Ozone Decomposition Rate Research Articles

Catalytic ozonation of atrazine and linuron on MnO x/Al 2O 3 and MnO x/SBA-15 in a fixed bed reactor

The catalytic ozonation of the herbicides atrazine and linuron was studied in a fixed-bed reactor using alumina-supported manganese oxide catalysts. Two manganese oxides were supported, one on activated alumina, MnO x /Al 2O 3, the other, MnO x /SBA-15, after impregnating mesoporous silica by the minimum volume method. The adsorption of both compounds was not significant and the kinetic data indicated that the reaction with molecular ozone was a non-catalytic process which took place in homogeneous phase. The results of catalytic runs also showed no evidence that any of the catalysts increased the rate of the hydroxyl-mediated ozonation. Both catalysts, however, considerably increased the ozone decomposition rate constant, particularly MnO x /SBA-15 for which a MnO x bed load of 1.0 wt.% as MnO 2 resulted in a 30 fold increase with respect to the homogeneous rate. The catalysts also improved the efficiency in the production of hydroxyl radicals from ozone with an average hydroxyl radical-to-ozone ratio as high as 10 −6 for MnO x /Al 2O 3 and 3.0 × 10 −6 for MnO x /SBA-15. The catalysts also led to lower ozone consumption per mole of converted organic compound, whether or not bicarbonate was present in the solution. Best results were obtained in all cases for MnO x /SBA-15, most probably due to a better distribution of the active phase on a larger surface.

Oxidation of nitrobenzene by ozone in the presence of faujasite zeolite in a continuous flow gas–liquid–solid reactor

This work investigates the oxidation of nitrobenzene (NB) by ozone in the presence of faujasite zeolite. Experiments were carried out in a gas-liquid-solid reactor were ozone transfer and NB oxidation took place at the same time. Three configurations of the reactor were compared: empty, filled with inert glass beads and filled with faujasite pellets. First, ozone transfer coefficient (k(L)a) and decomposition rate constant (k(C)) were determined for each configuration. In presence of solid, k(L)a was 2.0 to 2.6 times higher and k(C) was 5.0 to 6.4 times higher compared to the empty reactor. Then, the various configurations were evaluated in terms of NB removal and chemical oxygen demand (COD) decrease. The faujasite reactor showed higher removal of NB and decrease of COD compared to other configurations under the same conditions suggesting that the faujasite increases the oxidation rate of NB. Oxidation of NB in presence of faujasite also proved to be limited by the transfer of ozone from the gas to the liquid phase.

Ozone Mass Transfer in a Recirculating Loop Semibatch Reactor Operated at High Pressure

AbstractThe effects of water flow rate, mixing, gaseous ozone concentration, inlet gas flow rate, temperature, and pH on ozone hydrodynamics at high pressure were studied. Varying the cross flow rate had only a slight influence on the ozone mass transfer rates, indicating that sufficient mixing in the reactor was attained at the low flow rates used. The addition of an inline static mixer had a negligible effect on aqueous ozone concentrations in the reactor, suggesting that mixing was sufficient without the mixer. The ozone mass transfer increased with increasing gaseous ozone concentration and with the inlet gas flow rate. The dissolved ozone concentration decreased with increasing pH due to the greater rate of ozone decomposition at higher pH. Increasing the temperature resulted in a decrease in the ozone mass transfer. A model to describe the ozone mass transfer was developed. Good agreement between the model predictions and the experimental data was achieved.

