Gas-phase Ozone Concentration Research Articles

Particulate-bound alkyl nitrate pollution and formation mechanisms in Beijing, China

Abstract. Fine particulate matter (PM2.5) samples were collected between November 2020 and October 2021 at the Minzu University of China in Beijing, and the n-alkyl nitrate concentrations in the PM2.5 samples were determined to investigate n-alkyl nitrate pollution and formation mechanisms. C9–C16 n-alkyl nitrate standards were synthesized, and the n-alkyl nitrate concentrations in PM2.5 were determined by gas chromatography triple quadrupole mass spectrometry. Temporal trends in and correlations between particulate-bound n-alkyl nitrate, ozone, PM2.5, and nitrogen dioxide concentrations were investigated to assess the relationships between particulate-bound n-alkyl nitrate concentrations and gas-phase homogeneous reactions in the photochemical process and speculate the particulate-bound n-alkyl nitrates' formation mechanisms. The n-alkyl nitrate concentrations in the PM2.5 samples were 9.67–2730 pg m−3, and the mean was 578 pg m−3. The n-alkyl nitrate homologue group concentrations increased as the carbon chain length increased; i.e., long-chain n-alkyl nitrates contributed more than short-chain n-alkyl nitrates to the total n-alkyl nitrate concentrations in PM2.5. The n-alkyl nitrate concentrations clearly varied seasonally and diurnally, the concentrations decreasing in the order winter > spring > autumn > summer and the mean concentrations being higher at night than in the day. The particulate-bound n-alkyl nitrate and ozone concentrations significantly negatively correlated despite gas-phase alkyl nitrate and ozone concentrations previously being found to positively correlate. This indicated that long-chain alkyl nitrates may not be produced during gas-phase homogeneous reactions. The particulate-bound n-alkyl nitrate concentrations followed the same trends as and significantly positively correlated with the PM2.5 and nitrogen dioxide concentrations. Nitrogen dioxide is an important contributor of nitrates in particulate matter. This indicated that particulate-bound n-alkyl nitrates may form through non-homogeneous reactions between alkanes and nitrates on particulate matter surfaces. As secondary pollutants, particulate-bound alkyl nitrates are important components of PM2.5 during haze events and strongly affect haze pollution and atmospheric visibility.

Adsorption and catalytic electro-peroxone degradation of fluconazole by magnetic copper ferrite/carbon nanotubes

Copper ferrite modified carbon nanotubes (CuFe2O4/CNTs) were synthesized and employed as adsorbents/catalysts to assist electro-peroxone treatment of aqueous emerging pollutant fluconazole (FLC). Results suggest that the synthetic CuFe2O4/CNTs integrated the CNTs adsorption and ferrite magnetic abilities, showing a fast FLC removal and an excellent recyclability. The pseudo-second-order equation and the Langmuir isotherm model could well elaborate the adsorption of FLC on prepared catalysts. Compared to individual processes, electro-peroxone treatment exhibited a synergetic degradation of FLC. Approximately 89% FLC transformation was observed in the CuFe2O4/CNTs catalytic electro-peroxone process, 10% higher than that without catalysts, implying that CuFe2O4/CNTs could enhance the peroxone oxidation. Increasing of inlet gasphase ozone concentration (7.2–29.7 mg/L), catalysts dose (0.1–0.8 g/L), initial solution pH (3–11), and reaction temperature (10–30 °C) could improve the treatment efficiency, while initial FLC concentration (5–40 mg/L) and natural organic matter contents (humic acid, 0–20 mg/L) have opposite effects. The role of cathodic current density (10–60 mA/cm2) was complex, 40 mA/cm2 was observed as the optimal value. Furthermore, the degradation of FLC followed the hydroxyl radicals (HO) oxidation mechanism. The production of HO was mainly via peroxone reactions, and the presence of CuFe2O4/CNTs could catalytic ozone and H2O2 decomposition, thereby promoting HO generation. Although the magnetic CuFe2O4/CNTs had not shown obvious microelectrode characteristics, it combined adsorption and catalytic peroxone oxidation, may serve as the catalyst for electro-peroxone process.

