Objective
In the pulp and paper industry alkaline bleaching streams (E1) are produced in large volumes and represent a severe pollution concern. Besides the inorganic load resulting from the addition of chemicals there is a wide range of solutes resulting from the lignin dissolution and organochlorinated compounds formed by chlorination of different fractions of lignin. The removal of organo and organochlorinated compounds of low molecular weight was achieved through nanofiltration (NF). This operation yields also a partial demineralization with production of water that does not comply with the quality requirements of washing waters for pulp bleaching. In order to meet these requirements further processing by electrodialysis (ED) was carried out.
Using organic thin film composite membranes (poly(trans 2,5 dimethylpiperazinthiofuranamide on a porous support of polyethersulphone, and ampholytic polymer with sulphonate and quaternized groups on a polysulphone support) and inorganic tubular membranes (ultrafiltration zirconia support coated with a zirconia nanofiltration active layer), the following results were obtained:
the feasibility of nanofiltration to purify the E1 bleaching effluent and to bring down the pollution load and in particular the organochlorinated matter to levels acceptable for water discharge;
optimization of a sequence of pretreatment/nanofiltration/electrodialysis, to purify the E1 effluent and to recycle it as process water;
water production with a salt content of 350 ppm, acceptable as bleaching process water for recycling;
very low salt content of recycled water (mainly due to sodium chloride and the bivalent ions content). This is an asset with respect to industrial process waters and this fact should be incorporated in cost analysis of the produced water.
Fields of science
- natural scienceschemical sciencesinorganic chemistryalkali metals
- engineering and technologychemical engineeringseparation technologiesdesalinationelectrodialysis
- natural scienceschemical sciencespolymer sciences
- engineering and technologymaterials engineeringcoating and films
- natural sciencesearth and related environmental sciencesenvironmental sciencespollution
Topic(s)
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1000 LISBOA
Portugal