Kinetic Study of Pressurized Ozonation Reactor of Tap Water

A developed pressurized pilot scale ozonation system with the volume of 28 L was designed to simulate the field operating condition by transferring premixed ozone and tap water into this system under the influence of three system pressure (1, 2 and 3 kgf/cm2), seven initial pH (5, 6, 6.5, 6.8, 8, 8.5, 9). The system was running in a continuous mode and with only initial pH adjustment to study the dissolution, self-decomposition and mass transfer of ozone in these conditions. The effects of the operating pressure and pH on ozone dissolution concentration, ozone decomposition rates and the liquid phase overall mass transfer coefficients (KLa) were determined quantitatively. The data show the calculated average ozone decomposition rates for pH increase from 5 to 9 are 9.01E-7 to 2.64 E-6 mol/L-min by using mole balance equation at the system pressure 2 kgf/cm2. The calculated average of KLa at the pseudo-steady state are 0.039 min−1 and 0.069 min−1 for pH less 6.5 and greater than 6.8, respectively.

Influence parameters in the ozonation of phenol wastewater treatment using bubble column reactor under continuous circulation

The ozonation of phenol wastewater treatment system has been investigated with effective mass transfer between gas and liquid phase in a bubble column reactor. The designed bubble column reactor was investigated for increasing the rate of mass transfer of ozone, the rate of oxidation of phenol in the solution, the solubility and decomposition rate of ozone in the distilled water were also studied at different flow rates. The decomposition rate constants were calculated based on pseudo first order kinetics. The oxidation of phenol was investigated in order to provide the overall reaction rate constant for the reaction between ozone and phenol at 25 °C. The influence of the operating parameters like initial phenol concentration, ozone flow rate and pH for the destruction of phenol by ozonation were studied. The pseudo first order rate constant was depending on the initial concentration of phenol solution. A comparison of TOC removal percentage between bubble column reactor and bubble diffuser using ozonation were reported.

Plasma-enhanced catalysis of propane and isopropyl alcohol at ambient temperature on a MnO2-based catalyst

The removal of two volatile organic compounds (propane and isopropyl alcohol) by a nanosecond pulsed corona discharge serially combined with Al2O3–MnO2 catalytic post-treatment has been investigated in air at atmospheric pressure and room temperature. The degradation mechanism of VOCs in the non-thermal plasma is a serious problem: several hazardous organic compounds (acetone and formaldehyde) are produced, and the formation yield of CO is higher than CO2. The high concentration of ozone (up to 800ppm) produced in the corona discharge can be used to further oxidize the VOCs on the catalyst. The efficient decomposition of O3 on MnO2 at ambient temperature leads to the formation of reactive oxygen species susceptible to react with residual pollutants in the effluent. This results in a significant increase of VOCs destruction and removal efficiency. Moreover, the catalytic post-treatment greatly enhances the conversion of propane into CO2. The study of ozone-promoted decomposition mechanism of C3H8 on the catalyst has shown that organic by-products are adsorbed and gradually oxidized on the surface. However, concerning isopropyl alcohol, the oxidation remains incomplete: the formation yield of acetone increases after catalytic post-treatment, and the concentration of carbon oxides remains very low. The treatment of immobilized C3H7OH by ozone could be an alternative technique. Finally, the influence of the gas composition on the decomposition rate of ozone was also investigated.

Catalytic efficiency and stability of cobalt hydroxide for decomposition of ozone and p-chloronitrobenzene in water

Cobalt hydroxide, a stable and efficient catalyst prepared in the laboratory, has been successfully used in the decomposition of ozone and trace quantities of p-chloronitrobenzene (pCNB) in water. The cobalt hydroxide was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and the Brunauer-Emmet-Teller (BET) method. The decomposition rate of aqueous ozone was increased by 1.527 times in the presence of cobalt hydroxide. Increasing the catalyst loading from 0 to 500 mg/L increased the removal efficiency of pCNB from 59% to 99%. The catalyst morphology and its composition were found to be unaltered after the catalytic reaction. After five successive recycles, the catalyst remained stable in the catalytic ozonation of pCNB.

