Integrating water-use networks in a paper mill

Abstract

The pulp and paper industry is under regulatory pressure to reduce the volume of its water usage and wastewater discharge. To provide more efficient use of water resources and to minimise wastewater discharge, the design of water allocation networks has recently received increasing attention. Water system integration is often applied in the petroleum and chemical industry but much less so in the pulp and paper industry. We proposed a general methodology, nonlinear programming (NLP), for the design of optimal water use networks in a paper mill. The NLP requires specification of the lower and upper bounds on the contaminant concentrations flowing in and out of each process unit. This method can be effectively used to optimize the water network and minimise fresh water consumption and wastewater discharge in a paper mill. The minimised wastewater flows into a bio-treatment system where it is regenerated and can be reused for papermaking. We successfully achieved zero discharge of wastewater without affecting production and paper quality. Water consumption decreased from 90–110 m3 to 1.6 m3 per ton paper produced.