Reduction of greenhouse gas (GHG) emissions is one of the most important tasks facing municipal WWTPs. Electric power consumption typically accounts for about 90% of the total energy consumption. This study presents a benchmarking analysis of electric power consumption. The specific power consumption (SPC) ranged from 0.44 to 2.07 kWh/m(3) for oxidation ditch plants and from 0.30 to 1.89 kWh/m(3) for conventional activated sludge plants without sludge incineration. Observed differences of the SPC can be attributed to the difference in the scale of plants rather than to different kinds of wastewater treatment processes. It was concluded that economical benefits by centralizing treatment had contributed significantly to the reduction of energy consumption. Further analysis was carried out on the plant that had shown an extremely small SPC value of 0.32 kWh/m(3). In this WWTP, a large amount of digestion gas was generated by anaerobic digestion. In particular, it was used to generate power using phosphoric acid fuel cells to generate approximately 50% of the energy consumed in the plant. It was calculated that this plant had reduced the overall SPC by 0.17 kWh/m(3). The effect of power generation using digestion gas demonstrated clearly the advantage of implementing energy recovery schemes.

The performance of the sludge disintegration process by ozonation (SDPO) installed in six full-scale municipal WWTPs were evaluated, focusing on sludge reduction, effluent quality and sludge characteristics. As a result, the removal efficiencies of COD Mn , SS and T-P were lower than the typical values. In almost all WWTPs under investigation, the MLSS concentrations in the reactor were higher than that of typical OD plants without an installed SDPO. Furthermore, the MLISS/MLSS ratio was significantly higher than typical OD sludge and had kept on increasing even after 1 or 2 years of operation due to the higher influent inorganic SS concentration. The inorganic accumulation rate for the amount of influents was estimated to be 5.88 g/m 3 . Although a sludge reduction rate of about 88% would be possible, it is considered necessary to withdraw the sludge systematically depending on the amount of inorganic accumulation in the reactor in order to perform stable wastewater treatment.