Water in the Pulp and Paper Industry: Evaluation of Four Microfiltration Applications, 1998 Environmental Conference Proceedings

This paper describes four potential applications for microfiltration membrane processes in the recycling of specific liquid streams in pulp and paper mills. Each type of effluent was tested on a bench scale device: 1) old newsprint (ONP) de-inking effluent containing flexographic ink; 2) effluent from a paper coating operation; 3) effluent from a bleached chemi-thermo-mechanical pulp (BCTMP) mill; 4) effluent from a board mill using recycled old corrugated container (OCC). The first three were tested using a submerged microfiltration module, and the last using a submerged microfiltration membrane bio-reactor.

The microfiltration of ONP deinking effluent completely removes flexographic ink. The quality of the permeate was suitable for recycling to the paper mill. It was possible to concentrate the effluent from the paper coating operation to a consistency of 16.5%, removing 96% of the original water. The retention of suspended solids by microfiltration led to very good permeate quality. The integration of both the retentate and the permeate into the paper mill process is feasible. Although the microfiltration membrane retains the suspended solids in the BCTMP effluent, the permeate contains high levels of total dissolved solids which are not removed. Further treatment is required in order to allow the integration of this stream into the process. By treating OCC effluent using a membrane bio-reactor (MBR), overall removal of COD and BOD5 of 95% and 99%, respectively, was achieved. The quality of the final effluent meets requirements for recycling this stream into the process.