Phosphorus removal potential at sewage treatment plants in Bavaria – a case study

Controlling phosphorus emissions from sewage treatment plants is a key factor in preventing eutrophication of surface waters. Regarding surface waters in Germany, the orientation value for the "good ecological status" for total phosphorus (P_total) is set at 0.10 mg P_total/L. To achieve this value, a further reduction in the P_total emissions from sewage treatment plants (STPs) is required. The evaluation of 2,626 Bavarian STPs showed a high reduction potential of the P_total emissions in STPs treating more than 1,000 population equivalents (PE). To achieve the goal of improving the surface water quality as well as to investigate which option is most feasible for Bavaria, three alternative scenarios of tightening the discharge permits of P_total were considered. By these scenarios, a reduction of the P_total load by app. 35%-50% can be achieved. For example, to reduce 50% of the P_total load, the discharge permits should be set as follows: STPs from 1,000 to 10,000 PE should comply with 1.0 mg P_total/L, STPs >10,000 PE to 0.5 mg P_total/L. The required annualized specific capital investment and operating costs required to implement simultaneous precipitation are fluctuating between 2 and 5 €/(PE•y). In larger STPs, an average effluent concentration of 0.5 mg P_total/L can generally be achieved, if clarification is designed and operated in accordance with applied regulated designing standards.