Microsieving coupled with O3 or ClO2 for treatment and disinfection of combined sewer overflows

A compact combined sewer overflow (CSO) treatment unit is set up and evaluated in pilot-scale. The pilotplant consisted of flocculation, coagulation and a microsieving system followed by a disinfection unit with either O3 or ClO2. Efficiency of the pilot-plant was evaluated with respect to reduction of Escherichia coli, coliform bacteria and intestinal enterococci as well as removal of biocides. Results showed that 10 mg L-1 of ClO2 as disinfectant was sufficient to meet the European Union (EU) requirements as per Bathing Water Directive (2006/7 EC) while the same results were only achieved when higher O3 dose (20 mg O3 L-1) was applied. This study revealed that chlorine dioxide was the most effective disinfectant 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. Regarding biocides, the efficiency of the removal was highly dependent on the type of substance. However, ozone was found to be able to remove a broader range of the investigated biocides