a general introduction followed by a simulation "How to build a stabilization pond for a Community of 9000". Acknowledgement: The following was taken almost entirely from a handful of very useful web sites. Thank you to the creators of those sites Water for the World, CEPIS (Centro Panamericano de Ingeniena Sanitaria Y Ciencias del Ambiente), and Southwick Sewer and Drain. To adapt these instructions for a different size population, or for a different setting, it is highly recommended that you visit those sites, as well as the others in the bibliography. Within you will find references to the appendix, which, unfortunately, I can't easily post here in html. The numbered citations refer to the bibliography. Disclaimer: As the sources come from various parts of the world, with varying vocabularies and varying conditions, they contain some conflicting and even contradictory information. This occurs particularly in the classification of ponds, their applications, retention times, and depths. In this paper these have been reconciled wherever possible. A DESCRIPTION of the TECHNOLOGY 1. Southwick A waste stabilization pond is an artificial or man-made (excavated) lagoon or pond into which raw sewage (human waste and wash water) is discharged for treatment. This is not a pond of sewage. It is well diluted, so it does not have an odor or provide an environment for flies. The waste water always enters from one end of the pond and is treated as it slowly moves to the outlet at the opposite end of the pond. The degree of treatment provided depends on the type and number of ponds used. Aerated, aerobic, anaerobic or facultative (a combination of aerobic and anaerobic) ponds can be used, singly, or in a series, moving sewage from one pond into another. See Appendix 14 and Appendix 6. Generally, treatment of the sewage is accomplished by bacteria and algae existing in a symbiotic relationship. They create a cycle which breaks down organic waste. The heavy solids settle to the bottom where they are decomposed by bacteria. The lighter, suspended material is broken down by bacteria in suspension. In this process carbon dioxide is given off. Carbon dioxide, in the presence of light, along with dissolved nutrient materials such as nitrogen and phosphorus, are utilized by algae to make more algal cells. The by-product of algal activity is oxygen which is utilized by the bacteria to repeat the cycle of breaking down the sewage. The effluent can then be discharged. Pathogenic organisms such as Shigella, Salmonella, Escherichia, Leptospira, E coli., Vibria and Francisella are contained in some lagoons (stabilization ponds). Viruses and protozoa also exist in abundance in these ponds. Water is not the natural habitat of these organisms but it serves as a means of transport to new hosts. Although pathogenic organisms are usually unable to survive or multiply for long periods in water, studies have shown that viable numbers of organisms remain present in some lagoons at all times. This becomes a particular concern for lagoons which are located near high water tables that merge into nearby streams and reservoirs.11.V.Tech TERMINOLOGY STABILIZATION POND - may also be known as a sewage lagoon, or a waste water pond. There are four sub categories of stabilization pond, facultative ponds, anaerobic ponds, aerated ponds, aerobic ponds. OXIDATION POND - those stabilization ponds that rely on aerobic microbes. They may be facultative, aerobic, aerated, or maturation ponds. FACULTATIVE PONDS -It is a type of stabilization pond that receives sewage from a sewer system or an anaerobic pond. Facultative ponds are the most common type of pond. If a single pond is to be used, it will be of this type. They detain the effluent for l0-20 days, and discharge treated sewage to a dry ditch or, in some multi-pond systems, into a maturation pond. Facultative organisms function with or without dissolved oxygen. In a facultative pond, the biological action is both anaerobic and aerobic.2. SAN 2D6 They may also be called oxidation ponds. Some oxidation ponds use pumps to spray the sewage into the pond. This increases the oxygen available in the pond. AERATED POND - a pond through which oxygen is supplied through diffused or mechanical aeration. These ponds are generally 2 to 6 meters in depth with detention times of 3 to 10 days and they are advantageous because they require very little land area.11.V.Tech AEROBIC POND - Oxygen is present throughout the pond. All biological activity is aerobic decomposition. Not widely used.12.Itech MATURATION PONDS- Also know as "polishing ponds", these ponds are about lm deep. The action is by aerobic organisms requiring dissolved oxygen for their life processes. They receive treated sewage from facultative ponds, detain it for 3-10 days to improve its quality and safety, and discharge the treated sewage to a dry ditch or to an irrigation ditch leading to crop land. Maturation ponds can be used to grow food fish and aquatic birds. 2.SAN2D6 ANAEROBIC PONDS - A type of stabilization pond that receives sewage with such a high degree of solids that the pond has no aerobic zone. These ponds have average detention times of 20-50 days.11.V.Tech Anaerobic ponds allow solids to settle, partially treat the sewage, then discharge effluent into a facultative pond. The main biological action is by organisms that do not require oxygen. 2. SAN 2D6 The two dominant biological reactions are acid formation and methane fermentation. They produce odorous compounds. Sodium nitrate and grease crusts are used to combat these odors. These compounds, coupled with the acidic compounds formed through fermentation, can be very damaging to soil and ground water if the lagoon leaks. SEWAGE - All wash water, excreta, and water used to flush excreta that flows from a building or buildings through a sewer system and into a septic tank, cesspool, or stabilization pond. 2. SAN 2D6 TREATED SEWAGE - The liquid that flows out of a stabilization pond or series of ponds. It is safer than settled sewage and may be used to irrigate crops not intended for human consumption. 