Abatement of a complex mixture of dyes in the presence of chlorides by electrocoagulation and active chlorine-based photoelectro-Fenton-like processes

Abstract

This paper presents an innovative hybrid water treatment process combining electrocoagulation (EC) and active chlorine-based PEF-like (PEF-like) methods to eliminate a complex mixture of tannery dyes. The solution contained Acid Blue 113 (AB 113), Acid Blue 29 (AB 29), and Brilliant Green (BG) dyes in concentrations between 300 and 750 mg L−1 COD in 2000 mg L−1Cl−, 638 mg L−1NH4+ and 1700 mg L−1SO42− at neutral pH (resembling wastewater). The influence of mean linear flow velocity (0.69 ≤ u ≤ 3.47 cm s−1), applied current density (6 ≤ j ≤ 22 mA cm−2), and initial COD on the EC removal efficiency and discoloration was systematically examined. EC removed 32–48% COD; this modest depletion is due to the high load of organic matter. On the other hand, the •OH and HClO produced in the PEF-like process were insufficient to mineralize the organic matter (52–76%) due to the high initial COD. The latter suggested that the PEF-like process requires a previous EC to reduce the COD. The synergy between EC + PEF-like (hybrid process) allowed the COD abatement. The dye removal efficiency followed the order EC < PEF-like < EC + PEF-like. The hybrid process fulfilled the Mexican standard (COD < 210 mg L−1, and 100% discoloration) with total treatment costs of 0.683–0.696 USD m−3. XRF, XRD, SEM-EDS, OEA, and FTIR analyses on iron flocs indicated that AB 29, AB 113, and BG dyes are removed by adsorption. HPLC techniques followed the maleic and malic acids and ammonium and sulfate ions during the incineration of the dyes. The hybrid technology is promising for treating real wastewater containing complex dye mixtures.