Ozone In Aqueous Phase Research Articles

Ozone micro-nano bubble water preserves the quality of postharvest parsley

The production and use of ozone micro-nano bubble water (O3-MNBW) is an innovative technology that prolongs the reactivity of aqueous-phase ozone and maintains the freshness and quality of fruits and vegetables by removing pesticides, mycotoxins, and other contaminants. The quality of parsley treated with different concentrations of O3-MNBW was investigated during storage at 20 ℃ for 5 d, and found that a ten-minute exposure of parsley to 2.5 mg·L−1 O3-MNBW effectively preserved the sensory quality of parsley, and resulted in lower weight loss, respiration rate, ethylene production, MDA levels, and a higher level of firmness, vitamin C, and chlorophyll content, relative to untreated parsley. The O3-MNBW treatment also increased the level of total phenolics and flavonoids, enhanced peroxidase and ascorbate peroxidase activity, and inhibited polyphenol oxidase activity in stored parsley. Five volatile signatures identified using an electronic nose (W1W, sulfur-compounds; W2S, ethanol; W2W, aromatic- and organic- sulfur compounds; W5S, oxynitride; W1S, methane) exhibited a significant decrease in response to the O3-MNBW treatment. A total of 24 major volatiles were identified. A metabolomic analysis identified 365 differentially abundant metabolites (DMs). Among them, 30 and 19 DMs were associated with characteristic volatile flavor substance metabolism in O3-MNBW and control groups, respectively. The O3-MNBW treatment increased the abundance of most DMs related to flavor metabolism and reduced the level of naringin and apigenin. Our results provide insight into the mechanisms that are regulated in response to the exposure of parsley to O3-MNBW, and confirmed the potential use of O3-MNBW as a preservation technology.

Changes on epicuticular waxes and colour induced by ozone in blueberries (Vaccinium corymbosum L. ‘O’ Neal’)

The aim of the present work was to assess the effect of ozone in aqueous phase (5.1 mg L−1 of ozone for 10 min) on blueberry surface by analysing the changes in epicuticular waxes (EW) by attenuated total reflectance-Fourier transformed infrared (ATR-FTIR) spectroscopy during storage at 4 °C for 15 d. Besides, colour was studied as a critical quality index for consumers. Ozone treated and controls (untreated fresh fruit and washed fruit without ozone) samples were considered. Among them, three subsets of spectra were acquired: whole fruit, fruit without EW -removed by solvent- and isolated EW. The differences among these sample subsets were much higher than those produced by treatments or storage time as revealed by PCA analysis. Infrared analysis revealed that ozone per se produced chemical modifications on EW of intact fruit, as new bands appeared (such as stretch of CO at 1701 cm-1, from the oxidation of alcohols to carbonyls) and others shifted. However, no significant changes were observed in colour between treatments or time, showing that neither the alterations in EW nor their partial removal or changes in epidermis ultrastructure (evaluated by microscopy) affected this quality parameter. Further studies are needed to deeply understand the extent of the effect of the chemical alterations produced directly by ozone (and not by the process) in line with consumers demands of minimal processed and extended shelf-life products.

Freshness Maintenance of Blueberries (Vaccinium corymbosum L.) During Postharvest Using Ozone in Aqueous Phase: Microbiological, Structure, and Mechanical issues

