Evaluation on the nutrient reduction in sewage systems using ultra-rapid coagulation

This study was conducted to test the removal of nutrients in combined sewer overflows (CSOs) by using an ultra-rapid coagulation (URC) process. Alum and poly aluminum chloride (PAC) coagulants were each used to treat ten separate CSOs caused by rainfall events. Optimal injection ratios of 3 mol P/mol Al for alum and 2 mol P/mol Al for PAC were used, as determined by a preparatory experiment based on the phosphorous concentration of raw water. Total nitrogen (TN) removal efficiency was low for both coagulants, with only 33.5% for alum and 37% for PAC. In contrast, total phosphorus (TP) removal efficiency for alum and PAC were 86.1% and 91.4%, respectively. Removal efficiency of various phosphorous forms, including orthophosphate (Ortho-P), organic-phosphate (Org. P), and polyphosphate (Poly-P), in the raw water was highest for Ortho-P (alum 99.3%, PAC 99.6%). The sum of Poly-P and Org. P removal efficiency was lower than Ortho-P alone (alum 69.1%, PAC 77.9%). Removal efficiency of phosphorus increased with higher concentrations of particulate matter in the raw water.