Electro–oxidation of industrial wastewater containing 1,4-dioxane in the presence of different salts

Abstract

The treatment of 1,4-dioxane solution by electrochemical oxidation on boron-doped diamond was studied using a central composite design and the response surface methodology to investigate the use of SO42- and HCO3- as supporting electrolytes considering the applied electric current, initial COD value, and treatment time. Two industrial effluents containing bicarbonate alkalinity, one just carrying 1,4-dioxane (S1), and another one including 1,4-dioxane and 2-methyl-1,3-dioxolane (S2), were treated under optimized conditions, and subsequently subjected to biodegradability assays with Pseudomonas putida culture. Electro-oxidation was compared with ozone oxidation (O3) and its combination with hydrogen peroxide (O3/H2O2). Regarding the experimental design, the optimal compromise for maximum COD removal at minimum energy consumption was shown at the maximum tested concentrations of SO42- and HCO3- (41.6 and 32.8 mEq•L-1, respectively), and the maximum selected initial COD (750 mg•L-1), applying a current density of 11.9 mA•cm-2 for 3.8 hours. Up to a 98% of the COD was removed in the electro–oxidation treatment of S1 effluent using 114 kWh per kg of removed COD; and about a 91% of the COD from S2 wastewater applying 49 kWh per kg of removed COD. The optimal biodegradability enhancement was achieved after 1 h of electro-oxidation treatment. In comparison with O3 and O3/H2O2 alternatives, electrochemical oxidation achieved the fastest degradation rate per oxidant consumption unit; as well as it also resulted to be the most economical treatment in terms of kWh consumption and price per unit of removed COD.