A novel wastewater treatment process (S-TE PROCESS®) with significantly reduced production of excess sludge has been developed. The process consists of two different stages, one for a biological wastewater treatment and the other for a thermophilic aerobic digestion of the resulting sludge. A portion of return sludge from the wastewater treatment step is injected into a thermophilic aerobic sludge digester (TASD), in which the injected sludge is solubilized by the action of thermophilic aerobic bacteria. The solubilized sludge is returned to the aeration tank in the wastewater treatment step for its further degradation. Pilot-scale facilities of the S-TE process and the conventional activated sludge process as a control, both treating the same industrial wastewater, were comparatively operated for totally 270 days. As a result, 93% reduction in overall excess sludge production was achieved in the S-TE operation. The SS solubilization rate in TASD was stable at around 30%. Only a slight increase in the effluent SS and TOC concentrations was observed compared with those of the control facility. Otherwise the removal efficiency of TOC was approximately 95% for both plants. A full-scale plant treating domestic sewage was operated for three years, showing 75% reduction of overall excess sludge production. It was concluded that the new process was feasible.

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