Degradation of caffeine and identification of the transformation products generated by ozonation

The ozonation of caffeine in water was performed at different pH values, including acidic conditions. Kinetic experiments were conducted by adding pulses of a concentrated caffeine solution to ozone saturated water. The results showed a rapid decrease of ozone concentration during the first 15 s after injection, followed by a gradual decline at a much slower rate. The data were fitted to a second order kinetic model with rate constants increasing from 0.25 to 1.05 M −1 s −1 for pH in the 3–10 range. The initial ozone consumption per mol of ozonated caffeine was greater at high pH values, reflecting a higher ozone decomposition rate. The decomposition of ozone was positively affected by the concentration of caffeine, an effect that could be attributed to the presence of a reaction intermediate from the ozonation of caffeine that behaved as a strong promoter of ozone decomposition. A study of the transformation products identified by liquid chromatography in combination with time-of-flight mass spectrometry was carried out, which permitted a tentative degradation pathway to be proposed and several persistent by-products to be identified at both pH 3 and 8. Most transformation products were the result of the opening of the imidazole ring after breaking caffeine’s N9C8 double bond.

Influence of presence of tannic acid on removal of sodium dodecylbenzenesulphonate by O3and advanced oxidation processes

BACKGROUND: The objective of the present investigation was to determine the role of the tannic acid (TAN) component of organic matter dissolved in water, in the removal of sodium dodecylbenzenesulphonate (SDBS) by ozone and by O3/H2O2, O3/granular activated carbon (GAC) and O3/powdered activated carbon (PAC) advanced oxidation processes. RESULTS: Low doses of TAN (1 mg L−1) during SDBS ozonation cause (i) an increased ozone decomposition rate and (ii) an increased SDBS removal rate. The SDBS removal rate with ozone in the presence of TAN was reduced when HCO3− ions were added. A rise in TAN concentration increased the SDBS removal rate, with a linear relationship between added TAN and the removal rate. SDBS was removed more effectively by O3/GAC, O3/PAC and O3/H2O2 systems in the presence of TAN. CONCLUSIONS: Results obtained indicated two mechanisms involved in the generation of HO· radicals by the O3/TAN interaction: (i) direct generation of HO· radicals from the reaction between ozone and TAN, and (ii) increased generation of O2−· radicals in the medium, enhancing the transformation of ozone into HO· radicals by different radical reactions. In O3/GAC and O3/PAC systems, HO· radicals are mainly generated in the O3/TAN interaction, which is a homogeneous reaction with fast kinetics, whereas the O3/GAC and O3/PAC interactions are in a heterogeneous phase with much slower kinetics, and are therefore not competitive in the generation of HO· radicals. Copyright © 2008 Society of Chemical Industry

Benzene oxidation with ozone over supported manganese oxide catalysts: Effect of catalyst support and reaction conditions

Catalytic oxidation of gaseous benzene with ozone was carried out over supported manganese oxides to investigate the factors controlling the catalytic activities. The rate for benzene oxidation linearly increased with the surface area of catalyst, regardless of the kinds of catalyst support, whereas the ratio of ozone decomposition rate to benzene oxidation rate was larger for SiO 2-supported catalyst than Al 2O 3-, TiO 2-, and ZrO 2-supported catalysts. The rate for benzene oxidation and CO x selectivity increased with the reaction temperature (22–100 °C) and were improved by the addition of water vapor to reaction gases. Benzene conversion and carbon balance increased with ozone concentration.

The Impact of Traces of Hydrogen Peroxide and Phosphate on the Ozone Decomposition Rate in “Pure Water”

