Many large wastewater treatment plants (LWWTPs) face both an increased load due to population growth and urbanisationas well as more stringent effluent quality requirements. In Stockholm, Sweden, for example, commitment to the Baltic Sea Action Plan (BSAP) and the implementation of the European water framework directive combined with an annual growth rate of 1.5% require actions for efficient municipal wastewater treatment, meeting the new requirements. As it is difficult, or even impossible, for existing WWTPs surrounded by residential areas to expand physically, new treatment solutions are needed. Among others, Stockholm Water Company (Stockholm VattenAB) has therefore decided to upgrade the existing HenriksdalWWTP (850 000 pe), currently operating with a conventional activated sludge (CAS) process, to a membrane bioreactor (MBR). By converting current post-sedimentation basins to membrane separation units and by other related adaptations the facility will be able to increase its capacity by almost the double (1 600 000 pe).
Results from pilot scale studies on wastewater treatment with combined activated sludge and MBR in the main treatment line.