Treatment of real printing wastewater with an electrocatalytic process

Many chemicals used in modern printing processes are either toxic or difficult to decompose, which results in the production of complicated and refractory printing wastewater. In this study, an electrocatalytic technology with different catalytic electrodes was employed to treat a real printing wastewater, and the production rates of hydroxyl radicals were determined. The results indicate that under a voltage gradient of 11 V cm−1, the production concentration of hydroxyl radicals by various electrodes followed a decreasing order of TiO2 > DSA (dimensional sustainable anode with IrO2) > graphite, with the values of 8.21 × 10−3, 5.24 × 10−3, and 0.86 × 10−3 M, respectively. A lower wastewater conductivity could lead to a greater electric voltage thus contributing to a higher removal efficiency of TOC and chroma. At a current density of 50 mA cm−2 and using one pair of electrodes (IrO2 + stainless steel), the TOC and chroma removal efficiencies reached 71% and 53% after 60 min treatment. Under the same operation conditions but using two pairs of electrodes, the removal efficiencies of TOC and chroma were increased to 75% and 82%, respectively. The removal efficiencies of TOC and chroma could be further raised to 90% and 92% if the electrocatalytic effluent was polished by powder activated carbon absorption.