Simulating the environmental impact of stricter nitrogen and phosphorous discharge criteria

Swedish wastewater treatment plants (WWTPs) expect more stringent discharge criteria for nitrogen and phosphorous as new treatment permits are issued in the near future. Several WWTPs assume the new discharge criteria to be 6 mg/l of total nitrogen, 6 mg/l of BOD and 0.2 mg/l total phosphorous. It is not yet known if the criteria should be reached on a yearly, quarterly or monthly basis. New permits – effluent limits and averaging conditions – will require reconstructions and process adaptions at the wastewater treatment plants. It is today not known how and to what extent such new discharge criteria will affect the total environmental impact from Swedish wastewater treatment plants from a systems perspective. This presentation will show how mathematical process modelling combined with Life Cycle Assessment (LCA) modelling was performed for three Swedish wastewater treatment plants (Henriksdal, Käppala and Kungsängen WWTPs). The objective was to evaluate how the total environmental impact of the respective WWTP changes as measures are taken in order to meet new and more stringent discharge criteria for nitrogen and phosphorus.