Efficient Treatment of Rubber Wastewater by Electrochemical Oxidation and Polymerization Reaction to Achieve Zero Liquid Discharge

Zero liquid discharge (ZLD) technology has received widespread attention in order to improve water utilization and reduce ecological problems caused by wastewater discharges. ZLD usually involves water recycling and recovery of valuable salt products through membrane concentration and evaporation crystallization processes. However, residual organic pollutants in wastewater usually affect the purity of the salt product recovered by the evaporation crystallization process. In this work, Ir-doped cobalt antimonate electrodes were used to effectively treat the actual concentrated saline wastewater from the 2,2,4-trimethyl-1,2-dihydroquinoline rubber antioxidant process, thereby improving the purity of the byproduct salt. The characteristic pollutants in this wastewater were confirmed to be mainly aniline by UV–vis absorption and three-dimensional fluorescence spectroscopy. Furthermore, it was further demonstrated by cyclic voltammetry and Fourier transform infrared spectroscopy that the organic pollutant removal pathways included electrochemical indirect oxidation, direct oxidation, and electro-polymerization reactions. Continuous flow experiments showed that the COD removal could be stabilized at ∼71% over 300 h of operation with an operating cost of only ∼$1.06/m 3 . The purity of the salt before and after electrolysis was improved from 91.0 to 98.7%, which reached the first-grade standard of industrial salt (GB/T 5462-2015) and greatly contributed to the realization of ZLD.