Process integration of effluent treatment techniques - a way of decreasing the energy and resource use in pulp and paper industries

摘要

The operating costs for waste water treatment in pulp and paper mills are high and the treatment stages have so far only to a minor extent been integrated in the mill's total process systems. In a desk study it has been shown that process integrated methods could be cost and energy efficient ways to reduce the environmental impact. Anaerobic treatment and membrane methods combined in different treatment sequences were used for treatment of effluents from Kraft pulp, CTMP, TMP and RP mills with and without integrated paper production. The production capacities, effluent volumes and discharge levels were chosen to be representative for Scandinavian mills. Membrane filtered water (mainly of high temperature) was reused in the process and accordingly the fresh water consumption was reduced. The process integrated cases were compared with conventional processes including waste water treatment in an activated sludge plant. Part of the existing effluent treatment plant was used as polishing stage. The process integrated cases proved to be superior in almost all aspects. The Electric power use was reduced by 15-30 MWh/day, the cooling demand by up to 8 500 MWh/day and 35-90 MWh/day biogas could be generated. It must be stressed that the treatment and the mill concepts are simplified examples and cost calculations are based on generalised assumptions on capacity, treatment efficiency etc. Considering the encouraging results it is suggested that process integration approaches could lead to more resource and cost efficient alternatives compared to present effluent treatment plants.