A sustainable Two-Echelon waste collection routing: Understanding waste picker behavior

Waste collection is a key component of reverse logistics that represents a significant challenge for low- and middle-income countries, where the process is highly labor-intensive and often informal. The informal sector plays an important role in solid waste collection, however its operational reality is rarely considered in routing models. This paper aims to analyze how the behavior of waste pickers influences route definition by considering sustainability factors and the impact of node characteristics, the use of a heterogeneous fleet, stochastic demand, and waste price. The problem is modeled as a Two-Echelon Waste Collection Vehicle Routing Problem (2E-WCVRP) integrating the three components of sustainability, economic, environmental, and social. Social aspects and informality in routing, often overlooked in literature, are key considerations. The proposed model considers interactions between waste pickers (first echelon) and trucks (second echelon), incorporating factors such as profit, workload distribution, CO2 emissions, and social impacts. The waste pickers unload waste bags at satellite nodes, where urban trucks later collect them. The objective is to maximize the profit of the waste pickers and minimize the total costs of the urban trucks. A two-stage solution approach is developed, employing a metaheuristic based on Ant Colony Optimization (ACO). A key innovation is the integration of waste pickers’ decision-making behavior into the pheromone update mechanism, considering factors like profit maximization and node-vehicle compatibility. The model and solution methodology are demonstrated through test instances and a case study in Cali, Colombia. Experimental results demonstrate the effectiveness of this approach in optimizing routing and improving sustainability.