COMBINED OR SEPARATE SEWER SYSTEMS ? A CRITICAL COMPARISON USING A NEW DATABASE ON URBAN RUNOFF POLLUTION

Comparison of the traditional separate and the combined sewer system using measured concentration data for a range of pollutant parameters in the sewer. A simple long-term load balance was applied, accounting also for the pollutant loads in the wastewater treatment plant outflow which proved to be non-negligible. The results show that the separate system is superior to the combined for some parameters only, such as nutrients. For the other parameters (heavy metals and COD), the combined system yields less total loads.