This paper outlines an approach to the integrated optimization of wastewater, recycled andpotable water systems in an urban area. The approach will be demonstrated throughconsideration of a case study of the Hume corridor in Melbourne, Australia. A total of 44,000new residential lots are planned in this area. These houses will have their garden and toiletconnected to a Class A recycled water system. The recycled network will also incorporatesome industrial demands.As the recycled water system will receive its inputs from wastewater treatment plants, thethree networks had to be considered in an integrated fashion. The case study considered thedevelopment of two optimisation models, one for the wastewater system and the other for thepotable and recycled water systems. The interface between the two models occurred at thewastewater and recycled water treatment plants. Values were set for the capacities of theseplants 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 ofthe recycled system is to be considered, it was found that the potable water network needed tocarry flows greater than potable peak hour demands.The results obtained clearly indicated the value of using evolutionary algorithms in anintegrated fashion to optimize potable and third pipe systems. Application of this approach toother areas is likely to make third pipe systems more attractive and to lead to significantsavings in the use of limited water supplies.
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