Experimental study on the ozone absorption accompanied by instantaneous chemical reaction

ABSTRACTThis work deals with gas absorption accompanied by chemical reaction in a liquid phase. Ozone absorption in potassium indigotrisulfonate solution was investigated in a batch bubble column. Enhancement factor for absorption accompanied by instantaneous chemical reaction in the liquid phase was experimentally determined, as a ratio of the volumetric mass transfer coefficient for the absorption accompanied by reaction to that for pure physical absorption. The influence of (a) the initial concentration of the solute from liquid phase and (b) the ozone concentration in gas phase on the enhancement factor were experimentally examined. The absorption accompanied by instantaneous chemical reaction is a diffusion-controlled process, whose rate depends upon the diffusivities of the absorbing gas and the solute in liquid phase. The influence of these diffusivities was found to be more significant for lower values of the enhancement factor. The rate of ozone absorption was followed by the time change of the solution color, using new method based on the computer program SigmaScan Pro 5 (Systat Software, Inc., San Jose, CA, USA). This investigation is a contribution to the prediction of the ozone consumption in wastewater treatment, in cases when ozone instantaneously reacts with substances present in water.

Optimization of nitrobenzene wastewater treatment with O3/H2O2 in a rotating packed bed using response surface methodology

Effects on the removal efficiency of nitrobenzene treated by O3/H2O2 in a rotating packed bed (RPB) were optimized with response surface methodology (RSM). Interaction effects between influence of H2O2 concentration, gas-phase ozone concentration, liquid flow rate, and high-gravity factor on the removal efficiency of nitrobenzene wastewater treatment with O3/H2O2 in a RPB were investigated. The results indicate that the influence priority on nitrobenzene removal is high-gravity factor, gas-phase ozone concentration, H2O2 concentration, and liquid flow rate. Significant interaction effects of H2O2 concentration and gas-phase ozone concentration, gas-phase ozone concentration, and high-gravity factor were observed. The optimum treatment conditions after optimizing were H2O2 concentration 5.7 mmol L−1, gas-phase ozone concentration 50 mg L−1, liquid flow rate 125 L h−1, and high-gravity factor 100. Under the optimal reaction conditions, the actual removal efficiency of nitrobenzene could reach 76.1% fast in a short-treatment time of 10 min. And the theoretical value was 78.2%. The deviation between the experiment test result and the predicted value of RSM-fitting equation was 2.68%, which indicate that the RSM-fitting equation could be used to predict the removal efficiency of nitrobenzene treated by O3/H2O2 in a RPB and optimize the treatment conditions.

A Modified Indigo Method for the Determination of Ozone in Nonaqueous Solvents

The indigo method for the analysis of aqueous ozone was modified to allow analysis of dissolved ozone in nonaqueous liquid phases. The method was tested using the solvent decamethylcyclopentasiloxane 245 and a vegetable oil. The molar absorptivity at 600 nm of the indigo trisulphonate molecule was re-checked and found to be 20,069 ± 412 L mol−1 cm−1 which is in agreement with the generally accepted value. Linear correlation between liquid phase and gas phase ozone concentrations confirmed that ozone solubility in decamethylcyclopentasiloxane 245 obeyed Henry's law with a constant of 1.71 ± 0.09 mg L−1 per mg L−1 in the gas phase. Ozone solubility in the vegetable oil followed a power law model with k = 0.148 and n = 0.767 (liquid and gas phase concentrations in mg L−1). The stoichiometry of the reaction between ozone in the nonaqueous phase and indigo trisulfonate in acidic solution was also confirmed as being about one. Moreover, the reaction products were confirmed by chromatographic analysis. This method was found effective to analyze ozone in nonaqueous solvents with a lower limit of detection of 2.6 μg L−1 and upper limit of detection of 142.7 mg L−1.

