Greatly enhanced mass transfer coefficients kL are measured whilst simultaneously maintaining low ozone loss. Comparisons of kL and volumetric coefficient, kL a values, are made with more conventional packed or bubble columns.
Acetic acid, 2-propanol and 4-nitrophenol, representing a wide reactivity range, are used to elucidate the applicability of rotating contactors in effluent treatment. It has been possible to study the effects of surface activity on mass transfer with subsequent reaction and to generate design data for the next generation of rotating contactors. 相似文献
Kinetic equations for ozone absorption rate present in the model were derived from the application of film theory to an irreversible gas-liquid reaction. Parameters involved in the model, reaction rate and mass transfer coefficients, Henry's law constant, etc., were estimated from bench-scale experiments. The model was applied to ozonation in bubble contactors of height/diameter ratio equal to that of the bench scale contactor and to a pilot plant bubble column of a height/diameter ratio about 3.6 times higher. 相似文献
In each CSTR, the calculation of oxidant concentrations (O3, H2O2) is made through mass balance equations and a semi-empirical formula which gives hydroxyl radical concentrations as a function both of ozone concentration and the main characteristics of the water to be treated (pH, TOC, alkalinity). Another semi-empirical formula links ozone consumption to the same characteristics. 相似文献
It has been indicated that the removal of the five species of aromatic nitro compounds by ozonation can well be expressed mathematically by first order reaction equations. Besides, the reaction constants and half-life periods for various species of the tested nitro compounds were calculated at different temperatures and pH.
An ozonation effect index (OI) was developed in the study to express the degree of degradation of substrates by ozonation, by means of which the five aromatic nitro hydrocarbons were compared with each other and finally ranked in the following order from greatest to smallest degrees of degradation:
p-nitroaniline > nitrobenzene > p-dinitrobenzene > p-nitrotoluene > m-dinitrobenzene
It has also found that the CODm/M ratio increases with ozone doses. This means that some easily degradable intermediates are produced, and increase in concentration with increase of ozone dose in the ozonation process.
The mechanisms of removing the five aromatic nitro hydrocarbons are discussed from the viewpoint of orienting effects of substituent groups on the aromatic rings. 相似文献
The effect of ozonation on membrane flux was found to be largely dependent on raw water quality as well as ozone dose. In case of upstream water (A), preozonation achieved significant flux enhancement regardless of ozone dose. Whereas, for the downstream water (B), the steady state flux was increased or decreased depending on ozone dose.
The analysis based on the resistance-in-series model provided the mechanistic interpretation on the membrane flux variation. Ozonation in an ozone-ultrafiltration system always brought about a decrease in cake resistance (Rc) and an increase in fouling resistance (Rf). Based on the measurement of particle size distribution and zeta potential, the reduction in cake resistance through ozonation was attributed to an increase in particle size due to “ozone-induced particle destabilization”. However, the increase in the fouling resistance seems to be caused partly by the microbial characteristics of raw water.
Although there was little effect on TOC, ozone-UF treatment could get much higher removal of UV 254, THMFP (lday) and THMPF/TOC ratio than UF treatment alone. 相似文献
The direct reaction between substrates and ozone predominated at lower pH, which resulted in the efficient oxidation of the olefin, DCPE. At higher pH, ozonation resulted in more efficient oxidation of the chlorinated alkanes, with a corresponding decrease in the efficiency of DCPE oxidation. Consistent results were observed for ozone/H2O2 and ozone/UV treatment. Due to slow UV-induced decomposition of H2O2, the process using H2O2/UV (254 nm) resulted in very slow oxidation of all four compounds.
The total ozone requirement to achieve a given degree of elimination (to 37% of the original concentration), δ0.37, was used to assess the combined effects of the direct and indirect reactions for different types of waters. 相似文献
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
All these considerations have led us to use static mixers to transfer ozone into water. This process enables us to control the ozone concentration in water and detention time. It is a very simple system, with very low maintenance requirements due to the lack of moving parts. Civil engineering is minimized. A pilot scale study is presented here. It took place at the Méry-sur-Oise water treatment plant, on a pilot plant working at 8-12 m3/h. It is composed of a static mixer for the transfer of ozone from gas to liquid, linked to an air lift to separate gas from liquid, providing ozonated water.
