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Dodecyl dimethyl benzyl ammonium chloride (DDBAC), a non-oxidizing biocide, is commonly used in municipal wastewater reverse osmosis system. It has been used also as an ingredient in fabric softeners, disinfectants, detergents, phase transfer agent and numerous personal skin care products. In this study, the DDBAC degradation efficiency achieved using UV and persulfate (PS) oxidation processes was investigated. Substantial synergistic effects on DDBAC degradation were found when UV and PS oxidation processes were combined. During the UV/PS process, UV photolysis and reactions with radical species accounted for 42.7% and 57.3%, respectively, of DDBAC degradation. The OH and SO4 − radicals accounted for 4.6% and 52.7%, respectively, of DDBAC degradation. The calculated k OH,DDBAC and k SO 4 - ,DDBAC rate constants were (1.45 ± 0.16) × 109 and (1.51 ± 0.02) × 109 M−1 s−1, respectively. The kobs rate constant for DDBAC degradation increased from 0.047 to 0.150 min−1 when the PS dose was increased from 0.05 to 1.45 mM. The presence of natural organic matter (NOM), HCO3−/CO32−, and NO3− adversely affected DDBAC degradation. Five main intermediates were identified by high performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry. The proposed DDBAC degradation pathway involves benzyl-nitrogen bond cleavage (or subtraction of hydrogen from the alkyl chain), demethylation, hydroxylation, and hydrogen subtraction. UV/PS treatment decreased the acute toxicity of the DDBAC solution in less than 15 min. However, the residual toxicity indicated that toxic oxidation transformation products were formed when DDBAC was treated using the UV/PS process.

Chlorination is widely used for disinfection of water and wastewater. Ammonia/chlorine co-exposure can be easily achieved when ammonia is present in water. In this study, ammonia and chlorine showed synergistic effect on atrazine (ATZ) degradation. A degradation efficiency of 50.2% was obtained in 10 min with a Cl/N molar ratio of 1.6. By contrast, free chlorine and chloramines barely degraded ATZ. The synergistic effect involved formation of hydroxyl radicals ( OH) and reactive chlorine species. The radical concentrations followed the order of ClO (4.8 × 10−13 M) > OH (4.1 × 10−13 M) > Cl (3.0 × 10−15 M). The dominant radical was OH (>80% contribution), followed by ClO (less than18% contribution), which had relatively lower reactivity with ATZ. The synergism was pH dependent, with OH largely suppressed by 98% when the pH was acidic or basic rather than neutral, resulting in a decrease in ATZ degradation. The transformation products detected indicated that ATZ degradation involved dealkylation and dechlorination–hydroxylation, and lower yields of oxidation byproducts were obtained by ammonia/chlorine synergistic oxidation process compared to direct chlorination.