Ammonia/chlorine synergistic oxidation process applied to the removal of N, N-diethyl-3-toluamide

Abstract

The ammonia/chlorination process is important for the treatment of ammonia-rich water, such as the ammonia removal, disinfection strategies, and disinfection byproducts controlling. Recently, the simultaneous removal of recalcitrant micropollutants during ammonia/chlorination has attracted attention. In this study, ammonia/chlorination was employed to remove the chlorine-resistant micropollutant N, N-diethyl-3-toluamide (DEET). Using the optimal chlorine to ammonia molar ratio (Cl/N) of 1.6, nearly 60% of DEET was removed by ammonia/chlorination within 15 min, while chlorination or chloramination alone showed minimal DEET removal. The synergistic effect obtained from the combination of ammonia and chlorine is attributed to reactive species generated from the decomposition of chloramine over Cl/N 1.0 to 1.6, being proved by the significantly inhibited performance (almost 95%) by t-butanol. The aqueous matrix was found to affect the results, and acidic/basic solutions reduced DEET removal by 70% to 79%, while the presence of natural organic matter (NOM 6 mg-C/L) suppressed the removal by 33%. The quantity of DEET removed per mole of decomposed chloramine (α) is proposed as a measure of the efficiency of this synergistic oxidation process, and the α values were determined to be 0.034, 0.022 and 0.010 in the synthetic solution, a solution containing 6 mg-C/L NOM and a wastewater effluent, respectively. Trials using high resolution quadrupole time of flight mass spectrometry and 15N isotope labelling, allowed the transformation products to be identified, and hydroxylation was found to be the dominant DEET degradation pathway.