Orthogonal Experiment on Enhanced Coagulation Process for Advanced Treatment of Secondary Settling Tank Effluent

The effluent of secondary settling tank of a wastewater treatment plant (WWTP) were suggested to be further treated by enhanced coagulation process, and used as cooling water of a power plant. To guide this operation, the orthogonal experiment was performed to study the main factors of enhanced coagulation process. The results showed that the order of influencing factors was coagulant aid dosage> rotation speed> contact sludge concentration>pH at the stage of flocculation. The optimum parameters of the enhanced coagulation process were 0.3 mg/L coagulant aid (PAM), 2.5 g/L contact sludge, 80 r/min rotation speed for flocculation and pH 6.0. Under the optimum parameters, the turbidity of WWTP effluent was decreased from 10.0 NTU to below 0.5 NTU, and TP concentration was decreased from about 1.5 mg/L to below 1.0 mg/L (the lowest was 0.2 mg/L), which were better than the requirements in The Reuse of Urban Recycling Water – Water quality standard for industrial uses (GB/T19923-2005).