Advanced Oxidation and Degradation of Vinyl Chloride in Water

A kinetic model has been developed for the degradation of organic pollutants, by considering both the decomposition of ozone molecules and the interaction between ozone and hydrogen peroxide in the formation of a hydroxyl radical, and the subsequent reactions. Rate equations were derived for the depletion of ozone and pollutants in the advanced oxidation processes (known as the peroxone oxidation). Experiments were carried out at 298 K in the pH range 3 to 11. Kinetic data obtained experimentally from the hydrogen peroxide‐ozone reaction and advanced oxidation of vinyl chloride were analyzed by using the proposed rate equations, indicating that the depletion rate of ozone increases with the concentrations of ozone, hydrogen peroxide, and hydroxyl ion, as predicted by the kinetic model.     

Degradation of Organic Pollutants by the Advanced Oxidation Processes

A kinetic model hss been developed for the degradation of organic pollutants concerning with hydroperoxide ion as the initial step for generation of hydroxyl radical and its subsequent reac-tion mechanisms. Rate equstions were derived for depletion of ozone and pollutants in the peroxone oxidation process using ozone and hydrogen peroxide as combined oxidants. Kinetic data obtained experimentally form the hydrogen peroxide-ozone reaction and peroxone oxidstion of nitrohenzene were analyzed by using the proponse rate equations.     

OXIDATION OF C.I. ACID ORANGE 7 WITH OZONE AND HYDROGEN PEROXIDE IN A HOLLOW FIBER MEMBRANE REACTOR

The degradation of C.I. Acid Orange 7 by ozone combined with hydrogen peroxide was carried out in a hollow fiber membrane reactor, and batch recirculation mode of aqueous phase was employed. The effect of initial pH, hydroxyl radical scavenger, hydrogen peroxide concentration, liquid recirculation rate, gas flow rate, and gaseous ozone concentration on the decolorization of C.I. Acid Orange 7 was investigated. The results showed that the decolorization of C.I. Acid Orange 7 fits the pseudo-half-order kinetic model. The rate constant increased with the increase of initial pH, hydrogen peroxide concentration, liquid recirculation rate, gas flow rate, and gaseous ozone concentration. The presence of hydroxyl radical scavenger inhibited the decolorization rate by over 50%. The combination of ozone with hydrogen peroxide achieved a higher COD removal efficiency than ozone alone in the membrane reactor.     

Free Radical and Direct Ozone Reaction Competition to Remove Priority and Pharmaceutical Water Contaminants with Single and Hydrogen Peroxide Ozonation Systems

From the application of concepts derived from the gas-liquid absorption film model, the competition between ozone reactions with 72 water emerging or priority contaminants (pharmaceuticals, pesticides, polynuclear aromatic hydrocarbons, etc.) and the initiation steps of the hydroxyl radical decomposition of ozone in ozone alone and combined with hydrogen peroxide oxidation systems has been studied. With this information, the ozone preferential reaction, that is, the ozone direct reaction or the formation of free radicals and the kinetic absorption regime are known. In a second step, the ratio of removal rates of the contaminants studied by reacting with hydroxyl radical and ozone has also been estimated. With this, the way contaminants are preferentially removed (from their reaction with ozone or from the reaction with free radicals) can also be known and, hence, whether or not an ozone advanced oxidation system is convenient to be applied. For instance, most of the contaminants studied in this work at concentrations lower than 50 μgL^?1 and hydrogen peroxide at concentrations lower than 50 mgL^?1 react with ozone under chemical control regime so that both direct and free radical reactions theoretically compete. However, under chemical control, typical concentration of scavengers present in wastewater or surface water would inhibit the free radical reactions and, at least theoretically, for many contaminants studied here, the direct ozone reaction is the principal removal way. When mass transfer controls the process rate only contaminants with a hydroxyl and ozone rate constant ratio ≥ 1.6x10⁶ M^-1s^-1 would be preferentially removed through free radical way.     

Kinetic Study of Ozone Decay in Homogeneous Phosphate-Buffered Medium

The ozone decomposition reaction is analyzed in a homogeneous reactor through in-situ measurement of the ozone depletion. The experiments were carried out at pHs between 1 to 11 in H₂PO₄^?/HPO₄^2– buffers at constant ionic strength (0.1 M) and between 5 and 35 °C. A kinetic model for ozone decomposition is proposed considering the existence of two chemical subsystems, one accounting for direct ozone decomposition leading to hydrogen peroxide and the second one accounting for the reaction between the hydrogen peroxide with the ozone to give different radical species. The model explains the apparent reaction order respect of the ozone for the entire pH interval. The decomposition kinetics at pH 4.5, 6.1, and 9.0 is analyzed at different ionic strength and the results suggest that the phosphate ions do not act as a hydroxyl radical scavenger in the ozone decomposition mechanism.     

