Merits and Limitations of Radical vs. Nonradical Pathways in Persulfate-Based Advanced Oxidation Processes

Urbanization and industrialization have exerted significantadverseeffects on water quality, resulting in a growing need for reliableand eco-friendly treatment technologies. Persulfate (PS)-based advancedoxidation processes (AOPs) are emerging as viable technologies totreat challenging industrial wastewaters or remediate groundwaterimpacted by hazardous wastes. While the generated reactive speciescan degrade a variety of priority organic contaminants through radicaland nonradical pathways, there is a lack of systematic and in-depthcomparison of these pathways for practical implementation in differenttreatment scenarios. Our comparative analysis of reaction rate constantsfor radical vs. nonradical species indicates thatradical-based AOPs may achieve high removal efficiency of organiccontaminants with relatively short contact time. Nonradical AOPs featureadvantages with minimal water matrix interference for complex wastewatertreatments. Nonradical species (e.g., singlet oxygen,high-valent metals, and surface activated PS) preferentially reactwith contaminants bearing electron-donating groups, allowing enhancementof degradation efficiency of known target contaminants. For byproductformation, analytical limitations and computational chemistry applications are also considered. Finally, we propose a holistically estimatedelectrical energy per order of reaction (EE/O) parameter and showsignificantly higher energy requirements for the nonradical pathways.Overall, these critical comparisons help prioritize basic researchon PS-based AOPs and inform the merits and limitations of system-specificapplications.