OPTIMAL REHABILITATION STRATEGY IN WATER DISTRIBUTION SYSTEMS CONSIDERING REDUCTION IN GREENHOUSE GAS EMISSIONS

摘要

Water distribution systems (WDS) need a rehabilitation strategy due to infrastructure aging which leads to decreasing capacity, increasing leakage and consequently low performance of the WDS. Identifying an appropriate strategy including location, time of pipeline rehabilitation, rehabilitation technique and material types are the main challenge especially when the rehabilitation budget is limited. Furthermore, the environmental impacts of a rehabilitation strategy on global warming have yet to be addressed. This paper presents a multi-objective optimization model for a long-term rehabilitation strategy in WDS which minimize the two main criteria: (1) greenhouse gas (GHG) emissions from either fossil fuel & electricity or embodied energy of materials; (2) the leakage amount. The Pareto optimal front containing optimal solutions is determined using Non-dominated Sorting Genetic Algorithm NSGA-II. Decision variables are classified into a number of groups as: (1) pipeline rehabilitation including different rehabilitation techniques and material types; (2) addition of pumps; (3) addition of tanks. Rehabilitation techniques used here includes replacement, rehabilitation and lining, cleaning, pipe duplication. The long time planning horizon of the rehabilitation strategy is divided into a number of specific times for which the simulation model is applied separately. The effects of population growth, aging, hydraulic constraints and budget limitations on the WDS are considered. The developed model is demonstrated through its application to C-Town WDS. The rehabilitation strategy is analyzed for a 10 year planning horizon with 2 five-year time periods. The results show that the optimal rehabilitation strategy is able to efficiently control the total leakage amount in the WDS whilst considering environmental criteria by lowering GHG emissions.