the Central American land bridge that connects North America to South America. Costa Rica lies south of Nicaragua and north of Panama. Santa Elena is located in the western central region of Costa Rica on the Pacific side of the continental divide. Creoles settled in the Monteverde region in the 1920's followed by the North American Quakers in the 1950's. Monteverde has experienced significant unregulated growth in the past two decades due to the rise in eco-tourisms as a result of the biological work in the 60's and 70's 13 Development has proceeded in an ad-hoc fashion due to the lack of planning, a local government, and national enforcement in the region 6 This is a report on the current wastewater sanitation in Santa Elena, Costa Rica and a perspective on what the future might hold. It was done to meet the second of three parts of the Monteverde Institutes initiative to develop a complete understanding of the Monteverde zone. The focus of this wastewater feasibility study was on the Santa Elena area due to the fact that most of the population lives in that section of the zone. The Monteverde zone includes Monteverde, Cerro Plano, Santa Elena and the surrounding area. Sustainable Futures 2002 has focused on the town of Santa Elena. The overall project includes growth projects, zoning recommendations and the water study. Sustainable Futures 2002 work included the physical mapping of Santa Elena determining the number of houses, location of houses, ridgelines, roads, and commercial/institutional buildings, creating population estimates, talking to community members about their perceptions and ideas. We compared our findings to the work previously collected on maps (from 1984-6, and 1992), aerial photos, publications, and though community consultations to obtain the projected growth rates for Santa Elena. At this time the zone of Monteverde has no local government but as of December of 2002 it is anticipated that the Concejo Municipal de Distrito will be installed. This local government will have the power to collect local taxes and enforce the local and national laws. A spokesperson for the Concejo 2 has stated that zoning regulations for the Monteverde zone will be a primary point of focus; however, he believes that the local water municipality, Acueductos y Alcantarilllados (AyA), will be dealing with the details of the wastewater issues. For this feasibility study, we worked within perimeters that are currently being used for many Latin American countries. These perimeters have shown that in order for a wastewater management plan to be effective in developing countries it needs to meet specific criteria. In our recommendations for Santa Elena we have worked with these criteria to outline our main objectives. The objectives were: 1) a low capital cost budget 2) a low operational and maintenance budget
3) allow for growth in stages with the community 4) be sustainable 5) allow for community participation in all stages of the plan Sustainable Futures 2002 current projections call for a 7% per year increase in the population in and around Santa Elena. Currently, there are 342 residences and 115 commercial/industrial buildings in Santa Elena with an estimated six (6) people per household. Projections for 2010 show there will 634 residences and 254 commercial/industrial buildings with projections for 2020 showing there will 931 residences and 263 commercial/industrial buildings (table 1). These numbers reflect the movement of people into and out of the study area. Growth Projections # of residences # of people # of buildings 2002 342 2,166 115 2010 634 3,430 254 2020 931 5,507 263 Table 1. Current conditions projected forward to predict future growth. This report examines the current state of wastewater that has evolved as a result as of this development. Wastewater as used in this report, consists of 85% of the potable water that enters the building 2 As a design value we used the conservative number of 100% of potable water enter the wastewater system. Residential wastewater can be broken down into two categories, blackwater and greywater. Blackwater is wastewater that contains excrement and/or urine from humans. Blackwater has high concentrations of solids and contributes significant amount of nutrients like phosphorus and nitrogen, in addition to hazardous pathogens to the water cycles 12 In this zone, blackwater is generally treated in a septic tank with a leachfield. Greywater is all other wastewater that humans have utilized in their daily living such as the activities of washing laundry, bathing and showering. Greywater has a low concentration of solids and contributes less nutrients and hazardous pathogens to the water cycles 12 In this zone greywater is discharged untreated outside the home to the street, garden, or lawn. This type of wastewater discharge is currently affecting rivers in the area with the potential to further exacerbation due to the unregulated population growth of the area. Both of these wastewater products are examined in this report but since blackwater has a minimal treatment option in place, the emphasis has been placed on the more immediate problem of greywater. Commercial/industrial waste is not dealt with in this report; however, if these wastes were to enter into the residential treatment system, we would recommend that they meet or be treated to the quality level of residential discharge.
1.1 Latin America In general, in Latin America, 80% of the population is reported to have access to sanitation with urban areas having a higher percent of coverage then rural areas. Conventional sewerage covers 49% of the areas while 31% have on-site sanitation systems. Of the wastewater collected conventionally only 13% is treated. Most of the treatment plants are not meeting water quality discharge standards 10 In recent years there has been a focus on improving water supply. Wastewater, until recently, has not been addressed especially in small towns. Small towns are defined as settlements that are sufficiently large yet dense enough to benefit from a piped or community wastewater system, but to small too be able to afford a traditional deep sewerage with activated sludge treatment system. In a report by the Environmental Health Project, Sanitation in small towns in Latin America and the Caribbean: Practical Methodology for Designing a Plan for Sustainable Sanitation Services (2001), one of the conclusions reached was that sanitation clearly lags behind water supply and that very few small towns have managed to provide sustainable sanitation services 10 One important aspect for sustainable wastewater collection is the separation of blackwater, grey water, stormwater, and industrial wastes. In many communities in Latin American countries, including small towns like Santa Elena, the culture of separating blackwater and greywater and treating blackwater already exists 12 This condition is favorable for stepwise implementation of sustainable objectives. Industrial wastes need to be treated separately if they contain toxic substances 12 Often these wastes are discharged into the blackwater system or simply discharge untreated. If a separate treatment facility cannot be installed then pretreatment of industrial waste is required. If this does not happen the treatment of sludge will be more difficult due to industrial contamination (ex. heavy metal) and the re-use of sludge will be limited. Projections for the annual population growth rate in Latin America is 2.3%. Population growth for Santa Elena is currently 4.7% more than for the rest of Latin America. Without a stable sustainable wastewater plan, the wastewater/sanitation problems that much of Central America face may soon be prevalent in this community. 1.2. Sustainability as a Water Management Objective Sustainability has been defined by the World Commission on the Environment on Sustainable Development as: "Sustainable Development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs" 15 Natural ecosystem cycles are a basis for determining what are environmentally sustainable management practices. Discharge of wastewater that exceeds the natural purification capacity of that environment will result in an accumulation of organic matter
