Because of intensive animal farming, the problem of animal wastes disposal has become very acute in the Reunion Island, namely for liquid wastes such as pig slurry. In this paper we address the problem of determining efficient supply policies of a slurry treatment plant collectively managed by individual farmers. For this, we built a simulation model with a continuous part (i.e., slurry stocks modeled as ordinary differential equations) and a discrete part (i.e., transport allocation as a Linear Program). Simulations are carried out considering the specific constraints of farmers in a critical zone in the Reunion Island. The results emphasize the positive role of a closed-loop control, which means organizing slurry transportation according to the current states of individual stocks.