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 SO4− were determined to be kHO, DTAC (4.2 ± 0.18) × 109 M−1 s−1 and kSO4∙−, DTAC (2.5 ± 0.27) × 109 M−1 s−1, respectively. The contributions of HO and SO4− to DTAC degradation in the UV/PS were found to be 30% and 62% at pH 7, respectively. The contributions of SO4− 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 HCO3−, Cl− and humic acid inhibited the DTAC elimination, whereas NO3− and SO42− had no significant impact on its elimination. Moreover, the kobs,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.