(carbon), nitrogen, phosphorus and/or other pollutants that cannot be absorbed by the ecosystem. Accumulation of organic matter results in a high oxygen demand that cannot be met by the natural system 12 Natural cycles include water, carbon, nitrogen, phosphorus and other nutrients. Nature has the capacity to recycle these nutrients, until the system is altered by natural events or human influence. For example, water is part of the biosphere in oceans, lakes, rivers and other waterways. It exists in the ground as aquifers that can perculate up in springs, be used by vegetation for nutrients, and replenish the flow of rivers. Water from vegetation and waterways is then evaporated into the atmosphere as clouds. The water in the clouds can then be released to the biosphere in the form of precipitation. In a natural cycle this precipitation then peculates into the ground to replenish the ground water supply and enter the waterways. Incomplete cycles occur when impermeable surfaces are built causing the water to run-off the ground into streams and rivers instead of naturally percolating into the ground water supply. In wastewater management the nitrogen (N) and phosphorus (P) cycles are often incomplete. N & P are chemically manufactured from atmospheric nitrogen and phosphate rock and are used in agriculture as fertilizers for crops. These crops are consumed and the excess N & P discharged via excreta into the wastewater. When wastewater is not properly treated excess nutrients can enter the water cycle by leaching into the groundwater supply or through run-off enters rivers changing the chemistry of the waters. Biodiversity of the rivers is decreased due to the enhanced nutrient conditions. These linear processes, like removing phosphate from phosphate rock, eventually deplete supplies and pollute the waterways 12 Sustainability calls for a closing of the cycles. This does not generally occur with traditional wastewater treatment systems unless the system incurs great expense 11 Wastewater management can compliment the natural cycles by returning water to the environment for ground water recharge, irrigation of natural or cultivated lands or through other processes 15 Wastewater treatment can work in harmony with this concept. For example, human excreta are a valuable source for nutrients that can be used to help close the natural cycles (table 2). In Sweden it has been estimated that the nutrients values from the populations urine per year are equivalent to 15-20% of commercial fertilizer used in 1993 12 Natural wastewater processes, both aquatic and terrestrial, can provide low cost sanitation and environmental protection, which can be beneficial to water reuse. Mechanized wastewaters processes are harder to maintain, cost more, and generally do not contribute to sustainability. Natural technologies are appropriate in developing countries especially ones with environmental problems. Environmental problems can include deforestation, agriculture, and the use of pastureland for livestock, which create erosion and deplete the soils of nutrients. Groundwater depletion and be recharged with wastewater reuse. Terrestrial wastewater treatments (slow rates, overland flow, rapid infiltration) recharge
the groundwater supply while benefiting forests, some types of agriculture, and pastures 15 These natural systems are proven technologies in tropical regions. Human Excreta per capita quantities and their resource value Faeces Urine Excreta Quantity and consistency Gram/capita/day (wet) 250 1200 1450 Gram/capita/day (dry) 50 60 110 Chemical composition (% of dry solids) Organic matter 92 75 83 Carbon C 48 13 29 Nitrogen N 4-7 14-18 9-12 Phosphorus (as P2O5) 4 3.7 3.8 Potassium (as K2O) 1.6 3.7 2.7 Table 2(a). Comparison with other wastes (% of dry solids) N P2O5 K2O Human excreta 9-12 3.8 2.7 Plant matter 1-11 0.5-2.8 1.1-11 Pig manure 4-6 3-4 2.5-3 Cow manure 2.5 1.8 1.4 Table 2(b). Table 2 (a & b). Table (a) shows the amount of wet and dry excreta per person per day and it chemical composition. Table (b) compares human excreta to other natural wastes. International Source book on environmentally sound technologies for wastewater and storm water management. 2.0. Available Wastewater Treatment Technologies for Santa Elena In order to determine the most viable wastewater treatment options for Santa Elena a range of systems and technologies were considered. These systems include on-site and off-site treatment technologies and are described in more detail below (figure 1). (For a full account of how these systems work refer to Crites & Tchobanoglous, 1998). Capital costs, operational and maintenance costs were a primary objective. Figure 2, 3, 4, and 5 break these expenses down. Types of Treatment Options Oxidation Ditch Mechanical---------Extended Aeration Sequencing Batch Reactor Trickling filter SCP
Free-Water Surface or Facultative---Constructed Wetlands ------Subsurface Flow Water Hyacinth or Aquatic------Aerated -------Aquaculture ----------Duck Weed (lagoons) Hydrograph Intermittent or Controlled----Sand Filter ------------------Recirculating Release Flow-rate Terrestrial -----------Overland Flow Rapid Infiltration Subsurface Infiltration Figure 1. A summary of some of the different systems used for wastewater treatment. Modified from: Perez, Ernesto. Appropriate Technologies of Wastewater Treatment for Sustainable Development. Frequently used Wastewater Treatment Systems Treatment Systems Construction Costs (US$/Inhabitant) Preliminary Treatment 2 9 Primary Treatment 24 36 Facultative Ponds 12 36 Anaerobic Pond Facultative Pond 12 30 Facultative Aerated Lagoon 12 30 Complete Mixed Aerated Sedimentation Pond 12 30 Conventional Activated Sludge 71 142 Extended Aeration (Continuous Flow) 47 95 Sequencing Batch Reactor 59 95 Low Rate Trickling filter 59 107 High Rate Trickling Filter 47 83 Upflow Anaerobic sludge Blanket 24 47 Septic Tank Anaerobic Filter 36 95 Slow Rate Infiltration 12 24 Rapid Infiltration 6 18 Subsurface Infiltration 6 18 Overland Flow 6 18 Figure 2. Comparison among the most frequently used systems for wastewater treatment in developing countries as the cost per person. Updated to current rates with the Consumer Price Index 6 Modified from von Sperling, Marcos. 1996.
Present Worth 0 1.5 3 4.5 6 7.5 9 Mechanical plant Facultative lagoon Aerated lagoon Aquaculture Constructed Wetlands Sand filters Rapid Infiltration Overland Flow Slow Rate Process $/ m 3 / d Figure 3. Present worth represents costs as an equivalent cost that is the current investment require to satisfy all project costs over its lifetime. Modified from Perez, Ernesto. Appropriate Technologies of Wastewater Treatment for Sustainable Development and update to current rates with the C2onsumer Price Index 6 Capital Costs excluding land (1000$) 0 0.5 1 1.5 2 2.5 3 3.5 4 Mechanical plant Facultative lagoon Aerated lagoon Aquaculture Constructed Wetlands Sand filters Rapid Infiltration Overland Flow Slow Rate Process $ per cubic meter treated daily Figure 4. The capital costs of building a waste treatment facility not including the purchase of land depending. Figures are based on a 373785 m3 facility. (The Consumer Price Index 6 was used to update to 2001 prices.) Modified from Perez, Ernesto. Appropriate Technologies of Wastewater Treatment for Sustainable Development. Operational and Maintaince Costs 0 0.2 0.4 0.6 0.8 1 1.2 Mechanical plant Facultative lagoon Aerated lagoon Aquaculture Constructed Wetlands Sand filters Rapid Infiltration Overland Flow Slow Rate Process Dollars per m 3 /d of treated waste water
Figure 5. Operational and Maintenance costs for a 3785 -37 m3/d facility (The Consumer Price Index 6 was used to update to 2001 prices.) Costs include labor, energy, chemical such as replacement equipment and parts. Figures are based on a 373785 m3 facility. Modified from Perez, Ernesto. Appropriate Technologies of Wastewater Treatment for Sustainable Development. 2.1. On-Site Technology On-site treatment relies on the decomposition of organic wastes in human excreta by bacteria and includes technologies like the pit-latrine, composting toilet, pour flush toilet, septic tank, inverted trench and aerobic treatment unit 12 2.1.1. Composting Toilets Composting toilets decompose faecal sludge under aerobic conditions. Air is introduced through an opening that passes through the sludge and exits through a vent. Excess liquid is allowed to drain for collection or evaporation. Two adjoining composting chamber can be used alternately to allow one to mature for direct composting into gardens. Other organic food wastes can be added to the faecal sludge and the addition of items like sawdust or newspaper help to balance the carbon to nitrogen levels for optimal composting 12 2.2.2. Septic Tanks Watertight tanks, called septic tanks, can receive both black and grey water. In Santa Elena septic tanks are currently used for the collection of blackwater. A septic tank works by settling out solids and floating materials. The tank can be partitioned to reduce the impediment of flow and to improve solid removal. Overflow is directed to a leachfield, trench or into sewerage collection pipes. Processing effluent through onsite leachfields works well in soils with high permeability. In soils of low permeability on-site trenches provide a larger surface area of percolation then leachfields. When lots size does not allow on-site treatment effluent can be collected via condominial or conventional collection system to be treated off-site in treatment facilities such as lagoons 12 2.2.3. Improved On-Site Treatment Units These systems improve the performance of an on-site system by reducing the Biological Oxygen Demand (BOD), Suspended Solids (SS) or nutrients (appendix 1). The goal is to prevent groundwater pollution or enable water reuse 12 188.8.131.52. Inverted Trench Overflow from the septic tank is introduced at the base of a sand layer contained by an impermeable layer. The effluent then peculates up surrounding the sand particles allowing the sand to act as a slow filter. Bacteria growing on the surface of the sand can degrade organic material reducing the BOD. Daily fluxes of water into the system allow the upper layer of sand to alternate between aerobic and anaerobic conditions. Phosphate removing materials may also be added to the sand layer decreasing the N content 12