To obtain an idea of the magnitudes of the ozone loss rates rO3 in practical applications of ozone, an overall determination of the ozone decay profiles and rate constants was carried out in four different systems. These systems resemble different conditions for industrial application of ozone and the peroxone process, such as in the field of micro electronics, drinking water purification, disinfection, etc. Therefore, the behavior of ozone was monitored in the pH range from 4.5 to 9.0, in pure water and phosphate buffered systems in absence and presence of small amounts of hydrogen peroxide (10−7 M to 10−5 M H2O2). First the reproducibility of the ozone decay profiles was checked and from the various kinetic formalism tests, the reaction order 1.5 for the ozone decay rate has been selected. As expected, hydrogen peroxide increases the decay rates. In pure systems, added concentrations of 10−7M H2O2 already cause a remarkable acceleration of the ozone decay in the acidic and neutral pH range compared to the pure systems. However for alkaline pH conditions almost no effect of the low hydrogen peroxide concentrations was noticed. Contradictory to literature data, in the absence of hydrogen peroxide, ozone displays faster decays in the buffered systems of low ionic strength of 0.02 compared to pure water. This acceleration is more pronounced for acidic pH conditions. Low concentrations of phosphate may indeed accelerate the ozone decay in the presence of organic matter. Adding H2O2 concentrations below 10−5M to phosphate buffered solutions has a negligible effect on the ozone decay rate compared with pure water systems, except for pH 7. It appears that phosphate masks the effect of hydrogen peroxide below 10−5 M as tested here. Thus the application of AOP's by adding low concentrations of hydrogen peroxide is not well feasible in the presence of phosphate buffers in pure water systems.

Influence of surface texture and acid–base properties on ozone decomposition catalyzed by aluminum (hydroxyl) oxides

The decomposition of aqueous ozone in the presence of three aluminum (hydroxyl) oxides was studied, respectively. It was hypothesized that surface hydroxyl groups and acid–base properties of aluminum (hydroxyl) oxides play an important role in catalyzed ozone decomposition. The variables investigated were oxide dose, aqueous pH, presence of inorganic anions (sulfate and nitrate), the effect of tert-butyl alcohol (TBA) and surface hydroxyl groups density of the three aluminum (hydroxyl) oxides. All three aluminum (hydroxyl) oxides tested, i.e. γ-AlOOH (HAO), γ-Al2O3 (RAO) and α-Al2O3 (AAO), enhanced the rate of ozone decomposition. The net surface charge of the aluminum (hydroxyl) oxides favored in catalyzed ozone decomposition. The greatest effect on catalyzed ozone decomposition was observed when the solution pH was close to the point of zero charge of the aluminum (hydroxyl) oxide. Sulfate and nitrate were substituted for the surface hydroxyl groups of the aluminum (hydroxyl) oxides, which then complexed with Al3+ in a ligand exchange reaction. Therefore, inorganic anions may be able to inhibit catalyzed ozone decomposition. It was confirmed that surface hydroxyl groups were important for ozone decomposition with aluminum (hydroxyl) oxides as catalysts. TBA inhibited ozone decomposition in the presence of HAO, RAO and AAO. It was also tested whether aluminum (hydroxyl) oxides catalyzed ozone-transformed hydroxyl radicals. The relationship between surface hydroxyl groups and the ratio of hydroxyl radical concentration to ozone concentration (Rct) was investigated quantitatively. Higher density of surface hydroxyl groups of the aluminum oxide tested was favorable for the decay of ozone into hydroxyl radicals.

Behavior of two different constituents of natural organic matter in the removal of sodium dodecylbenzenesulfonate by O 3 and O 3-based advanced oxidation processes

The objective of this study was to analyze the role played by two components of natural organic matter (NOM), gallic acid (GAL) and humic acid (HUM), in the removal of the surfactant sodium dodecylbenzenesulfonate (SDBS) from waters by O 3-based oxidation processes, i.e., O 3/H 2O 2, O 3/granular activated carbon (GAC), and O 3/powdered activated carbon (PAC). It was found that the presence of low concentrations of these compounds (1 mg/L) during SDBS ozonation increases both the ozone decomposition rate and the rate of SDBS removal from the medium. Because of the low reactivity of SDBS with ozone, these effects are mainly due to an increase in the transformation rate of ozone into HO • radicals. Results obtained demonstrate that the presence of GAL and HUM during SDBS ozonation increases the concentration of O −• 2 radicals in the medium, confirming that GAL and HUM act as initiating agents of ozone transformation into HO •. It was also found that this effect was smaller with a larger molecular size of the acid. Presence of GAL and HUM during SDBS removal by O 3/H 2O 2, O 3/GAC, and O 3/PAC systems also increases the SDBS degradation rate, confirming the role of these compounds as initiators of ozone transformation into HO • radicals.

