Abstract
Blue-green algae commonly bloom in fresh water in summer, producing extra- and intra-cellular algal organic matters, which are important precursors for disinfection byproduct (DBP) formation. In this study, we evaluated the effect of pre-oxidation with ferrate(vi) (FeO42−, Fe(vi)) on the characterization of intracellular organic matter (IOM) and extracellular organic matter (EOM). The results indicated that soluble microbial-like products of EOM and IOM decreased and humic acid-like products of IOM increased, which would influence the DBP formation in the subsequent chlorination step. Therefore, in this study, the effect of Fe(vi) pre-oxidation on the DBP formation from IOM and EOM with subsequent chlorination was also investigated. For Chlorella sp., EOM presented no significant change, and IOM presented a reduction of THMs (8.2%) after Fe(vi) oxidation at a dosage of 16 mg L−1. For P. limnetica, EOM and IOM both exhibited reduction of trihalomethanes (THMs) and chloral hydrate (CH) after Fe(vi) oxidation. Besides, THMs had the lowest concentration at pH 8.0 in all four solutions. Haloacetonitriles (HANs) and haloketones (HKs) showed slight changes with increasing pH values. Due to the frequent detection of bromide (Br−) in surface water, the effect of bromide existence on THM formation was also investigated. The results indicated that all brominated DBPs increased, and chlorinated DBPs decreased with the increase in bromide concentration. In addition, the bromine substitution factor (BSF) of Chlorella sp. and P. limnetica both increased with the increase in Br− concentration.
Highlights
The ratio of UV253/UV203 of intracellular organic matter (IOM) was lower than that of extracellular organic matter (EOM) because the aromatic moisture of IOM was highly activated, and EOM had a higher substitution tendency of activated aromatic rings.[29,30]. These results were consistent with the results of previous studies, which showed that EOM and IOM of Chlorella sp. had a relatively low SUVA value (
Korshin et al reported that the UV253/UV203 value and THM formation potential had a strong linear correlation,[31] which indicated that IOM was likely a higher yielding precursor of THMs than EOM
The lower DON value in EOM than in IOM was attributed to the dominance of nitrogen-rich organic compounds,[32] which indicated that IOM had more potential to form N-disinfection byproduct (DBP)
Summary
Bromide (BrÀ) is detected in surface water in the range from 10 to 1000 mg LÀ1 as an important parameter for the formation of brominated DBPs.[19] During chlorination, BrÀ could be oxidized to form hypobromous (HOBr and OBrÀ) products, which had stronger oxidation ability to react with AOM to form brominated DBPs.[20] A few studies have reported THM and HAA formation during chlorination at initial BrÀ concentrations of 50 and 100 mg LÀ1.21,22 Besides, a previous study con rmed that Fe(VI) oxidation with a high concentration of BrÀ could form a little amount of brominated DBPs.[23] Brominated DBPs are cytotoxic and genotoxic to Chinese hamster ovary (CHO) cells,[24] which made it essential to consider the effect of bromide on Fe(VI) pre-oxidation with subsequent chlorination
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