184.108.40.206. Aerobic Treatment Unit This unit is similar to a septic tank that is partitioned. Partitioning encourages sedimentation of wastewater, aeration, and decomposition of organic matter 12 2.3. Off-Site Treatment Technologies Off-site treatment systems include aquatic, terrestrial and mechanical systems. 2.3.1 Aquatic Systems Aquatic systems include several types of lagoons including facultative, anaerobic, aerated, and hydrograph controlled release. Lagoons are the oldest methods of water treatment. Lagoons can be supplemented with constructed wetlands, aquaculture, and sand filters (figure 6). 220.127.116.11. Lagoons Lagoons contributions to sustainable development include low capital costs, low operational and technical requirements. They have been used to serve small communities and are often accompanied by additional treatment like constructed wetlands, sand filters, or aquaculture systems 15 Lagooning is as effective in treating wastewater and can reduce BOD and SS to the same levels as conventional treatment plants. Because of the longer residence time of wastewater in a lagoon, removal of the pathogenic bacteria and viruses by natural die-off is greater then in conventional systems 12 Lagoons are shallow lined or unlined excavation in the ground 1-2 meters deep. Percolation into the soil takes place in unlined lagoons but is reduced overtime due to a sedimentation layer. If this is a concern a layer of clay or black plastic can line the lagoon. Sedimentation occurs as wastewater enters the lagoon. Residence time of the wastewater in this system allow much of the solids in the original wastewater to settle out of the effluent. Aeration occurs from the atmosphere by simple diffusion and wind turbulence. Oxygen is also supplied during the day by the algae thriving in the nutrient rich environment 12 A series of lagoons is common. The first collects the sludge, which can then be removed and treated for reuse 12
Overview of Systems Waste Water Systems Processes Costs Technical Requirements Land Requirements Advantages Disadvantages start-up operational Aquatic Primary Facultative lagoons aerobic/ anaerobic Low Low Low High High effluent solids Aerated lagoons Aerated stabilization ponds Medium Medium Medium Medium smaller and deeper than a facultative lagoon High effluent solids, requires mechanical devices Hydrograph Controlled Release lagoons storage facilities near river Medium Medium Medium Medium discharge only when river volume is adequate Secondary Constructed wetlands plant roots for bacteria growth & oxygen transfer, long narrow basin ~ 2 feet deep Aquaculture systems shallow ponds with floating plants, water detained several days ! ~ 3 foot and filter, recirculating or intermittent, perforated pipe base, biological breakdown Terrestrial Slow-rate systems biological breakdown Medium Medium Medium Varies positive impact on sustainable development by providing a return on crop Overland flow sedimentation, filtration and biochemical Low Low Low Varies nitrogen removal in low permeable soils Rapid infiltration peculation through soils Low Low Low Varies ground water recharge moderate to high permeability soils Subsurface infiltration biological breakdown Low Low Low Medium small municipalities Mechanical systems combine physical, biological and chemical High High High Low ! Figure 6. An overview of some of the systems, their comparative costs, advantages, and disadvantages.
Facultative lagoons are one of the most common lagoon types currently used. The surface water layer is aerobic and the bottom layer is anaerobic. The middle layer, known as the facultative zone mixes these areas 15 Aerated lagoons use two types of aeration devices in stabilization ponds; either mechanical or diffused air systems. They are deeper and smaller then facultative lagoons, which means less of a land requirement 15 Hydrograph Controlled Release (HCR) is a new system that discharges water from a storage tank when the river volume is sufficient to handle the increased load of nutrients 15 18.104.22.168. Constructed Wetlands Two types of constructed wetlands can form supplemental support to lagoons. Free-water surface (FWS) and subsurface flow (SF) both utilizes plant roots for bacteria growth and oxygen transfer. FWS are long and narrow basins less than two feet deep and most closely approximate a wetland. In SF systems a gravel and sand medium ~ 46 cm deep is used. SF are also known as reed beds 15 22.214.171.124. Aquaculture Aquaculture systems use floating plants, typically water hyacinths or duckweed, for bacteria growth, in a shallow pond with a detention time of several days 15 126.96.36.199. Sand Filters Two common types are intermittent and recirculating. The main differences are in the application of wastewater. Intermittent systems are first flooded and then allowed to completely drain. Recirculating systems use a pump to recirculate the effluent at a specific water to solid ratio 15 2.4. Terrestrial Systems Terrestrial systems rely on the action of soil bacteria to degrade the organic wastes in the wastewater. Raw wastewater can be used in any of these systems if the application rate is small; otherwise, settled sewerage is needed 12 Terrestrial systems can contribute to groundwater recharge, reforestation, agriculture and livestock feed encouraging sustainable development by using physical, chemical and biological reactions on and within the soil. Slow-rate and overland flow systems require vegetation 15 The term soil aquifer treatment is used for wastewater that is applied to unlined basins in cycles of flooding and drying of approximately one week each. Flooding wastewater percolates through the soils beneath the basin to the unconfined groundwater aquifer leaving organic substances to be consumed by soil bacteria. As the suspended solids are
trapped in the bottom of the basin, percolation decreases. During the dry intervals these solids are consumed by bacteria, rejuvenating the percolation capacity of the soil 12 2.4.1.Slow Rate Systems Slow rate systems are the most costly of these systems but are the most advantageous by providing and economic return through the reuse of water and nutrients by producing marketable crops. Either primary or secondary wastewater can be applied with sprinklers or flooding furrows 15 Slow-rate land application system is applied to land through channels in the upper part of a gradient and treated wastewater is collected in channels in the lower part. Application is intermittent and dependant of the permeability of the soil combined with the loss of water due to evaporation 12 Wastewater is treated as it passes via the soil through absorption, filtration, ion exchange, precipitation, microbial action and plant uptake. Vegetation is vital to extract nutrients, reduce erosion and maintain soil permeability 15 The vegetation can be harvested by grazing animals 12 2.4.2. Rapid Infiltration Rapid infiltration applies wastewater directly the soil and leaves the treated effluent to naturally percolate through to the ground water contributing to sustainability. It is a low cost, low maintenance system that can be used with soils of moderate and high permeability. Application is through spreading basins or by sprinklers and vegetation may or may not co-exist. Ammonia nitrogen conversion to nitrate nitrogen before discharge is a major treatment goal 15 2.4.3. Subsurface Infiltration Subsurface infiltration systems are often designed for individual homes (septic tanks) but may be used for communities of up to 2,500. This can be a low cost system but requires specific site conditions 15 2.5. Mechanical Systems Mechanical systems, such as conventional activated sludge processes, use a series of tanks along with mechanical devices including pumps, blowers, screens, and grinders to meet the treatment objectives. The processes utilized are a combination of physical, biological and chemical in either an activated sludge process that used a suspended growth system or a trickling filter solids contact process that uses an attached-growth system 15 Mechanical systems often work in a linear process, which does not contribute to sustainability. 2.6. Treatment Performance Treatment performance is determined by 5 primary factors (figure 7):
1) secondary limits (defined as Biological Oxygen Demand (BOD) and Total Suspended Solids (TSS) (<30mg/L) 2) advanced treatment (BOD and TSS, < 20 mg/L) 3) ammonia conversion (<2mg/L) 4) total phosphorus (<2 mg/L) 5) total nitrogen (<2 mg/L) Both slow rate and mechanical systems meet the minimum requirements for all areas. Wastewater treatment systems are equal in treating effluent and only lagoons do not meet the advanced treatment limits. Ammonia conversion limits are met by sand filters, overland flow, and rapid infiltration. Total phosphorus limits are only also met by subsurface infiltration. Even though lagoons have the lowest performance rates they also require the fewest manpower hours and when used with a secondary system they can provide good wastewater sanitation. For a 3,875 m 3 mechanical system 2.6 man-years are required whereas for a 3,875 m 3 facultative lagoon 1.6 man-years are required 15 Pathogen survival times are included in figure 8. Treatment Performance Secondary Limits Advanced Treatment Ammonia Conversion Total Phosphorus Total Nitrogen Mechanical yes yes yes yes yes Lagoons yes no no no no Sand Filters yes yes yes no no Constructed Wetlands yes yes maybe no no Aquaculture yes yes maybe no no Slow Rate yes yes yes yes yes Overland Flow yes yes yes no no Rapid Infiltration yes yes yes no no Subsurface Infiltration yes yes maybe yes no Secondary limits are defined by biological oxygen demand (BOD) and total suspended solids (TSS) <30mg/L Advanced treatment is defined by BOD and TSS <20mg/L, Ammonia Phosphorus and Nitrogen limits are 2 mg/L Figure 7. Treatment performance achieved by various wastewater treatment systems. Modified from Perez, Ernesto. Appropriate Technologies of Wastewater Treatment for Sustainable Development. Typical Pathogen Survival Times at 20 30 degrees C Survival Time (days) Pathogen Fresh Water & Sewage Crops Soil Viruses <120 (<50) <60 (<15) <100 (<20)
