Moles Of Ozone Research Articles

Assessment of an hybrid process coupling ozonation and anodic oxidation in a monophasic configuration

This prospective study assessed a hybrid process that combines ozonation with anodic oxidation (AO/O3) with two boron-doped diamond (BDD) electrodes to treat a model aqueous solution containing 30 ppm of alachlor at pH 5 in a phosphate buffer. An innovative monophasic configuration, operated batch-wise, in which an ozone-stock solution was injected at t0 in the electrochemical reactor, was proposed in order to avoid introduction of ozone-enriched gas bubbles. The alachlor parent molecule was almost entirely degraded within around 150 min of reaction time by anodic oxidation alone, whatever the applied current intensity (200, 500 and 800 mA). The mineralization efficiency varied from 50 % at 200 mA to 80 % at 800 mA after 120 min. The results emphasized that the anodic oxidation was a diffusion-controlled process. Addition of ozone at a low ozone dose of 1.9–2.3 mol of ozone per mol of alachlor allowed to decrease the ozone half-life time 2.7 times with the hybrid process compared to ozonation alone. This faster ozone consumption was concomitant with an enhanced alachlor degradation rate, with a corresponding half-life time around two-times lower. However, owing to the low ozone dose applied and the short ozone lifetime in solution (around 25–30 min), similar mineralization efficiencies were noticed for both AO/O3 and AO processes. Thus, the application of pulse ozone-stock solution re-injections every 20 min to prolong the ozone exposure was assessed to overcome this limitation. However, the effect on the mineralization rate remained small, even if it allows to enhance even more the alachlor parent molecule degradation rate. The low influence of the hybrid process on the mineralization rate was attributed to the production of aliphatic fatty acids by-products that are poorly reactive with hydroxyl radicals, and whose the degradation by AO is the rate limiting step.

Ozonation of municipal wastewater effluent containing metal sulfides and metal complexes: Kinetics and mechanisms

Ozonation can be applied to mitigate the discharge of organic micropollutants from municipal wastewater treatment plants (WWTPs) to the aquatic environment. The toxicity of metals also present in WWTP effluents strongly depends on their speciation. Therefore, knowledge on the change of the metal speciation during ozonation of a WWTP effluent is essential to assess possible negative impacts. The kinetics and the stoichiometries of the reactions of ozone with three metal sulfides (ZnS, CuS and CdS) and metal-ethylenediaminetetraacetate (EDTA)/nitriloriacetic acid (NTA) complexes of Cu(II), Cd(II), Ni(II), Zn(II), Mg(II) and Pb(II) were investigated. With a stoichiometric factor of 2.6–3.9 moles of ozone per mole of sulfide and apparent second-order rate constants at pH 8 > 104 M−1 s−1, a complete oxidation of the sulfides and a concomitant release of the respective metals is expected during ozonation of a WWTP effluent for enhanced micropollutant abatement. The apparent second-order rate constants at pH 8 for the reactions of metal-EDTA complexes with ozone ranged from 42 M−1s−1 to 2.0 × 104 M−1s−1 and increased in the order Cd(II) < Cu(II) < Mg(II) < Ni(II) < Zn(II). Approximately 40% of Cd(II)-EDTA spiked to a WWTP effluent was oxidized at typical specific ozone doses of 0.5–0.7 gO3/gDOC. For the other metal-EDTA complexes a significantly higher fraction was oxidized. The bioavailable fraction determined by the diffusive-gradient thin films (DGT) method in the WWTP effluent increased during ozonation, due to the oxidative release of the metal ions. Algal toxicity (chlamynomodas reinhardtii) tests with CuS/CdS spiked WWTP effluent revealed a high tolerance toward Cu and Cd in the respective media. A toxic response was only observed at Cu concentrations above 10 μM, which is above typical WWTP effluent concentrations. Biological post-treatment after ozonation generally reduced the bioavailability of the metals, which resulted in a lower toxicity. Therefore, the biological post-treatment serves as an additional barrier to protect the downstream ecology of receiving waters.

