Relevance of the electro-Fenton process as a pre-treatment prior to biological degradation for azo dyes removal.
Résumé
The aim of this study was to examine the feasibility of combining an electro-Fenton pre-treatment and a biological treatment to remove azo dyes from aqueous effluents. The electro-Fenton reaction was performed in a two-compartment system involving a reference (saturated calomel electrode), a platinum anode and a graphite felt cathode. For the three considered dyes, high discoloration (in the range 77.1-97.8%) and low mineralization (in the range 7.7-18.8%) after 4-h reaction were in favor of the hybrid process, which was confirmed during subsequent experiments with methyl red sodium salt (MRSS) as a model dye. When potential-controlled electrolysis at −0.5 V/SCE was performed with a carbon-felt cathode surface of 378 cm2 and a catalytic amount of ferric iron of 1 mmol L−1, less than 1-h reaction was needed for an almost total discoloration (90.5%); while mineralization and oxidation remained low even after 48-h reaction, 11.1 and 57.2%, respectively. High discoloration level concomitantly to low mineralization and oxidation for MRSS removal which were in favor of a hybrid process, confirmed by the decrease of the COD on DOC ratio (45.1%) and the increase of the average oxidation state AOS (2.1). Final BOD5 on COD ratio of 0.24 and an absence of toxicity of the treated solution (EC50 = 165%) also showed the positive impact of an electro-Fenton pretreatment.