Study on the degradation performance and toxicity reduction mechanism of electroplating wash wastewater by a hydrolysis–acidification–MPR synergistic system

This study focuses on high-strength, low-biodegradability electroplating wash wastewater (COD ≥20,000 mg/L, BOD₅/COD ≤0.1). A laboratory-scale hydrolysis-acidification (HA)-micro-pressure internal circulation multiphase reactor (MPR) combined treatment process was constructed. In the HA stage, wastewater biodegradability was significantly improved, with the BOD₅/COD ratio being increased from 0.03 to 0.31. The MPR stage then further deepened degradation, enabling the system to maintain a COD removal rate above 97% during stable operation, linear alkylbenzene sulfonate (LAS) and TN removal rates were achieved at over 99% and 96.8%, respectively. Vibrio fischeri luminescence inhibition was reduced from >95% in the influent to approximately 65% in the HA effluent and <10% in the MPR effluent. GC-MS analysis revealed that the HA stage cleaved high-molecular-weight pollutants such as long-chain alkanes and esters into mid- and small-molecule products (e.g., 3-methylcyclohexanone and 2,5-dimethylnonane), while the MPR stage further converted these intermediates into low-toxicity small molecules (e.g., trimethylsilanol and hexamethylcyclotrisiloxane). Metagenomic analysis showed that facultative anaerobic fermenters (Aminivibrio, Alcaligenes) were enriched in the HA stage, whereas aerobic bacteria (Pseudomonas, Brevundimonas) predominated in the MPR stage. Key functional genes (alkB, cyp450, gpmB) were significantly enriched during the stable period, promoting carbon metabolism and stress resistance. This study elucidated that the HA-MPR synergistic system achieved efficient and stable degradation and toxicity mitigation of electroplating wash wastewater through a multi-stage cooperative mechanism of acidification cleavage and aerobic deep mineralization, providing theoretical and technical support for the engineering application of this process.