An interval nonlinear program for the planning of waste management systems with economies-of-scale effects – A case study for the region of Hamilton, Ontario, Canada

In practical environmental systems with the effects of economies-of-scale (EOS), most relationships among different system components are nonlinear in nature, which can be described precisely only if a nonlinear model is employed. In this study, an interval nonlinear programming (INLP) model is developed and applied to the planning of a municipal solid waste (MSW) management system with EOS effects on system costs. The INLP has a nonlinear objective function and linear constraints. It handles nonlinearity presented as exponential functions. When exponential term p = 1 (in the INLP's objective function), the model becomes an interval linear program; when p = 2, it becomes an interval quadratic program. Therefore, the INLP is flexible in reflecting a variety of system complexities. A solution algorithm with satisfactory performance is proposed. Application of the proposed method to the planning of waste management activities in the Hamilton–Wentworth Region, Ontario, Canada, indicated that reasonable solutions have been generated. In general, the INLP model could reflect uncertain and nonlinear characteristics of MSW management systems with EOS effects. The modeling results provided useful decision support for the Region's waste management activities.