2. Pre-treated effluent treatment techniques and water disposal

Domestic wastewater treatment and drainage can be carried out jointly in a single soil-based system, or separately, with a system providing only treatment, with the drainage function devolved either to the soil or to the surface water environment.

The combined treatment and disposal of septic effluent involves two systems in natural soil: underground seepage through trench filtering and seepage beds. Treatment in a reconstituted filter bed prior to infiltration into natural soil also calls for two systems: spreading in an undrained sand filter bed, and the infiltration mound (above-ground undrained sand bed).

Two systems are used for purification prior to discharge into the surface water environment: the vertical-flow drained filter bed on a sand bed and the vertical-flow drained filter bed on a zeolite bed. A third system, the horizontal...