Comparison of Overflows from Separate and Combined Sewers – Quantity and Quality

The use of separate sewerage systems to solve pollution problems associated with combined systems is examined. Overflows from combined stormwater-sewer systems have been found to be one of the major causes of receiving water pollution. Experiences in two countries which have predominantly one system or the other provided a basis for comparison. Wet weather overflow was found to be a major problem with similar quality of overflow produced for both systems. Minimising overflows was feasible, however proper and integrated control of stormwater and sewage flows, related to receiving water impacts, is indicated as the best solution. The use of separate sewerage systems to solve pollution problems may not be justified.