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

Dodecyltrimethylammonium chloride (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 μM (UV/PS) and UV fluence of 870 mJ·cm −2 . The second-order rate constants of DTAC with HO and SO 4 − were determined to be k HO , DTAC (4.2 ± 0.18) × 10 9  M −1  s −1 and k SO 4 ∙− , DTAC (2.5 ± 0.27) × 10 9  M −1  s −1 , respectively. The contributions of HO and SO 4 − to DTAC degradation in the UV/PS were found to be 30% and 62% at pH 7, respectively. The contributions of SO 4 − and HO were not significantly influenced by acidic medium (pH 3–pH 7), whereas they were significantly affected by basic medium (pH 7–pH 11). The wastewater matrixes of HCO 3 − , Cl − and humic acid inhibited the DTAC elimination, whereas NO 3 − and SO 4 2− 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 μM. 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.