Risk-Based Water Quality Management in an Integrated Urban Wastewater System under Future Uncertainties

Abstract

Climate change and urbanisation are key factors potentially affecting the future of water quality and quantity in urbanised catchments and are associated with significant degrees of uncertainty. Maintaining or even improving urban recipient water quality under this uncertain future will be a major challenge. The study reported in this paper explores the potential for managing water quality within a novel risk-based framework in the context of an Integrated Urban Wastewater System (IUWS) comprised of a sewer system, wastewater treatment plant and the recipient. In the study, we explore the potential for managing water quality failure risk by optimising the operational control and/or design of the wastewater system. Water quality failure risk is defined as the product of the likelihood and impact of water quality standard breaches. The optimisation objectives are the minimisation of water quality failure risk in terms of both dissolved oxygen and ammonia concentrations. The decision variables are a set of IUWS operational control and design parameters. The above optimisation problem was solved using the modified MOGA-ANN method. The results obtained from a semi-hypothetical case-study undergoing urbanisation and subject to climate change indicate that operational control optimisation has the potential to reduce the risk of recipient water quality failure but, in this particular case, cannot fully meet appropriate water quality standards. It was found that an acceptable level of risk can only be achieved by combining improved operational control and system (re)design.