Investigation of Ozone Reaction in River Waters Causing Instantaneous Ozone Demand

Ozone consumption by water can be characterized by the instantaneous ozone demand (IOD) and a pseudo first order decay constant. Utilizing the flow injection analytical system for measuring IOD, the instantaneous ozone demand characteristics of two river waters (Korea) were investigated, utilizing a ?OH probe compound and ?OH scavenger, and were compared with those of two commercial humic acids (the Suwannee River humic acid and Aldrich humic acid). The major findings were as follows; (1) The IOD in river waters was found to be mainly due to the reaction of the ozone with natural organic matter (NOM), which constituted approximately 0.26–0.29?mg/mg DOC, and was responsible for the consumption of more than 40% of the applied ozone. Whereas, the IOD of the two commercial humic acids were three times more than those of the river waters. (2) The IOD in the river waters was mainly caused by the direct ozone reaction with dissolved organics, not from the ?OH mediated ozone reaction. However, for the two commercial humic acids, more than 40% of the IOD came from the ?OH mediated ozone reaction. (3) The hydrophobic fractions of the dissolved organics in the river waters were mainly responsible for the IOD. The IOD of the hydrophobic organics was approximately ten times larger than that of the hydrophilic organics. Although the exact magnitude of the IOD, and the relative importance of the direct/indirect ozone reaction with river water may vary greatly depending upon the source of the NOM, the characteristics of the IOD compromise a significant fraction of the ozone dose need (especially in achieving good ozone disinfection) in water treatment plants.     

Seawater Ozonation of Bacillus subtilis Spores: Implications for the Use of Ozone in Ballast Water Treatment

The potential of ozone for disinfection of ships’ ballast water was investigated using Bacillus subtilis spores as an indicator. The effects of pH, presence of iron, and bacterial strain on disinfection efficacy in seawater, under simulated ballast conditions, were investigated. Ozone dosages of 9 mg/L (pH 7) and 14 mg/L (pH 8.2) and 24 h contact achieved a 4-log inactivation with the various oxidant residuals formed. Iron surface at a ratio to water of 9 m²/m³ impaired the oxidant residuals and the disinfection of spores. Different strains of B. subtilis resulted in different CT values. Ozone does not seem to be a good choice for the control of spore-forming organisms in ballast water, but may be suitable for the control of other species.     

Effects of Ozone-Gas Bubble Size and pH on Ozone/UV Treatment

A series of ozone/UV treatment under injection of ozone with different ozone-gas bubble sizes was performed at pH 1.7 and 7.4. The increase in the bubble size and the decrease in pH enhanced the ozone utilization efficiency. The enhancement of ozone utilization efficiency was caused by the shift of the production pathway of hydroxyl radical (OH) from the OH production via O₃ ^– to the UV photolysis of H₂O₂. The lower pH caused this shift through the chemical equilibrium of H₂O₂ and HO₂ ^–, and the large bubbles caused this shift through the augmentation of H₂O₂ transport from the bubble surface to the bulk solution.     

Modification of the Standard Neutral Ozone Decomposition Model

The modified Staehelin, Buhler, and Hoigné model for aqueous ozone decomposition was tested over a wide range of hydroxyl radical scavenger concentrations at a pH of 7.1–7.2. Results from these experiments showed that the modified model appeared to underpredict the residual ozone concentration and overpredict the residual hydroxyl radical probe compound, tetrachloroethylene, concentration. The modified Staehelin, Buhler, and Hoigné model was recalibrated and two rate constants, the rate constant of the initiation reaction of ozone decomposition of hydroxide ion and the rate constant of the promotion reaction of ozone decomposition by hydroxyl radical, were reestimated. The new estimates of these rate constants are 1.8 × 10² M^?1s^?1 (initiation reaction) and 2 × 10⁸ M^?1s^?1 (promotion reaction), while the values estimated by Staehelin, Buhler, and Hoigné for these rate constants are 70 M^?1s^?1 (initiation reaction) and 2 × 10⁹ M^?1s^?1 (promotion reaction). The recalibrated-modified model was tested and validated by conducting experiments at different pH values and hydroxyl radical scavenger concentrations. Also, the effect of phosphate buffer as a hydroxyl radical scavenger was investigated at phosphate buffer concentrations of 10 mM and 1 mM.     

