A Discrete-Continuous Hybrid Approach to Periodic Routing of Waste Collection Vehicles with Recycling Operations

Waste management agencies need to plan their waste collection activities in an efficient way such that they not only provide high-quality and timely service to customers but also maximize their net profit from recyclable waste, i.e., the total recycling revenue minus total operating costs. This paper proposes a mixed-integer linear program model for the waste collection problem in urban areas while considering the recycling operation at the sorting facility. A hybrid solution approach with both discrete and continuous optimization components is developed to solve the problem. The continuous component builds upon asymptotic routing cost formulas from the continuous approximation literature, while it is integrated into the discrete optimization component via an iterative stochastic approximation procedure. A series of numerical experiments are conducted, and results show that the proposed model and hybrid solution approach significantly outperform state of the art benchmarks from the literature.