Abstract
A first step toward the goal of using a sewage treatment plant as a base for water, materials, and energy circulation in a watershed is to improve the independent generation of electric power by utilizing the organics including sewage influent. An analysis was made of the behavior of organics within the plant, together with electric power consumption. A model plant (48,000m3/day) based on a conventional activated sludge process was studied. The energy potential was calculated from COD and the behavior in each process was studied. About 10% of the energy potential could be recovered by digestion gas generation, but most of the energy potential was lost in mineralization in the aeration tank and incinerator. The raising electric power independence was evaluated by "COD concentration necessary for independence." Estimated values compared to 5800 mg/L in the case of a normal primary settling tank were as follows: 2800 mg/L (51% down) when the high-efficiency solids-liquid separation was introduced; 1800 mg/L (69% down) when activated carbon from sludge was charged; and 4900 mg/L (16% down) when a high-efficiency air diffuser was used. It may be concluded that electric power independence is difficult to achieve with any single method, but it might be achieved when these methods are combined.
