The demands for fresh process waters and heating/cooling utilities arise intermittently in batch plants. Due to equipment constraints, the quality and flow-rate of each resulting wastewater stream are required to be controlled within specified limits before treatment/regeneration. In this paper, a general mathematical programming model is developed to design the optimal buffer system for equalizing the flow-rates and contaminant concentrations of its outputs. Three examples are provided to illustrate the effectiveness of proposed approach. (c) 2005 Elsevier Ltd. All rights reserved.