10.4122/1.1000001584 Uhl, M. Janiczek, M. Grobe, S. Merkel, W. Enhanced treatment of CSO with vertical flow sand filters DTU Library, Technical University of Denmark (DTU) 2005 Ammonium COD CSO enhanced treatment faecal coliforms faecal streptococci sand filters University of Applied Sciences M\303\274nster, Laboratory of Water Resources Management IWW Rheinisch-Westf\303\244lisches Institut f\303\274r Wasserforschung Gemeinn\303\274tzige GmbH en Conference full text 10.4122/1.1000001583 application/pdf 1 Experimental studies of vertical flow sand filters for CSO treatment were conducted in lab and semi scale to investigate the dependency of processes and treatment efficiencies on filter material characteristics and operational boundary conditions. It was found out that sands with grain sizes of 0/2 mm and carbonate additives offer the best material conditions for high elimination rates. Artificial throttling of the outflow to constant 0.01 l s-1m-2 proved to be essential for high treatment efficiency for ammonium, COD and faecal bacteria. Long impoundage causes adverse effects resulting in high outflow concentrations and low treatment efficiencies. After each feeding the filters must be emptied for regeneration which is completed within 1-2 days. Too long dry periods impair the treatment abilities due to reduced bacteria population in the filter. Treatment efficiencies reached medians over 90 % for ammonium, medians about 70 % for soluble COD and medians about 90 % for total COD. Bacterial concentration of hygienically relevant microorganisms can be reduced by 1-2 log steps.