title: Sequential electrochemical treatment of dairy wastewater using aluminum and DSA-type anodes.
abstract: Dairy wastewater is characterized by a high content of hardly biodegradable dissolved, colloidal, and suspended organic matter. This work firstly investigates the performance of two individual electrochemical treatments, namely electrocoagulation (EC) and electro-oxidation (EO), in order to finally assess the mineralization ability of a sequential EC/EO process. EC with an Al anode was employed as a primary pretreatment for the conditioning of 800 mL of wastewater. A complete reduction of turbidity, as well as 90 and 81% of chemical oxygen demand (COD) and total organic carbon (TOC) removal, respectively, were achieved after 120 min of EC at 9.09 mA cm(-2). For EO, two kinds of dimensionally stable anodes (DSA) electrodes (Ti/IrO₂-Ta₂O₅ and Ti/IrO₂-SnO₂-Sb₂O₅) were prepared by the Pechini method, obtaining homogeneous coatings with uniform composition and high roughness. The (·)OH formed at the DSA surface from H₂O oxidation were not detected by electron spin resonance. However, their indirect determination by means of H₂O₂ measurements revealed that Ti/IrO₂-SnO₂-Sb₂O₅ is able to produce partially physisorbed radicals. Since the characterization of the wastewater revealed the presence of indole derivatives, preliminary bulk electrolyses were done in ultrapure water containing 1 mM indole in sulfate and/or chloride media. The performance of EO with the Ti/IrO₂-Ta₂O₅ anode was evaluated from the TOC removal and the UV/Vis absorbance decay. The mineralization was very poor in 0.05 M Na₂SO₄, whereas it increased considerably at a greater Cl(-) content, meaning that the oxidation mediated by electrogenerated species such as Cl₂, HClO, and/or ClO(-) competes and even predominates over the (·)OH-mediated oxidation. The EO treatment of EC-pretreated dairy wastewater allowed obtaining a global 98 % TOC removal, decreasing from 1,062 to <30 mg L(-1).
authors.affiliation: Centro de Investigación y Desarrollo Tecnológico en Electroquímica, Unidad Tijuana, Carretera Tijuana-Tecate km 26.6, Consorcio Tecnológico de Baja California, 22444, Tijuana, B.C., Mexico.
authors.forename: Brenda
authors.initials: B
authors.lastname: Borbón
authors.forename: Mercedes Teresita
authors.initials: MT
authors.lastname: Oropeza-Guzman
authors.forename: Enric
authors.initials: E
authors.lastname: Brillas
authors.forename: Ignasi
authors.initials: I
authors.lastname: Sirés
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry; D003612:Dairying; D055664:Electrochemical Techniques; D004566:Electrodes; D004572:Electrolysis; D006861:Hydrogen Peroxide / Q000032:analysis; D007211:Indoles; D010084:Oxidation-Reduction; D013431:Sulfates; D014025:Titanium / Q000737:chemistry; D014865:Waste Disposal, Fluid / Q000379:methods*; D062065:Wastewater; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D000535:Aluminum; D002712:Chlorides; D006861:Hydrogen Peroxide; D007211:Indoles; D013431:Sulfates; D014025:Titanium; D062065:Wastewater; D014874:Water Pollutants, Chemical; C030374:indole