An Evaluation of Bench and Pilot-Scale Primary Wastewater Treatment Processes to Meet More Stringent Wastewater System Effluent Regulation

Abstract

Canada’s national wastewater effluent quality standards of wastewater treatment must not exceed 25 mg/L of total suspended solids (TSS) and 25 mg/L of carbonaceous biochemical oxygen demand (cBOD5). The objective was to investigate optimization to meet these standards through bench-scale and pilot-scale studies. Key findings of the bench-scale study found a 2 to 4 mg/L increase in coagulant dose (i.e., Aluminum sulfate 5 to 7 mg/L) and a 0.25 mg/L increase in flocculant dose (i.e., 1.25 mg/L of polymer) improved water quality. Chemical optimization could not consistently improve water quality when the hydraulic retention time (HRT) was around 24 minutes or less. The pilot-scale ballasted flocculation study identified that the average TSS reduction for the pilot-scale was 79-85%. The studies suggest that optimizing chemicals and adding ballast to the CEPT process would improve effluent water quality, but not enough to meet the WSER cBOD5 limit because of emerging soluble cBOD5.