Multi-Commodity Multi-Transformed Network Flows with an Application to Residuals Management

This paper presents a network model for the analysis of waste management systems. In the "waste management network" that we develop waste-generating activities correspond to sources, each node corresponds to a specific flow (waste) form, and each arc to a flow transformation; a chain from a source to a destination represents in turn waste generation, treatment, and disposal, while a feasible flow pattern constitutes a possible waste management system. The model resembles the maximal multi-commodity flow model with positive gains (single transformation) along the arcs, but in addition it admits multi-transformations, interrelations among arc flows, and flow-dependent budget restrictions. The problem is formulated as a linear program where each column in the constraint matrix corresponds to a chain in the network. The solution procedure uses a column-generation scheme based on a shortest route algorithm adapted for multi-transformed flows. Recycling, discharge and effluent standards, charges, damage costs and various budgeting schemes can be handled. An illustrative hypothetical example is given.