Mechanism and practical application of homogeneous-heterogeneous hybrid catalysts in electrolytic system for high COD chemical waste acid treatment

Treatment of organic contaminants in waste acid via electrochemical oxidation process has drawn sustained attention. Inspired by the electro-generation of persulfate from homogeneous sulfate (SO42-) in waste acid and the catalytic activity of heterogeneous tourmaline, this study aimed to investigate the feasibility of in-situ persulfate electro-generation and activation via utilizing homogeneous-heterogeneous hybrid catalysts system (SO42-/tourmaline) for organic contaminants removal in high chemical oxygen demand (COD) sulfate-containing waste acid. p-Aminodiphenylamine (RT-Base) was selected as a model organic contaminant to explore the mechanism of electrolysis/SO42-/tourmaline system. No RT-Base was detected after 60 min reaction in electrolysis/SO42-/ tourmaline system. The formation of (OH)-O-center dot and SO4 center dot- in electrolysis/SO42-/tourmaline system made contributions to the RT-Base degradation. Degradation intermediates of RT-Base were identified and possible degradation pathway was proposed. Additionally, the application of electrolysis/SO42-/tourmaline system in treating the real RT-Base waste acid, which contained high COD and SO42-, was explored. Results showed that the COD removal rate was 67.94% under the optimal conditions, and the electrolysis/SO42-/tourmaline system could enhance the biodegradability of RT-Base waste acid. Furthermore, the electrolysis/SO42-/tourmaline system followed by the activated sludge process achieved a high COD removal efficiency (99.09%). Microbial DNA analysis suggested that Bacteroidetes, Proteobacteria, and Actinobacteria were the dominant bacterial phyla in the activated sludge; and metabolism was the predominant microbial function. In-situ electro-generation of persulfate/SO4 center dot- for organics degradation achieved efficient utilization of waste sulfate. Electrochemical oxidation process with activated sludge process as a post-treatment showed great potential in the treatment of organics in high-sulfate waste acid.