The effect of aqueous ozone at different doses on fungal incidence, microstructure, mechanical properties, and weight loss of blueberry fruit (Vaccinium corymbosum, cv. O’Neal) throughout 20 days of storage at 4 ± 1 °C was studied. Fruits were exposed to 10 and 18 mg O3 L-1 in a bubble column for different periods of time ranging from 10 to 30 min. Native mycobiota and Botrytis cinerea incidences were reduced by ozone exposure. After 15 days of storage, exposure to 18 mg O3 L-1 for 10 and 20 min reduced the percentage of infected fruit in ~ 34 and 40 %, respectively, when compared with untreated blueberries. Slight but no significant differences among ozone treatments were observed for native mycobiota and B. cinerea incidence. Stiffness, rupture force, and mechanical work required to break the fruit epidermis were not significantly affected by ozone treatments. The effect of ozone treatment on weight loss of blueberries was dose-dependent and was partially correlated with microstructural changes induced by ozone: disruptions in outer tangential and epidermal cell walls and alteration of the cuticle. Exposure times beyond 15 min significantly increased weight loss and did not achieve greater fungal inhibition with respect to 10- and 15-min ozonized fruit. Thus, the ozone dose to be selected would be limited by the negative effect on weight loss. Exposure to 18 mg O3 L-1 for 10 min would be the most suitable treatment to reduce fungal decay without causing an excessive loss of weight along cold storage.

Stabilization and prolonged reactivity of aqueous-phase ozone with cyclodextrin

Recalcitrant organic groundwater contaminants, such as 1,4-dioxane, may require strong oxidants for complete mineralization. However, their efficacy for in-situ chemical oxidation (ISCO) is limited by oxidant decay and reactivity. Hydroxypropyl-β-cyclodextrin (HPβCD) was examined for its ability to stabilize aqueous-phase ozone (O3) and prolong oxidation potential through inclusion complex formation. Partial transformation of HPβCD by O3 was observed. However, HPβCD proved to be sufficiently recalcitrant, because it was only partially degraded in the presence of O3. The formation of a HPβCD:O3 clathrate complex was observed, which stabilized decay of O3. The presence of HPβCD increased the O3 half-life linearly with increasing HPβCD:O3 molar ratio. The O3 half-life in solutions increased by as much as 40-fold relative to HPβCD-free O3 solutions. Observed O3 release from HPβCD and indigo oxidation confirmed that the formation of the inclusion complex is reversible. This proof-of-concept study demonstrates that HPβCD can complex O3 while preserving its reactivity. These results suggest that the use of clathrate stabilizers, such as HPβCD, can support the development of a facilitated-transport enabled ISCO for the O3 treatment of groundwater contaminated with recalcitrant compounds.

Ozone correlates with antibacterial effects from indirect air dielectric barrier discharge treatment of water

Ambient-condition air plasma produced by indirect dielectric barrier discharges can rapidly disinfect aqueous solutions contaminated with bacteria and other microorganisms. In this study, we measured key chemical species in plasma-treated aqueous solutions and the associated antimicrobial effect for varying discharge power densities, exposure times, and buffer components in the aqueous medium. The aqueous chemistry corresponded to air plasma chemistry, and we observed a transition in composition from ozone mode to nitrogen oxides mode as the discharge power density increased. The inactivation of E. coli correlates well with the aqueous-phase ozone concentration, suggesting that ozone is the dominant species for bacterial inactivation under these conditions. Published values of ozone-water antibacterial inactivation kinetics as a function of the product of ozone concentration and contact time are consistent with our results. In contrast to earlier studies of plasma-treated water disinfection, ozone-dependent bacterial inactivation does not require acidification of the aqueous medium and the bacterial inactivation rates are far higher. Furthermore, we show that the antimicrobial effect depends strongly on gas-liquid mixing following plasma treatment, apparently because of the low solubility of ozone and the slow rate of mass transfer from the gas phase to the liquid. Without thorough mixing of the ozone-containing gas and bacteria-laden water, the antimicrobial effect will not be observed. However, it should be recognized that the complexity of atmospheric pressure plasma devices, and their sensitivity to subtle differences in design and operation, can lead to different results with different mechanisms.

Solubilization of Multi Walled Carbon Nanotubes Under a Facile and Mild Condition

Multi-walled carbon nanotubes (MWCNTs) functionalized with amino groups was prepared via chemical modification of carboxyl groups introduced on the carbon nanotube surfaces. Oxidation of MWCNTs was performed with ozone in aqueous phase and amidation of generated carboxylic groups, was occurred with amines in the presence of HATU as a coupling agent. Obtained functionalized MWCNTs are soluble in many common organic solvents. The functionalized MWCNTs were characterized in detail using FTIR-ATR, Raman CHN and SEM methods.