2. SAN 2D6 INFLUENT - Liquid flowing into a sewage treatment unit such as a stabilization pond. 4. SAN 2D5 EFFLUENT - Settled sewage. 2. SAN 2D6 AEROBIC ORGANISMS - require dissolved oxygen for their feeding and reproduction PERCOLATION- seepage of water into the ground. ORGANIC LOAD - The amount of organic material (expressed in grams per liter) present in sewage that must be acted upon before it can be discharged as treated sewage. 4.SAN2D5 BOD - Biochemical Oxygen Demand - a measure of the quantity of dissolved oxygen used by bacteria as they break down organic wastes. It is used as a measurement of amount of pollutant organic material, or "organic load", in water, and is recorded in grams per liter.9.Kstate SIMULATION EXERCISE: Stabilization Pond for a refugee Camp of 9000 People Refugee camps normally rely on pit latrines. There will be no sewer system. Some camps exist for extended periods of time, requiring the lit latrines be emptied. For this simulation we'll assume pour flush latrines which require 2 liters per flush. The organic load (BOD), ratio of organic waste to water, will be relatively high. One way to handle that heavy load would be to design a series of two ponds, the first an anaerobic pond for pretreatment. Because an anaerobic pond would have a strong odor it would need to be some distance from the camp. Most camps exist in a restricted space, so that may not be possible. Instead, the recommended design for this simulation is a single pond, large enough to allow the dilution that will facilitate a facultative, odor free pond. Treated sewage will be discharged onto a dry ditch. SITE SELECTION: � Existing ponds can not be used. The run-off they normally receive would fill the pond with silt. 2. SAN 2D6 � Locate a site in which the soil can tamped or treated to seal water such that the "percolation" is less than one inch per forty five minutes. � Estimate the ground water depth to decide whether the pond must be specially sealed. � Ponds should be outside any flood plane, 300 meters from any habitation, and at least 9 meters from potable water lines. � Consider the direction of the prevailing winds. � Ponds can only be used when � Elevation: To protect the aquifer, the bottom of the pond should be at least1.2 meters above the highest ground water level. In order to operate without the use of pumps, the dry ditch should be lower than the bottom of the pond. DESIGN Pond volume and size will be determined by three things 1. expected daily flow of sewage into the pond 2. the organic load (BOD) of that sewage 3. required detention time Detention time is a function of a. average water temperature and b. desired quality of the effluent. There are two basic ways to calculate pond size. 1. Volume method: Pond volume is first calculated. Then the depth and area must be determined. The depth depends on the type of pond desired (See Appendix 14). The surface area then varies accordingly. 2.SAN2D6 2. Surface Area Method: See Appendices 1,2, and 3 for the calculation of pond size using this formula which prioritizes a minimum necessary surface area. 4.SAN 2D5 Here too, depth is determined by the type of pond desired. Volume is not considered per se. � Configuration: Ponds are generally rectangular with the length 2 or 3 times the width. For this simulation the pond will require a surface area of 1285 m2. This can be 64m x 20m. The outlet pipe will be at surface level at the end of each pond. See Appendices 4 and 5 for diagrams. � Depth: A facultative pond should be 1.25-2.5 meters. � In order to prevent contamination of ground water, pond seepage must not be allowed to occur. Pond sealers fall into three categories: 1.) cement liners, 2.) synthetic and rubber liners, and 3.) chemical and natural treatment sealers. Assuming an acceptably low percolation rate, natural sealing will suffice for human waste except where the water table is high. � Clearance: Wind and sunlight are both desirable,1. Southwick so trees should be removed within 100m of the pond(6). � Embankments should be 1 meter higher than the surface of the pond. In order to prevent erosion, their slope should be no steeper than 1 unit of elevation for 3 units of distance, and they should be cultivated with grass. � Inside edges of corners should be rounded to prevent the accumulation of debris there. � Because well run ponds will look clean and appealing, it must be fenced off with warning signs. CONSTRUCTION 6. CEPIS Preparing the Site 1. Roughly mark the site. 2. Assemble all labor, materials, and tools needed to begin construction. 3. See Appendix 8 Sample Materials List and Appendix 9 Sample Work Schedule 4. Clear the pond and embankment site of all trees, bushes, stumps, brushwood, large rocks, and any other material not suitable for building the embankment. Haul this list material to a landfill or other disposal site. 5. Remove any trees upwind from the site for a distance of l00 - 200m. This will create an unobstructed wind path, which will improve the efficiency of the pond after it is put into operation. 6. Remove topsoil or sod from the site and place it to one side. This will be used later to finish the embankment. Staking Pond Site and Pipe Locations. See Appendix 7 1. Set reference stakes 5 -10m apart indicating the boundaries of the bottom of the pond. Find the elevation of each stake using a surveyor's level and rod from the base point used in constructing the sewer. 