During drinking-water treatment, ozone used as a preoxidant and chlorine required for final disinfection, lead to competing chemical reactions, in the case of raw water containing both organic compounds and inorganic salts (such as bromides and ammonia).
The study of the interactions between those reactants has been made according to the following main topics :
As for THM formation, experiments conducted on simple organic compounds or on natural fulvic acids show important decreases in THM or TCAA formation after ozonation. It may be noticed, however, that the ozonation of surface waters may induce the formation of haloform precursors, usually with a low level of reactivity.
In water supplies containing bromide ions, oxidation of the latter through hypobromous acid may take place during the ozonation stage. Failing preozonation treatment, hypobromous acid is generated very rapidly during chlorination, thus inducing the formation of chloro- brominated organic compounds.
During the ozonation of fulvic acid solutions, the presence of small amounts of bicarbonate was found to improve precursor removal significantly.
It can be concluded that the partial analogy of the action of ozone or chlorine on aromatic structures, whether simple or complex (such as humic and fulvic acids), seems to indicate that the consequence of preozonation is the destruction, at least in part, of the most reactive sites for THM production, thus leading to a decrease of the volatile organochlorinated compounds formed during the post-chlorination. However, some ozonation products of natural waters are THM precursors, though of low reactivity. Then, in the presence of bromide ions, the formation of volatile organobrominated compounds may be observed during ozonation. 相似文献
Four different sources of humic substances were studied to determine the effects of ozonation on molecular weight-distributions, based on dissolved organic carbon (DOC) and trihalomethane formation potential (THMFP). Solutions of two soil-derived fulvic acids and a one soil-derived humic acid, as well as dissolved organic matter (DOM) associated with a natural water source were studied. Both gel permeation chromatography (GPC) and ultrafiltration (UF) were employed to define apparent molecular weight (AMW). Applied ozone doses ranged from 2.0 to 2.5 mg O3/mg DOC. Overall samples of untreated and ozonated waters, as well as individual molecular weight fractions, were characterized according to DOC, UV absorbance, and THMFP. Ozonation resulted in a significant disappearance of higher AMW material with a corresponding increase in lower AMW material. Although little overall reduction in DOC concentration was observed, significant overall reductions in UV absorbance and THMFP levels were observed. 相似文献
Anionic, cationic and nonionic surfactants being frequently employed in the textile preparation process were subjected to H(2)O(2)/UV-C treatment. As a consequence of the considerable number of parameters affecting the H(2)O(2)/UV-C process, an experimental design methodology was used to mathematically describe and optimize the single and combined influences of the critical process variables treatment time, initial H(2)O(2)concentration and chemical oxygen demand (COD) on parent pollutant (surfactant) as well as organic carbon (COD and total organic carbon (TOC)) removal efficiencies. Multivariate analysis was based on two different photochemical treatment targets; (i) full oxidation/complete treatment of the surfactants or, alternatively, (ii) partial oxidation/pretreatment of the surfactants to comply with the legislative discharge requirements. According to the established polynomial regression models, the process independent variables "treatment time" (exerting a positive effect) and "initial COD content" (exerting a negative effect) played more significant roles in surfactant photodegradation than the process variable "initial H(2)O(2) concentration" under the studied experimental conditions. 相似文献
The oxidation of two model molecules (salicylic acid and a peptide) and humic substances in aqueous solution was studied using ozone in the presence of various catalysts. Experiments were performed in reactors operated either in batch (TOCo = 2.5 mg C.L?1) or in semi-continuous flow mode (TOCo = 42 mg C.L?1). 相似文献
The effect of bromide ion, organic carbon concentration (natural aquatic humic substances), pH, and solar irradiation on the formation of bromoform in ozonated groundwater has been studied. The studies were conducted on four unique samples of groundwater taken from different regions of the Biscayne Aquifer in southern Florida. All other conditions being equal, increases in bromide ion concentrations resulted in increases in CHBrg formation. In three of the four samples, CHBr3 formation decreased as the pH level increased from 5 to 9. The fourth sample exhibited an opposite trend whereby the CHBr3 concentration increased with increasing pH. Bromoform concentration increased with increased O3 concentration over an ozone dosage range of 3.4 to 6.7 mg/L. 相似文献
For arbitrarily chosen thirty types of natural resources which have been widely used in oriental traditional herb medicine,
supercritical CO2 extraction (SFE) and organic liquid solvent extraction (LSE) withn-hexane, chloroform and methanol were carried out to extract pharmaceutical substances. To evaluate relative advantages and
shortcomings between the SFE and LSE, five types of bioactivity assays as well as gas- and thin layer-chromatographic analysis
were performed for all the extracts obtained by the two extraction methods. Types of bioassays performed included cytotoxicity,
bleb forming, DNA binding, oxygen free radical scavenger and Xanthine oxidase inhibitor tests. To evaluate economic viability
of the SFE over the traditional LSE, extractability of prodrug substances was evaluated as the functions of extraction temperature
and pressure. SFE was proven to be a feasible alternative over LSE. Also, the optimum SFE conditions which provided maximum
extraction and cytotoxicity for each selected sample were presented. 相似文献