Hydrophilicity modification of polypropylene microfiltration membrane by ozonation

To improve surface hydrophilicity and to reduce fouling, commercial polypropylene microfiltration membranes were ozonated to generate peroxides as grafting sites for hydrophilic monomers. Ozonation was conducted in aqueous and gaseous phases, respectively. In both phases, the amount of peroxides increased with the ozonation time. A novel way to enhance the generation of peroxides was tested, i.e., adding homogeneous catalyst, CuSO4, to aqueous ozonation. Results showed that with an optimum dose of 0.05g/L of CuSO4, the peroxides generated were 18.2% more than that by the non-catalyzed ozonation in aqueous phase. It was also confirmed by scavenger tests that during the aqueous ozonation both molecular ozone and free radicals contributed to the oxidation of the membranes, the latter was formed from the self-decomposition of ozone in water. Graft polymerization was also conducted after the generation of peroxides. A hydrophilic monomer, acrylic amide, was graft polymerized onto the membrane surface. The successful grafting of acrylic amide was confirmed by the formation of new peaks corresponding to amide groups in FTIR spectra. Results of contact angle measurements and filtration tests indicated that aqueous ozonation was more effective than its gaseous counterpart in terms of hydrophilicity improvement. In addition, the XRD analysis revealed that the ratio of the membrane surface crystallinity to amorphousity was changed by both ozonation and graft polymerization. Results of SEM scanning also showed changes in membrane surfaces after modification.

Impact of Food Disinfection on Beneficial Biothiol Contents in Strawberry

In this study, the impact of four food disinfectants including hydrogen peroxide, free chlorine, and gaseous- and aqueous-phase ozone with industrial doses on the concentration of biothiol compounds gamma-glutamylcysteinylglycine (GSH) and cystein (CYS) in strawberry was investigated for 1, 5, 15, 30, and 60 or 120 min. Additionally, the amount of oxidized glutathione (GSSG) was analyzed for calculation of the GSH/GSSG ratio as an indicator of oxidative stress. After this treatment, thiol contents of strawberry samples were examined using high-performance liquid chromatography (HPLC) technique. According to the results of measurements, free chlorine treatment for only 60 min significantly decreased CYS content in strawberry (p < 0.05). A significant decline in the GSH/GSSG ratio was also observed when H2O2 was applied for all time intervals except for 1 min (p < 0.05). However, aqueous-phase ozone treatment did not significantly affect the thiol levels (p < 0.05). In conclusion, this study may provide optimum disinfection methods for strawberry to minimize loss of beneficial biothiols.

Use of an ejector for phenol containing water treatment by ozonation

Mass transfer of ozone in aqueous phase is a major aspect of ozonation and advanced oxidation processes. The aim of this study is to compare the performances of an ejector with those of a more traditional gas/liquid contactor: a bubble column. The hydrodynamic study showed that the volumetric mass transfer coefficient of the ejector ( K L a = 7.2 × 10 −2 to 1.35 × 10 −1 s −1) was greater than that of the bubble column's ( K L a = 1.5 × 10 −2 to 2.8 × 10 −2 s −1). Very important differences in the values of the residence time and gas retention rate were also observed. A study of phenol degradation was performed. Due to its specifications the ejector is very efficient when the kinetics of reaction is fast (diffusion-controlled regime). In both semi-batch and open circuits, the phenol was quickly eliminated and the ozone transfer was very high (up to 98%). It is to be noted that these results were obtained for a processing time of approximately 1 s.

