The effects of inorganic anions on degradation kinetics and isotope fractionation during the transformation of tris(2-chloroethyl) phosphate (TCEP) by UV/persulfate

Tris(2-chloroethyl) phosphate (TCEP), as a typical chlorinated flame retardant, is attracting more attention as a carcinogen. Although persulfate-based oxidation exhibits good performance in removing refractory organic pollutants, the kinetics of persulfate-based remediation are affected by inorganic anions, which causes inaccurate remediation efficiency. This study combines steady-state radical concentration modelling with isotope fractionation to investigate the effects of inorganic anions on TCEP degradation by UV/persulfate (UV/PS). In the absence of anions during UV/ PS system, the observed degradation rate was (9.7 +/- 0.1) x 10(-5) s(-1), which was approximately 93 % attributed to sulfate radical (SO4-.) oxidation based on radical modelling. Carbon isotope fractionation, coupled with the identification of transformation products by mass spectrometry, suggests a carbon bond split during TCEP degradation with a carbon isotopic fractionation value (epsilon) of -1.6 +/- 0.2%(+/- 95 % confidence intervals). With respect to co-existing anions in UV/PS system, the addition of chloride (Cl-) had a negligible effect on degradation rates, while the addition of hydrogencarbonate (HCO3-) caused them to decrease, and the addition of hydrogenphosphate (HPO42-) caused them to increase. Radical modelling suggested that SO4-.was transformed to chlorine radicals (Cl./Cl-2(-.)), phosphate radicals (HPO4-.), and carbonate radicals (CO3-.). Furthermore, the overlapping 95 % confidence intervals (C.I.) and the statistical tests (p > 0.05) both agree that Cl- and HPO42- - gain identical epsilon values. Nevertheless, when HCO(3)(-)coexisted in the UV/PS system, the e values were distinct. The addition of HCO3- would result in e variation of TCEP in the UV activated PS process, which should receive more attention when applying remediation.

Automated summary

This study investigates the effects of inorganic anions on the degradation of TCEP by UV/persulfate (UV/PS) through steady-state radical concentration modeling and isotope fractionation. The addition of chloride (Cl-) has negligible effects on the degradation rates, while the addition of hydrogencarbonate (HCO3-) decreases the rates and the addition of hydrogenphosphate (HPO42-) increases them. The findings suggest that attention should be given to the variation of TCEP in the UV activated PS process when HCO3- is present.