Multi-objective optimization of phosphorus and organic substances removal from reject water by coagulation

The multi-objective optimization for phosphorus and organic substances removal from reject water by coagulation was conducted using normalized scoring method for multiple response variables. Separate and combined effects of Al/P ratio, polyacrylamide (PAM) dosage and initial suspended solids (SS) concentration on phosphorus and organic substances removal were analyzed by the response surface methodology (RSM). The results showed that adding aluminum polychloride along with PAM effectively removed phosphorus and organic substances from reject water, and improved settlability of SS in reject water. Normalized single-objective RSM optimization showed that Al/P ratio was the dominant factor for simultaneous removal of phosphorus and organic substances, followed by initial SS concentration and PAM dosage. The optimized removal efficiencies of phosphorus and total organic carbon were 93.1% and 53.9%, respectively, under the condition of Al/P ratio of 3.0, PAM dosage of 1.22 mg·L^-1 and SS concentration of 3.58 g·L^-1. Compared with optimization based on multiple response variables, the introduction of normalized scoring method solved the magnitude differences between response variables, and simplified the analysis and calculation.