Meta-cresol degradation by persulfate through UV/O3 synergistic activation: Contribution of free radicals and degradation pathway

Abstract

The kinetic and pathway of meta-cresol (m-cresol) degradation were studied by persulfate oxidation through UV/ozone activation (UV/O3–Na2S2O8) to improve m-cresol removal to eliminate ecological risks. Experimental results showed that the degradation effect of m-cresol with an initial concentration of 50 mg/L was 99.8% in 30 min under the optimization conditions. The reaction kinetic model in the UV/O3–Na2S2O8 system shows that the initial pH value, the respective ozone, and the persulfate dosage were positively correlated with the degradation rate constant value (k). The apparent degradation rate of m-cresol in the UV/O3–Na2S2O8 system was 0.2216 min−1, and the synergy factor (f) was larger than 1, thereby demonstrating a synergistic effect of UV, ozone, and persulfate. The dominant free radicals in the system were sulfate radical (SO- 4·) and hydroxyl radical (·OH), and the contribution ratio of SO- 4· to m-cresol degradation was higher than ·OH. The degradation process of m-cresol by UV/O3 − Na2S2O8 was mainly through the electrophilic addition reaction to substitute the ortho- and para-positions of the hydroxyl group on the benzene ring, followed by the ring-opening reaction and mineralization of the aliphatic compound to achieve the complete degradation of m-cresol.