Degradation of sulfamethoxazole using ozone and chlorine dioxide - Compound-specific stable isotope analysis, transformation product analysis and mechanistic aspects

The sulfonamide antibiotic sulfamethoxazole (SMX) is a widely detected micropollutant in surface and groundwaters. Oxidative treatment with e.g. ozone or chlorine dioxide is regularly applied for disinfection purposes at the same time exhibiting a high potential for removal of micropollutants. Especially for nitrogen containing compounds such as SMX, the related reaction mechanisms are largely unknown. In this study, we systematically investigated reaction stoichiometry, product formation and reaction mechanisms in reactions of SMX with ozone and chlorine dioxide. To this end, the neutral and anionic SMX species, which may occur at typical pH-values of water treatment were studied. Two moles of chlorine dioxide and approximately three moles of ozone were consumed per mole SMX degraded. Oxidation of SMX with ozone and chlorine dioxide leads in both cases to six major transformation products (TPs) as revealed by high-resolution mass spectrometry (HRMS). Tentatively formulated TP structures from other studies could partly be confirmed by compound-specific stable isotope analysis (CSIA). However, for one TP, a hydroxylated SMX, it was not possible by HRMS alone to identify whether hydroxylation occurred at the aromatic ring, as suggested in literature before, or at the anilinic nitrogen. By means of CSIA and an analytical standard it was possible to identify sulfamethoxazole hydroxylamine unequivocally as one of the TPs of the reaction of SMX with ozone as well as with chlorine dioxide. H-abstraction and electron transfer at the anilinic nitrogen are suggested as likely initial reactions of ozone and chlorine dioxide, respectively, leading to its formation. Oxidation of anionic SMX with ozone did not show any significant isotopic fractionation whereas the other reactions studied resulted in a significant carbon isotope fractionation.

Ozonation of Sulfur Dioxide in Sulphuric Acid Solution

In this study, the oxidation rates of sulfur dioxide (SO2) in sulphuric acid solution by ozone and oxygen were compared, and the oxidation mechanism of ozone on SO2 was investigated. The results showed that the oxidation-reduction potential of the acidic solution was enhanced, the transformation rate of sulfuric acid to sulphuric acid was increased and the absorption driving force was improved in the presence of ozone. By comparing the amount of sulfate ions measured in the experiments and the theoretical amount of sulfate ions calculated from the amount of ozone consumed in the reaction, it can be confirmed that oxygen free radicals from dissociation of ozone are reactive as an efficient oxidant and oxygen from ozone generator participates in the reaction with SO2. 0.602 mol of effective oxygen was introduced into the reaction by one mole of ozone in 10.15 min at sulphuric acid concentration of 3% (by mass), SO2 concentration of 1.33% (by volume) and oxygen flow rate of 1.5 L·min−1 from ozone generator.

Homogeneous oxidation of hydrogen selenide with ozone in an argon-oxygen medium

Homogeneous oxidation of hydrogen selenide with ozone present in deficiency was studied. One of the reaction products is elemental selenium Se8, which can be formed by multistep radical-chain polycondensation of hydrogen selenide. One mole of ozone is consumed per mole of hydrogen selenide. The observed rate constant of the reaction of hydrogen selenide with ozone at 20 ± 1°C is no less than (1.9 ± 0.2) × 105 l mol−1 s−1.

Modeling of the Reaction of Ozone with Dehydroabietic Acid

The oxidation of dehydroabietic acid (DHA) by ozone in solution was examined using a spectrophotometric method in combination with the computer program MATLAB to empirically fit the data. The reaction rate constant between the two compounds was determined to be 1.1×102 L/mol·s at 23 ºC. This value is in line with previous work on multiply-substituted aromatic compounds. The stoichiometric ratio of the ozone/DHA reaction was found to be 3 moles of ozone per mole of DHA consumed. Furthermore, a stoichiometric ratio of 3:1 H2O2 produced:DHA oxidized was determined to have the best fit with experimentally derived results.

Ozonation of 2,6-, 3,4-, and 3,5-Dichlorophenol Isomers within Aqueous Solutions

The kinetics and mechanisms associated with the ozonation of 2,6-, 3,4-, and 3,5-dichlorophenols (DCPs) in aqueous solutions were studied. It was found that 2 moles of ozone are required for the initial degradation of 1 mole of DCP. The overall reaction between ozone and a DCP was found to be second order (first order per reactant). The overall reaction rate constants of all three DCPs increased with pH because of increased dissociation of the dichlorophenol molecules to dichlorophenoxide ions. Due to its high dissociation constant, 2,6-DCP is most reactive of the three with ozone with the overall reaction rate constants varying from 1.31×105 to 3.36×105M-1 s-1 within the pH range of 2.0–4.0. Various chlorobenzenediols, chlorocyclohexadienediones, ketones, esters, and carboxylic acids were identified as intermediate and final ozonation products using gas chromatography/mass spectrometry analysis. The initial electrophilic addition of ozone at the ortho and para positions of the molecular and ionic forms i...

