Need Filtration or Equivalent? Demonstration Testing Prepares Communities for Low Level Phosphorus Effluent Limitations

As nutrient removal becomes more common place, the need to achieve low effluent concentrations of phosphorus is spreading. Typically, low effluent concentrations are defined as 0.3 mg/L or less, as these concentrations require increased chemical addition and effluent filtration. In the State of Wisconsin, many facilities are facing upcoming effluent phosphorus limits of 0.1 to 0.075 mg/L. While membrane filtration was originally considered the main alternative for these low limits, several less complex systems have been developed that can achieve these low level limits. Two of these technologies, disc filtration and high rate ballasted flocculation, were tested at several sites in Wisconsin during 2013 and 2014. Results indicate that effluent concentrations of 0.075 mg/L are achievable with both technologies, although at relatively high coagulant dosing rates. Filtration sizing and capital costs were also developed, and achieving these low level concentrations averaged $40 per pound of phosphorus removed per yearfor the initial cost and averaged $10 per pound for the annual chemical cost.