Harnessing bromide ions to boost peroxymonosulfate for reactive yellow 145 dye degradation

Bromide (Br^-) was found in the fresh waters at concentrations from 0.1 to 1 mg/L and can be used to activate peroxymonosulfate (PMS) as a widely used chemical oxidation agent. In the present study, the reaction between PMS and Br^- ions (PMS/Br^- process) for the effective degradation of reactive yellow 145 (RY-145) dye was investigated by changing operational parameters vis solution pH, dosage of Br^- ions and PMS, RY-145 concentration, and reaction time. Based on the results, the simultaneous presence of PMS and Br^- ions in the solution led to efficient degradation of RY-145 with a synergistic index of 11.89. The degradation efficiency of RY-145 was decreased in severe basic pH and the presence of CO₃^2- ions as a coexisting anion. Likewise, 4 mg/L of humic acid (HA), used as a classic scavenger, led to a 26.53% decrease in the RY-145 degradation efficiency. The free bromine (HOBr/OBr^-), superoxide radical (^●O₂^-), and singlet oxygen (¹O₂) was the dominant oxidation agents in RY-145 degradation, which confirmed the nonradical degradation pathway. In addition, PMS/Br^- process showed excellent ability in mineralizing RY-145 in different aqueous solutions (total organic carbon (TOC) decreased 86.39% in deionized water and 78.23% in tap water). Although pollutants such as azo dyes can be effectively removed in the PMS/Br- process, the formation of byproducts should be strategically controlled and special attention should be paid when the PMS-based advance oxidation process is applied to treat Br^- containing solutions.