Nanofiltration of bleaching pulp and paper effluents in tubular polymeric membranes

A systematic investigation of the nanofiltration (NF) of alkaline bleaching effluent (El) from the pulp and paper industry is carried out through a first assessment of NF of model systems, namely, solutions of salts-NaCl and Na2SO4-and organic solutes-glucose, saccharose, and raffinose-which develop membrane-solute(s) interactions similar to those developed by the bleaching effluent. The ampholytic polymer of the membrane active layer, under controlled feed conditions,develops a surface charge distribution which determines the membrane performance. The verification of the effects of the anion valence and the feed concentration on the salts rejections, in accordance with the Donnan exclusion principle, is an important feature of this work. For the bleaching effluent, the NF performance is strongly dependent on the pH due to the influence of this parameter on the membrane surface charge. The contribution of this work toward the optimization of the NF operating conditions would allow for future scale-up of this separation process for E-1 effluent purification and water recovery in the pulp and paper industry.