Optimizing a waste collection system with solid waste transfer stations

In recent years, stricter environmental regulations, as well as an increased public concern, have progressively forced new landfills to be located more and more away from urban centers. This has stimulated the use of solid waste transfer stations, where the solid waste is transferred from small collection vehicles to large transportation vehicles. In this paper, we tackle the problem of determining the routes for both collection and transportation vehicles, as well as their synchronization at the transfer stations. We divide the problem into two phases and propose an exact approach utilizing a mathematical formulation, as well as a constructive heuristic and a matheuristic for the first phase, and a heuristic approach for the second phase. Computational results show that the approach combining the matheuristic for the collection phase with the heuristic for the transportation phase is able to achieve consistent reductions in terms of number of collection vehicles needed.