JOINT CONSIDERATION OF COMBINED SEWERAGE AND WASTE-WATER TREATMENT PLANTS

Wastewater treatment plants, combined sewerage, catchment areas, storage tanks and overflows have to be regarded together. Stormwater runoff results in discharges at combined sewer overflows and higher pollutant loads in the effluent of the treatment plants. Characteristics of catchment areas and sewerage, number and capacity of storage tanks and overflows determine the characteristics of the combined water influent of the treatment plant. The plant has to cope with a higher hydraulic load and often with higher pollutant loads at the beginning of combined water flows. Some of the effects are displacement of sludge to the secondary clarifier, higher solids concentrations in the effluent and high loads of ammonia nitrogen for the nitrifying reactor. To decide on bigger stormwater storages or improvement of the treatment plant all effects in the whole system have to be considered. This can only be done with dynamic models, although simulation of combined water flows still have to be improved.