An Approach for Integrated Optimization of Wastewater, Recycled, and Potable Water Networks

This paper outlines an approach to the integrated optimization of wastewater, recycled and potable water systems in an urban area. The approach will be demonstrated through consideration of a case study of the Hume corridor in Melbourne, Australia. A total of 44,000 new residential lots are planned in this area. These houses will have their garden and toilet connected to a Class A recycled water system. The recycled network will also incorporate some industrial demands. As the recycled water system will receive its inputs from wastewater treatment plants, the three networks had to be considered in an integrated fashion. The case study considered the development of two optimisation models, one for the wastewater system and the other for the potable and recycled water systems. The interface between the two models occurred at the wastewater and recycled water treatment plants. Values were set for the capacities of these plants for each model and they were adjusted to ensure compatibility between the two models. The recycled network was designed to the same level of service as the potable water network, e.g. 25 m minimum allowable pressure head at all demand nodes. As potable water top-up of the recycled system is to be considered, it was found that the potable water network needed to carry flows greater than potable peak hour demands. The results obtained clearly indicated the value of using evolutionary algorithms in an integrated fashion to optimize potable and third pipe systems. Application of this approach to other areas is likely to make third pipe systems more attractive and to lead to significant savings in the use of limited water supplies.