Impact of Food Disinfection on Beneficial Biothiol Contents in Vegetables

In this work we investigated the impact of food disinfection on the beneficial biothiol contents in a suite of vegetables consumed daily, including spinach, green bean, asparagus, cucumber, and red pepper. Four disinfection technologies commonly studied and/or used in food processing and preservation, including hydrogen peroxide, free chlorine, and gaseous- and aqueous-phase ozone, were examined with common dosages and contact times. Results indicate that the common disinfection technologies may result in significant loss of beneficial biothiols in vegetables which are essentially important to human health. For example, as much as 70% of biothiols were lost when spinach was treated with hydrogen peroxide (5.0 wt %) for 30 min. Approximately 48-54% of biothiols were destroyed by free chlorine and gaseous- and aqueous-phase ozone under typical contacting conditions. In red pepper, about 60-71% of reduced glutathione was oxidized by the disinfectants. The potential decrease in biothiols during disinfection was dependent upon the biothiol type, the disinfectant, and the vegetable. The effectiveness of total bacterial inactivation by the four disinfection technologies was concurrently evaluated. Results show that free chlorine is most effective, achieving disinfection efficiencies of greater than 4 log for all study vegetables. This study may provide important information for the food industry to design optimum contacting methods for vegetables to simultaneously achieve sufficient bacterial disinfection while minimizing loss of beneficial biothiols.

Development and Experimental Validation of the Model of a Tall, Continuous-Flow, Countercurrent, Bubble-Type Ozone Contactor

The objective of this study was the development of a fully mechanistic model for the description of ozone mass transfer from gaseous to aqueous phase and the aqueous-phase ozone decomposition in a continuous-flow, countercurrent, tall, bubble-type ozone contactor. The developed model was used to simulate the effects of changes in aqueous-phase pH and scavenger concentration on ozone mass transfer and decomposition. Simulation results could be adequately explained based on the current understanding of ozone mass transfer and aqueous ozone chemistry. Experimental determination of steady-state aqueous ozone profiles and corresponding effluent gaseous ozone concentrations in a tall contactor was made at various influent aqueous pH's and scavenger concentrations using an experimental contactor fabricated for this purpose. Comparison of the simulated and experimentally obtained aqueous ozone profiles showed adequate agreement. However, the experimentally obtained effluent gaseous ozone concentrations were consistently lower than the corresponding simulated values by approximately 13%. This discrepancy is probably due to gas-phase ozone decomposition occurring inside the reactor and in the headspace above the reactor.

Ozonation in aqueous phase of sodium dodecylbenzenesulphonate in the presence of powdered activated carbon

Ozonation in aqueous phase of sodium dodecylbenzenesulphonate in the presence of powdered activated carbon

Ozonalytic kinetic order of dye decoloration in aqueous solution

The intrinsic kinetic order of reaction between a dye (Acid Blue 9) and dissolved ozone in aqueous phase was measured by a pulse-ejection microreactor (PEMR) in this research. The reaction orders and reaction rate constants were evaluated by the variation of initial slope method, the half-life method, and the general order equation. Results of this study indicated that the commonly literature-cited pseudo-first-order may not be suitable for all ozonation conditions. The pseudo-first-order was only valid with an ozone to dye molar ratio ( Z) between 5.57 and 9.31. When the value of Z increased from 13.91 to 30.83, the reaction order increased rapidly from 1.03 to 1.76. On the other hand, when the value of Z was smaller than 1.74, the reaction order seemed closer to zero order. Furthermore, the reaction order may not be constant throughout the treatment process. It might vary with variation of ozone to dye ratio as the reaction is proceeding.

Effect of the ozone–carbon reaction on the catalytic activity of activated carbon during the degradation of 1,3,6-naphthalenetrisulphonic acid with ozone

The present work investigated the evolution of catalytic activity of activated carbon in 1,3,6-naphthalenetrisulphonic acid (NTS) ozonation in aqueous phase. Activated carbons pre-treated with ozone showed a reduction in NTS oxidation rate and efficacy of TOC removal that increased with ozone exposure time. The ozone treatment increased the number of surface oxygenated (electron-withdrawing) groups on the carbon, therefore reducing its basic character and its reductive properties. This effect reduced the reactivity of the activated carbon to ozone and, therefore, the extent of the ozone decomposition into highly oxidative species.

