A scenario analysis for reducing organic priority pollutants in receiving water using integrated dynamic urban fate models

Abstract

The Water Framework Directive (WFD) has the objective of a catchment-oriented water quality protection for all European waters with the purpose of achieving a good ecological and chemical quality status by the year 2015. To that end, necessary measures should be identified and implemented, with the aim of progressively reducing pollution from priority substances. The objective of this paper is to demonstrate how a dynamic model of the integrated urban wastewater system (IUWS) can be used to test different emission reduction strategies for organic priority pollutants (PPs) in a semi-hypothetical case study on di(2-ethylhexyl)phthalate (DEHP). The IUWS is composed of coupled entities: sources, urban catchment surface (run-off/infiltration), sewer system, stormwater treatment unit, wastewater treatment plant (WWTP) including sludge handling, and receiving surface water (river). State-of-the-art dynamic fate models were selected from literature and extended with an organic pollutant fate sub-model. Dynamic DEHP release profiles were estimated using a dynamic model input generator and fed to the model to predict the fate and concentration of DEHP in each IUWS sub-system. The model was then used to test eight scenarios on environmental performance, namely (1) reduction of impervious urban area, (2) reduction of infiltration in the sewer system, (3) input reduction (excluding the main pollutant sources), (4) separating the combined sewer system, (5) treatment of stormwater by stormwater infiltration ponds (separate sewer systems), (6) placement of retention basins at main sewer junctions, (7) sand filtration of secondary effluent, and (8) pre-precipitation of phosphorous. The simulation results revealed that the most effective measure in terms of river water quality improvement for DEHP (annual average and spikiness reduction) and PP concentration in the disposed WWTP sludge, is reducing release of this substance into the environment, not surprisingly. In general, this will heavily depend on the parameterisation of the scenarios.