A FREILP Approach for Long-Term Planning of MSW Management System in HRM, Canada
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The municipal solid waste (MSW) management system is consisted of planning, development, execution of capital works, and so on. Too many factors in the system make the decision making process plagued with uncertainties, vagueness and complication. Interval-parameter Linear Programming (ILP) is widely used to deal with uncertainties existed in the MSW system and to assist optimal decision making. However, the existing ILP solution algorithms, i.e., best-worst case algorithm and 2-step algorithm, are found to be ineffective through a validity checking process. Moreover, the results from ILP can not reflect the linkage between decision risks and the system return. In this study, a fuzzy risk explicit interval-parameter linear programming (FREILP) model is developed and applied to the long-term planning of the MSW management system in Halifax Regional Municipality (HRM). This method is specifically designed to deal with extensive uncertainties existed in the MSW management system and to provide decision supports to HRM planners. In the model, ILP is used to reflect uncertainties existed in both objective function and constraints. Based on the basic ILP, a risk function is defined to assist in finding solutions with minimum system cost while minimizing the system risk, under certain aspiration levels. The aspiration level could be conservative, medium or aggressive, and can thus be presented as a fuzzy set to reflect the preference of decision makers. Three sets of solutions are obtained accordingly. Besides, the model was also solved under the aspiration level from 0 to 1, with a step of 0.1, for providing a comprehensive decision support. This approach can effectively reflect dynamic, interactive, uncertain characteristics, as well as the interactions between overall cost and risk level of the MSW management system, thus provide valuable information to support the decision-making process, such as waste allocation pattern, timing and expansion capacities of the municipal solid waste management activities. The result can directly reflect the tradeoff between decision risks and the system return.