Degradation of naphthalenesulfonic acids by oxidation with ozone in aqueous phase

Sulfonic aromatic compounds are widely used in the textile industry for the synthesis of azo dyes. The presence of the sulfonic group endows these compounds with high water-solubility and resistance to biological treatment. The present work analysed the efficacy of oxidation with ozone in the treatment of waters containing naphthalene-1-sulfonic acid, naphthalene-1,5-disulfonic acid and naphthalene-1,3,6-trisulfonic acid. The reactivity to ozone significantly decreased with an increase in the number of sulfonic groups in the aromatic ring, and naphthalene-1,3,6-trisulfonic acid showed the lowest reaction rate. The stoichiometry of the direct ozonization reaction was around one mole of sulfonic acid per mole of ozone in all cases. The activation energy value of the direct ozonization reaction was very similar in all studied cases (37–42 kJ mol−1). The contribution of the direct reaction to the global oxidation at pH 2 was observed to decrease with more sulfonic groups in the aromatic ring, from a contribution of 69% for naphthalene-1-sulfonic acid to around 20% for naphthalene-1,3,6-trisulfonic acid. The radical reaction rate constant was found to be of the order of 109×M−1 s−1 in all cases, although it showed a slight reduction as the number of sulfonic groups in the aromatic ring increased. A follow-up study of the oxidation products of each sulfonic aromatic acid revealed the presence of highly oxidized organic acids and sulfate ions. A theoretical study of the electronic density at the bond critical point showed that double bonds with highest electron density in the three acids are in positions 1–2, 3–4, 5–6 and 7–8. These bonds are initially attacked by ozone via 1,3-dipolar cycloaddition.

Oxidative Degradation of 2,4,6-Trinitrotoluene by Ozone in an Electrohydraulic Discharge Reactor

The electrohydraulic discharge process in the presence of ozone has been used to investigate the rapid degradation and mineralization of aqueous 2,4,6-trinitrotoluene (TNT) solutions that were directly exposed to high-energy electrical discharges between two submerged electrodes. The 165 μM solutions of TNT were completely (>90%) mineralized over the course of 300 electrical discharges of 7 kJ each. The kinetics of TNT degradation were investigated as a function of the aqueous-phase ozone concentration, pH, discharge energy, and electrode gap length. The rate of TNT degradation increases with an increase in aqueous-phase ozone concentration of up to 150 μM, an increase in pH from 3.0 to 7.9, an increase in discharge energy from 5.5 to 9 kJ, and a decrease in the electrode gap length from 10 to 6 mm. The rapid rates of mineralization (e.g. 12 ms) are attributed to the action of UV light in the reactor chamber on O3 to produce a high flux of hydroxyl radicals per discharge (1 μM discharge-1). The primary reaction intermediates were 2,4,6-trinitrobenzaldehyde and trinitrobenzene.

Mathematical Interpretation of Aqueous‐phase Ozone Decomposition Rates

Experimental data and hypothetical process behavior are analyzed in an attempt to elucidate the kinetics of aqueous phase ozone decomposition reactions. Three commonly accepted mathematical techniques (integral, differential, van't Hoff) for the analysis of rate data are employed. The results indicate that when single‐order dependencies are used to model autocatalytic reactions, timevariable behavior of the rate constant and order is exhibited. This can partially explain existing controversy within the scientific community regarding the apparent order of ozone decomposition reactions. A simple autocatalytic rate expression is developed that accurately describes the decomposition rate data. The conclusions from the work have implications not only for development of an understanding of ozone decomposition kinetics, but for the analysis of rate data derived from nonelementary reactions in general.