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Whole Systems Approach to Ecological Design Organic Agriculture and Local Food Appropriate Technology: Energy Green Building & Retrofitting |
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Sizing of Wetlands for Sewage Treatment Following Pre-Treatment in Septic TanksConstructed wetlands are sized using temperature dependent process equations. For an Ecovillage application, the following table will provide a guide. This is only a guide and the process calculations should be checked by a qualified engineer before construction. A person equivalent (pe) gives the daily wastewater influent to the treatment system. It is 60 grams of BOD per day, which is typically 200 litres with a BOD concentration of 300 mg/l (parts per million). For the same daily flow, typically the ammonia will be ~35 mg/l and the Total Suspended Solids (TSS) 250 mg/l. As will be seen, the higher the temperature of the wastewater, the greater is the biological activity asnfd the more the treatment. This a wetland in a tropical country will be smnaller for the same level of treatment than one in a cold country. The chart to the side gives the size of the working area of the wetland (between the manifolds) per pe for four influent sewage water temeperatures. The effluent treatment concentrations are also shown. It is recommended that at least 30% should be added to the size for berming of the edges, access and so on. Typically constrcted wetlands are built 50 m to 100 m from the nearest house, although when properly built there is no odour. For very small wetlands (less than 50 people, the actual footprint should be calculated as berming can be a greater percentage of the total area required. |
Size of working area of the wetland Can you send me this chart bigger? |
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