Bacteria <60 (<30) <30 (<15) <70 (<20) Protozoa <30 (<15) <10 (<2) <20 (<10) Helminthes many months <60 (<30) many months () are the usual survival time lines Figure 8. Typical pathogen survival times at normal tropical temperatures in two types of wastewater reuse systems. Perez, Ernesto. Appropriate Technologies of Wastewater Treatment for Sustainable Development. Mechanized systems require more education, experience, and money to maintain the system. All natural systems are significantly more cost effective than mechanical systems is the costs analyzed (table ) 15 Education and Salary Requirements for Personnel Natural System Mechanical System 0 3.785 m 3 /d Over 3.785 m 3 /d Education High School High School High School BS engineering or or GED* or GED or GED HS or GED + experience Experience 1 year 2 years 3 years BS 3 years HS 6 years Salary $23,695 $26,403 $30,465 $34,527 Operator class consensus I II III IV Graduate Equivalency Diploma (GED) Table 3. Education and salary requirement for natural through mechanical processes. (Consumer Price Index 6 used to update to 2001 salaries for the United States.) Modified from Perez, Ernesto. Appropriate Technologies of Wastewater Treatment for Sustainable Development for 1992 in the United States. 2.7. Treatment Systems Impact on Sustainable Development Water reclamation and reuse is an attractive option for conserving water. The relative importance of the natural systems contributions toward sustainable development can be divided into three categories (figure 9): 1) Low operational and capital costs, and low technical manpower requirements while capable of achieving high degree treatment. Lagoons supplemented by sand filters, constructed wetlands, aquaculture, or overland flow systems are available. 2) Groundwater recharge occurs with rapid infiltration and to a lesser extent slow rate systems. 3) Reforestation, pastures, and crop irrigation are possible with slow rate systems. Any reuse program requires steps to assure the health protection of the field workers and consumers. Pathogenic microorganisms and chemical constituents are the principle infectious agents. Secondary treatment maybe acceptable for reuse application such as irrigation of non-food crops 15 Impact on Sustainable Development Low Cost Low Man Power Ground Water Recharge Forestation Agriculture
Lagoons S S Sand Filters III III Constructed Wetlands III III Agriculture III III Slow Irrl III III III S S Overland Flow III III III Rapid Infiltration III III S III = Important S = Some Importance Figure 9. The impact several systems have on sustainable development. Modified from Perez, Ernesto. Appropriate Technologies of Wastewater Treatment for Sustainable Development for 1992 in the United States. The range of hectares needed for treatment ranges between large areas for slow rate systems to a small area for mechanical treatment systems (figure 10). Natural systems generally need to include a facultative lagoon as a primary treatment unit 15 Hectares Required per process for M 3 /d 0.0 0.5 1.0 1.5 2.0 2.5 Mechanical plant Facultative Aerated lagoon HCR lagoon Aquaculture Constructed Sand filters Rapid Overland Flow Slow Rate Process Hectare Figure 10. Range of hectares needed for treatment of wastewater. Modified from Perez, Ernesto. Appropriate Technologies of Wastewater Treatment for Sustainable Development for 1992 in the United States. 2.8. Site Limitations Site limitations for these processes include geology, topography, ground water and climate (figure 11). In some technologies these individual limitations are only slightly important. In other technologies the limitation may be so unfavorable (critical) that construction is not possible due to costs. Regardless of the technology all of these limitations need to be considered as each has the possibility of adding considerable cost to the project 15 Site Limitations Geology Topography Ground Water Climate Mechanical I SN I SN Lagoons I I I I Sand Filters SN I SN SN Constructed Wetlands I I I I
Aquaculture I I I C Slow Rate C I C I Overland Flow SN C SN I Rapid Infiltration C I C SN Subsurface Infiltration C I C SN C = Critical I = Important SN = Slight to none Figure 11. Factors affecting site selection in various systems. Modified from Perez, Ernesto. Appropriate Technologies of Wastewater Treatment for Sustainable Development. 2.9. Collection (Sewerage )Systems In the collection of wastewater gravity is used to reduce costs. Combined wastewater sewerage carries both black and grey water. Separate sewerage carries them individually. The International Source book on Environmentally Sound Technologies for Wastewater and Storm Water Management (2002) divides wastewater sewerage into three major types: 1) Conventional sewerage or deep sewerage has pipes laid deep in the ground that usually require pumping. Diameter of the pipes depends on the planned population increase. Capital cost, operational costs, and maintenance costs are high 12 2) Condominial or simplified sewerage have pipes placed at shallower depths then conventional sewerage and minimum requirements are not as conservative as conventional sewerage. The result is reduced capital (construction), operational and maintenance costs 12 3) Settled sewerage originated to convey effluent way from the settled solid particles to an area that was capable of dealing with the demands of the effluent 12 Conventional wastewater treatment systems call for piping the wastewater from each individual house to a main trunk in the center of the road (figure 12). To reduce costs a condominial collection system can be installed. The benefits of condominial sewerage is: 1) less pipeline by routing wastewater networks across pavements and yards connecting blocks of houses to a main trunk line. 2) narrower pipeline installed then conventional systems. 3) shallower depth then conventional systems 21 The cost for condominial sewerage can be up to 40% less then conventional sewerage. This savings is obtained in materials (10-20%) and reduced excavation costs due to shallower trenches (20-30%) and less main pipeline 21 If settled sewage is used than an even smaller pipe size can be used in the collection system to convey effluent to a treatment facility. Community participation can extend the advantages of a condominial system. Communities learn to understand the infrastructure, which can be an entry point for
educational activities. Community effort can further reduce the costs of installation of the system for a total of up to a 50% savings. Community participation can also serve to increase the proportion of households that connect to the sewerage network 21 Figure 12. The differences between conventional sewerage connections and condominial sewerage connections. Conventional sewerage connects each house to a main line, whereas with condominial sewerage a block of houses met on one line then flows out to a main line. 2.10. Sludge Treatment Sludge is a product of the treatment of wastewater in on-site (septic tanks) and off-site (activated sludge) systems. Options for treatment include stabilization, thickening, dewatering, drying and incineration. Sludge always needs to be handled with care to prevent the contact with pathogens 12 This study looks at two types of sludge treatment in depth because they are excellent marketable soil amendments. Both these processes, when handled correctly, produce a humus-like material that can improve the structure and water-holding capacity of the soil, while improving soil aeration and drainage. This product is bought buy homeowners, nurseries, and sod farms. In the United States the Environmental Protection Agency (EPA) regulates this process. The EPA has published regulations in the Code of Federal Regulations (CRF), 40 CRF part 503 7 2.10.1. Vermistabilization Vermistabilization is the use of earthworms and sawdust or coffee husks to dewater and stabilize sludge. According to Crites and Tchobanoglous (1998), 2 kg/m 2 of live worms are place on a bed in a single application. Sludge is loaded on weekly at no greater then 1kg/m 2 If sawdust is also added the sludge application rate can be increased. The earthworms can be moved to other beds to maintain the beds. Earthworms do accumulate Conventional Condominial
