Simulation model for real-time decision support in controlling the impactsof storm sewage discharges

The impacts of combined sewage discharges on river water quality are studie d using the MCSTR (Multiple Continuously Stirred Tank Reactor) dynamic mode l. The potential for applying this model in a real-time context is demonstr ated as a tool to support decisions regarding treatment plant operation dur ing storm events, when it is often not possible to sustain full treatment o f the incoming sewage flow. Discharges to the River Cam of treated and untr eated urban wastewaters from Cambridge and the Cambridge Sewage Works are a ddressed as a hypothetical case study. Alternative treatment strategies are defined for improving receiving water quality and assessed through simulat ed water quality downstream of the discharge; the stare variables of the mo del include the concentrations of biochemical oxygen demand, ammoniacal- an d nitrate-nitrogen, and dissolved oxygen (chlorophyll-a concentrations are also calculated but not considered herein). Strategies are assessed and ran ked according to the reduction in maximum pollutant concentration (or the i ncrease in minimum concentration, in the case of dissolved oxygen) promoted by each alternative, relative to conventional operation. The consequences of discharging overflows at an alternative position in the river, rather th an together with the treatment-plant effluent, are also evaluated. Run time s for the MCSTR model are of the order of just a few minutes (at most), thu s allowing the potential for its use in real time as a decision-support aid . (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.