Kinetics of the ozone oxidation of Reactive Orange 16 azo-dye in aqueous solution

Reactive azo-dyes present environmental concerns since they are persistent organics which are difficult to remove with conventional treatment processes. In this study, the ozonation of Reactive Orange 16 dye, C.I. 177757 (synonym Remazol Brilliant Orange 3R) was investigated at different experimental conditions in a semi-batch ozone reactor (25–100 mg/L dye; 20–80 g/m 3 NTP O 3 gas (NTP: 0 °C and 1 atm); pH 2, 7, 11). Ozone was very effective to remove completely the colour within a short period of time (few minutes). High gas-phase ozone concentrations and low dye concentrations resulted in high decolourisation rates. The decolourisation of the dye has also improved as pH increased from 2 to 11. Direct ozone reactions are assumed to predominate and hydroxyl radicals formed as a result of ozone decomposition at high pH reacted mostly with the products of the main decolourisation reaction. The reaction was assumed second order and Danckwerts model was used to determine the values of its rate constant, k 2, at different pHs. Values of k 2 were 2.5 × 10 5, 3.2 × 10 5, and 1.4 × 10 6 L/mol s for pH values of 2, 7, and 11, respectively. The stoichiometric ratio of the reaction was found equal to 3 mol O 3/mol dye and a degradation pathway was proposed.

Substrate effects in the photoenhanced ozonation of pyrene

Abstract. We report the effects of actinic illumination on the heterogeneous ozonation kinetics of solid pyrene films and pyrene adsorbed at air-octanol and air-aqueous interfaces. Upon illumination, the ozonation of solid pyrene films and pyrene at the air-aqueous interface proceeds more quickly than in darkness; no such enhancement is observed for pyrene at the air-octanol interface. Under dark conditions, the reaction of pyrene at all three interfaces proceeds via a Langmuir-Hinshelwood-type surface mechanism. In the presence of light, Langmuir-Hinshelwood kinetics are observed for solid pyrene films but a linear dependence upon gas-phase ozone concentration is observed at the air-aqueous interface. We interpret these results as evidence of the importance of charge-transfer pathways for the ozonation of excited-state pyrene. The dramatically different behaviour of pyrene at the surface of these three simple reaction environments highlights the difficulties inherent in representing complex reactive surfaces in the laboratory, and suggests caution in extrapolating laboratory results to environmental surfaces.

Degradation kinetics of anthracene by ozone on mineral oxides

To further understand the role of substrates on the heterogeneous reactions of polycyclic aromatic hydrocarbons, the reactions of ozone with anthracene adsorbed on different mineral oxides (SiO 2, α-Al 2O 3 and α-Fe 2O 3) and on Teflon disc were investigated in dark at 20 °C. No reaction between ozone and anthracene on Teflon disc was observed when the ozone concentration was ∼1.18 × 10 14 molecules cm −3. The reactions on mineral oxides exhibited pseudo-first-order kinetics for anthracene loss, and the pseudo-first-order rate constant ( k 1,obs) displayed a Langmuir–Hinshelwood dependence on the gas-phase ozone concentration. The adsorption equilibrium constants for ozone ( K O3) on SiO 2-1, SiO 2-2, α-Al 2O 3 and α-Fe 2O 3 were (0.81 ± 0.26) × 10 −15 cm 3, (2.83 ± 1.17) × 10 −15 cm 3, (2.48 ± 0.77) × 10 −15 cm 3 and (1.66 ± 0.45) × 10 −15 cm 3, respectively; and the maximum pseudo-first-order rate constant ( k 1,max) on these oxides were (0.385 ± 0.058) s −1, (0.101 ± 0.0138) s −1, (0.0676 ± 0.0086) s −1 and (0.0457 ± 0.004) s −1, respectively. Anthraquinone was identified as the main surface product of anthracene reacted with ozone. Comparison with previous research and the results obtained in this study suggest that the reactivity of anthracene with ozone and the lifetimes of anthracene adsorbed on mineral dust in the atmosphere are determined by the nature of the substrate.

