Treatment of Bleach-Plant Effluents with Membrane Filtration and Sorption Techniques

Laboratory experiments have been run with the combination of ultrafiltration (UF) and sorption techniques/reverse osmosis (RO). The use of negatively charged membranes improved both the filtration capacity (flux) and the rejection of organochlorine compounds. The combination of UF and RO used to treat retention in the caustic extraction stage showed high removal of COD, AOX and chloride ions (98.8 - 99.9 %). The content of AOX in the RO-permeate was 0.08 g per ton pulp. The ultrafiltration of three different total bleachery effluents showed a COD removal of 55-60 % and a AOX removal of 65-75 %. The decrease in toxicity was about 50 % and the removal of substances with a bioaccumulation potential was around 90 %. The treatment of this UF-permeate with a weak-base anion exchanger gave even higher removal efficiencies especially for the chlorophenolic compounds (>93 %), and the toxicity decreased 5 times (Microtox). The sorbent did not show any remarkable loss in removal efficiency during the 48 loading and reactivation cycles. When treating the total bleachery effluents the combination of UF and RO also showed high removal efficiencies. It is not meaningful to make a cost estimation before these combinations have been studied for longer periods, on larger scales and with a wide range of effluents. The problem of the final destruction of the pollutants which have been removed remains to be solved.