Insights into the relationship of reactive oxygen species and anions in persulfate-based advanced oxidation processes for saline organic wastewater treatment

Over the past two decades, persulfate-based advanced oxidation processes have attracted considerable attention because of their high efficiency and great versatility in the degradation of organic pollutants. Various radical and nonradical reactive oxygen species (ROS) with different features produced by persulfate activation have facilitated the efficient treatment of complex effluents, especially saline organic wastewater (SOW). To completely assess the advantages and shortcomings of persulfate-based advanced oxidation processes for the SOW treatment, in this review, we present the properties and verification methods of key ROS in persulfate activation and summarize the effect of anions (nitrates, halide ions, carbonates, etc.) in kinds of different catalytic systems. This review aims to provide insights into the relationship between ROS and anions to clarify the key steps in degradation processes, hence avoiding research pitfalls and empowering better investigation in SOW treatment. Finally, we propose perspectives on challenges related to accessing the selectivity of nonradical ROS to intermediates, designing targeted catalysts, coupled purification technologies, accessing the biological toxicity of intermediates and the effect of sulfates on the environment.