| Since drinking water sources were micro-polluted by the increasingly wide range of pollutants, especially organic pollutants into the water in different ways, disinfection by-products (DBPs) precursors in micro-polluted source water have been gradually extended from humic acid (HA) and fulvic acid (FA) to the algal cells, algal extra-cellular organic matters (EOMs) and some other potential organic matters of important sources. In view of microbially-derived precursors in micro-polluted source water and inorganic precursors such as bromide and iodide due to seawater intrusion, the characterization of brominated and iodinated DBPs generated from micro-polluted source water during water treatment process are comprehensively discussed in this paper, which could provide quantities of reference for establishing drinking water risk control technology and engineering demonstration.The species of brominated and iodinated DBPs were investigated in two types of micro-polluted source water and in the effluents of each unit after the conventional drinking water treatment process (A plant) and the advanced drinking water treatment process (B plant). The CHCl2I and CHBrClI were identified for the first time in chloramine disinfection process, sand filtration and effluents of B plant. Furthermore, the effect of bromide and iodide on brominated and iodinated DBPs formation was explored in A and B plants. It was found that THM4 formation was largely affected by the concentrations of bromide ion in A plant. The concentrations of CHCl3 of raw water, sedimentation, filtration and effluent of A plant ranged from 2.02?/L to 4.58?g/L, CHCl2Br ranged from 3.53?g/L to 9.93?g/L, CHClBr2 of 15.31?g/L-35.03?g/L, and CHBr3 of 94.95?g/L-158.35?g/L. When bromide ion was 1mg/L, the concentration of CHBr3 generated from A plant treatment process exceeded the national standards for drinking water limits. While THM4 level of B plant treatment process was less affected by bromide ion, and the concentrations of the specific DBPs were lower than those of A plant. With the iodide ion concentrations increased, CHCl2I and CH2I2 were the main species in effluents of A and B plants treatment process. The CHCl2I of A plant treatment process which ranged from 6.06?g/L to 13.55?g/L was higher than that of CH2I2 (2.36-10.06?g/L), while the CH2I2 from B plant treatment process which ranged from 1.01?g/L to 9.78?g/L was higher than that of CHCl2I (1.27-6.19?g/L). THM4 from A and B plants treatment process were maintained at low levels, but the concentrations of CHcl2Br, CHClBr2 and CHBr3 of chloramine disinfection process, filtration and effluent of B plant, were higher than not only other process of B plants but also the corresponding process of A plant.In this experiment, Bovine serum albumin, starch, humic acids, fish oil and DNA were chosen as the surrogate model compounds of microbial protein, carbohydrate, HA, lipid and DNA respectively. The brominated and iodinated DBPs formation from the model compounds in the presence of bromide or iodide were investigated. With increasing bromide ion concentration, CHCl3 decreased continuously, CHCl2Br and CHClBr2 increased initially and then decreased, and CHBr3 increased continuously. DNA produced the least chlorinated and brominated DBPs among these five model biomolecules. BSA appeared to be the most reactive precursor to produce CHCl3 (100.19?g/L), while fish oil and HA generated lower concentration of CHC13 (63.72?g/L and 55.58?g/L respectively) than BSA. HA was the most reactive to produce CHBr3 (356.05?g/L), while BSA and fishoil produced 258.22?g/L?193.72?g/L of CHBr3 respectively. However, with increasing iodide ion concentration (0-2mg/L), fish oil appeared to be important precursor of CHCl2I (13.63?g/L-16.98?g/L), and the specific contribution order to CHcl2I as follow:fish oil> HA?starch>BSA?DNA. Moreover, it showed that Microcystis aeruginosa cell and its EOMs generated the same DBPs species as BSA, while EOMs produced the same species as HA. With the iodide ion concentration increased, CHCl3, CHCl2I and CH2I2 were generated from both the Microcystis aeruginosa (including algal cell and its EOMs) and EOMs.Finally, the formation of brominated and iodinated DBPs resulting from chlorination and chloramine in various source water, including the raw water of A, B, and C drinking water treatment plants and D reservoir were investigated. The results showed that the raw water of C plants produced 50 times higher levels of TTHMs upon chlorination than those from chloramine, and the most highest concentration of TTHMs upon the chlorination among the four raw water. The DBPs species from BAC and biological pretreatment of B plants during the chloramine were more than those from the chlorination, and the concentration of TTHMs upon the chloramine increased continuously. Similarly, the levels of TTHMs from BAC of C plants were higher than that from the raw water. Not only CHCl3 was generated from BAC, but also CHClBr, CHClBr2 and CHBr3 were generated. In addition to the brominated DBPs,0.42?g/L of CHC?2I was produced from the raw water of D reservoir. Although the levels of the iodinated DBPs was low, the risk of iodinated DBPs formation from D reservoir can not be ignored because of its higher toxicity. |
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