Infrared spectroscopic studies of the heterogeneous reaction of ozone with dry maleic and fumaric acid aerosol particles

Dicarboxylic acids, either directly emitted or formed in chemical processes, are found to be a significant component of tropospheric aerosols. To assess any potential chemical transformation of short unsaturated dicarboxylic acids in tropospheric heterogeneous chemistry, maleic and fumaric acid were selected as surrogates in this study. A novel aerosol flow tube apparatus is employed to perform kinetic studies of the oxidation of these organic compounds by gas-phase ozone. The system consists of a particle generation system, a vertically oriented glass flow tube and an infrared observation White cell with a Fourier transform infrared (FTIR) spectrometer for the detection system. A flow of single component organic aerosols with mean diameters ranging between 0.7 and 1.1 microm is introduced in a flow tube, in which the particles are subsequently exposed to a known concentration of ozone for a controlled period of time. A band assignment of infrared vibrational frequencies for dry maleic and fumaric acid aerosol spectra is presented. These studies are complemented with off-line analysis on the reaction products. The reaction exhibited pseudo-first-order kinetics on gas product formation, and the pseudo-first-order rate coefficients displayed a Langmuir-Hinshelwood dependence on gas-phase ozone concentration for both materials. By assuming a Langmuir-Hinshelwood behaviour, the following parameters were obtained: for the reaction of maleic acid aerosols, K(O3) = (3.3 + 0.5) x 10(-16) cm3 molecule(-1) and k(I)(max) = (0.038 + 0.004) s(-1); for the reaction of fumaric acid aerosols, K(O3) = (1.6 + 0.5) x 10(-16) cm3 molecule(-1) and k(I)(max) = (0.048 + 0.007) s(-1), where K(O3) is a parameter that describes the partitioning of ozone to the particle surface and k is the maximum pseudo-first-order coefficient at high ozone concentrations. Apparent reactive uptake coefficients were estimated from the pseudo-first-order rate coefficient and a trend of decreasing uptake coefficients with increasing ozone concentrations was observed, in good agreement with literature values.

Formation of N-nitrosodimethylamine (NDMA) by ozonation of dyes and related compounds

Formation of N-nitrosodimethylamine (NDMA) by ozonation of commercially available dyes and related compounds was investigated. Ozonation was conducted using a semi-batch type reactor, and ozone concentration in gas phase and the ozone gas flow were 10 mg L −1 and 1.0 L min −1, respectively. NDMA was formed by 15 min of ozonation of seven out of eight selected target compounds (0.05 mM) at pH 7. All the target compounds with N, N-dimethylamino functions were NDMA precursors in ozonation. The lowest and highest NDMA concentrations after ozonation of the target compounds were 13 ng L −1 for N, N-dimethylformamide (DMF) and 1600 ng L −1 for N, N-dimethyl- p-phenylenediamine (DMPD), respectively. NDMA concentrations after 15 min of ozonation of 0.05 mM methylene blue (MB) and DMPD increased with an increase in pH in its range of 6–8. The effects of coexisting compounds on NDMA concentrations after 15 min of ozonation of 0.05 mM MB and DMPD were examined at pH 7. NDMA concentrations after ozonation of MB and DMPD increased by the presence of 0.05 mM (0.7 mg L −1 as N) nitrite ( NO 2 - ) ; 5000 ng L −1 for MB and 4000 ng L −1 for DMPD. NDMA concentration after MB ozonation decreased by the presence of 5 mM tertiary butyl alcohol (TBA), a hydroxyl radical (HO·) scavenger, but that after DMPD ozonation was increased by the presence of TBA. NDMA concentrations after ozonation of MB and DMPD were not affected by the presence of 0.16 mM (5.3 mg L −1) hydrogen peroxide (H 2O 2). When 0.05 mM MB and DMPD were added to the Yodo and Tone river water samples, NDMA concentrations after 15 min of their ozonation at pH 7 increased compared with those in the case of addition to ultrapure water samples.

