The anaerobic treatment of liquid wastes or wastewaters provides the opportunity to rapidly reduce the organic content of the waste while minimizing treatment process energy consumption and production of microbial biomass or sludge. The conversion of organic compounds in wastewater into sludge produces a by-product which requires further treatment or disposal. Reduction in sludge and energy consumption are the two attributes which have made consideration of direct anaerobic pretreatment of wastewater economically attractive for municipal and industrial waste streams. For relatively warm wastewater containing significant degradable organic compounds, direct anaerobic treatment may also provide excess energy. But even with low strength wastewater the energy savings which can be achieved by avoiding most of the cost of aeration is significant. However, effluents from anaerobic treatment are often not suitable for direct discharge into receiving waters without further treatment which may require aerobic polishing. Yet, the reduced aeration demand and sludge production in aerobic treatment following anaerobic pretreatment may justify this treatment scheme.