A novel strategy of successive non-radical and radical process for enhancing the utilization efficiency of persulfate

During the process of persulfate oxidation, side reactions such as the recombination of radicals can usually result in the low utilization efficiency of persulfate, which decreases the mineralization of target pollutants. In this study, the successive oxidation strategy was proposed based on successive non-radical and radical process (SNRP), to enhance the utilization efficiency of peroxymonosulfate (PMS), and further enhance the mineralization of sulfonamides. The results indicated that 0.04 mM of sulfonamide could be completely removed within 240 min at 1.2 mM PMS and initial pH 6.8 in the non-radical process, but the mineralization was very low (<2%). Moreover, the decomposition efficiency of PMS was less than 10% within 480 min. Fe(II) was added into the solution in which non-radicals process was performed, to initiate radical process by activating residual PMS. Compared to Fe(II)/PMS process, the SNRP process significantly increased the mineralization of sulfonamides, reaching 27.0%, 19.0%, 16.7% and 17.2%, respectively for sulfamethoxazole, sulfanilamide, sulfadiazine and sulfamerazine. The increased mineralization was due to the enhanced PMS utilization. Seven degradation products were identified in the SNRP process. Among them, hydrolyzed 3-amino-5-methyl isoxazole, (3-amino-5-methylisoxazole) sulfonic acid and 4-aminobenzenesulfinic acid produced in the non-radical oxidation process showed resistance to the subsequent radical oxidation. This study can provide a possible way to enhance the utilization efficiency of PMS as well as the mineralization of organic pollutants.