Role of the Aerosol Substrate in the Heterogeneous Ozonation Reactions of Surface-Bound PAHs

To probe how the aerosol substrate influences heterogeneous polycyclic aromatic hydrocarbon (PAH) oxidation, we investigated the reaction of surface-bound anthracene with gas-phase ozone on phenylsiloxane oil and azelaic acid aerosols under dry conditions in an aerosol flow tube with offline analysis of anthracene. The reaction exhibited pseudo-first-order kinetics for anthracene loss, and the pseudo-first-order rate coefficients displayed a Langmuir-Hinshelwood dependence on the gas-phase ozone concentration on both aerosol substrates. The following parameters were found: for the reaction on phenylsiloxane oil aerosols, K(O3) = (1.0 +/- 0.4) x 10(-13) cm(3) and k(I)(max) = (0.010 +/- 0.003) s(-1); for the reaction on azelaic acid aerosols, K(O3) = (2.2 +/- 0.9) x 10(-15) cm(3) and k(I)(max) = (0.057 +/- 0.009) s(-1), where K(O3) is a parameter that describes the partitioning of ozone to the surface and k(I)(max) is the maximum pseudo-first-order rate coefficient at high ozone concentrations. The K(O3) value for the reaction of surface-bound anthracene and ozone on azelaic acid aerosols is similar to the K(O3) value that we obtained in our previous study for the reaction of surface-bound benzo[a]pyrene and ozone on the same substrate. This finding supports our earlier hypothesis that the substrate influences the partitioning of ozone to the surface irrespective of the organic species (i.e., PAH) adsorbed to it. Preliminary ab initio calculations were performed to investigate whether there is a relationship between the relative binding energies of the ozone-substrate complex and the K(O3) values for the different substrates studied. A comparison between kinetic results obtained on aerosol substrates and thin films is presented.

Kinetic and Product Yield Study of the Heterogeneous Gas−Surface Reaction of Anthracene and Ozone

Little quantitative information exists regarding the products of the heterogeneous reaction of polycyclic aromatic hydrocarbons (PAHs) and ozone. We have, therefore, performed the first quantitative study investigating the kinetics and products of the heterogeneous gas-surface reaction of anthracene and ozone as a function of ozone concentration and relative humidity (RH). The reaction exhibited pseudo-first-order kinetics for anthracene loss under dry conditions (RH < 1%) and the pseudo-first-order rate coefficients displayed a Langmuir-Hinshelwood dependence on the gas-phase ozone concentration, which yielded the following fitting parameters: the equilibrium constant for ozone adsorption, K(O3) = (2.8 +/- 0.9) x 10(-15) cm3 and the maximum pseudo-first-order rate coefficient, k(I)max = (6.4 +/- 1.8) x 10(-3) s(-1). The kinetics were unchanged when experiments were performed at approximately 50% and 60% RH. In the product study, a nonlinear dependence, similar to a Langmuir adsorption plot, of the anthraquinone product yield as a function of ozone concentration was observed and resulted in the following fitting parameters: K(O3) = (3.4 +/- 1.5) x 10(-15) cm3 and the maximum anthraquinone yield, ANQmax % = 30 +/- 18%. Experiments performed under higher relative humidity conditions ( approximately 50% and 60% RH) revealed that the anthraquinone yield was unaffected by the presence of gas-phase water. It is noteworthy that both the anthracene loss kinetics and the anthraquinone yields have a similar dependence on the degree of ozone partitioning to the surface. This can be understood in terms of a mechanism whereby the rate-determining steps for anthracene loss and anthraquinone formation are both driven by the amounts of ozone adsorbed on the surface. Our results suggest that at atmospherically relevant ozone concentrations (100 ppb) the anthraquinone yield from the ozonolysis of anthracene under dry and high relative humidity conditions would be less than 1%.

Laboratory-scale application of fiber optic transflection dip probe (FOTDP) for in situ monitoring of gas phase ozone in unsaturated porous media

A fiber optic transflection dip probe (FOTDP) system was developed for in situ and real-time monitoring of the transport of gas phase ozone in unsaturated porous media. A unique property of this system is the employment of a dip probe, which is inserted within the porous media. At the probe's tip, incoming light interacts with gas phase ozone and is partially reflected back into the probe by a mirror attached to the tip. Calibration of the FOTDP system was successfully carried out with various ozone concentrations using a column packed with glass beads. The ozone breakthrough curves (BTCs) were obtained by converting normalized UV intensities into gas phase ozone concentrations. The FOTDP system worked well for in situ monitoring of gas phase ozone using a column packed with sand under various water saturations in the presence of SOM and reflected the ideal transport phenomena of gas phase ozone for various flow rates.