Ozone decomposition in concentrated aqueous solutions of salts

Effect of high concentrations of electrolytes (Na2SO4, NaCl, and NaNO3) on the rate of ozone decomposition in water was studied. The conversion kinetics of O3 dissolved in these solutions was analyzed. The rate constants of ozone decomposition were determined.

Ozonation of oxytetracycline and toxicological assessment of its oxidation by-products

Antibiotic formulation effluents are well known for their difficult elimination by traditional bio-treatment methods and their important contribution to environmental pollution due to its fluctuating and recalcitrant nature. In the present study the effect of ozonation on the degradation of oxytetracycline (OTC) aqueous solution (100 mg l −1) at different pH values (3, 7 and 11) was investigated. Ozone (11 mg l −1 corresponds the concentration of ozone in gas phase) was chosen considering its rapid reaction and decomposition rate. The concentration of oxytetracycline, chemical oxygen demand (COD), biochemical oxygen demand (BOD) and BOD 5/COD ratio were the parameters to evaluate the efficiency of the ozonation process. In addition, the toxic potential of the OTC degradation was investigated by the bioluminescence test using the LUMIStox 300 instrument and results were expressed as the percentage inhibition of the luminescence of the marine bacteria Vibrio fischeri. The results demonstrate that ozonation as a partial step of a combined treatment concept is a potential technique for biodegradability enhancement of effluents from pharmaceutical industries containing high concentration of oxytetracycline provided that the appropriate ozonation period is selected. At pH 11 and after 60 min of ozonation of oxytetracycline aqueous solutions (100 and 200 mg l −1) the BOD 5/COD ratios were 0.69 and 0.52, respectively. It was also shown that COD removal rates increase with increasing pH as a consequence of enhanced ozone decomposition rates at elevated pH values. The results of bioluminescence data indicate that first by-products after partial ozonation (5–30 min) of OTC were more toxic than the parent compound.

Catalytic activity and stability of Y zeolite for phenol degradation in the presence of ozone

As a stable microporous material, de-aluminated Y zeolite has been used for the first time as an ozonation catalyst and showed remarkable activity for the removal of phenol and chemical oxygen demand (COD) in aqueous solution. The Y zeolite exhibited excellent repetitive-use performance even after continuous operation for 10 cycles. The ozone decomposition rate, influence of hydroxyl radical scavenger and influence of reaction temperature were investigated. The results indicate that Y zeolite accelerates the decomposition of ozone and the generation of hydroxyl radicals, consequently enhances the degradation of phenol and the removal of COD.

Theoretical analysis of physicochemical processes occurring during water treatment by ozone and ultraviolet radiation

The paper presents a kinetic model developed for ozone dissolution in water and taking into account convective and diffusion processes occurring in the vicinity of floating bubbles that contain an ozone-air mixture. It was shown that the gradient of ozone concentration in a convective-diffusion layer and consequently the rate of ozone transfer from bubbles to the solution depended on the rate of ozone decomposition both in its reaction with organic admixtures and in the conditions of exposure to ultraviolet radiation. The obtained kinetic curves of destruction of organic compounds and changes of ozone concentration in water and ozone-air mixture are compared with experimental data for humic acids. The paper also analyzes additional factors affecting the kinetics of ozone dissolution and the rate of resultant reactions.

