Treatment of cellulose bleaching effluents and their filtration permeates by anodic oxidation with H2O2 production

SALAZAR, C.; SIRÉS, I.; SALAZAR, R.; MANSILLA, H.; ZAROR, C.
Journal of Chemical Technology and Biotechnology 90 (2015) 2017-2026.

DOI: 10.1002/jctb.4501

Abstract

BACKGROUND

Electrochemical advanced oxidation processes (EAOPs), particularly those based on either cathodic electrogeneration of H2O2 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-H2O2 in a tank reactor with an air-diffusion cathode, which allowed efficient reduction of O2, and a DSA-RuO2 or BDD anode at constant cell voltage (2–12 V). Due to the complexity of the matrix, a larger H2O2accumulation in the acid effluents was observed. DSA favoured the accumulation of CIO2 ions, whereas BDD allowed their further transformation into CIO3 owing to the larger oxidizing power of its physisorbed OH. The contribution of this species, along with H2O2 and active chlorine, accounted for the significant TOC abatement reached in the different individual and coupled treatments.

CONCLUSIONS

AO-H2O2 and UF/AO-H2O2 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-H2O2 coupling yielded the largest mineralization of alkaline effluents (96% instead of 75% obtained by AO-H2O2) with low EC. © 2014 Society of Chemical Industry

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