Ozone kinetics and diesel decomposition by ozonation in groundwater

The ozone kinetics (ozone auto-decomposition; effects of pH and solubility) and diesel/TCE/PCE decomposition (effects of hydroxyl radical scavenger, pH, and ozone/H₂O₂) by ozonation process were investigated in aqueous phase using deionized water, simulated groundwater, and actual groundwater. Reactions with deionized water and groundwater both showed the second-order reaction rates: the reaction rate was much higher in groundwater (half-life of 14.7 min) than in deionized water (half-life of 37.5 min). It was accelerated at high pH condition in both waters. The use of ozone showed high oxidation rates of TCE, PCE, and diesel. Hydroxyl radical scavengers acted as inhibitors for diesel decomposition, and high pH condition and addition of hydrogen peroxide could promote to degrade diesel in groundwater indicating ozone oxidation process could be effectively applied to treating diesel contaminated-groundwater.     

枯草芽孢杆菌对黑土中可培养微生物的生态效应

研究了微生物农药枯草芽孢杆菌对东北黑土中可培养微生物的生态影响.其动态变化表明:低质量分数枯草芽孢杆菌对细菌总数没有明显影响,较高质量分数枯草芽孢杆菌町促进细菌总数的显著增加,其中质量分数在3200 mg/kg时,枯草芽孢杆菌对细菌的刺激强度最高,为对照的11倍.枯草芽孢杆菌对土壤中的放线菌也有刺激作用,刺激强度最高时,放线菌数量可增至对照的8.3倍左右.枯草芽孢杆菌对真菌的敏感性较低,只有质量分数高达3200 mg/kg时,才对真菌产生明显刺激作用,最高刺激强度为同时期对照的29倍.     

枯草芽孢杆菌对土壤呼吸作用和脲酶活性的影响

通过模拟实验研究了微生物农药枯草芽孢杆菌对黑土的呼吸作用和脲酶活性的生态毒理效应.结果表明:枯草芽孢杆菌各质量分数处理均表现为对土壤呼吸作用的刺激效应,并且土壤巾枯草芽孢杆菌质量分数越大,对土壤呼吸强度的刺激作用越大,其中最高质量分数(3200 mg/kg干土)处理在第42天时达到最大刺激强度,刺激率为69.1%.与对照相比,除第1天外,所有处理(32～3200 mg/kg干土)对土壤脲酶均表现出刺激效应,其中最高质量分数(3200 mg/kg干土)处理在第28天脲酶活性上升到最高,刺激率达到101.1%.     

Investigation on the Kinetics of Heterogeneous Catalytic Ozone Decomposition in Aqueous Solution over Composite Iron-Manganese Silicate Oxide

The kinetics of heterogeneous catalytic ozone decomposition in aqueous solution over composite iron-manganese silicate oxide (FMSO) was investigated. Results showed that the presence of FMSO significantly accelerated the ozone decomposition rate from 0.022 (without FMSO) to 0.101 min^?1. The effects of inorganic anions and solution pH indicated that surface hydroxyl groups on FMSO were the active sites for catalyzing ozone decomposition and neutral charge surface seemed to show the highest catalytic performance. Tert-butanol inhibition experiments demonstrated that FMSO effectively accelerated the transformation rate of ozone into hydroxyl radicals. The contribution of hydroxyl radicals on ozone decomposition with and without FMSO was subsequently determined.     

