Development and validation of system design principles for water reuse systems

Decision support software (DSS) for Water Treatment for Reuse with Network Distribution (WTRNet) has been developed within the AQUAREC project on “Integrated Concepts for Reuse of Upgraded Wastewater”, under the Fifth European Community Framework Programme. The overall objective of work conducted as part of the AQUAREC project has been the development and validation of system design principles for water reuse systems. The DSS provides an integrated framework for optimisation of treatment and distribution aspects of water reuse and the selection of end-users, and has been used in the development of the design principles. The principle components of the software (simulation and optimisation models) are presented, followed by the discussion on the software validation. A case study is then illustrated, on which WTRNet has been applied to develop least-cost design alternatives. Design principles for water reuse systems that were achieved by applying the WTRNet tool are presented, in which the importance of utilising formal optimisation in determining the most promising design alternatives is demonstrated.

Planning of integrated water reuse systems is a highly complex exercise, which needs to consider the selection of treatment processes required to achieve the desired effluent quality, the distribution system required to deliver the reclaimed water to customers, and the selection from a set of possible end-users with potentially differing quantity and quality requirements. The WTRNet decision support tool presented in this paper provides a platform that can be used to conduct the integrated assessment of water reuse options in an efficient manner. The application of WTRNet is illustrated in a case study of water reuse options in the city of Kyjov, on a relatively small scale with few potential end-users. The application allowed for the following design principles to be derived by analysing the optimisation results: • The variability in lifecycle cost of water reuse schemes is a direct result of the distribution system costs, while treatment costs are relatively proportional to the volumes of water treated. • Costs of distributing reclaimed water can comprise a significant portion of the total scheme lifecycle cost, and have to be included in the evaluation. • Patterns have been observed in the selection of least-cost treatment trains as a function of both the reclaimed water end use type and the size of the scheme. • A fixed investment (lifecycle) cost can result in satisfying a relatively wide range of the percentage of projected demands. The motivation for the development of the design support tool presented here was the fact that a water reuse system is likely to have many possible design options, which are all linked to give multiple interactions and a very large number of design combinations. The developed tool allows efficient exploration of design alternatives to be conducted, which should aid planners in the development of more efficient water reuse schemes.