Evaluation of activated persulfate under real solar light for degradation of organic pollutants: Kinetics, mechanism, and ecotoxicity

Abstract

Activation of persulfate (PS) under artificial light sources has been extensively studied as PS based advanced oxidation process (AOP) for degradation of organic pollutants. Here, we demonstrate the enhanced photodegradation of organic pollutants under real sunlight (Sun) in presence of persulfate (PS), (Sun/PS system). Sun/PS caused complete degradation of acid orange (AO7, a colored-dye pollutant), with pseudo-first-order rate constant value (kobs (AO7)) of 0.052 min−1 (sunlight dosage, Qlight 3.9–5.6 kJ/L and 58.3–64.8 kJ/L in the UV range 300–400 nm and visible range 400–800 nm respectively, AO7 = 2 mg/L (5.7 µM), PS = 0.6 mM). In contrast, AO7 degradation was incomplete under Sun alone (0.2 %), and PS alone (1.6 %). Moreover, Sun/PS caused 91 % reduction of total organic carbon (mineralization) within 240 min. Radical scavenging and ESR results confirmed the formation of SO4.− and HO. in Sun/PS system, revealing PS activation by Sun enhances degradation, and mineralization of AO7. Other pollutants such as, acetaminophen (AAP, a colorless pharmaceutical contaminant), and, Malachite Green (MG, a carcinogenic pollutant), were effectively degraded, and mineralized by Sun/PS system in comparison to Sun and PS alone. Moreover, Aliivibrio fischeri (A. fischeri) bioluminescent assay reveals AO7 and AAP pollutants were moderately toxic while, MG was highly toxic. Importantly, the toxicity of these pollutants was removed after Sun/PS treatment. The present findings on evaluation of Sun/PS system highlight, Sun/PS may be applied as an activated PS based AOP for water treatment to remove organic pollutants, and it would be useful as a clean, low-cost approach for resource poor environment but having abundant Sun.