Ozonation characteristics of bisphenol a in water

Ozonation characteristics of bisphenol A were investigated as a function of gaseous ozone dose, initial concentration of bisphenol A, pH, radical scavenger (tert‐butanol), and radical initiator (hydrogen peroxide). The ozonation led to a complete removal of bisphenol A in water within a certain period of time. The overall rate of the ozonation linearly increased with the ozone dose. The stoichiometry in the ozonation of bisphenol A was found to be 1.5 ‐ 1.8 mole of ozone per mole of bisphenol A. The direct reaction rate constants were 1.3 × 104 M‐1s‐1 for bisphenol A (at pH = 2) and 1.6 × 109 M‐1s‐1 for dissociated bisphenol A (at pH = 12). Bisphenol A degraded via the direct reaction with molecular ozone in the pH range from 2 to 12. Degradation by OH radical was minor even at pH = 12. The overall degradation rate in heterogeneous conditions was independent of pH as it was limited by ozone mass transfer rate. Use of hydrogen peroxide did not alter the main degradation route and the molecular ozone remained a principal oxidant as a substantial portion of the OH radical is scavenged by hydrogen peroxide. Effective ozone mass transfer may appear essential to enhance the ozonation kinetics of bisphenol A.

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.

Oxidation of diethylene glycol with ozone and modified Fenton processes

This paper describes a study of oxidation of diethylene glycol (DEG) by ozone and modified Fenton process (hydrogen peroxide and ferric salt mixture) in aqueous solution. Both oxidation processes were able to oxidize relatively high concentrations of DEG effectively. DEG reacted primarily through hydroxyl radical produced by decomposition of ozone, and about 3 mol of ozone were consumed per mole of DEG removed during the process. For modified Fenton oxidation, stepwise addition of hydrogen peroxide (H 2O 2) and ferric salt (Fe(III)) resulted in much higher removal of DEG than one-time pulse addition of the chemicals. The extent of DEG removal increased with increasing concentrations of both H 2O 2 and Fe(III). Oxidant consumption per mole of DEG oxidized was one order of magnitude higher for hydrogen peroxide than those observed for ozone. Overall, ozonation produced higher concentrations of aldehydes, and modified Fenton treatment produced higher concentrations of carboxylic acids for the same levels of DEG oxidation. The major products of ozonation were glycolaldehyde, glyoxal, formaldehyde, acetaldehyde, and acetic, formic, pyruvic, oxalic and glyoxalic acids. The major products of modified Fenton oxidation were formaldehyde, and formic and acetic acids.

Isolation and chemical--structural identification of a novel aromatic amine mutagen in an ozonized solution of m-phenylenediamine.

The mutagenicity of a m-phenylenediamine (m-PD) solution was markedly enhanced by oxidation with ozone. The ethyl acetate extracts from a m-PD solution ozonized at pH 10.7 were fractionated by normal-phase and reversed-phase column chromatography to isolate mutagens by monitoring mutagenic activities on Salmonella typhimurium TA98 in the presence of a mammalian metabolic activation system (S9 mix). From fraction 5-3-2, which exhibited the strongest mutagenicity (308000 revertants/mg), a major mutagenic compound was isolated. On the basis of the high-resolution EI-mass, (1)H NMR and (13)C NMR spectral, and X-ray crystallography data, the structure of this compound was determined to be 2-amino-5-[(3-aminophenyl)amino]-4-[(3-aminophenyl)imino]-2, 5-cyclohexadien-1-one (PDT-1), which is a novel compound. PDT-1 is a newly identified frame-shift type mutagen, inducing 65400 revertants and 295000 revertants of S. typhimurium TA98 and YG1024 per micromole, respectively, in the presence of S9 mix. When a m-PD solution was oxidized with 1 or 2 mol of ozone at pH 4.0, 7.0, and 10.7, the contribution of PDT-1 to the mutagenicity of ethyl acetate extracts from the ozonized m-PD solution was 5-23%.