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.     

废水中氨及甲苯的O3／H2O2氧化降解及其动力学

研究了废水中的无机污染物氨和有机污染物甲苯在Ｏ３／Ｈ２Ｏ２ 中的氧化降解过程。根据Ｏ３／Ｈ２Ｏ２ 反应产生自由基ＯＨ·的机理和污染物在Ｏ３／Ｈ２Ｏ２ 中的氧化降解过程,推导出污染物被Ｏ３／Ｈ２Ｏ２氧化降解时的动力学模型,实验结果与理论模型相符。     

Peroxone Oxidation of Toluene and 2,4,6-Trinitrotoluene

This paper discusses oxidation of toluene and 2,4,6-trinitrotoluene (TNT) by ozone and hydrogen peroxide mixtures (known as peroxone oxidation) at 25[ddot]C. The overall reaction in alkaline solutions is first order with respect to the concentration of dissolved ozone, and is nearly independent of the pollutant concentrations. The oxidation of toluene is one-half order in hydrogen peroxide, and the rate constant changes in proportion to the hydroxyl ion concentration with an exponent of 0.67.

In the pH range of 7 to 9, the TNT destruction rate increases with the hydrogen peroxide and hydroxyl ion concentrations with exponents of 0.104 and 0.15 respectively. It is technically feasible to treat toluene and TNT contaminated waters by the peroxone oxidation process to achieve the residual level of a few parts per billion in treated waters to meet environmental requirements.     

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.     

2，4-二氯苯氧乙酸臭氧化过程中过氧化氢的生成

引言2,4-二氯苯氧乙酸(2,4-D,又名2,4-滴)是一种广泛使用的除草剂[1],应用历史较长,是我国主要的除草剂品种之一,用量也比较大。2,4-D属于苯氧羧酸类除草剂的一种,可有效去除阔叶杂草,目前仍广泛用于农作物除草和草坪养护[2]。2,4-D的水溶性较高,挥发性较低,在自然界中难以生物     

异丙醇的O3/H2O2复合氧化动力学研究

采用停流光谱仪研究了异丙醇在T=298K和pH=3～11范围内O3 / H2O2复合氧化的反应动力学.结果表明异丙醇的O3 / H2O2复合氧化反应动力学随反应体系的pH值不同而不同.在酸性和中性条件下,反应相对于O3浓度、异丙醇浓度都为1级;在碱性条件下,异丙醇较容易被O3/H2O2复合氧化降解,总反应级数为2级,相对于O3浓度、异丙醇浓度和H2O2浓度分别为1级、0级和1级,可见异丙醇的降解速率与它的浓度无关.在T=298K,当pH值从9增大到11, 反应速率常数从3486.1(mol·L-1)-1·s-1增大到38239.2(mol·L-1)-1·s-1. 表明在酸性条件下,异丙醇的O3/H2O2复合氧化是O3分子直接攻击异丙醇的反应占主导;在碱性条件下,自由基型反应占主导.     

Aqueous degradation of atrazine and some of its main by-products with ozone/hydrogen peroxide

This laboratory study was designed to investigate the removal of atrazine (ATZ) and its first main by-products, deethylatrazine (DEA) and deisopropylatrazine (DIA) by O₃/H₂O₂. At least 76% of the oxidation rate of atrazine is due to free radical reactions. At neutral pH and 20°C, an initial hydrogen peroxide concentration of 10⁻³ M is optimum to reach a maximum oxidation rate of these compounds. Experimental results of oxidation in the presence of high hydrogen peroxide concentrations allow the mass transfer coefficient of ozonation to be determined. This coefficient, reactor flow analysis and kinetic data obtained have been applied to mol balance equations of atrazine, deisopropylatrazine, deethylatrazine, ozone (both in the gas and water) and hydrogen peroxide to obtain their corresponding concentrations at different conditions. © 1998 SCI     

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.     

Use of the axial dispersion model to describe the O3 and O3 /H2O2 advanced oxidation of alachlor in water

Experiments on alachlor degradation by ozonation alone and combined with hydrogen peroxide using different surface waters have been conducted in a reactor bubble column and a kinetic model of the advanced oxidation process has been proposed. Variables studied were the nature of the surface water (four surface waters were treated), pH (3.5–9.7) and hydrogen peroxide to ozone mass ratio at the column inlet (0.1–1.85 g g^?1). Data on residence time distribution, rate constants and the absorption kinetic regime were considered to prepare the kinetic model, which was also based on the axial dispersion model of non‐ideal flow. The model gives good predictions of alachlor and hydrogen peroxide conversions and the fraction of dissolved ozone (deviations were lower than ±15%) although it fails, in some cases, to yield accurate estimates of the observed experimental trends of concentrations in water at the reactor column outlet. The calculated results were close to those obtained from the more classical N well‐mixed tanks‐in‐series model (deviations with this model were lower than ±20%). It is concluded that quantitative deviations from experimental observations were likely due to the lack of rate data on ozone reactions with organic matter present in the surface waters investigated. © 2002 Society of Chemical Industry     

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.     

