Various sections involved in the collection, transport, treatment and discharge of sewage and stormwater together comprise the urban wastewater system (UWS). In this chain of interlinked elements, the starting point for generation of wastewater/stormwater is the urban catchment. Sewage is generated from households and industries while stormwater is mainly the runoff from urban surfaces during rain events.
The invisible underground sewer network transports the generated wastewater to the wastewater treatment plant (WWTP). As the name suggests, the WWTP is involved in removing the pollutants present in the raw sewage before discharging the treated effluent into receiving waters. Receiving waters form the final link in this chain. In many cases, this receiving water system is the starting point for the drinking water system for any downstream city (although this is outside the scope of this thesis). Historically, the objective of an UWS has been to convey the sewage away from the city in order to avoid health hazards to urban dwellers. However, owing to our increasing understanding of anthropological pressures on the natural ecosystem, the European Union has (re-)defined the objective of an UWS as to “protect the chemical and ecological status of a river” (Council of the European Communities, 2000).
In this context, it is essential to understand the interactions between different parts of an UWS in order to improve their performance individually as well as to protect the receiving waters in a holistic manner. Modelling can be a valuable tool not only for understanding the individual sections and their interactions but also for serving as an engineering tool to explore the potential for improvement in the performance using different approaches (e.g. process control, upgrading the existing infrastructure).