Investigation on decolorization of biologically pretreated cellulosic ethanol wastewater by electrochemical method

The biologically pretreated cellulosic ethanol wastewater poses a serious environmental concern because of its refractory and color compounds. The decolorization of electrochemical oxidation using Sb doped Ti/SnO2 electrode for advanced treatment of cellulosic ethanol wastewater under different current density (5-30 mA·cm−2), initial pH (3-8.9) and supporting electrolyte (0-0.25 M NaCl) was investigated in this study. Complete decolorization, 8.5% chemical oxygen demand (COD) and 69.1% dissolved organic carbon removal efficiencies were achieved under the optimal conditions (20 mA·cm−2, pH 5 and supporting electrolyte of 0.1 M NaCl) after 150 min. The energy consumption required to meet National Discharge Standard (GB 27631-2011) is 93.8 kWh kg COD−1. Further investigation revealed that hydroxyl radicals played a primary role in the degradation of organic contaminants, while active chlorine formed from chloride oxidation played a less important role. Direct anodic oxidation and indirect reaction via peroxodisulfate generated from sulfate oxidation could be negligible. The formation of chlorination by-products appeared to be low since the final total Trihalomethanes concentration detected was 263 µg L−1, with the detection of chloroform as the main Trihalomethanes.