The optimization of transfer was achieved by studying the impact of water flow, gas flow and ozone concentration in the gas. It is possible to reach 90% of transfer in less than 15 s. Headloss (ΔP) across the mixer is a function of gas and water flows and remains economically very acceptable as 0.15 bar for 12 m3/h.
Atrazine removal was studied using a static mixer, an air lift and a contact pipe 80-m long, providing an optimum contact time phase, working as a plug flow reactor. Ozone and H2O2/O3 treatments were compared. The maximum reduction of atrazine concentrations (e.g., for an infinite contact time) is a function of the amount of transferred ozone, but H2O2 influences the kinetics of the reaction. In the presence of H2O2 with a ratio of H2O2 to O3 of 0.4 w/w, maximum elimination is reached in 2 min 30 s.
The effect of such treatments on environmental bacteria also was followed. A counting of total germs at 20°C showed a decrease of 1- to 3-logs 10 after 1 min 30 s of contact time for about 2 mg/L of transferred ozone. No significant difference between treatments with or without H2O2 was shown. The same conclusions were obtained from heterotrophic plate counts (37°C) and epifluorescence countings. 相似文献
The operation of these water treatment systems has shown that safe and high quality pool water is obtained reliably and economically. One pool (Main Pool) is of Olympic size, the other (Learner pool) is designed especially for use by children. Both pools utilize a full corona discharge ozone water treatment system. They were the first ozone systems in the U.S. to be built for public pools using the process of ozonation, flocculation, filtration, ozone removal and residual chlorination.
An extensive testing program was initiated in cooperation with the Wisconsin Department of Health. The bacteriological water quality from these swimming pools was in compliance with Wisconsin State Health Regulations and the German DIN Standard 19,643.
The first year of operation of the Peck Aquatic Center has shown that the corona discharge ozone pool water treatment process can:
1) Operate reliably in a public swimming pool environment without the need for highly or special operator qualifications.
2) Produce continuously bacteria- and virus-free pool water without the harmful and unpleasant effects of chlorine.
3) Creates a user constituency group praising and promoting the use of “minimal chlorine swimming” in the community. 相似文献
ke was expressed in terms of a stagnant contribution, due to the heat conduction through the solid and the fluid in the void space, and a radial mixing contribution of the gas and liquid phases, due to the radial component of the velocity of both fluids. The radial mixing contribution of the liquid ( ke ) L was compared with radial mass dispersion data, and a satisfactory agreement was obtained.
Moreover, ( ke )was much higher than the gas mixing and the stagnant contributions.
Correlations for hw and ke ) L have been proposed in accordance with the hydrodynamic regimes of the two-phase flow. 相似文献
For distillery wastewaters all parameters investigated have the highest decreases during the first minutes of ozonation, A254 showing the highest disappearance rates. Thus, during the first fifteen minutes of ozonation an important decrease of the 254 nm absorbance (? 75%) was observed. At further reaction times values of all parameters studied decrease slowly, eventually reaching a plateau value. During approximately the first two hours of reaction, dissolved ozone was never found, which suggested that fast or moderate gas-liquid reactions took place in the wastewaters. 相似文献
The experiments were conducted both on a synthetic water, with or without addition of humic substances, and on raw water from the Moulin-Papon dam. While iron was easily removed by simply increasing the pH measurement from 8.2 to 8.5 without intermediate oxidation, ozonation applied to water with a pH of nearly 8.4 did not enable the manganese to be removed with a low ozone dose (about 1 mg/L) unless a significant amount of bicarbonates (120 to 130 mg/L as CaCO3) were injected prior to the ozonation-filtration stage.
