Performance of (in)active anodic materials for the electrooxidation of phenolic wastewaters from cashew-nut processing industry

• Published in: Chemosphere (Oxford) 2018-06, Vol.201, p.740-748
• Main Authors: Oliveira, Edna M.S., Silva, Francisco R., Morais, Crislânia C.O., Oliveira, Thiago Mielle B.F., Martínez-Huitle, Carlos A., Motheo, Artur J., Albuquerque, Cynthia C., Castro, Suely S.L.
• Format: Article
• Language: English
• Subjects: Active chlorine; Anacardium - chemistry; Anodic oxidation; Boron - chemistry; Boron doped diamond; Diamond - chemistry; Dimensionally stable anode; Electrochemical degradation; Electrodes; Electrolysis - instrumentation; Electrolysis - methods; Food Industry; Lactuca - drug effects; Nuts - chemistry; Oxidation-Reduction; Phenols - analysis; Phenols - toxicity; Ruthenium Compounds - chemistry; Titanium - chemistry; Wastewater - chemistry; Wastewater treatment; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - toxicity; Water Purification - instrumentation; Water Purification - methods
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2018.02.037

This study investigated the anodic oxidation of phenolic wastewater generated by cashew-nut processing industry (CNPI) using active (Ti/RuO2-TiO2) and inactive (boron doped diamond, BDD) anodes. During electrochemical treatment, various operating parameters were investigated, such as current density, chemical oxygen demand (COD), total phenols, O2 production, temperature, pH, as well as current efficiency and energy consumption. After electrolysis under optimized working conditions, samples were evaluated by chromatography and toxicological tests against L. sativa. When both electrode materials were compared under the same operating conditions, higher COD removal efficiency was achieved for BDD anode; achieving lower energy requirements when compared with the values estimated for Ti/RuO2-TiO2. The presence of Cl− in the wastewater promoted the electrogeneration of strong oxidant species as chlorine, hypochlorite and mainly hypochlorous acid, increasing the efficiency of degradation process. Regarding the temperature effect, BDD showed slower performances than those achieved for Ti/RuO2-TiO2. Chromatographic and phytotoxicity studies indicated formation of some by-products after electrolytic process, regardless of the anode evaluated, and phytotoxic action of the effluent. Results encourage the applicability of the electrochemical method as wastewater treatment process for the CNPI, reducing depuration time. •Electro-oxidation using DSA and BDD removes efficiently the COD from wastewater.•BDD electrode shows better performance for removal COD.•DSA electrode operates with lower energy consumption.•Cl- favors the indirect electro-oxidation by formation of hypochlorous acid /hypochlorite.