Effect of chlorine dioxide pre-oxidation on algal non-protein amino acid degradation and DBPs formation during subsequent chlor(am)ination

Abstract

As a neurotoxin produced by cyanobacteria, 2,4-diaminobutyric acid (DAB) posed a significant threat to human health and served as an important precursor to disinfection by-products (DBPs). In this study, ClO2 showed the highest DAB oxidation efficiency among the four oxidants, in the order of ClO2 (86%) > HOCl (80%) > KMnO4 (20%) > NH2Cl (13%). The increase of ClO2 dosage (from 0.06 to 1.4 mg L-1) not only increased the oxidation efficiency of DAB, but also decreased the formation of DBPs after ClO2 pre-oxidation during post-chlorination, but the DBPs formation varied during post-chloramination. The enhanced formation of dichloroacetic acid (DCAA) and dichloroacetonitrile (DCAN) should be of concern when ClO2 pre-oxidation was performed at pH 7.0. In the presence of Br−, the overall concentration of formed THMs and brominated species increased. ClO2 pre-oxidation of β-N-methylamino-l-alanine (BMAA), alanine, leucine, and serine followed by post-chloramination has advantages over post-chlorination in controlling the overall and individual DBPs concentration. A possible degradation pathway and reaction schemes during ClO2 pre-oxidation of DAB were proposed. ClO2 pre-oxidation followed by post-chloramination could be an effective treatment process in the abatement of both DAB and toxicity. Results of this study about DAB oxidation and DBP formation contributed to the guidance of ClO2 pre-oxidation in the water treatment plants to cope with cyanobacterial blooms.