A mathematical optimisation approach for wastewater minimisation in multipurpose batch plants: Multiple contaminants

This paper presents a methodology for wastewater minimisation in multipurpose batch plants characterised by multiple contaminant streams. Firstly a situation in which central reusable water storage does not exist is considered. In this case, water from one operation is directly reused in another operation as long as the source and sink operations, respectively, end and begin simultaneously. Secondly, the case with central reusable water storage is considered. In this case water from a source operation can temporarily be stored in dedicated storage before use by the sink process. The methodology is based on an existing scheduling framework which then makes it possible to generate the required schedule to realise the absolute minimum wastewater generation for a problem. The methodology involves a two-step solution procedure. In the first step the resulting MINLP problem is linearised and solved to provide a starting point for the exact MINLP problem.