Sustainable Operating Practices for Achieving Low Phosphorus Effluents

Wastewater treatment plants (WWTPs) operating to achieve total phosphorus (TP) limits of approximately 0.1 mg/L and lower face special challenges. To meet very low effluent TP concentrations, chemical phosphorus removal tends to be the preferred option for reliable and consistent performance. As TP limits decrease, chemical dosages, energy and manpower costs can substantially increase. Enhanced biological phosphorus removal (EBPR) can achieve effluent ortho-P concentrations of less than 0.1 mg/L, but to meet very low levels consistently, chemicals are required for standby, for precipitation of residual ortho-P and for coagulation of the remaining particulate and colloidal phosphorus. Under the WERF Nutrient Challenge Program, sustainable practices for operation of WWTPs that must achieve very low TP limits are being evaluated under an ongoing project. This paper provides an update and summarizes several of the issues being examined, with a focus on operating practices associated with reaching very low TP limits.