D21.3 Technical conclusions from testing during site specific development and specifications for final design

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An innovative high rate filtration (HRF) system has been developed and applied for treatment of a combined sewer overflow (CSO) by Inrigo AS from Norway. In the EU-project DESSIN, a container type HRF plant was built to investigate and later demonstrate the treatment efficiency for treatment of CSO. The HRF plant was placed at Hoffselva, Norway, where site specific testing has been performed to give basis for final design. Eleven (11) CSO events were recorded during the testing and demonstration period, so far from September 2015 until May 2016. Test results indicate that HRF solution is a promising technology to reduce emissions of particulate pollutants from CSO. Up to 80% of suspended solids (SS) removal and 75% of chemical oxygen demand (COD) removal were documented during the first flush. The overall removal of SS and COD were about 47% and 56%. Nutrient removal is relatively low because of the major soluble nitrogen and phosphorus compositions in CSO. However, 6.3% total nitrogen (TN) and 15% total phosphorous (TP) were retained together with particles. The HRF system also shows promising treatment efficiency of heavy metals with 48% Al, 48% Zn, 57% Cu, and 31% Cr removed, respectively.