Aluminum and ferric salts are commonly used in municipal wastewater treatment plants (WWPTs) for phosphorus (P) removal.In this study,on-site jar tests were conducted to determine the removal of different P species from the fresh samples in the presence and absence of activated sludge (AS) with different doses of alum,poly-aluminum chloride,and ferric chloride at different pH.The soluble P (SP) concentration in the samples was about 0.63 mg/L.When the mixed liquor containing AS was treated with 8 mg/L ofAl,SP could be reduced to 0.13 mg/L,while it was reduced to 0.16 mg/L with only 1 mg/L of Al after sedimentation removal of AS from sample.Chemical analysis determined that AS contained 59.8 mg-P/g-TSS and 43.8 mg-Al/g-TSS and most of the P was associated with the aluminum hydroxide.We discovered that the phosphate in the AS could readily be released from it,which was mainly responsible for ineffective removal of P to low levels in mixed liquor even with very high alum dose.This study provides new insight into the behavior and fate of P in the wastewater treatment plants that use alum to enhance P removal in the final effluent.