Application of a neural observer to phenols ozonation in water: Simulation and kinetic parameters identification

Presented in this study, a dynamic neural network (DNN) is employed to estimate the states dynamics of the phenols-ozone-water system. A new technique based on the dynamic neural network observer (DNNO) with relay (signum) term is applied to estimate the decomposition dynamics of phenols and to identify their kinetic parameters without any mathematical model usage. The decomposition of phenols (phenol (PH), 4-chlorophenol (4-CPH) and 2,4-dichlorophenol (2,4-DCPH)) and their mixture by ozone, realized in a semi-batch reactor, is considered as a process with uncertain model (“black-box”). Only one parameter monitoring, namely, the ozone concentration in gas phase in the reactor outlet, is measured during ozonation. The variation of this variable is used to obtain the summary characteristic curve for the phenols ozonation. Then, using the experimental decomposition dynamics of phenols and of their mixture, obtained by HPLC method, the proposed DNNO is applied to estimate the ozonation constants of phenols at the different pH 2–12. A good correspondence between the decomposition dynamics and the estimated ones by DNNO is obtained.

Kinetics of Surface-Bound Benzo[a]pyrene and Ozone on Solid Organic and Salt Aerosols

An aerosol flow tube apparatus was developed to perform the first kinetic study of the oxidation of particulate-bound BaP on solid organic and salt aerosols by gas-phase ozone. The studies on azelaic acid aerosols were performed with submonolayer coatings of BaP under both dry (RH < 1%) and high relative humidity (RH ∼ 72%) conditions. The reaction exhibited pseudo-first-order kinetics for BaP loss and the pseudo-first-order rate coefficients displayed a Langmuir−Hinshelwood dependence on gas-phase ozone concentration. Under high relative humidity conditions the kinetics were faster but also displayed a similar functional dependence on the gas-phase ozone concentration. By assuming Langmuir−Hinshelwood behavior, the following parameters were obtained: ozone-surface equilibrium constant KO3(< 1% RH) = (1.2 ± 0.4) × 10-15 cm-3, KO3(72% RH) = (2.8 ± 1.4) × 10-15 cm-3, the maximum pseudo-first-order rate coefficient (< 1% RH) = (0.048 ± 0.008) s-1, (72% RH) = (0.060 ± 0.018) s-1. Uptake coefficients were ext...

Hydrogen Peroxide and Ozone Formation in Hybrid Gas–Liquid Electrical Discharge Reactors

Ozone in the gas phase and hydrogen peroxide in the liquid phase were simultaneously formed in hybrid electrical discharge reactors, known as the hybrid-series and hybrid-parallel reactors, which utilize both gas phase nonthermal plasma formed above the water surface and direct liquid phase corona-like discharge in the water. In the series configuration the high voltage needle-point electrode is submerged and the ground electrode is placed in the gas phase above the water surface. The parallel configuration employs a high voltage electrode in the gas phase and a high voltage needle-point electrode in the liquid phase with the ground electrode placed at the gas-liquid interface. In both hybrid reactors the gas phase concentration of ozone reached a power-dependent steady state, whereas the hybrid-parallel reactor produced a substantially larger amount of ozone than the hybrid series. Hydrogen peroxide was produced in both hybrid reactors at a similar rate to that of a single-phase liquid electrical discharge reactor. The resulting concentration of H/sub 2/O/sub 2/ in the hybrid reactors, however, depended on the pH of the solution and the gas phase ozone concentration since H/sub 2/O/sub 2/ was decomposed by dissolved ozone at high pH.

