Genetic algorithm optimisation of water distribution systems accounting for greenhouse gas emissions

Abstract

The optimisation of water distribution systems (WDSs) has been a focus for civil and environmental engineers for over 30 years. In previous research, attention has mainly been given to the minimisation of the cost of the networks, due to the high expenditure associated with the construction and maintenance of WDSs. However, the impacts of WDSs on the environment usually have not been considered adequately. The study described in this paper extends previous research by incorporating into the optimisation of WDSs the environmental criterion of minimising greenhouse gas (GHG) emissions as a second objective. A multi-objective genetic algorithm has been developed to solve this problem. The impacts of minimising GHG emissions on the results of WDS optimisation have been explored for a case study. The results indicate that the inclusion of GHG emission minimisation as one of the objectives results in significant tradeoffs between economic and environmental objectives. Furthermore, a sensitivity test has been conducted by using different discount rates in present value analysis for computing total cost and GHG emissions. The results obtained show that the Pareto-optimal front is very sensitive to the discount rates used. As a result, the selection of discount rates has a significant impact on final decision making.