Ozonation and Advanced Oxidation of Wastewater: Effect of O3 Dose, pH, DOM and HO•-Scavengers on Ozone Decomposition and HO• Generation

The decomposition of ozone in wastewater is observed starting 350 milliseconds after ozone addition. It seems not to be controlled by the autocatalytic chain reaction, but rather by direct reactions with reactive moieties of the dissolved organic matter (DOM). A larger ozone dose increases ozone consumption prior to 350 milliseconds but decreases the rate of ozone decomposition later on; this effect is predicted by a second-order kinetic model. Transferred Ozone Dose (TOD) is poorly correlated with ozone exposure (= ∫[O3]dt) indicating that TOD is not a suitable parameter for the prediction of disinfection or oxidation in wastewater. HO• concentrations (> 10−10 M) and Rct (=∫[HO•]dt/∫[O3]dt > 10−6) are larger than in most advanced oxidation processes (AOP) in natural waters, but rapidly decrease over time. Rct also decreases with increasing pre-ozonation doses. An increase in pH accelerates ozone decomposition and HO• generation; this effect is predicted by a kinetic model taking into account deprotonation of reactive moieties of the DOM. DOC emerges as a crucial water quality parameter that might be of use to normalize ozone doses when comparing ozonation in different wastewaters. A rapid drop of absorbance in the water matrix—with a maximum between 255–285 nm—is noticeable in the first 350 milliseconds and is directly proportional to ozone consumption. The rate of absorbance decrease at 285 nm is first order with respect to ozone concentration. A kinetic model is introduced to explore ozone decomposition induced by distributions of reactive moieties at sub-stoichiometric ozone concentrations. The model helps visualize and comprehend the operationally-defined “instantaneous ozone demand” observed during ozone batch experiments with DOM-containing waters.

The influence of various factors on aqueous ozone decomposition by granular activated carbons and the development of a mechanistic approach

The decomposition of aqueous ozone in the presence of various granular activated carbons (GAC) was studied. The variables investigated were GAC dose, presence of tert-butyl alcohol (TBA), aqueous pH as well as textural and chemistry surface properties of GAC. All the GAC tested enhanced the rate of ozone decomposition to some extent. From the analysis of experimental results it was deduced that ozone transformation into HO radicals mainly occurred in the liquid bulk through a radical chain reaction initiated by OH − and HO 2 - ions. Hydroperoxide ions arise from the formation of H 2O 2 on surface active sites of GAC and its further dissociation. No direct relationship between textural properties of GAC and the rate of ozone decomposition was found. However, a multiple regression analysis of data revealed that basic and hydroxyl surface oxygen groups (SOG) of GAC favor the kinetics of the ozone decomposition process. It is thought that these groups are the active sites for ozone transformation into H 2O 2. Repeated used of GAC in ozonation experiments resulted in loss of basic and hydroxyl SOG with formation of carboxyl, carbonyl and lactone-type groups. Then, pre-ozonation of GAC reduces its ability to enhance the aqueous ozone transformation into hydroxyl radicals.

Effect of Micro-Mixing Conditions on Predictions of Cryptosporidium Inactivation in an Ozone Contactor

The U.S. EPA is considering segregated flow analysis as an alternative calculation method to determine Cryptosporidium parvum inactivation credit in continuous-flow ozone contactors in drinking water treatment facilities. A computer method is presented in which C. parvum inactivation in the reactive flow segment of a hypothetical ozone contactor with a pre-determined residence time distribution is calculated based on the assumption of either completely segregated or completely micro-mixed flow. In a series of computer simulations using typical ozonation conditions in a water treatment facility, inactivation predicted assuming complete segregation was 0.3 to more than 2.0 log greater than that predicted assuming complete micro-mixing, depending on the level of back-mixing, ozone decomposition rate and inactivation level. CFSTR-in-series model predictions of inactivation were between those of segregated flow analysis and micro-mixed analysis. It was concluded that segregated flow analysis calculations may result in significant over-prediction of C. parvum inactivation credit in ozone contactors and should be used with caution.