Sulfate radical-based advanced oxidation processes for industrial wastewater treatment

Recently, sulfate radical-based advanced oxidation processes (SR-AOPs) have been known as an alternative to hydroxyl radical-based advanced oxidation processes (•OH-AOPs) in the treatment of different industrial wastewaters. During the SR-AOPs, various precursors such as peroxymonosulfate (PMS), peroxydisulfate, and bisulfite (BS) are usually employed to generate sulfate radical (SO4•−) through a series of activations (e.g., O3, UV, and transition metal). Although these strategies contribute to the improvement of the removal efficiency of recalcitrant and/or toxic contaminants and wastewater biodegradability, the high energy consumption and low efficiency in real water treatment limit the practical applications. In this chapter, the degradation kinetics and activation mechanisms of the SR-AOPs, especially in homogeneous catalytic processes [O3/PMS, UV/persulfate (PS), Fe(II)/PS, and Mn(VII)/BS], are systematically assessed and analyzed. Generally, there are several types of oxidative intermediates (e.g., SO4•−, HO•, and high-valent transition metal) with high redox potential and different selectivity during these processes; it is necessary to integrate quenching experiments, electron spin resonance experiments, and competitive kinetics experiments for the examination of the activation mechanisms. The influencing factors, practical applications, and integrated treatment processes of the SR-AOPs are discussed in detail in the industrial wastewaters treatment. The advantages and shortcomings of SR-AOPs for practical applications are also discussed, emphasizing the integrated treatment processes of SR-AOPs, which are desired for future exploration.