heavy metals during this process if industry wastewater is included in the management system, resulting in them not being a marketable aspect of the process 7 2.10.2 Composting Composting is an aerobic bacterial decomposition process to stabilize organic wastes and produce humus. Humus contains nutrients and organic carbon that create excellent soil conditioners. Composting can be carried out in windrows that are regularly turned to assist with mixing, oxidation, and the heat dispersal that is essential for the destruction of pathogens. Turning is required every two to three days for the first two weeks when the temperature is at 55 C or above. Thereafter, it is less frequent while the compost undergoes maturation 12 Composting techniques include windrow composting, aerated static pile composting, and in-vessel mechanical composting. Design considerations found in Crites and Tchobanoglous (1998) include sludge type, amendments, degradability, pH of mixture and temperature The end product can be marketed to improve soil aeration and drainage 12 Windrow composting consisted of the sludge/amendment mixture that is placed in long pile 1 to 2 m high and 2 to 5 m wide at the base. This process is normally conducted on uncovered pas and relies on natural ventilation with frequent mechanical mixing to maintain the aerobic conditions. Under normal conditions piles are turned every other day allowing moisture to escape and the pile to maintain a temperature of 55 C 7 Aerated Static Pile composting the material to be composted is placed in a pile and oxygen is provided through mechanical aeration systems. Paved surfaces permit the capture and control of runoff and allow operation in all weather conditions 7 In-Vessel reactors are enclosed in a building or a closed reactor to control temperature, moisture and odors. The are more expensive and better suited to large systems 7 3. Santa Elena Study This feasibility study of sanitation option for Santa Elena examined current conditions of the area. Climate, soils, rainfall data, current wastewater conditions, and current water quality are explained below. 3.1 Climate The mean annual temperature at 1460 m from 1956-1995 was 18.5 C with a minimum of 9.0 C and a maximum of 27.0 C. Mean annual precipitation at the same elevation and during the same time period was 2519mm with minimum precipitation of 1715mm (1959) and maximum precipitation of 3240mm (1996). Topographic position and exposure to trade wind-driven clouds and precipitation play major roles in controlling the
microclimate. Day length oscillates between 11 hr 32 min on December 22 to 12 hr 42 min on June 23 13 Rainfall data for the Monteverde Zone collected from 1973 to 1998 by John Campbell and Alan Pounds showed during the wet season an average of 337.4 mm (high 701.4, low 71.3), the transition season an average of 148.1 mm (high 466.6, low 21.1) and the dry season an average of 48.06 mm (high 190.1, low 8.1) 4 The three seasons are recognized on the basis of cloud and precipitation types. The wet season is from May to October and is characterized by clear morning skies and cumulus cloud formation and convective precipitation in the afternoon to early evening. Maximum monthly precipitation occurs during this season in June, September and October. The transition season is November to January and is characterized by strong NE trade winds, stratus and stratocumulus clouds. Wind-driven precipitation and mist occurs at all times. The dry season is from February to April and is characterized by moderate trade winds, stratus clouds or clear-sky conditions with wind-driven mist and cloud water particularly at night 13 3.2. Soils The soils of the area have not been investigated in depth. The A horizon ranges from silt to sandy loam with a varying amount of clay and is characterized by high porosity and low bulk density. The color of this soil is light to dark brown primarily due to the accumulation of organic material. Most soils in the area are formed on slightly to moderately weathered volcanic parent materials and are classified as Andisols. This classification is characterized by poorly to moderate differentiated soil horizons. Where the soil is well defined the B horizon generally has a higher bulk density and lower hydraulic conductivity then the A horizon. The texture of the B horizon varies from gravelly to sandy loams. Clay content typically decreases with depth. The soils are typically deep on low-angle slopes and benches 13 The Sustainable Futures 2002 students at the Monteverde Institute did percolation tests in June of 2002. Two test holes were dug to a depth of 1 meter. The percolation rate averaged 3.6 cm per ten minutes (test A 3.8cm, test b 3.4 cm) after one hour. This is moderate to rapid rate of infiltration 7 A rate of 3 cm/ 10 minutes (18 cm/ hour) was used for design purposes in this study. 3.3. Current Wastewater Conditions Potable water of sufficient quality and quantity at a low price is largely taken for granted in Santa Elena. The 2001 water tariff of 740 colones (US $2.25) for the first 15 kL/house/month allow for typical domestic consumption of water. Acueductos y Alcantarilllados (AyA), the local water authority, design figure for domestic waster supply is 150 l/p/d. As stated earlier, 85% of potable water is discharged as wastewater (table 4).
% of Potable Water going to Wastewater l/p/d % Potable water 150 100 greywater 89.25 59.5 blackwater 38.25 25.5 other 22.5 15 Table 4. The percentage of potable that is discharged as blackwater, greywater or other. The prevailing wastewater and treatments in Santa Elena consists principally of a septic tank for household blackwater. Greywater is disposed of directly onto the ground, into the street or nearest stream. This separation of black and grey water can make the implementation of a staged plan easier to obtain both financially and through community support. Both grey and blackwater may contain pathogens; however, blackwater has a significantly higher number of fecal coliform. The volume of wastewater and pollutants depends on the methods of anal cleaning, the volume of water used and conserved. Dry anal cleaning results in higher solids and fiber content. The use of dry pit latrines and practicing water conservation produce a low volume, highly concentrated wastewater, whereas the use of flushing toilets results in a higher volume, lower concentration of wastewater 12 3.3.1. Greywater Run-off of greywater is rapid due to the regions steep terrain allowing the health risk that is associated with stagnant and ponding water to be avoided. Dallas, Scheffe, & Ho (2001) reported that the public perception of greywater appears largely to be only one of nuisance value due to odor and appearance, which is diluted during the wet season and amplified in the dry season 9 Concerns about environmental degradation and health impacts associated with this discharge are starting to arise especially with those citizens who have directly experienced the growth of the region 6 Greywater totals 70-80% of all wastewater and for design purposes we have used a figure of 70%. In a follow-up report to the paper written by Dallas, Scheffe, & Ho (2001), the BOD of one of the greywater treatment systems flow inlet tested between 91.0 and 196.7 with a range between 100 150 mg/L. A DOB value of 150 mg/L has been used for design purposes in the study. At the inlet, the N content was 0 with an average P of 2.0 mg/L and an average PO 4 of 6.0mg/L 8 3.3.2. Blackwater Blackwater consists mostly of flushing toilets, which are standard in most dwellings. This drains to a septic system then a leachfield. There is concern over how the shrinking lots sizes that are a result of population growth will impair the capacity of these leachfields. Blackwater totals 20-30% of as wastewater. For a design figure we used 30%.
3.4. Research into Water Quality The Monteverde Institute and Smith College have undertaken water quality monitoring of three rivers surrounding Santa Elena since January 2001. Four rivers drain from the catchment basin of Santa Elena: Rio Guacimal, the Quebrada Maquina, Quebrada Sucia, (all studied) and the Quebrada Rodriguez (not studied). In all three studied rivers the water quality upstream is better then the water quality downstream. (In appendix __ the criteria for this evaluation is established.) Downstream all three rivers have consistently contained more fecal coliform bacteria then is recommended for swimming (FC>200) and drinking (FC>1) but the remaining parameters have been met. The highest fecal coliform levels have been 860 for the Rio Guacimal, 1,200 for the Quebrada Maquina, and 11,200 for the Quebrada Sucia. 3.5. Data Collection In researching the most viable, sustainable options for wastewater treatment in Santa Elena the following information was collected by Sustainable Futures 2002. 3.5.1Water Survey A water survey (appendix3) was conducted by to determine the amount of water used in nine (9) student homestays for an average of three days during the months of June and July. This survey ascertained the amount of water used (during the wet season) per household and per person. The survey also included the uses of water within the household including but not limited to bathing, cleaning, laundry, and washing cars. From this survey the average number of liters used per person was 179. The average number of liters used per household was 805 with an average of 4.9 persons per household. Per person usage in this survey conducted during the wet season are higher then AyA's current prediction of 150 liters. Per household usage is lower then AyA's current predictions (1000 liters); however, AyA based households on 6 family members, which this survey did not average. This survey was restricted in size and duration. Further study is needed to determine the amount of potable water used per person and per household and to determine the percent of that water that goes into the wastewater system. 3.5.2. Mapping The physical mapping of Santa Elena to determine the number of houses, their location, ridgelines, roads, and commercial/institutional buildings, and interviews with community members about their perceptions and ideas. This information was compared to work previously collected on maps (from 1984-6, and 1992), aerial photos, publications, and though community consultations to obtain the projected growth rates for Santa Elena. Growth projections were made for 2010 and2020 and are given in table 1.
