Treatment of effluent from alkali extraction with ultrafiltration and reverse osmosis

Effluent from alkali extraction of chlorinated pulp was treated with ultrafiltration (UF). Three different ultrafiltration (UF) membranes were tested. The permeate from one of the UF membranes was further treated with reverse osmosis (RO). Titration curves for the permeates from the different UF and R0 membranes were determined. The concentration of charged compounds was calculated from the titration data and compared with the COD and AOX of the permeates. The retention of COD and AOX was between 50 and 90% for the UF membranes, whereas the retention of carboxylic acid groups was considerably lower, 15-45%. During the R0 treatment the retention of all compounds was found to be very high. For the densest R0 membrane the retention of AOX and compounds with carboxylic acid groups was higher than 99%. The retention of COD was 96%.