Kinetics of Ozonation of Pentachlorophenol in Aqueous Solutions

This research investigates the kinetics of the reaction between dissolved ozone and pentachlorophenol in acidic and neutral buffer solutions over the temperature range of 10° to 40°C. The reaction is very fast and five to six moles of ozone are required for conversion of each mole of pentachlorophenol. The overall kinetics are second order, with first order each in the concentrations of ozone and pentachlorophenol. At 25°C, the overall rate constant ranges from 7.55 x 104 to 2.49 x 107 L/Ms as the solution pH changes from 2 to 7. The ozonation rate increases as the fraction of pentachlorophenate in the solution increases, and the rate constant varies in proportion to [HO−]0.75 in the pH range of about 2 to 5. The reaction is enhanced by temperature, and correlations by the Arrhenius equation yield an average activation energy of 27 kJ/mole.

Removal of substituted pyridines by combined ozonation/fluidized bed biofilm treatment

3-Methylpyridine (MP) and 5-ethyl-2-methylpyridine (EMP) were quantitatively removed in batch ozonation. Formate, acetate and oxalate where detected as ozonation products representing only about 10% of the total organic carbon after 90% removal of MP. Only 30% of the nitrogen was detected as nitrate. 5 moles of ozone were needed per mol of MP removed but at this time dissolved organic carbon (DOC) was only reduced by 10%. EMP was initially oxidised much faster but the reduction of DOC was only 5% when EMP was removed by 90%. Only 15% of the nitrogen was converted to nitrate. Small amounts of formate, acetate and oxalate were accumulated. 4 moles of ozone were required to remove one mole of EMP. In continuous combined experiments, wastewater was fed to a fluidised bed biofilm reactor with a mixed culture. The liquid was circulated through an ozonation bubble column. Ozone supply was controlled to keep the dissolved ozone concentration at a low level in the oxidation reactor. Complete mineralisation of MP and extensive mineralisation of EMP was observed during the whole experiment. During adaptation of biomass the ozone requirement decreased from 10 mol mol−1 of MP oxidised to 4 mol mol−1.

Removal of substituted pyridines by combined ozonation / fluidized bed biofilm treatment

3-Methylpyridine (MP) and 5-ethyl-2-methylpyridine (EMP) were quantitatively removed in batch ozonation. Formate, acetate and oxalate where detected as ozonation products representing only about 10% of the total organic carbon after 90% removal of MP. Only 30% of the nitrogen was detected as nitrate. 5 moles of ozone were needed per mol of MP removed but at this time dissolved organic carbon (DOC) was only reduced by 10%. EMP was initially oxidised much faster but the reduction of DOC was only 5% when EMP was removed by 90%. Only 15% of the nitrogen was converted to nitrate. Small amounts of formate, acetate and oxalate were accumulated. 4 moles of ozone were required to remove one mole of EMP. In continuous combined experiments, wastewater was fed to a fluidised bed biofilm reactor with a mixed culture. The liquid was circulated through an ozonation bubble column. Ozone supply was controlled to keep the dissolved ozone concentration at a low level in the oxidation reactor. Complete mineralisation of MP and extensive mineralisation of EMP was observed during the whole experiment. During adaptation of biomass the ozone requirement decreased from 10 mol mol-1 of MP oxidised to 4 mol mol-1.

Non-Hydrolytic Decay of Formyl Chloride into CO and HCl in Aqueous Solution

Formyl chloride has been generated in aqueous solution (i) by stopped-flow ozonation of vinyl chloride and (ii) by reacting dichloromethyl radicals with OH radicals using the pulse radiolysis technique. Vinyl chloride reacts in water with ozone (k = 1.7 × 104 dm3 mol-1 s-1, as determined by stopped-flow) yielding as final products (mol per mol of ozone) chloride ions (1.05), CO (1.01), and formate ions (0.06). Hydroxymethyl hydroperoxide (formaldehyde plus H2O2; 1.08) is also formed. HCl and formic acid are formed in less than 2 ms (the detection limit of the stopped-flow setup). At high pH the CO yield decreases (at pH 13.6 by 50%). It is concluded that the precursor of CO, HCl, and formic acid is formyl chloride. It predominantly decays into CO and HCl, and only at very high pH can hydrolysis to formic acid and HCl compete successfully. Using the pulse radiolysis technique dichloromethyl radicals are generated in Ar-saturated solutions from chloroform by reacting it with the solvated electron (originati...