3.5.3. Catchments Santa Elena topography was examined through aerial photos, topography maps and field work. This study revealed that in terms of wastewater collection by gravity there are four principle catchment basins. The topography of region and the location of waterways were based on USGS information on Santa Elena. Sustainable Futures 2002 made field observations to obtain the placement of individual buildings and to determine the ridgelines of the topography. Four catchment basins were determined from these data and based on drainage patterns a schematic sewerage collection system was established per catchment. This information was compiled using AutoCAD (version 2000) (table 5 and appendix 4). 2002 # of B % Greywater % Blackwater Catchment R C R C R C 1 77 15 45,815 8,925 19,635 3,825 2 49 7 29,155 4,165 12,495 1,785 3 50 1 29,750 595 12,750 255 4 166 92 98,770 54,740 42,330 23,460 Totals 342 115 203,490 68,425 87,210 29,325 ! 2010 # of B % Greywater % Blackwater Catchment R C R C R C 1 165 40 98,175 23,800 42,075 10,200 2 53 8 31,535 4,760 13,515 2,040 3 138 41 82,110 24,395 35,190 10,455 4 278 165 165,410 98,175 70,890 42,075 Totals 634 254 377,230 151,130 161,670 64,770 ! 2020 # of B % Greywater % Blackwater Catchment R C R C R C 1 181 47 107,695 27,965 46,155 11,985 2 65 9 38,675 5,355 16,575 2,295 3 390 41 232,050 24,395 99,450 10,455 4 295 166 175,525 98,770 75,225 42,330 Totals 931 263 553,945 156,485 237,405 67,065 # of B = number of buildings, R=residential, C = commercial/industrial Table 5. Commercial and residential buildings per catchment with projected growth for 2010 and 2020. Figures given are the percent of potable water in liters that is disposed of as wastewater (assumed to be 85%). Greywater consists of 70% of wastewater and blackwater is to consist of 30% of wastewater. 3.6. Summary
For a sustainable, affordable wastewater treatment system to be implemented, there are many factors to consider. Santa Elena's projected growth rates are 4.7% higher then Central America as a whole. Currently, Santa Elena is in the process of installing a local government. When it is in place, creating a plan regulador (zoning master plan) is a priority. (Some possible assumptions have been developed in Sustainable Futures 2002 scenario planning report.) Wastewater is seen as a problem to be handled by AyA. Investigations of the best options for the region were concluded by reviewing the latest literature, interviewing people, assessing and mapping the site conditions for the region. This lead to the conclusion that there are four-principle catchments zones each with substantial room for growth over the next eighteen years. In order to maintain the current quality of life consideration needs to be paid to many varying factors present here. In our research we have found that greywater is the largest present problem. Greywater makes up 70% of all wastewater and is discharged from most buildings without treatment. This practice has caused poor river quality and with the projected population growth the problem will be exacerbated. Blackwater is mainly discharged to on-site septic systems. At this time these systems are sufficient; however, if lot sizes continue to shrink as the population grows there may not be sufficient land to treat wastewater on-site. In addition to this, there appears to be no sludge treatment facility readily available, which leads to the minimum requirement for desludging of septic tanks to not be met. A local facility for vermistabilization or composting of septic sludge is a sustainable, marketable way to handle this issue. Since Santa Elena is located in the tropics, albeit at 1,400 meters above sea-level, where natural biological wastewater systems can perform optimally. These treatment systems work within the objectives set out at the beginning of this report. Conventional sewage treatment (conventional collection with activated sludge treatment) does not meet the objectives of low capital costs, low operational and maintenance, growth in stages or community participation. Conventional sewage may be sustainable but only at a significant additional cost. For the most financially successful plans to work, each catchment needs to work to treat its own waste. If this is not possible, due to land constraints or other difficulties, then additional costs will be incurred with the transportation of the wastewater elsewhere. In Santa Elena the current land prices and development preclude wastewater treatment and reuse within these individual catchments. Settled sewerage effluent can, however, be piped in an overall downhill direction with just the use of gravity to a rural area that would be suitable to treatment and agricultural reuse. 4. Recommendations Deciding factors for this project in Santa Elena included all the material presented above with special emphasis on the primary objectives:
1) a low capital cost budget 2) a low operational and maintenance budget 3) be able to grow in stages with the community 4) sustainability 5) community participation is required in all stages of the plan Efficiency, reliability, sludge disposal aspects and land requirements are also important The philosophy behind these recommendations is low cost, (including construction costs, operational cost and maintenance costs) sustainability, and simplicity. The current practice of separating black and grey water at the household level leaves Santa Elena in a good position to implement a step-wise wastewater management strategy. Blackwater can successfully be treated in a septic system as long as the minimum specifications for the tanks and leachfields are followed (Appendix 2). An important aspect of this system not currently being met is the removal of the sludge from the settled sewerage system on a regular basis. This arrangement leaves the town in a good position to collect the effluent from a settled sewerage system when the treatment plant design has been chosen and the facility built. Since greywater is an immediate problem, a condominial collection system of piping greywater to a main treatment system is a viable option that has been proven (for combined wastewater) in other Latin American countries 12 The proposal presented here however for a "greywater only" collection and treatment system is novel. Each house or group of houses will need an interceptor tank to collect greases and solid materials. The tank will need to meet the minimum requirements stated in Appendix 2 and follow a regular desludging and maintenance program. The effluent from this system can be treated in range of natural aquatic or terrestrial systems. Our research has lead us to conclude that three of the most appropriate treatment systems would be lagoons, constructed wetlands, rapid infiltration, or a combination of these systems. Treatment system designs are in Appendix 3. Interestingly, all three of these systems require 1,500 to 2,000 m 2 per 100 m 3 /d. This area is sufficient to treat settled effluent from100 houses producing an average of 1,000 liters of greywater per day. This was chosen for the design figure as a base number of houses from which other projections can be extrapolated. 4.1 Recommendations for Wastewater Collection and Treatment Options Collection 1.Settled sewerage with mid-level capital costs and low operational and maintenance costs 3 1.1 Set-up to collect blackwater, greywater or both. 1.2 Each house or grouping of houses will require its own
1.2.1 Septic tank for blackwater 1.2.2 An interceptor tank for greywater 1.3 Requires a site for handling and treating the black and greywater sludge 2. Condominial sewerage 2.1 Set-up to collect blackwater, greywater or both. On-Site Treatment 1.Septic systems are acceptable when specific requirements are met: 1.1 On-site percolation tests 1.2 groundwater table information is needed. 1.3 design and installation must meet minimum requirements (Appendix 3). 2. Small on-site composting systems may be suitable. 3. Small scale constructed wetlands (reed beds) for greywater treatment. Off-site Treatment 1. Facultative lagoons with secondary support from land based treatments. The capital cost will depend on the cost of the land. Operational and maintenance costs are low. 2. Rapid rate land application systems with or without settled wastewater as a primary treatment. Reuse of wastewater for agriculture. 3. A sludge treatment facility will be required within the design area to receive and treat sludge from both septic tanks and interceptor tanks (blackwater and greywater). Desludging of these tanks will be required on a periodic basis and maybe best achieved through a contract arrangement. A range of option exists for the treatment of sludge including composting or vermistabilization of the sludge. Both these treatment are good options for the tropics. These natural systems require half the manpower (figure 13) and less energy then a conventional system, such as the activated sludge system used in many industrialized countries, making them the most attractive and logical choice for town of Santa Elena. These systems also close the natural cycles making them a sustainable choice for the area. Comparative Manpower Requirements for System of 3785 m 3 /d 0 0.5 1 1.5 2 2.5 3 Facultative Lagoon Aerated Lagoon Mechanical System Man-years required
Figure 13. The number of people required to maintain a system during the period of a year for a system of 3785m3/day. Perez, Ernesto. Appropriate Technologies of Wastewater. 5. The Future All of the options presented here can be implemented in sustainable stages to meet object 5. A starting point needs to be decided upon and an implementation plan designed. 5.1 Future Studies Future studies need to include feasibility studies on location of lagoons, constructed wetlands, and medium to rapid rate infiltration. A through study of water use per household during all three seasons could determine a precise quantity of potable water consumed and the percentage of that water that ends up as black and/or grey water. For further information regarding the most recent WHO international guidelines on water quality, wastewater reuse and health implications etc please refer to http://www.who.int/water_sanitation_health/Documents/IWA/iwabooktoc.htm 5.2 Community Education Community education can be implemented through open forums to collected ideas and promote 'good will'. A pamphlet emphasizing the need for hygiene, the problems with greywater and the benefits of a sustainable wastewater system based on the idea of Reconstruyamos y Nicaragua 14 could be widely distributed to the local community at local congregation points (the churches and the supermarkets). Community leaders could also make arrangements to enter the public school systems to educate young people on the advantages of having a properly functioning black and greywater system. 5.3 Summary When all this data was collected we determined that the most effective wastewater treatment would be collected through condominial piping with either settled sewage or condominial sewerage. On-site treatment (sites can be one house or a collection of houses) of both black and grey water is feasible with effluent piped into a facultative lagoon. The treated wastewater could then be used in a mid-to-rapid rate land application system or constructed wetland.