As it removes the manganese from the water, intermediate ozonation also removes the abatement of organics on the filters, and lowers the THM buildup potential. 相似文献
For large target compounds like humic acid, the adsorption efficiency was improved with higher ozone dosages, whereas the combined effect of ozonation coupling with GAC for small model compounds seems to be negative. In addition, there is a selective adsorption between the chlorinated disinfection by-product (DBP) precursors and other non-precursors, and most of the non-precursors are less adsorbable than the precursors. 相似文献
The batch reactor designed for the studies consisted of a cylindrical section for holding effluent, and a top spherical section for ozone/oxygen mixture. The reactor proved to be effective for controlling ozone dose. The variation in the applied ozone dose was less than 5 mg/L.
Bleach and primary effluents were treated with 50 and 100 mg/L ozone doses. Duplicate experiments were conducted for these effluents. Secondary effluent was studied for 50,100,150 and 200 mg/L ozone doses. Six replicate experiments were conducted for 50 and 100 mg/L ozone doses, whereas two experiments were carried out for 150 mg/L and one experiment for 200 mg/L ozone dose.
The results were analyzed using 't' test for paired experiments and ANOVA table for statistical confirmation. Residuals were plotted to check the assumptions of constant variance and normal distribution. The results indicated that 50 and 100 mg O3/L effectively removed color from bleach effluent and primary effluent, but did not significantly change the BOD. Ozone was found to be effective for secondary effluent, as BOD5 was increased by 65% for 50 and 100% for 100 mg O3/L doses. The corresponding reduction in color was 62% and 82%, respectively. Ke and Lo values for the BOD equation were calculated by using the non-linear least square method for the BOD equation, giving joint confidence regions for the calculated parameters. It was concluded that ozone is most effective for the removal of color and the increase of BOD in secondary effluent. 相似文献
High filtration rates were tested in this study. The 2.1m deep filters were run at a hydraulic loading rate (HLR) of 35 m/h with an empty bed contact time (EBCT) of only 3.6 minutes.
The important findings of this work are
?The high-rate biologically active carbon (BAC) filters met the objective of controlling ozone DBPs. These results confirm that high rate, low EBCT filters can provide significant biodegradation. Anthracite biofilters provided significantly less removal of ozone DBPs.
?The high rate BAC filters showed significant reduction of background HAAs. BAC reduced the background HAAs to below the long-term target of 30 μg/L. Anthracite biofilters did not exhibit HAA removal.
?Biological filtration with either media was ineffective for background THM removal. The long-term target of 40 μg/L could not be achieved without GAC adsorption. 相似文献
Experience shows that the measures taken to ensure the safety of employees also improve safety for plant and equipment, and vice versa. The solutions applied demand extra effort at the design stage of the plant, but in return, they result in notable improvements in operating conditions and costs. 相似文献
The results indicated that compared with conventional ABO, the co-effect of AC addition and short-termed (less than 1 week) or intermittent ozonation improved the removal of COD and BOD, while the longer period of ozonation resulted in reduction of excess sludge concentration in the bioreactor. The impact of AC and ozone on the ABO in the combined process did not concern only increased biomass activity, but AC and ozone improved also settleability of activated sludge and enhanced stability of the bioreactor to shock loadings. 相似文献
At 100 psia (0.69 MPa) Xclean < Xcont
At 300 psia (2.1 MPa) Xclean?Xcont
At 500 psia (3.5 MPa) Xclean > Xcont
The effect of contamination on CHF was found to be a function of pressure, initial contaminant concentration, and the relative steam quality at which CHF conditions occur. These results are compared to data available in the open literature where Xclean is always greater than Xcont. A method for correlating these data is also illustrated. 相似文献
Oxidation experiments have also been extended to pyrazine, and its sensitivity to only radical ozonation is shown. 相似文献
In order to exclude its toxic effect on the pulmonary epithelium, the medical ozone/oxygen mixture is administered so that exposure of the respiratory tract is avoided at all times, i.e., without the disturbing effects of its odor. 相似文献