Treatment of cellulose bleaching effluents and their filtration permeates by anodic oxidation with H 2 O 2 production

BACKGROUND Electrochemical advanced oxidation processes (EAOPs), particularly those based on either cathodic electrogeneration of H 2 O 2 or anodic oxidation (AO) via • OH, have become attractive technological options for the complete detoxification of wastewaters. Their integration with separation pre‐treatment such as ultrafiltration (UF), nanofiltration (NF) or reverse osmosis (RO) may be a plausible way to reduce processing time and costs. RESULTS Raw effluents from the acid and alkaline elemental chlorine free bleaching stages of a hardwood‐based kraft pulp mill, as well as their UF, NF and RO permeates, have been characterized and then treated by AO‐H 2 O 2 in a tank reactor with an air‐diffusion cathode, which allowed efficient reduction of O 2, and a DSA‐RuO 2 or BDD anode at constant cell voltage (2–12 V). Due to the complexity of the matrix, a larger H 2 O 2 accumulation in the acid effluents was observed. DSA favoured the accumulation ofClO 2 −ions, whereas BDD allowed their further transformation intoClO 3 −owing to the larger oxidizing power of its physisorbed • OH. The contribution of this species, along with H 2 O 2 and active chlorine, accounted for the significant TOC abatement reached in the different individual and coupled treatments. CONCLUSIONS AO‐H 2 O 2 and UF/AO‐H 2 O 2 yielded similar mineralization levels (65–68%) for acid effluents, but lower energy consumption (EC) resulted in the latter process due to the lower conductivity of the permeates. NF/AO‐H 2 O 2 coupling yielded the largest mineralization of alkaline effluents (96% instead of 75% obtained by AO‐H 2 O 2 ) with low EC. © 2014 Society of Chemical Industry