Secondary Treatment Process in Beishiqiao WwTP Coarse Pump Fine Alternative Secondary selector Disinfectio greenI removal oxidation ditch clarifier Effluent Influent judge return Solid disposal Sludge thickening DisposalSecondary Treatment Process in Beishiqiao WWTP Coarse screening Alternative oxidation ditch selector Grit removal Secondary clarifier Disinfection Sludge thickening Fine screening Sludge dewatering Disposal Influent Sludge return Pump Effluent Solid disposal