Electrochemical Treatment of Segregated Effluents from the D-Stage in ECF Kraft Cellulose Bleaching

Experimental results of electrochemical treatment of acid filtrate effluents from the first ClO2 stage (D-0) of kraft cellulose ECF bleaching are presented here. Real industrial effluents from an eucalyptus based cellulose mill, with no additional supporting electrolytes, were used here. Stainless steel cathode, and graphite, and DSA-Ti/RuO2 anodes were tested, at current densities in the range 1-50 A/m(2). In all cases, COD, AOX, and chloride concentrations decreased with electrochemical treatment, reaching 40-50% removal after 20 min treatment. The rate of COD removal significantly increased at greater pH. Significant active chlorine formation from chloride anodic oxidation was also observed, and no further formation of organic-chlorinated by products was detected. Experiments conducted with p-chlorobenzoic acid show that significant hydroxyl free radicals were generated in all tested anodes, with slightly greater effect in the case of graphite anode. Finally, both mutagenic and genotoxic activity was totally removed by electrochemical treatment, although toxic intermediates were detected within the first 2 min, at high current densities.