Works Referenced 1 Acueductos y Alcantarilllados (AyA) 2 Acueductos y Alcantarilllados (AyA). 4-2001. Saneamiento Basico. Santa Elena. 3 Brenes, Virgilio. 2002. Personal communication. 4 Campbell, J. & Pounds, A. Date Unknown. Monteverde Institute. 5 Campos, H.M. & von Sperling, M. 1996. Estimation of domestic wastewater characteristics in a developing country based on socio-economic variables. Water Science tech. v. 34, n. 3-4, p. 71-77. 6 Consumer Price Index. July 29, 2002. http://www.globalfindata.com/trial/CPUSAM.csv 7 Crites, R. & Tchobanoglous, G. 1998. Small and Decentralized Wastewater management Systems. McGraw-Hill. Boston. 8 Dallas, S. 2002. Personal Communication. 9 Dallas, S., Scheffe, B., &Ho, G. 2001. A community-based ecological greywater treatment system in Santa ElenaMonteverde, Costa Rica. IWA Conference: Water & Wastewater Management for Developing Countries, Kuala Lumpur. 10 Environmental Health Project Summary: Sanitation in small towns in Latin America and the Caribbean practical methodology for designing a plan for sustainable sanitation services. 2001. 11 Ho, Goen. 2002. International Water Association Foundation Workshop, Monteverde Institute, Costa Rica. July 17-19 th 2002. 12 International Source Book on Environmentally Sound Technologies for Wastewater and Storm Water Management. Abridged version. 2002. 13 Monteverde: Ecology and Conservation of a Tropical Cloud Forest. 2000. ed. N.M. Nadkarni & N.T. Wheelwright. Oxford University Press. New York. 14 Normativ Ambiental. Reconstruyamos y Nicaragua. date unknown. 15 Perez, Ernesto. Appropriate Technologies of Wastewater Treatment for Sustainable Development. Roundtable II-Water Supply and Sanitation Infrastructure in a Sustainable Development Context. www.oas.org/usde/publications/unit/oea74e [accesse s 7-1-02]. 16 Small and Decentralized Wastewater Management systems. 1998.McGraw-Hill Companies Inc.
17 Stapp, W.B. & Mitchell, M.K.1995. Field Manual for Global Low Cost Water Quality Monitoring. Thomson-Shore Printers, Michigan. 18 Steer, D., Fraser, Lauchlan., Boddy, J., Seibert, B. 2002. Efficiency of Small Constructed Wetlands for Subsurface Treatment of Single-family Domestic Effluent. Ecological Engineering. v. 18, p 429-440. 19 Unda Opazo. 1999. Ingenieria Sanitaria: Aplicada a Saneamiento y Salud Publica. Editorial Limusa. 20 von Sperling, Marcos. 1996. Comparison among the most frequently used systems for wastewater treatment in developing countries. Water Science Tech. v. 33, n. 3, p. 59-72. 21 Water and Sanitation Program. Lower costs with higher benefits: water and sewerage services for low-income households. Date unknown. Swedish International Development Agency.
Appendix 1. PhysicalChemical Data This information was modified from the Field Manual for Global Low-Cost Water Quality Monitoring. The national Sanitation Foundation selected 142 people that represented a wide range of positions to develop a set of inclusive tests to determine water quality. These are the nine most important tests to determine water quality. Dissolved Oxygen Oxygen in the presence of water is an indication of good water quality and the absence of oxygen is a signal of server pollution. Dissolved Oxygen (DO) is essential for the maintenance of a healthy water system. Rivers range widely in their levels of DO. The amount of DO that is requires varies for different species in a river: carp and catfish flourish in waters with low DO levels, pike and trout require medium to thigh levels of DO. Generally river with high DO level are considered healthy. Sudden or gradual depletion in DO can cause major shifts in the types of aquatic organisms with a shift from pollution intolerant species to pollution tolerant species. Generally rivers that have a consistent DO of 90% or higher are considered healthy. River below 90% may have a large amount of oxygen demanding material like organic wastes. Fecal Coliform Fecal coliform bacteria are found in the feces of humans and other warm-blooded animals. The bacteria enter rivers through direct discharge from mammals and birds, from agriculture and storm run-off carrying wastes, and from sewerage discharge. Fecal coliform bacteria occur naturally in the human digestive tract to aid in food digestion. Only in infected individuals do pathogenic organisms occur with fecal coliform bacteria. Fecal coliform counts are high when over 200 colonies exist per 100 mL of water showing a greater chance that pathogenic organisms are present. Use Standard (Colonies/ 100mL) Drinking water 1 FC Total Body Contact (swimming) 200 FC Partial Body Contact (boating) 1000 FC Treated Sewage Effluent Not to exceed 200 FC pH Water contains both H + ions and OH ions. The pH test measures the H + ion concentration on a scale that ranges from 1 to 14. Pure deionized water contains and equal number of
H + and OH and is considered neutral at pH 7. If the sample has more H + then OH it is considered acidic (>7) and if it has less it is considered neutral (<7). The pH scale is on a logarithmic scale hence each change in whole number is actually a ten-fold change. natural water generally has a pH between 6.5-8.5. Changes in pH values are important to many organisms as most organisms adapt to water with a specific pH. Serious problems occur in waterways that have a pH of less then 5. pH Units Excellent 6.5 7.5 Good 6.0-6.4, 7.6-8.0 Fair 5.5-5.9, 8.1-8.5 Poor <5.5, >8.6 Biochemical Oxygen Demand Decaying aquatic plants and their decomposers demand oxygen during plant decomposition. Nutrients (like nitrates and phosphates) added to the water source increases plant growth eventually leading to more plant decay. As this organic matter decomposes it is broken down and oxidized by microorganisms. The biochemical oxygen demand is a measure of the quantity of oxygen used by microorganisms in the aerobic oxidation of organic matter. In polluted rivers most of the dissolved oxygen is consumed in this process leaving little oxygen for other species to live in the river. Biochemical oxygen demand (mg/L) Excellent <2 Good 2-4 Fair 4.1-10 Poor >10 Temperature Water quality is greatly affected by water temperature. Many physical, biological and chemical characteristics of a river are directly affected: cool water can hold more oxygen then warm water, the rate of photosynthesis and metabolic processes vary with temperature. Some species prefer a specific temperature. Temperature increase raises the rate of photosynthesis and plant growth increases creating more organic material in the waterway. This in turn decreases the oxygen available to organisms in the water. Humans seriously change the temperature of rivers through thermal pollution when they add warm water to an existing body of water. Industries may cause this type of pollution. Another ways to affect the temperature is by cutting down trees along waterways that provide shading and with soil erosion adding more suspended particles for any number of reasons. Total Phosphate
Phosphorous is usually present in natural water as phosphate (PO 4 -P). Total phosphates included organic phosphorus and inorganic phosphate. Organic phosphate is a part of living plants and animals, whereas inorganic phosphates (H 2 PO 4 HPO 4 = and PO 4 = ) to soil particles and phosphates present in laundry detergents. Phosphorus is an essential element in life. Cultural eutrophication is am enrichment of the water, usually from phosphorus obtain through human activities. Water in advanced stages of cultural eutrophication can become anaerobic producing the 'rotten egg' smell. Total Phosphate (mg/L) Excellent 0-1 Good 1.1-4 Fair 4.1-9.9 Poor >10 Nitrates Nitrogen is an essential element required by all living things. Because it is a plant nutrient it also causes eutrophication. The eutrophication process cause more plant growth and decay which in turn stimulates a biochemical oxygen demand. Turbidity Turbidity measures the relative clarity of the water. Increases in turbidity are a result of increase suspended solids in the water that reduce the transmission of light and can be caused from soil erosion, waste discharge, the presence of excess nutrients and other factors. At higher levels the water loses it ability to supports a diversity of aquatic organisms. In increase in temperature is common, which leads o decreased dissolve oxygen content. NTUs* Secchi disk** Excellent 0-10 >91.5 cm Good 10.1-40 30.5-91.5 cm Fair 40.1-150 5-30.5 cm Poor >150 <5cm *NTUs are Nephelometer Turbidity Units that are obtained when using a specialized instrument called a turbidimeter. **Secchi disks are a homemade measuring system that works well in slow moving deep waterways. Total Solids Total solids measure the amount of dissolved solids that can pass through a filter compared to those that cannot. These solids can include material like calcium, bicarbonate, ions, silt and clay particles. High concentrations cause the water balance problem for individual organisms and low concentrations may limit growth.
