Effect of preozonation on the characteristic transformation of fulvic acid and its subsequent trichloromethane formation potential: Presence or absence of bicarbonate

Abstract

The effects of bicarbonate on the characteristic transformation of fulvic acid (FA) and its subsequent trichloromethane formation potential (TCMFP) were investigated in the process of preozonation. Dissolved organic carbon (DOC) removal rate and the residual aqueous ozone concentration during preozonation were measured with different bicarbonate concentration. The presence of bicarbonate inhibited DOC removal and decreased TCMFP yields in the initial oxidation period. In order to explain these phenomena, the molecular weight (MW) distribution (<5, 5-10, 10-30, and >30 kDa) and corresponding TCMFP were investigated for FA and its subsequent oxidation products. Furthermore, transformation of molecular structure, based on MW distribution, was also characterized with Fourier transform infrared (FTIR) spectrum. Bicarbonate showed different inhibiting effects on TCMFP of organic species with different MW, and more significant TCMFP decrement was observed for the high MW fraction (>30 kDa) than for the low MW fractions. Preozonation led to obvious reduction on DOC and UV 254 in most of MW fractions wherever bicarbonate was present or not, demonstrating that ozone contributed to both organics mineralization and structure variation, synchronously. As being indicated from the results of FTIR and gas chromatography-mass spectrometry, the functional groups such as alcohols, epoxides and phenols, the formation of which was promoted with hydroxyl radicals ( Å OH) and would be remarkably inhibited by bicarbonate, were responsible for the increment of TCM precursor's concentration during ozonation. Results of these studies confirmed low dosage bicarbonate affecting the ozonation pathways, influencing the intermediate species formation and impacting its subsequent TCMFP yields through inhibiting the Å OH radicals reactions mainly occurred in high MW fractions.

Characterization of dissolved organic matter from surface waters with low to high dissolved organic carbon and the related disinfection byproduct formation potential

“…After being dosed with chlorine, samples were stored at 25 ± 2 • C in the dark for 24 h. Free chlorine residuals of the samples were measured by an N, N-diethyl-p-phenylenediamine (DPD) titrimetric method [20]. After the addition of the sodium sulfite into the water samples, the concentrations of trihalomethanes formation potential (THMFP) and haloacetic acids formation potential (HAAFP) were determined according to the procedure [21].…”

Isolation of dissolved organic matter in effluents from sewage treatment plant and evaluation of the influences on its DBPs formation

“…Recalcitrant dissolved organic matter (DOM) has been observed to accumulate in lake water in China, even though an extensive effort has been made to cut down organic pollutant loadings generated in their catchment areas [1,2]. Imai et al [3] suggested that DOM sources resulting from human activities -anthropogenic DOM sources -may play a substantial role in the observed DOM increase in lake water.…”

Ozone oxidation of nanofiltration concentrates alleviates membrane fouling in drinking water industry

“…2(c) [9]. These two observations are not unexpected, because it is well-known that molecular O 3 transforms reactive sites in the NOM into aldehydic, ketonic and especially carboxylic groups [8,45].…”

“…The stronger decrease for the optical density is explained by the selective reaction of O 3 with unsaturated bonds. O 3 transforms these unsaturated bonds into oxygenated saturated bonds, such as aldehydic, ketonic and especially carboxylic groups [8,47]. However, these saturated reaction products typically react very inefficiently with O 3 , so they are not further mineralized into CO 2 and H 2 O, which explains the difficulties to achieve an extensive COD removal with O 3 oxidation.…”