Application and Kinetics of Ozone in Food Preservation

Ozone is activated oxygen and it is referred to as a triatomic form of oxygen. It is a natural agent and has a broad antimicrobial property, which together with an oxidation potential, make it an attractive option for the food industry. This article focuses on the use of ozone for preservation of vegetables, fruits and fruit juices, and highlights the inactivation mechanism of microorganisms. The application of ozone in grain storage and the quality of ozone treated grains is discussed, along with the reaction kinetics of ozone in grains.     

Reaction Kinetics of Ozone Gas in Green Gram (Vigna radiate)

This study was carried out to evaluate the reaction kinetics of ozone gas in different height (5 and 10 cm), moisture content (10.6 and 13.4% (d.b.)) and gas flow rate (2 and 4 L/min). The decomposition kinetics obtained was first-order model. As far as the half-life of ozone is considered, the highest value obtained was equivalent to 8.72 min for grains ozonated at 5 cm height, 10.6% (d.b.) moisture content and 2 L/min gas flow rate. In the process of ozone reaction rate in green gram grains, height (p < 0.01) and moisture content (p < 0.01) were found to be the key factor for the effectiveness of ozone fumigation.     

Numerical Simulation and Validation of Mass Transfer Process of Ozone Gas in Rice Grain Bulks

Ozone is a potential alternative to commercial fumigants. The development of ozone fumigation technology for insects control requires a precise prediction of the distribution of introduced ozone gas in grain bulks. Hence, this study was conducted to investigate the mass transfer process of ozone gas in rice grain bulks. Experiments were conducted in a 0.6-m diameter flat-bottom bin filled with rice grains and ozonated using 5 g h^?1 capacity ozone generator. Simulation of transfer process of ozone through the rice grain bulks was conducted using the principle of the law of conservation employing the continuity equation. The experimental data for ozone transfer through connected the column of rice was used to validate the model. The relative error between the actual and predicted ozone concentration for the entire bin geometry was less than 33%. The predictions from the projected model were in accordance with the ozone concentrations obtained from the experimental results.     

A Multi-Channel Stopped-Flow Reactor for Measuring Ozone Decay Rate: Instrument Development and Application

The ability to accurately estimate ozone decay rate through empirical measurement is often fundamental to efficient reactor design and operation in ozone disinfection processes. Variations of ozone decay rates in natural waters and difficulty to estimate them through mechanistic approach highlight the need for reliable methodologies to measure these parameters. In this study, a novel, multi-channel stopped-flow reactor that allows for automatic, continuous analysis of ozone decay kinetics under controlled conditions was developed and verified. Data presented includes instrument design and operation parameter optimization, precision and accuracy verification, and applicability demonstrated with representative synthetic waters.     

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.     

Numerical Simulation and Validation of Ozone Concentration Profile in Green Gram (Vigna radiate) Bulks

The new fumigant ozone offers an alternative to contact insecticides such as phosphine and methyl bromide as a grain fumigant. This study was carried out to test the flow characteristics of ozone from points of release to the available concentration of ozone to kill pests at other areas along the storage bin. A mass transfer model which predicts ozone concentration as a function of time was applied along with continuity equation to simulate the ozone transfer in a storage bin. Ozone exchange rate based on grain bed thickness was taken into account and evaluated using the correlation developed during the experiment. The relative error between the experimental and predicted ozone concentration values for the entire bin geometry was less than 25.7%. Overall, the general trends of measured ozone concentration were compatible with the simulated ones.     

Obtaining Real-Time Kinetic Parameters on Ozone Decay from a Full-Scale Ozone Contactor Using the Axial Dispersion Reactor Model

Ozone decay kinetic parameters, including fast ozone demand ([D]₀), ozone decay rate constant (k_D), and rate constant for ozone reaction with ozone demand (k_R), are required for a numerical simulation targeting the design and operational optimization of an ozone contactor. The kinetic parameters of ozone decay and dispersion number were obtained from a full-scale ozone contactor for the axial dispersion reactor model simulation. The sensitivity analysis showed that the influence of k_R was minor and the constant 13 L mg^?1 min^?1 for k_R was suitable for carrying out simulations for sand-filtered raw water without measuring it. Curve fitting with on-site ozone concentrations and the ADR simulation results using a trial-and-error method could successfully provide kinetic parameters on ozone decay (i.e., k_D and [D]₀). Using these real-time kinetic parameters, we successfully predicted the CT, residual ozone, C. parvum log inactivation, and bromate formation. Compared to a method based on the CSTR in series, this method could provide more accurate CT and residual ozone for an ozone contactor with horizontal meandering flow and low dispersion number.     

