Performance analyses of existing sanitary sewers with the selection of household water-saving schemes.

Abstract

The widespread uptake of household water-saving systems (i.e. appliances, fittings, rainwater harvesting tanks, etc.) usually aims to reduce the gap between water demand and supply without considering the performances of downstream sanitary sewers (SSs). This paper presents an analysis approach that examines the lifespan interaction of water-saving schemes (WSSs) and operation of existing SSs. Examined are three probable ways of using (or not using) these water systems, including the conventional (baseline), full application and optimal selection of efficient WSSs. For optimality, a method that maximises the WSS potential efficiency (overall) and minimises the cost of WSSs including the associated savings across the entire existing SS subject to constraints at the end of the planning horizon has been formulated. The problem is solved using a non-dominated genetic algorithm to obtain optimal solutions. Decision variables include various water use (or saving) capacities of water-saving schemes at different inflow nodes (locations). The method was demonstrated on the subsystem of the Tsholofelo Extension SS. The results indicate impactful and revealing interactions between water use efficiency, instantaneous hydraulic performances and existing SS upgrade requirements due to different applications of WSSs. The impacts and revelations observed would inform decisions during lifespan operations and management of SSs.