2. Measuring the distance and elevation from the reference stakes, set slope stakes indicating the points at which to begin building the embankment and excavating the pond. 3. Set stakes to indicate pipe locations. This will eliminate re-excavating portions of the embankment. Excavating the Pond 1. Begin excavating at the inside slope stakes. Dig at the slope specified by the project designer until the bottom elevation is reached. Check this elevation with a surveyor's level and rod. See Appendix 11. 2. Continue excavating along the bottom elevation of the pond. Use excavated soil to build up the embankments 3. Make the bottom of the pond as level and as uniformly compacted as possible. If there are soft spots or tree roots, dig them out, fill with moist soil, and compact. 4. Make the corners of the pond rounded. 5. Leave some excavated soil on the pond bottom if small dikes are to be built for the start of pond operation 5. SAN 2O5. Building Embankments 1. Begin building embankments as the pond is excavated. Embankments must be well tamped, with sides sloped according to design specifications. 2. Leave gaps in the embankment at pipe locations as shown in Appendix 12. It may also be convenient to leave one or more wide gaps for removal of excavated soil. 3. The top of the embankment must be level, well-tamped, and at least 1.0m wide. The horizontal distance from the top of the embankment to the bottom of the pond must equal the design depth of the pond plus 1.0m. Laying Pipes 1. Excavate trenches for pipes at the design depth and locations. The bottoms of the trenches should be well-tamped. 2. Build bases about 0.5m high for the inlet pipes from concrete or stone. The purpose of the bases is to raise the inlet pipe above the bottom of the pond. See Appendix 5. 3. Build slabs for the outlet pipes from concrete or stone. The purpose of the slab is to support the outlet pipe and. to prevent erosion due to the discharge of treated sewage. Build support slabs under all valve locations. 4. Lay sewer pipe and mortar together sections; Install valves. 5. Build the vertical outlet from sleeved sections of pipe. The height of the vertical outlet determines the depth of the pond. It must be equal to the design depth calculated by the project designer. The sleeved sections will allow the pond to be drained when necessary. See Appendix 5. 6. Build a protective screen around the vertical outlet . with creosote-treated wood posts and rust-proof wire screen. The screen should extend at least 0.3m above and 0.3m below the vertical outlet. It will prevent floating debris from entering the outlet pipe after the pond is put into operation. 7. Carefully fill in pipe trenches with moist soil and tamp. Finishing Embankments 1. Fill in any gaps in the embankment that were used for laying pipe or removing excavated soil. Thoroughly tamp the top and slopes and make them uniform with the existing embankment. See Appendix 13. 2. Line the entire inside of the embankment slope with rocks and flat stones. This will prevent erosion due to wave action during pond operation. Rocks and stones should be smoothly graded to conform to the design slope of the embankment. Avoid using gravel and pebbles because this material tends to move down slope. 3. If topsoil or sod was initially removed from the site, use it now to cover the outside slope and top of the embankment. If no sod is available, plant grass seed. This will help prevent erosion of the embankment from wind and rain. See Appendix 13. 4. Excess soil excavated from the pond can be used to build small dams to divert surface water away from the pond. If not, it should be graded level or hauled away from the pond site. 5. Line the area immediately around the outlet pipe with a concrete pad to prevent erosion. 6. Form the dry ditch to contain the treated discharge while it evaporates and percolates into the ground. 7. Pond should be equipped with a post having markings to check water depth. 8. Erect a fence around the pond. 9. Fill the pond before allowing any input of wastewater. OPERATION and MAINTENANCE 1. Southwick, 9. Kstate Water Level The desired level should be maintained. If the level exceeds 2.5 meters, consider "dewatering", draining it to a grassy area. If level exceeds the maximum more than once each year, consider enlarging the pond, or adding a second cell. Intake Waste should always be dumped into the same place, at the "start" of the pond, opposite the dry ditch. Content Although a normal level of soap water is not a problem, do not allow large doses of disinfectants or other chemicals to be discharged into the system. A pond will have a green color when a flourishing algae population has been established. Changes in color usually indicate changes in the sewage entering the pond. Odor is also a sign of a problem. Such changes should be investigated immediately. See Appendix 10. Vegetation Control Keeping the edge of the pond clear of vegetation will normally provide adequate mosquito control. Grass on embankments should be allowed to grow no taller than 15 centimeters. Pond should be free of plants that grow in or on the water, both rooted and floating. These will block sunlight. Mats of floating algae must be broken up. Surface Conditions A boat and rakes should be kept ready. Should mats of leaves. sludge, scum, or algae collect on the surface, the rakes can be used to break them up. Embankment Maintenance Leaks or seeps in the embankment must be corrected by restoring the embankment, and sealing the inside surface of the pond. Leakage can be controlled by compaction, bentonite, or clay. Sludge Control Measure sludge depth once each year. Use a boat, and take the measurement near the inlet. A measuring stick can be made with a long wooden pole covered with a light colored clotheSAN205. Sludge must be removed when its depth exceeds 1/3 the depth of the pond. For an Anaerobic Pond this will occur after 2-12 years, and for a Facultative Pond after 8-20 years 5. SAN 2.O.5