Total pollution discharge as a planning concept for urban pollution management

This paper describes some results of an integrated model application in the Høvringen wastewater system in Trondheim/Norway. The model includes wastewater production, surface run-off, infiltration, transport and treatment under a joint Matlab/Simulink platform. The model also allows to simulate the effects of real time control. The objective was to minimize pollution discharges to receiving waters and to define design loads for the extension of the treatment plant. Several sets of remedial measures in the catchments and the sewer system were evaluated; including the investigation of real time controlled gates in the main sewer tunnel to use its volume for storage. Some combined sewer overflows (CSO) were detected as critical points in the sewer network. Their discharge, in terms of water volume as well as pollutant loads, can be reduced by half with the application of sets of remedial measures. Due to separation the discharge of suspended solids via stormwater outfalls increases. The influence of remedial measures is smaller for the total phosphorus balance, but nevertheless decisive for single CSOs. Real time control of the activated tunnel storage can reduce the treatment plant bypass by 30%. The possibility of simulating remedial measures in the complete drainage and wastewater system is a powerful planning tool and a prerequisite for comprehensive cost-benefit analyses.