Wastewater minimization in multipurpose batch plants with a regeneration unit : multiple contaminants

Abstract

The generation of wastewater in processing industries is an inevitable activity since almost all operations require water at some point. Process equipment cleaning is a universal wastewater generating operation as it is practiced in all segments of manufacturing industries. This is especially important in batch plants due to inherent sharing of equipment by different tasks. Wastewater minimization can be achieved by employing water reuse opportunities. In the past, an optimal batch schedule was assumed before the minimization of wastewater, which was an oversimplification of the problem. This is because the batch schedule impacts on the starting and finishing times of water-using operations, hence any wastewater target obtained is specific to the schedule given. This dissertation presents a methodology to address the problem of wastewater minimization by extending the concept of water reuse to include a wastewater regenerator. The regenerator purifies wastewater to such a quality that it can be reused in other operations. This further increases water reuse opportunities in the plant, thereby significantly reducing freshwater demand and effluent generation. The mathematical model presented determines the optimum batch production schedule that achieves the minimum wastewater generation within the same framework. The effectiveness of the method was demonstrated in its application to two case studies involving multiple contaminants and wastewater reductions of 19.2% and 26% were achieved.