Formation of Bromate Ion Through a Radical Pathway in a Continuous Flow Reactor

The contribution of ozone and hydroxyl radical to the formation of bromate ion was investigated in a continuous flow reactor. Experiments were conducted under a wide range of ozone dose (0.7 ～ 3.8 mgL), pH (6.5 ～ 8.5), and t-butanol concentration (0 ～ 0.5 mM). The formation of bromate ion was found to depend on radical reaction pathway, because the amount of bromate ion formed increased with pH and decreased with t-butanol, a radical scavenger, even when dissolved ozone concentrations were almost the same. In fact, the amount of bromate ion formed was reduced by 90% in the presence of t-butanol. Furthermore, the formation of bromate ion occurred even when dissolved ozone was not significantly detected in the presence of organic matter (TOC of 1 mgCL). The second-order reaction rate constant of hydroxyl radical with bromide ion, k _HO,Br^? of 1.7 × 10⁹ (M^?1s^?1), was obtained on the assumption that the reactions of bromide ion and t-butanol with hydroxyl radical were competitive with each other in the presence of t-butanol and that the formation of bromate ion depended on the reaction of bromide ion with hydroxyl radical. Therefore, it is concluded that the reaction of bromide ion with hydroxyl radical dominated in the overall reaction from bromide ion to bromate ion in the continuous flow reactor.     

Kinetic Study and Optimum Control of the Ozone/UV Process Measuring Hydrogen Peroxide Formed In-situ

This study was conducted to develop a kinetic model of the ozone/UV process by monitoring the trend of in-situ hydrogen peroxide formation. A specifically devised setup, which could continuously measure the concentration of hydrogen peroxide as low as 10 μg/L, was used. The kinetic equations, comprised of several intrinsic constants with semi-empirical parameters (k_chain and k_R3) were developed to predict the time varied residual ozone and hydrogen peroxide formed in situ along with the hydroxyl radical concentration at steady state,[OH°]_ss, in the ozone/UV process. The optimum ozone dose was also investigated at a fixed UV dose using the removal rate of UV absorbance at 254 nm (A₂₅₄) in raw drinking water. The result showed that the continuous monitoring of hydrogen peroxide formed in situ in an ozone/UV process could be used as an important tool to optimize the operation of the process.     

Hydroxyl Radical/Ozone Ratios During Ozonation Processes. I. The Rct Concept

The ozonation of model systems and several natural waters was examined in bench-scale batch experiments. In addition to measuring the concentration of ozone (O₃), the rate of depletion of an in situ hydroxyl radical probe compound was monitored, thus providing information on the transient steady-state concentration of hydroxyl radicals (√OH). A new parameter, R_ct , representing the ratio of the √OH-exposure to the O₃-exposure was calculated as a function of reaction time. For most waters tested, including pH-buffered model systems and natural waters, R_ct was a constant value for the majority of the reaction. Therefore, R_ct corresponds to the ratio of the √OH concentration to the O₃ concentration in a given water (i.e. R_ct = [√OH]/[O₃]). For a given water source, the degradation of a micropollutant (e.g. atrazine) via O₃ and √OH reaction pathways can be predicted by the O₃ reaction kinetics and R_ct .     

Comparing Static Mixer Performances at Pilot and Full Scale for Ozonation,Inactivation of Bacillus subtilis,and Bromate Formation in Water Treatment

The potential benefits of using a static mixer for ozone dissolution was evaluated through comprehensive pilot- and full-scale studies under a variety of operating conditions and source waters. The static mixer pilot unit was operated side-by-side to a full-scale plant which also employed static mixers for ozonation. Based on the results obtained from this pilot study (and at other sites), it appears that an optimal ozone dose (≤0.5mgO₃/mgC) applied through a static mixer dissolution system integrated with a well-designed downstream contactor can result in enhanced microbial inactivation while keeping bromate formation below 10μg/L.     

氯灭活水中枯草芽孢杆菌的效果

以枯草芽孢杆菌(ATCC6633)作为难灭活微生物的代表,研究了氯对水体中芽孢的灭活效果,考察了氯浓度、作用时间、反应体系pH值、温度以及芽孢初始浓度等因素的影响。结果表明,氯对芽孢的灭活过程可分为延滞期和灭活期;初始氯浓度在2.06~10.30 mg·L^-1,反应时间0~166 min,pH值6~9,温度1~30℃,初始芽孢浓度10²~10¹² cfu·ml^-1范围内,消毒剂浓度和反应时间共同影响着氯对芽孢的灭活效果,提高消毒剂投量或延长消毒反应时间,均可提高灭活率;酸性条件下氯灭活芽孢的能力强于碱性条件下;随着温度的上升,氯对芽孢的灭活能力增强;芽孢的初始浓度对氯灭活芽孢的效能影响不大。初始氯投量为8.30 mg·L^-1,pH=7,芽孢初始浓度10⁶ cfu·ml^-1,温度分别为5℃和25℃下,枯草芽孢杆菌对氯消毒剂的抗性强于炭疽芽孢杆菌。     

