An evaluation of the efficiency of the combined sewer – wastewater treatment system under transient conditions

Abstract

The paper considers the efficiency of alternative sewer and wastewater treatment plant management schemes with respect to the effluents to the receiving waters. The input time series for the flows and concentrations at the CSO structures and at the treatment plant intake are obtained through a continuous sewer simulation model. The wastewater treatment plant model is based on a structured dynamic model describing COD removal and final settling. Special emphasis is put on the sludge inventory of the plant since this is considered to be the main problem area under storm conditions. The methodology is illustrated on the combined sewer network of Brussels. Scenarios without and with CSO control measures in the sewer are considered. At the treatment plant, the simulation study evaluates the effect of potential control strategies such as ratio control of the RAS, step feed and retention of first flush in a storm tank.