Biological Sewage Plants
Biological Sewage Plants or overgrown soil filter belong to the so-called near-natural sewage plants. The cleaning of the water happens with a complex soil micro-organisms plants system. In this process the soil (gravel/sand) plays the leading role as the carrier of the micro-organisms. The number and variety of organisms is significantly greater in the watery environment of technical sewage plants. Because of the long residence time of the wastewater in the soil filter a high buffering towards the quantitative and qualitative inflow-variation comes as a result. Biological Sewage Plants are functional after longer terms without any inflow and temporary overload and there is no excess sludge, which has to be disposed. The bioactivity is in a uniformly warm climate consistently high. This means that they are perfectly suitable for the use in tropical and subtropical climate.
The only disadvantage is the large area requirements. Because the only visible thing is the high vegetation, they are not noticeable as sewage plants and can be placed as wind screen and sight protection.
You don’t need external energy in a slightly declining land (Use of hydraulic lifters). In a flat land you need wastewater pumps. This gives a maximum energy parameter per population equivalent of 0,5 to 1,0 kWh/POPxa (kWh per population equivalent and year).
Additionally, the biological sewage plant system doesn’t need a lot of technical installations. Essential is to guarantee the surge feeding of the soil filter. This happens with mechanical lifters or automatic valves (in declining land) or with standard wastewater pumps (e.g. Grundfos wastewater pumps stations).
Calculation basis is the energy consumption of lifter pump and the annual emptying of the three chamber system into the soilification bed (composting of sludge).
Mechanical sewage plants (European standard)
A mechanical sewage plant works – with the difference to biological sewage plants – with activated sludge. To maintain the activity of sludge, air is going to be blown into the biomass. This requires an enormous electrical energy use to operate the high-performance compressor. This gives an energy parameter per population equivalent of 75 kWh/POPxa (kWh per population equivalent and year) for sewage plants up to 1000 population equivalent.