A Simple Model to Predict Formation of Bromate Ion and Hypobromous Acid/Hypobromite Ion through Hydroxyl Radical Pathway during Ozonation

A simple model is developed to predict the formation of bromate ion as well as hypobromous acid/hypobromite ion through the hydroxyl radical pathway. For simplicity of the model, hydroxyl radical concentrations are represented by the concentration ratio of hydroxyl radical to dissolved ozone under the different pH conditions. A kinetic analysis is conducted to evaluate the ratio under the different pH conditions based on the experimental data. The different extent of the ratio by one pH unit is found to be 3–4 times. This model can favorably simulate the formations of bromate ion as well as hypobromous acid/hypobromite ion in spite of the simplicity of the model. So it is likely that this model will be applicable to the prediction of bromate ion formation in water purification process such as drinking water treatment by introducing the concentration ratio of hydroxyl radical to dissolved ozone.     

Enhancement of Radical Chain Reactions of Ozone in Water in the Presence of an Aquatic Fulvic Acid

In this work, the rate constants of ozone consumption by an aquatic fulvic acid were determined in a special batch reactor atifferent pH values and in the presence or absence of t–butyl alcohol, a well known free–radical scavenger. We have found, for ratios [FA]_o/[O₃]_o 17 mole C/mole O₃, that reactions are of first order for ozone consumption (between pH 2 and 8). Results show that the fulvic acid does not participate in the radical type decomposition of ozone at strongly acidic pH (pH = 2), and that it becomes, with increasing pH (increased dissociation degree of its acidic groups), promoter of the decomposition of ozone in water.     

Hydroxyl Radical/Ozone Ratios During Ozonation Processes. II. The Effect of Temperature,pH, Alkalinity,and DOM Properties

The influence of temperature, pH, alkalinity, and type and concentration of the dissolved organic matter (DOM) on the rate of ozone (O₃) decomposition, O₃-exposure, ?OH-exposure and the ratio R_ct of the concentrations of ?OH and O₃ has been studied. For a standardized single ozone dose of 1 mg/L in all experiments, considerable variations in O₃-exposure and ?OH-exposure were found. This has important implications for water treatment plants regarding the efficiency of oxidation and disinfection by O₃. In oligotrophic surface waters and groundwaters, minimal calibration experiments are needed to model and control the ozonation process, whereas in eutrophic surface waters more frequent measurements of O₃ kinetics and R_ct values are required to evaluate seasonal variations.     

Ozone and Anthrax - Knowns and Unknowns

Mailings of envelopes containing anthrax spores (Bacillus anthracis) have caused serious disruptions of business operations in various parts of the United States, and several people tragically have lost their lives from resulting exposure to anthrax. These incidents have caused U.S. government agencies to investigate this material and to evaluate methods of neutralizing it. Ozone is one candidate countermeasure.

In this paper, what is known about ozone and its ability to destroy B. anthracis spores (and accepted surrogates) is discussed. High relative humidity is required to “soften up” the spore coating prior to addition of any disinfectant. Ozone clearly is a sufficiently powerful oxidant to destroy B. anthracis in relatively short exposure times. Of major concern, however, is ozone's equally clear ability to produce collateral damage in areas where it is used.

Research on ozone is needed to fill data gaps, in order to convince government authorities in charge of anti-terrorism activities that ozone should be included as a prime candidate for combating anthrax contaminations. It is equally important that those in the ozone industry be aware of the known facts and data gaps concerning ozone — in order to minimize the number of (well-intentioned) overclaims for ozone that may be doomed to failure and give ozone a black eye in this field.