Studies on Ozone Bleaching. I. The Effect of PH,Temperature, Buffer Systems and Heavy Metal-Ions on Stability of Ozone in Aqueous Solution

Ozone was found to be reasonably stable at moderately low pH (～pH 3) and ambient temperature in acetic, sulfuric and nitric acid solutions. In these cases, the exact kinetic order of ozone decomposition could not be established. However, second order with respect to ozone was preferred on the basis of statistical analysis of the data. At pH 3, the ozone decomposition rate was found to be slightly higher at 15°C and moderately higher at 35°C than at 25°C for all three buffer systems. At lower concentration level (～ 0.5 ppm), only Co(II) ion enhanced decomposition of ozone in sulfuric acid solution at pH 3 and 25°C. In contrast, at the higher concentration level (～ 3.0 ppm), Ca(II), Cr(III), Fe(II), Fe(III), Co(II), Ni(II) and Cu(II) ions were found to contribute the decomposition of ozone; the effect of Co(II) and Fe(II) ions was very pronounced as compared to the other ions. Using acetic acid instead of sulfuric acid as buffer reagent resulted in drastic and moderate reductions of the ozone decomposition catalyzed by Co(II) and Fe(II) ions, respectively. These indicate that acetic acid acts as radical scavenger for hydroxyl radical as postulated by Walling et al. Thus, the drastic increase in the ozone decomposition in the sulfuric acid solution with the presence of Co(II) or Fe(II) ion is caused by free radical chain reactions initiated by free radicals produced in the process.     

Ultraviolet-Enhanced Ozonation of Organic Compounds: 1,2-Dichloroethane and Trichloroethylene as Model Substrates

1,2–Dichloroethane (DCE) and trichloroethylene (TCE) were used as model compounds to study the oxidation of organic chemicals by ozone/ultraviolet radiation, ozone, and hydrogen peroxide/ultraviolet radiation. It was found that ozone/ultraviolet radiation oxidized both 1,2–dichloroethane and trichloroethylene in batch systems, at pH = 2 (phosphate buffer). At ozone concentrations in the 1 to 5 mg/L range, the reaction was first order in both ozone and substrate. At pH = 2 and initial ozone concentration 2.2–2.6 mg/L, rate constants (k)Q = 25 and 130 M^-1sec^-1 were observed for the ozone/ultraviolet radiation oxidation of DCE and TCE, respectively. The rat e constants for ozone oxidation of DCE and TCE without ultraviolet radiation were 4.3 and 47 M^-1sec^-1, respectively.

The higher rate of TCE oxidation implies that direct reaction occurs with the double bond. Finite reaction rate of DCE with ozone, and substantial increases in rate at higher pH imply the participatation of hydroxyl radicals in the oxidation of both compounds. For example, at pH = 7, initial ozone concentration of 2.3 mg/L, the k_o for TCE oxidation by ozone/ultraviolet radiation is approximately 500 M^?1 sec^?1 almost too fast to measure in a batch system.The rate also is increased by increased ultraviolet radiation intensity, and by the presence of hydrogen peroxide, which acts as a catalyst.     

Chemical degradation of aldicarb in water using ozone

The use of ozone to degrade aldicarb in water was investigated under different conditions. The oxidation develops through the direct attack of ozone since the presence of hydroxyl radical inhibitors, such as tert-butanol, does not affect the degradation rate of aldicarb. The combination of ozone with hydrogen peroxide does not improve the oxidation rate which also confirms the absence of radical reactions to eliminate aldicarb. However, TOC removal increases 51% in the presence of hydrogen peroxide after 65 min of oxidation. The oxidation rate is strongly affected by the type of device for feeding ozone, which indicates that a fast gas-liquid reaction is taking place. Therefore, mass transfer and chemical reaction steps are important factors in the establishment of the global rate of oxidation. Application of kinetic equations derived from gas absorption theories allows the determination of the rate constant of the direct ozone–aldicarb reaction, which was found to be: k = 3·18 × 10¹¹ exp(–6000/T) m³ mol^?1s^?1.     

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.