Recent advances in catalytic sulfate radical-based approach for removal of emerging contaminants

One of the many processes that utilize cost-effective materials for safe and efficient remediation of emerging contaminant pollution is the catalytic sulfate radical-based advanced oxidation process (cSR-AOP). SR (SO4•−) generation is at the heart of this technology. SR is desirable because of its better selectivity (compared to hydroxyl radical (HR)) which results in fewer secondary reactions. While several studies have demonstrated the effectiveness of SR, formation of SR is based on the activation of peroxymonosulfate (PMS) or peroxydisulfate (PDS) or sulfite using heat, high pH, ultraviolet radiation or catalyst. Among the activation methods, heterogeneous catalytic activation involving the use of carbonaceous materials, transition metals and their oxides, and natural minerals offer promising benefits such as high pore volume, high specific surface area, and relatively lower production costs. The opportunities and challenges of cSR-AOP are not fully explored. This paper presents a critical review covering SR activation methods and mechanisms, the influence of operating conditions on SR generation and oxidative efficiency, and applications of cSR-AOPs for the removal of contaminants of emerging concern. Results obtained by recent studies on cSR-AOP applications are summarized vis-à-vis the influence of SR precursor, catalyst type, pH, temperature, and the reactor type/configuration that ensures catalyst regeneration/reusability. cSR-AOP has been applied for the remediation of contaminated groundwater and soil, treatment of leachate, and removal of potential endocrine disruptors (4-hydroxylbenzoic acid, 2,4-dichlorophenol, bisphenol A, and ortho-phenylphenol), herbicides (atrazine and chloroacetanilide herbicide metolachlor), analgesics (acetaminophen), azo dyes (acid orange 7 and methylene blue), antibiotics (tetracycline and sulfamethoxazole) from water in recent studies. cSR-AOP also holds future promise for drinking water treatment and total mineralization.