The application of UV/PS oxidation for removal of a quaternary ammonium compound of dodecyl trimethyl ammonium chloride (DTAC): The kinetics and mechanism

Dodecyltrimethylammoniumchloride (DTAC) is a quaternary ammonium compound (QAC) that is a widespread contaminant in environmental media and therefore of increasing concern. The synergistic effect with UV irradiation and persulfate (UV/PS) was used to degrade DTAC. The removal of DTAC was 91% with the PS dosage of 75.6 mu M (UV/PS) and UV fluence of 870 mJ.cm(-2). The second-order rate constants of DTAC with HO center dot and SO +/-(-)(4) were determined to be k(HO center dot, DTAC) (4.2 +/- 0.18) x 10(9) M-1 s(-1) and k(SO4 center dot-, DTAC) (2.5 +/- 0.27) x 10(9) M-1 s(-1), respectively. The contributions of HO center dot and SO center dot(-)(4) to DTAC degradation in the UV/PS were found to be 30% and 62% at pH 7, respectively. The contributions of SO center dot(-)(4) and HO center dot were not significantly influenced by acidic medium (pH 3-pH 7), whereas theywere significantly affected by basic medium(pH 7-pH 11). The wastewater matrixes of HCO3-, Cl- and humic acid inhibited the DTAC elimination, whereas NO3- and SO42- had no significant impact on its elimination. Moreover, the k(obs),(DTAC) in the reverse osmosis influent (ROI) and reverse osmosis concentrate (ROC) were examined to be 0.04 to 0.1 min(-1) and 0.02 to 0.05 min(-1), respectively, as the PS dosage increased from 18.9 to 113.4 mu M. The inhibitive effects of matrix in ROI and ROC was 70% and 81%, respectively. The contribution of radical scavenging effect by matrix ROI and ROC was more significant to DTAC degradation than UV scattering effect in ROI and ROC matrices. A UV fluence of 1305 mJ.cm(-2) was necessitated for complete detoxification and DTAC solution by UV/PS. (c) 2018 Published by Elsevier B.V.