Optimization for the catalytic oxidation system of O₃/H₂O₂ micro-nano bubbles for the treatment of highly saline chemical wastewater

Chemical wastewater treated via reverse osmosis (RO) generates concentrate with high salt and organic matter concentrations. Traditional ozone oxidation treatment has low efficiency in removing organic matter from such wastewater. Ozone/hydrogen peroxide (O₃/H₂O₂) micro-nano bubble catalytic oxidation can enhance the removal efficiency of recalcitrant organic matter in RO concentrate, but it faces challenges such as low oxidation efficiency and incomplete mineralization. This study treated RO concentrate from two sources in a chemical industrial park: biological treatment effluent and circulating cooling water (referred to as effluent and circulating water). It applied O₃/H₂O₂ micro-nano bubble catalytic oxidation technology and optimized the H₂O₂ dosing strategy. The effects of initial pH, H₂O₂ dosing schemes on organic matter removal efficiency were analyzed. The study also explored the use of online monitoring of ORP to guide H₂O₂ dosing schemes and its impact on the oxidation treatment effectiveness of the ozone stage in actual high-salinity chemical wastewater treatment projects. The results indicated that under weakly alkaline conditions with pH=7.4, the ozone micro-nano bubble system alone achieved the best organic matter removal efficiency for effluent and circulating water. H₂O₂ dosing based on ORP changes during the process improved organic matter removal efficiency compared to a single initial dosing, with TOC removal rates for effluent and circulating water increasing by 48.0% and 2.3%, respectively. During the process dosing, when H₂O₂ was dosed at 1 mL per dosage (three doses for effluent and four doses for circulating water), setting the ORP threshold to 900 mV resulted in the best H₂O₂ dosing effect, with TOC removal rates for effluent and circulating water increasing by 17.0% and 4.6%, respectively, compared to 300 mV. While high-frequency, multi-stage H₂O₂ dosing based on ORP changes was more beneficial for organic matter removal, a three-stage dosing strategy was more reasonable and feasible in engineering design (H₂O₂ was dosed once when d(ORP)/dT=200-300 mV/min, with a total of three doses). The research indicates that in the O₃/H₂O₂ micro-nano bubble treatment process, the strategy of dosing H₂O₂ in three stages based on online ORP monitoring ensures treatment efficiency and has engineering feasibility.