Decay of Ozone in Water: A Review

Scientific publications on ozone decay kinetics in water report very wide result variations, depending on a multiplicity of factors, such as ozone concentration, pH, temperature, alkalinity, fluid-dynamic conditions, presence of UV radiations, and concentration of organic and inorganic carbon. This paper intends to provide an engineering-oriented review that summarizes and compares the main results reported in the recent literature so that the condensed information can guide the reader in getting operational indications to assist applications and research.     

Kinetics of Heterogeneous Catalytic Ozone Decomposition in Water on an Activated Carbon

Ozone decomposition in water in the presence of an activated carbon has been studied. Variables investigated were agitation speed, carbon particle size, temperature and pH. In all cases, the presence of activated carbon improved the ozone decomposition rate. Between pH 2 and 7 the ozone decomposition rate due to both the homogeneous and heterogeneous mechanisms hardly varied while a significant increase was noticed with increasing pH. A kinetic study based on a Langmuir-Hinselwood type mechanism for the heterogeneous surface reaction was undertaken. According to this mechanism the heterogeneous ozone decomposition kinetics can be simplified to follow a first order process. Fit of experimental results to the kinetic equations derived from the mechanism allowed for the determination of the apparent first order rate constants of the ozone surface heterogeneous reaction and adsorption equilibrium constants.     

苯的气相O3氧化动力学

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Kinetics of Estrone Ozone/Hydrogen Peroxide Advanced Oxidation Treatment

Ozone/hydrogen peroxide batch treatment was utilized to study the degradation of the steroidal hormone estrone (E1). The competition kinetics method was used to determine the rate constants of reaction for direct ozone and E1, and for hydroxyl radicals and E1 at three pH levels (4, 7, and 8.5), three different molar O₃/H₂O₂ ratios (1:2, 2:1, and 4:1) and a temperature about 20°C. The average second-order rate constants for direct ozone-E1 reaction were determined as 6.2?×?10³?±?3.2?×?10³ M^?1s^?1, 9.4?×?10⁵?±?2.7?×?10⁵ M^?1s^?1, and 2.1?×?10⁷?±?3.1?×?10⁶ M^?1s^?1 at pH 4, 7, and 8.5, respectively. It was found that pH had the greatest influence on the reaction rate, whereas O₃/H₂O₂ ratio was found to be slightly statistically significant. For the hydroxyl radical-E1 reaction, apparent rate constants ranged from 1.1?×?10¹⁰ M^?1s^?1 to 7.0?×?10¹⁰ M^?1s^?1 with an average value of 2.6?×?10¹⁰ M^?1s^?1. Overall, O₃/H₂O₂ is shown to be an effective treatment for E1.     

Theoretical Aspects Of The Kinetics Of Competitive Ozone Reactions In Water

Competition of direct and decomposition reactions that ozone can undergo in water when a given compound is present is studied according to concepts of absorption theories. The importance of different parameters, such as pH, rate constants, mass transfer coefficients and concentration of reactants, is considered to clarify which reaction prevails. Parameters like Hatta numbers (film theory) or diffusion and reaction times (surface renewal theories) are key factors to check the competition of these reactions.     

Investigation of Ozone Loss Rate Influenced by the Surface Material of a Discharge Chamber

Decay characteristics of ozone concentration in oxygen in a chamber with three types of wall material (stainless steel, copper, and aluminum) are measured using the 254 nm photoabsorption method. Effective lifetimes of ozone are estimated from decay curves of ozone concentration. These values depend on the wall material: They are largest for stainless steel and smallest for aluminum. The relationship between effective lifetime and gas pressure is investigated precisely to determine three values. The equivalent diffusion coefficient of ozone in oxygen and the reflection coefficient of ozone at the wall correspond to the loss rate of ozone at the wall. The collisional loss (quenching) rate coefficient of ozone in oxygen is also determined.     

