Treatment of a mixture of chloromethoxyphenols in hypochlorite medium by electrochemical AOPs as an alternative for the remediation of pulp and paper mill process waters

SALAZAR, C.; SIRES, I.; ZAROR, C.:
Electrocatalysis 4:4 (2013) 212-223.

DOI: 10.1007/s12678-013-0130-9

Abstract

Here, 100 mg L⁻¹ of dissolved organic carbon of aromatics including chloromethoxyphenols were prepared by exposition of a mixture of guaiacol, syringol, and vanillin in 200 mM NaClO at pH 3.0 and 25 °C for 14 h and further degraded by electrochemical advanced oxidation processes (EAOPs) like anodic oxidation with electrogenerated H₂O₂ (AO-H₂O₂), electro-Fenton (EF), and photoelectro-Fenton (PEF). Electrolyses were performed with a cell containing either a Pt or boron-doped diamond (BDD) anode and an air-diffusion cathode at constant current density. Oxidants were hydroxyl radicals (^•OH) formed at the anode surface from water oxidation and in the bulk from Fenton’s reaction between added Fe²⁺ and H₂O₂ generated at the cathode, as well as active chlorine species produced from the anodic oxidation of HClO. Oxychlorine ions like ClO₃ ⁻ using Pt and ClO₃ ⁻ + ClO₄ ⁻ using BDD were detected in the electrolyzed solutions. A poor mineralization was found using the Pt/air-diffusion cell, with increasing relative oxidation ability in the sequence AO-H₂O₂ < EF < PEF. In contrast, overall mineralization was achieved in all EAOPs using the BDD/air-diffusion cell due to the larger amounts of highly oxidizing ^•OH generated at BDD. For this latter system, the effect of UVA light, current density, and NaClO and/or Fe²⁺ concentration on the mineralization rate was examined. Up to 11 chloroderivatives of the parent molecules including four chlorophenols, six chloromethoxyphenols, and one chloromethoxynaphthalene were identified by GC–MS. The removal of these aromatics in AO-H₂O₂ with Pt or BDD was monitored by UV–vis spectrophotometry, HPLC, and GC–MS.