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.

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