Quantities of all forms of energy consumed for collection and treatment of municipal wastewater are estimated. Heat energy is equated to electrical energy by a conversion factor of 10,500 Btu/kwh. Total energy consumption, expressed as kwh/mg of wastewater treated, ranges from 2300-3700 kwh/mg. Energy used for construction of the treatment plant and the sewerage system represents 35-55% of the total energy consumed. The remainder used for plant operation is predominately (65-75%) electrical energy. The use of high efficiency aeration devices combined with good maintenance practices appears to offer the best opportunity for conservation of energy within the plant. Recovery of energy from the sludge produced at the plant can be accomplished by anaerobically digesting the sludge and using the digester gas as fuel for internal combustion engines. In large plants, when the sludge is sufficiently dewatered, it is also possible to recover energy by incinerating the dewatered sludge with production of steam in a waste heat boiler. The steam can then be used within the plant or expanded through a steam turbine to produce mechanical or electrical energy.

Surveys the solution of complex problems at national and regional levels and outlines possible future developments