Abstract
The sewage sludge disposal systems involving anaerobic digestion process were investigated from points of economics and energy. Four optional systems with eight alternatives were analysed, setting the plant at three fixed scale, and the separate and combined sewer collection systems were chosen as the model. Profit of the additional investment to the conventional one and net profit were calculated and compared with each other. Net energy consumption, production and self-sufficiency of electricity were discussed. The optimal type of these systems depends on the scales and sewer systems of plants, and the digestion with heat treatment and dewatering without chemicals were the most effective systems.