Total Solids (mg/L) Excellent <100 Good 100-250 Fair 250-400 Poor >400
Appendix 3. Design philosophy Domestic blackwater treated via septic tank with leachfield. Greywater collected via settled sewerage using condominial pipe network. Design Parameters Average household: 1. Wastewater volumes: 1,000 l/day 2. Number of people/household: 6 3. Grey/blackwater percentage 70/30% (i.e. 700/300 liters per day) 4. Soil infiltration rate: 3cm /10 minutes for leachfield design Criteria Septic Tank 1. Periodic (2 yearly) tank desludging required contractor 2. All tanks to be water tight and located for easy inspection and pumpout 3. Minimum 20m from any potable water source 4. Minimum 2m from property boundary 5. Distance from leachfield 2m 6. Minimum 2m from other buildings, existing or future 7. Minimum 10m from any potable water storage tank Black water (aguas negras) Septic tank and leachfield design V = QPt V= volume of septic tank (liters) Q = design flow (people/day/day) P = no. of people served T = retention time (days) Therefore V = 30% x 1,000 x 3 = 900 l. Say 1,000 l for septic tank internal volume Dimensions: 1.2 m long, 0.6 m wide, 1.5 m deep with internal baffle or use two culverts as separate chambers instead Criteria Leachfield
1. Minimum 30m from any potable water source 2. Minimum 15m from any potable water storage tank 8. Minimum 1.5m from property boundary 9. Minimum 3m from other buildings, existing or future 10. Minimum 3m from large trees 11. Minimum 3m from water pipes 12. Minimum 2m between drain lines Leachfield L = Nd/Ak L = lineal length (m) N = number of people D = inflow (day/person/day) A = width of trench (m) K = infiltration (l/m2/day) Therefore L = 1 x 300/(0.3 x 70) = 14.3 lm Say 2 x 7.5 m or 2 x 5m drain lines !! Greywater ('aguas grises) Allow 1.5 days retention Volume = 1.5 x 70% x 1,000 = 1,050 l use same dimensions as for septic tank Connect to 'settled' sewer system via condominial network. Rapid Rate Inflitration 1mg/d = 3785.4m 3 /d Infiltration Rate = 18 cm/ hr = 0.18m/hr BOD = 150mg/l design% factor = 3% Q=100m 3 /d L w = 3/100*(24*365)*0.18 = 47.3m/year BOD loading = 100m 3 1000*150 mg/l = 15kg/d
For <336 kg/Ha*d BOD Loading A = 15/336 = 0.0446 Ha = TINY = 446m 2 On basis of hydraulic loading rate A = (QF)/L w = 100m 3 F) / 47.3m/year = 771.7 m 2 1 Ha = 100*100=10,000
Appendix 2. Water Survey Questionnaire Santa Elena, Monteverde Use of water in the home With the help of you and your home-stay family we can begin to gain an understanding of water use in the home in the Monteverde area. Basically what we are trying to learn is how much water comes in to the home, how it is used and then what happens to the wastewater. Water In: To do this we need to read the water meter. It is usually located in the front yard, probably near the road. If it is in a sealed metal box come and see Stew! If not, lift the black plastic lid and read the meter (generally in cubic metres m3 or kilolitres kL). What I would like you to do is to read the meter twice a day oncein the morning and once in the evening for three consecutive days (ideally at the same time if you can manage it). Also and this is very important write down the number of people who were living in the house during this time (spent the night). 1. Medidor de agua: Escribe la indicacin de su medidor durante tres dias. 1.1) Indicacin: _______ (m3/kL) Hora: ______ Fecha: _______ Personas ______ 1.2) Indicacin: _______ (m3/kL) Hora: ______ Fecha: _______ Personas ______ 1.3) Indicacin: _______ (m3/kL) Hora: ______ Fecha: _______ Personas ______ 1.4) Indicacin: _______ (m3/kL) Hora: ______ Fecha: _______ Personas ______ 1.5) Indicacin: _______ (m3/kL) Hora: ______ Fecha: _______ Personas ______ 1.6) Indicacin: _______ (m3/kL) Hora: ______ Fecha: _______ Personas ______ Water Use in the home: This is harder to quantify! Just from your general observations how many of the following take place: 2.1 Number of showers taken per day: ____________ !! When? __________________ 2.2 Number of loads of clothes washing per week: ________ What time of day ? ______ 2.3 Watering of garden number of times/week ______________________________ 2.4 Washing of cars, motorbikes/week ______________________________________ 2.5 Any visible leaks (taps dripping, etc) ? How many? _________________________ 2.6 Washing of dishes number of times/day _________________________________ 2.7 Any other uses of water that you observe _________________________________ ! Wastewater: Where does the greywater go? __________________________________ Where does the blackwater go? ____________________________________________
Have a chat with your homestay family about water and wastewater in Monteverde, about this project and see what they have to say. ! Calculations from Responses Starting point M 3 Ending point # Of days # Of people Average M 3 per day per house Average M 3 per day per person Average L per day per house Average L per day per person 6417.1 6419.3 3 5.8 0.733 0.128 733.333 127.536 1174.75 1177.5 4 6 0.688 0.115 687.500 114.583 1829 1831 2 2.8 1.000 0.364 1000.000 363.636 445.2 448.9 3 5 1.233 0.247 1233.333 246.667 2490 2493 3 6 1.000 0.167 1000.000 166.667 1695.2 1696.6 2.5 6 0.560 0.093 560.000 93.333 281.1 281.9 3 4.5 0.267 0.059 266.667 59.259 866.4 869.3 3 4 0.967 0.242 966.667 241.667 221.9 224.3 3 4 0.800 0.200 800.000 200.000 Averages 5.3 0.805 0.179 805.278 179.261 Note: My addition 21/4/03 of ave. # of people/house = 5.3. This includes one student therefore ave. is 4.3 p/household. With ave. water consumption of 179.3 l/p = 779 l/household.