KINETICS AND MECHANISM OF THE REACTION BETWEEN OZONE AND O-CRESOL IN AQUEOUS SOLUTIONS

Abstract The stopped-flow spectrophotomctric method was applied to study the kinetics of the ozonation of o-cresol in aqueous solutions of pH values varying from 2 to 9 at 10 to 40°C. The fast reaction between o-cresol and ozone is second order overall with first order in each reactant. The ozonation rale increases with the temperature and pH value of the solution. In neutral solutions, the overall rate constant increases from 422,000 M-1S-1 at 10°C to 1,549,000 M-1 S-1 at 40°C. The activation energy is about 30 KJ/mol in the neutral solutions; it increases slightly with the acidity of the solution. A mechanism based on the initial attack of ozone moleculesat the ortho and para positions of o-cresol is proposed for the ozonation reaction. According to this mechanism, three moles of ozone are required to react with each mole of o-cresol resulting in the rupture of the aromatic ring and production of various acids. The oxidation products were identified by these and other investigators. The proposed mechani...

Kinetics of the bentazone herbicide ozonation

Abstract The kinetics of ozonation of the herbicide Bentazone (3‐isopropyl‐lH‐2,1,3‐benzothiadiazin‐4–3H‐one 2,2 dioxide) is studied, the experiments being carried out in a bubble reactor, and using a porous plate as gas sparger. The increases of temperature, ozone partial pressure, initial Bentazone concentration and pH values under 5 have a positive effect on the degradation rate. A consumption of 2 moles of ozone per mol of herbicide degraded is determined for the direct reaction. Following a model based in the film theory which is applied to the experimental data, the reaction orders with respect to both, ozone and Bentazone, and the rate constants are evaluated for the herbicide ozonation.

Comparative Study of Ozonation of Two Lignin Model Compounds: Coniferyl Alcohol and Ferulic Acid. Identification of some by-Products

Abstract The objective of our study was to compare the reactivity of coniferyl alcohol and ferulic acid with ozone at acidic pH in terms of ozone demand and byproducts formation. Both structures exert an ozone demand of about two moles of ozone per mole of initial compound. Similar ozonation byproducts were identified using gas chromatography/mass spectrometry analysis. Using a low ozone dose (below the ozone demand), byproducts were principally aromatic structures, with vanillin, 3,4-dihydroxy-5-meth-oxybenzaldehyde and vanillic acid as the main compounds. Applying a higher ozone dose (above the ozone demand), furan structures were produced. A reaction mechanism is suggested to explain the formation of such structures. A quantitative study showed that coniferyl alcohol was a stronger precursor of vanillin and vanillic acid than ferulic acid.

Aqueous phase ozonation of chlorophenols

This research investigates the kinetics and mechanisms of the reactions between dissolved ozone and mono-chlorophenols in distilled water. The stoichiometric determination indicates that three moles of ozone are required for complete conversion of each mole of chlorophenol. A stopped-flow spectrophotometer system was applied to obtain the kinetic data. p-Chlorophenol is the most reactive of the three isomers with ozone yielding second order rate constants of 10800–56000 1/ M s as the temperature increases from 10 to 35°C. The ozonation reaction is first order in ozone, and independent of the concentration of o- or m-chlorophenol. The kinetic results suggest that the reactions of the three isomers are governed by different pathways though all of the ozonation reactions might be initiated by electrophilic addition.

Destruction of cresols by chemical oxidation

This work investigates the reaction rates and kinetics of the oxidative destruction of cresol isomers in water by ozone and hydrogen peroxide. Cresols are oxidized slowly by hydrogen peroxide though the reaction rates are enhanced in the presence of Fenton's reagent and other catalysts. Rapid oxidation takes place between ozone and a cresol isomer for complete conversion to intermediates in less than 0.1 second. Further reactions or decomposition of the intermediates result in rupture of the aromatic ring and production of carbon oxide, acetic and other acids. Three moles of ozone are required for the destruction of a cresol isomer, and the overall kinetics is first order with respect to the concentrations of ozone and cresol isomer. At 25°C, the reaction rate constants are 32240, 60870 and 45 460 M −1s −1 respectively, for the ozonation of o-, m- and p-cresol. In the temperature range of 10 to 40°C, m-cresol is the most reactive species of the three isomers with ozone in the aqueous phase.