Efficiency and mechanism of microbubble O₃/H₂O₂ advanced treatment of secondary effluent from a resin factory

Aiming at the problem that traditional biodegradation can not degrade the chemical oxygen demand (COD) of benzene series, polyvinyl alcohol and other macromolecular organic compounds in resin wastewater, and can not meet the discharge standard, a microbubble O₃/H₂O₂ system was constructed to treat the secondary effluent of a resin factory deeply. The COD degradation effects of microbubble O₃ aeration and ordinary O₃ aeration were compared, and the effects of inlet O₃ concentration, H₂O₂ concentration and initial pH on COD degradation efficiency of microbubble O₃/H₂O₂ system were investigated. The mineralization effect of the system was verified by total organic carbon (TOC), and the active substances in microbubble O₃/H₂O₂ were detected by electron paramagnetic resonance spectrometer (EPR). Finally, the types of main organic substances in wastewater before and after degradation were analyzed by GC-MS, and the mechanism and path of COD degradation by microbubble O₃/H₂O₂ system were analyzed. The results showed that: (1) In the microbubble O₃/H₂O₂ system, the particle size of microbubbles was mainly distributed in the range of 10-50 μm, with an average particle size of 32.82 μm. Compared with ordinary aeration, microbubble O₃ system had a higher degradation rate of COD, which indicated that microbubbles could prolong the rising time of O₃ bubbles, increase the specific surface area of O₃ bubbles, and improve the mass transfer coefficient and utilization rate of O₃. (2) The analysis of influencing factors of COD degradation by microbubble O₃/H₂O₂ system showed that when O₃ concentration was 60 mg/L, H₂O₂ concentration was 29.37 mmol/L, and pH was 7 after 60 minutes of reaction, the COD degradation rate of secondary effluent of the resin factory by microbubble O₃/H₂O₂ system was 89.53%, and the treated effluent COD was 15.05 mg/L, meeting the requirements of Emission Standard of Pollutants for Synthetic Resin Industry (GB 31572-2015). (3) The EPR test showed that H₂O₂ could promote the microbubble O₃ system to produce more superoxide radicals (\cdot\mathrmO_2^- ) and hydroxyl radicals (·OH), thus improving the oxidation capacity of the system and the degradation effect of COD. According to the results of GC-MS, the possible degradation path was inferred. Macromolecules in the secondary effluent from the resin factory, mainly composed of long-chain alkanes and cycloalkanes, underwent chain-breaking and ring-opening by O₃, and were mineralized or degraded into micromolecule substances, mainly small-molecule organic acids, under the action of ·OH and other free radicals