UNSATISFACTORY INTERMITTENT DISCHARGES FROM COMBINED SEWER OVERFLOWS: AN ALTERNATIVE TO STORAGE SOLUTIONS

During wet weather conditions, wastewater flows in combined sewers systems can be enormous, resulting in untreated spills from combined sewer overflow structures to the receiving water. Where such intermittent discharges are judged to be unsatisfactory, the conventional solution has been to either increase the pass forward flow or store the wet weather overflow in large tanks for later treatment. An alternative to this storage solution, known as Equivalent Treatment, is to treat the overflow to a desired standard and discharge it as and when necessary directly to the receiving water. Process technology including clarifiers, filters and ultra violet disinfection is being trialed by United Utilities to assess this approach to solving unacceptable intermittent discharges. Results have shown that suspended solids concentrations, ultraviolet transmissivity levels and faecal coliform concentrations can be improved to a level where ultraviolet disinfection becomes viable for the destruction of microorganisms. UU are actively pursuing this approach to storm water management for a number of intermittent discharges across the North West of England.