Multistage Decomposition Kinetics of Ozone In Dilute Aqueous Solutions

AbstractDecomposition of ozone in dilute aqueous solutions was found to be a complex process kinetically. Initial ozone dose-time had a significant impact on reaction order. Solutions dosed initially for less than one minute displayed uniform second-order kinetics. For doses applied over 5 and 15 min periods at a pH -2, reaction order changed from 2 to 1 to 0 as ozone decomposition progressed. At a pH of 6.65, the transition was from a reaction order of 2.5-3 to 2. This behavior has been ascribed to the effect of accumulated ozone decomposition products on the decomposition process.     

Wastewater Disinfection by Ozone: Influence of Water Quality and Kinetics Modeling

Wastewater disinfection by ozone was investigated at pilot scale on different effluents. The organic matter (COD and TOC) was shown to have the biggest influence on the ozone demand of the effluents. Disinfection of fecal indicators could be modeled as the reaction on a double population. The presence of more resistant microorganisms results in the need for higher treatment doses and a tertiary filtration when the effluent has to meet the stringent Title 22 standard. Eventually, the high virucidal power of ozone makes it very attractive when viruses are targeted.     

Absorption Kinetics of Ozone in Aqueous Solutions of Malathion

A laboratory study on the absorption of ozone in aqueous solutions of malathion has been conducted, using a semicontinuous tank reactor. Liquid mass transfer coefficients, specific interfacial areas and the stoichiometric ratio between ozone and malathion were determined previously. Applying the film mass transfer theory to the experimental data, orders of reaction and kinetic rate constants as a function of temperature and pH have been deduced. The results confirm that the process takes place in the slow reaction regime.     

Mechanism and Kinetic Study on Elemental Mercury Oxidation in Flue Gas by Ozone Injection

The mechanism and kinetics of the elemental Hg oxidation in flue gas by ozone injection are investigated in detail by using quantum chemistry, kinetic simulation and experimental research. The reaction processes, activation energies and kinetic parameters are calculated and analyzed by quantum chemistry. From the comparison of activation energies, the Hg⁰ oxidation ability of oxidizing radicals is that: NO₃>O₃>NO₂. The calculated results are in good agreement with literature experimental results. The calculated kinetic parameters are employed for kinetic simulation. The results of kinetic simulation are in good agreement with the experimental results. Results show that, the Hg⁰ oxidization increases linearly when the mole ratio of O₃/NO becomes larger or the reaction temperature becomes higher. The reaction Hg+NO₃ = NO₂+HgO is the key elemental reaction and the concentration of NO₃ is the most important factor for affecting Hg⁰ oxidation.     

Kinetic and Energetic Analysis of the Ozone Synthesis Process in Oxygen-fed DBD Reactor. Effect of Power Density,Gap Volume and Residence Time

The analysis of measurements of ozone synthesis process rate in pure oxygen with the use of the unique plasma reactor was presented. The kinetic measurements have been made using the integral and the differential method. The effect of energy stream delivered (i.e., power) and gas residence time in a discharge gap on the rate and energy efficiency of the process carried out in dielectric barrier discharge was shown. It was presented how the process rate and energy efficiency change along a discharge gap and the way they depend on both power density and a residence time.     

Toward Elucidating Mechanism And Kinetics Of Ozone Decolorization And Dechlorination Of Pulp Mill Effluents

This study elucidated the mechanism and kinetics of ozone decolorization and dechlorination of composite wastewaters obtained from various pulp mill effluents by means of ultrafiltration and freeze drying. These raw samples had similar initial true color but varied color intensity (C.I.) and biodegradability. Both raw and ozone-treated samples were separated into four components to assess the effects of ozonation on individual components. Analytical HPSEC was employed to determine the changes induced by ozonation in molecular weight distribution of lignins and their derivatives.     

Ozone Concentration and Temperature Effects on Disinfection Kinetics

The cysts of the nonpathogenic soil and water amoeba, Naegleriagruberi strain (NEG), were inactivated using aqueous ozone in batch reactors at controlled temperatures (5–30°C) at pH 7. The semi-log plots of survival ratio vs. time consisted of an initial shoulder followed by a linear portion. The log-log plots of ozone concentration against time for 99 percent inactivation were essentially linear. The relationship between the overall inactivation rate and absolute temperature was well expressed by the Arrhenius theory. An empirical relationship was developed between the extent of cyst inactivation, ozone dose, temperature, and contact time.