Heterogeneous reaction of ozone with hydrocarbon flame soot

The reaction of ozone with toluene and kerosene flame soot was studied over the temperature range 240 to 350 K using a low pressure (a few Torr) flow reactor coupled to a modulated molecular beam mass spectrometer. A flat-flame burner was used for the preparation and deposition of soot samples from premixed flames of liquid fuels under well controlled and adjustable combustion conditions. Soot was found to be deactivated in reaction with ozone, the uptake coefficient (γ) being dependent on the time of exposure. The values of (1.8 ± 0.7) × 10−4 and (3.8 ± 1.5) × 10−4 independent of temperature in the range 240–350 K were determined for the initial uptake coefficient of ozone on toluene and kerosene soot, respectively. The process of soot ageing (deactivation) was parameterized, the uptake coefficient being expressed as a function of time and gas phase ozone concentration: γ = γ0/(1 + γ0k[O3]t), with temperature independent values of k = (1.1 ± 0.4) × 10−10 and (6.2 ± 2.5) × 10−11 cm3molecule−1s−1, for toluene and kerosene soot, respectively. From the soot surface saturation experiments the following maximum number of ozone molecules taken up were determined: ≃7 × 1014 for toluene and ≃9 × 1014 molecule cm−2 for kerosene soot. Experiments on soot ageing confirmed that soot deactivation occurs under real ambient conditions. The present results support current considerations that heterogeneous loss of ozone on soot has negligible impact on ozone concentration throughout the atmosphere.

Inactivation of Cryptosporidium Oocysts in a Pilot-Scale Ozone Bubble-Diffuser Contactor. I: Model Development

A mathematical model was developed to simulate the performance of a pilot-scale ozone bubble-diffuser column. The reactor hydrodynamics was represented with the axial dispersion reactor model. An analytical solution was developed for the liquid and gas phase ozone mass balances in which dissolved ozone decomposes by first-order kinetics. Numerical approximations were provided for the mass balances for viable microorganisms and the more general case of dissolved ozone decomposition through a second-order reaction with fast ozone demand in natural organic matter. Model components required to predict the liquid and gas phase ozone concentration and viable microorganism number density profiles throughout the bubble-diffuser column included input parameters (liquid and gas flow rates, influent gas and dissolved ozone concentrations, temperature, and countercurrent or cocurrent operation mode), empirical correlations (dispersion number, volumetric mass transfer coefficient, Henry's law constant), and batch or semibatch kinetic information (ozone decomposition rate constants and fast-ozone demand, and microorganism inactivation lag phase and rate constant). A sample model run for the case of first-order ozone decomposition revealed that the analytical and numerical solutions were practically identical.

Effect of pH and Gas-Phase Ozone Concentration on the Decolorization of Common Textile Dyes

This paper presents the results of a laboratory study on the effect of pH (2, 5, and 9) and gas-phase ozone concentration (1, 7, and 11 wt %) on the decolorization efficiency via ozonation for seven common textile dyes. Higher gas-phase ozone concentrations resulted in higher decolorization rates due to more rapid ozone transfer. Higher gas-phase ozone concentration, however, was also observed to have a positive, neutral, or negative effect on ozone dose requirements for different dyes. In general, greater ozone utilization efficiency was achieved at lower pH levels where direct ozone reactions predominate. It was observed that because ozonation can cause significant resolubilization of precipitated dyes, complete removal of dye precipitate should be accomplished prior to polishing via ozonation. The results point to the need for laboratory and/or pilot testing for dye-laden wastestreams to allow process optimization.

Interaction of Ozone and Water Vapor with Spark Discharge Soot Aerosol Particles Coated with Benzo[a]pyrene: O3 and H2O Adsorption, Benzo[a]pyrene Degradation, and Atmospheric Implications

The interaction of ozone and water vapor with spark discharge soot particles coated with the five-ring polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) has been investigated in aerosol flow tube experiments at ambient temperature and pressure (296 K, 1 atm). The investigated range of ozone volume mixing ratio (VMR) and relative humidity (RH) was 0−1 ppm and 0−25%, respectively. The observed gas-phase ozone losses and pseudo-first-order BaP decay rate coefficients exhibited Langmuir-type dependencies on gas-phase ozone concentration and were reduced in the presence of water vapor, which indicates rapid, reversible and competitive adsorption of O3 and H2O on the particles followed by a slower surface reaction between adsorbed O3 and BaP. At low ozone VMR and RH, the half-life of surface BaP molecules was found to be shorter than previously reported (∼ 5 min at 30 ppb O3 under dry conditions). At higher RH and for multilayer BaP surface coverage, however, a strong increase of BaP half-life was observed a...