Model-based comparison of two ways to enhance WWTPcapacity under stormwater conditions

摘要

Two different approaches to increase the fraction of combined water treated in the wastewatertreatment plant (WWTP) which would otherwise contribute to combined sewer overflows (CSO)are presented and compared based on modelling results with regard to their efficiencies duringvarious rain events. The first option is to generally increase the WWTP inflow according to its actual capacity rather than pre-setting a maximum that applies to worst case loading. In the second option the WWTP inflow is also increased, however, the extra inflow of combinedwater is bypassing the activated sludge tank and directly discharged to the secondary clarifier.Both approaches have their advantages. For the simulated time series with various rain events,the reduction of total COD load from CSOs and WWTP effluent discharged to the receiving waterwas up to 20% for both approaches. The total ammonia load reduction was between 6% forthe bypass and 11% for inflow increase. A combination of both approaches minimises theadverse effects and the overall emission to the receiving water.