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Point sources such as wastewater treatment plants (WWTP), combined sewer overflows (CSO) and separate sewer outlets (SSO) are acknowledged to be major pathways for pollutants to enter surface water. As response, retention soil filters (RSF) have been installed among others in the Erft river catchment area over the past two decades to treat outflows of combined sewer systems and rainwater from separate sewer systems. Studies conducted on several of these RSFs have shown that besides reducing solids by filtration, RSFs have good chemical and biological cleaning capacities for a variety of parameters. Concentrations of both nutrients and heavy metals are reduced. Numerous micropollutants such as pharmaceuticals, pesticides and industrial compounds as well as faecal bacteria are eliminated at high rates. With this background a new type of RSF (RSFplus) has been designed for the flexible treatment of WWTP effluent and CSO. The RSFplus treats CSO during rain events. During dry weather periods, the RSFplus is used for polishing WWTP effluent. The RSFplus is divided into three segments which are fed alternately to guarantee aerobic conditions and is equipped with innovative distribution channels to ensure homogeneous feeding. Granulated activated carbon is used as an additive for the filter medium for advanced treatment. The effectiveness of WWTP effluent polishing and reliability of operational parameters have already been tested for 2.5 years on a pilot scale. The first full-scale demonstration site will be built in 2017 at the WWTP Rheinbach in North Rhine-Westphalia (Germany).
combined sewer overflow, micropollutants, nutrients, retention soil filter, wastewater treatment plant
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