Water Distribution System Optimisation Accounting for a Range of Future Possible Carbon Prices

Climate change, especially global warming caused by human activities presents serious global risks. Mitigating global warming by reducing greenhouse gas (GHG) emissions is a unique challenge facing our generation. In order to tackle this challenge, many measures are being developed, among which carbon trading is a popular one. In this paper, a new paradigm for the design of water distribution systems (WDSs) is being developed under a possible emission trading scheme. In this paradigm, minimisation of the costs of GHG emissions is incorporated into the optimisation of WDSs either as one part of the objective or as a second objective. A multi-objective genetic algorithm (MOGA) called WSMGA (water system multi-objective genetic algorithm) has been developed to solve this problem. The time value of both the system costs and the costs from GHG emissions has been taken into account by using present value analysis. Following the Stern Review Report there is controversy as to what discount rate should be used in present value analysis for mitigation of climate change, consequently two different discount rates have been used in this study. The impacts that the carbon prices used in the emission trading scheme have on the optimisation of WDSs have been explored for two hypothetical case studies. The optimisation results show that the different carbon prices used lead to different solutions in the single-objective optimisation formulation. In general, a network with larger pipes is chosen when a higher carbon price is used. In contrast, the carbon price used has no impact on the multi-objective optimisation results. However, different carbon prices lead to different amounts of savings in greenhouse gas costs resulting from the same amount of increase in system costs for the same ordered set of Pareto-optimal solutions.