The document provides a technical overview of the modules used in DEWATS (Decentralized Wastewater Treatment Systems), including septic tanks, biogas settlers, anaerobic baffled reactors, anaerobic filters, and planted gravel filters. It describes the basic functions and treatment processes of each module, such as sedimentation, anaerobic digestion, filtration, and removal of solids and contaminants. Efficiencies generally range from 25-40% for septic tanks and biogas settlers to 75-90% for anaerobic baffled reactors and anaerobic filters. Planted gravel filters focus more on removing odor and color and require pre-treated wastewater.

1. Technical overview of DEWATS Modules

2. Technical overview Septic tank / Settler Anaerobic Baffled Reactor Biogas settler Anaerobic Filter Planted Gravel Filter Pond Systems

3. Technical overview Septic tank / settler Consists of min. 2 to 3 compartments Settling / sedimentation tanks for retaining particle Outlet is free from settleable solids, Dissolved & suspended matter passes untreated to next treatment stage Efficiency 25% to 40%, Desludging period 1 to 3 yrs - depends on sludge storage

4. Technical overview Biogas settler Sedimentation tanks for retaining particles Biogas is formed due to digestion of settled organic matter in anaerobic condition Outlet is free from settleable solids Dissolved & suspended matter passes untreated to next treatment stage Efficiency 25% to 40%, Desludging period 1 to 3 yrs depends on sludge storage Biogas production: Gas storage is needed (gas tight)

5. Technical overview Anaerobic baffled reactor Treatment in absence of oxygen (anaerobic) Wastewater passes through a series of chambers in up-flow form Sludge (activated) at the bottom of each chamber Further treatment (degradation) of suspended & dissolved solids by available bacteria Efficiency 75% to 85% Desludging needed only if excess sludge (activated) is generated

6. Technical overview Anaerobic fixed bed Treatment occurs in absence of oxygen (anaerobic) Wastewater passes in a series of chambers through the filter material in up-flow form Filter is made out of gravel, slag or plastic elements To avoid plugging pre-treatment (sedimentation) is necessary Efficiency 75% to 90%, Desludging is needed only if excess sludge (activated) is generated

7. Technical overview Planted gravel filter Treatment occurs in presence of oxygen (aerobic) Treatment concentrates more on removal of smell & color Planted Gravel Filter consist of plants (reeds) & filter materials (graded gravels, river pebbles) Filter is permanently soaked (up to 50 cm from bottom) in water Flow direction is horizontal Suitable for pre-treated wastewater

8. Technical overview Flow principle of horizontal filter

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