Transporting Sludge to the 106-Mile Site: An Inventory/Routing Model for Fleet Sizing and Logistics System Design

This paper develops a model that is being used by the City of New York to design a new logistics system to transport municipal sewage sludge from city-operated wastewater treatment plants to a new ocean dumping site 106 miles offshore. The model provides an integrative framework for considering such strategic planning issues as fleet sizing, choice of vessel size, sizing local inventory holding capacities, and analyzing system behavior with and without transshipment. A unique feature of the model is that plant visitation frequencies are determined naturally by the characteristics of the problem (vessel size, inventory holding capacities, statistics of sludge production, proximity of other plants), rather than stated as exogeneous constraints. The formulation should be useful in a more general class of depot-to-customer distribution systems, including the distribution of industrial gases. The paper concludes with a description of additional research that is required in refining both the assumptions and the mechanisms of execution of the model.