Advanced Electrochemical Oxidation of Ultrafiltration Permeates from Cellulose Bleaching Effluents

This paper reports experimental results on the use of electrochemical oxidation to reduce the organic load in ultrafiltration permeates from cellulose bleaching effluents. Alkaline and acid bleaching effluents from industrial production of ECF bleached kraft cellulose from pinewood, were treated by ultrafiltration at 20 kDa, 10 kDa and 1 kDa, using a laboratory scale high performance UF unit. Electrochemical treatment of UF permeate was conducted in a dual cell electro-reactor, featuring stainless steel cathode, and graphite, DSA-RuO2 and DSA-Pt anodes. Experiments were conducted under potentiostatic conditions, at 2V with current densities in the range 1-5 A/m(2), and without any additional supporting electrolyte. Depending on process conditions, 35-80% COD removal was obtained, with specific energy consumption below 3 kWh/Kg COD removed; and DSA-RuO2 showed better performance. It is concluded that electrochemical removal of residual COD present in acid and alkaline permeate streams is technically feasible, without addition of supporting electrolyte. Although no additional supporting electrolyte was added, reasonable COD oxidation was achieved, with low specific energy consumption. Larger treatment time, and current densities would be necessary to achieve greater COD removal.