Disinfection of combined sewer overflow with micro-screening combined with ozone or chlorine dioxide: NordIWA 2013

A pilot-scale pre-treatment (micro-screening) of incoming wastewater at Öresundsverket WWTP consisting of flocculation (17.4-19.5 mg PAX 100/l), coagulation (3.6-4.1 mg Kemira 5060 cationic polymer/l) and filtration (100 µm disc filter) was set up at Öresundsverket WWTP. The pre-treated wastewater was then subjected to 5, 10 and 15 mg ClO2/l in lab-scale as well as 3, 6, 9, 12 and 20 mg O3/l in pilot-scale. The disinfection efficiency of the pre-treatment as well as the two disinfection agents was thereafter evaluated by analysis of E. Coli, coliform bacteria and intestinal Enterococci. The treatments were further evaluated by analysis of COD-, total phosphorus-, SS-, turbidity and biocide reduction. To reach the limits of bacterial content stipulated in the EU Bathing Water Directive (2006/7 EC) 10 mg ClO2/l was needed. For ozone, the same results were only achieved when 20 mg O3/l was applied. However, the CD and IP biocides were significantly reduced by ozone while no substantial effect on the biocide content could be discerned when chlorine dioxide was applied. This study concludes that chlorine dioxide was the most efficient disinfection agent in reducing the number of bacteria to below the limits set by the EU Bathing Water Directive and that the pre-treatment used was highly efficient.