Degradation of dodecyl dimethyl benzyl ammonium chloride (DDBAC) as a non-oxidizing biocide in reverse osmosis system using UV/persulfate: Kinetics, degradation pathways, and toxicity evaluation

Abstract

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 kOH,DDBAC and kSO4-,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.