The SO4-• is the predominant radical responsible for TC degradation at acidic pH, whereas both SO4-•and OH• are contributing in TC degradation at natural pH. Thus, three reactions compete with each other in natural pH: the reaction between SO4-• and HO•, the reaction between SO4-• and TC, and the reaction between HO• and TC, the simultaneous occurrence of these reactions may reduce the TC degradation rate [37, 65].