Combined Absorption and Self-Decomposition of Ozone in Aqueous Solutions with Interfacial Resistance

A theoretical analysis is performed employing the film model for the isothermal absorption and self-decomposition of ozone in aqueous solutions with interfacial resistance, which is inversely proportional to the interfacial mass transfer coefficient k_s. A closed-form solution has been obtained. The effects of system parameters on the ozone mass transfer rate are examined. These parameters include the interfacial resistance (1/k_s), the acidic and basic self-decomposition reaction rate parameters (M_m ^0.5, M_n ^0.5.; M_m = [2D_Ak_mC_Ai ^m-1/(m+1)]/(k_L ⁰)², M_n=(2D_Ak_nC_Ai ^n-1/(n+1))/(k_L ⁰)², the reaction orders (m,n), the pH value of solution, and the liquid-phase mass transfer coefficient (k_L ⁰). The results indicate that the reduction effect of the interfacial resistance on the absorption rate is most significant for the situation with the larger values of M_m and M_n as well as with higher pH values. Also, for any particular finite value of k_L ⁰/k_s, the reduction effect encountered is greater for a gas liquid contactor with a lower k_L ⁰. The reduction effect should be avoided in order to maintain a higher mass transfer rate of ozone in aqueous solution. This analysis is of importance for the efficient use of ozone in water/wastewater treatment processes in the presence of interfacial resistance substances such as surface active agents. For some known special cases (for example, cases with no interfacial resistance), the present solution reduces to the previous works of other investigators.     

Axial Dispersion Model for Estimation of Ozone Self-Decomposition

A new method using the axial dispersion model for estimation of ozone self-decomposition kinetics in a semibatch bubble column reactor was developed. The reaction rate coefficients for literature equations of ozone decomposition and the gas phase dispersion coefficient were estimated and compared with literature data. The reaction order in the pH range 7–10 with respect to ozone 1.12 and 0.51 the hydroxyl ion were obtained, which is in good agreement with literature. The model parameters were determined by parameter estimation using a nonlinear optimization method. A sensitivity analysis was conducted to obtain information on reliability and identifiability of the estimated parameters.     

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.     

Ozone Decomposition over Cobalt Supported on Olive Stones Activated Carbon: Effect of Preparation Method on Catalyst Activity

Aqueous ozone decomposition was studied over highly dispersed cobalt nanoparticles supported on olive stones activated carbon (AC) prepared by: wetness impregnation (Co/AC_w) and incipient wetness impregnation (Co/AC_iw) with respect to pore volume. Nitrogen adsorption-desorption at 77K, SEM, XRD and XPS analyses were used to characterize the catalysts. Analyses results show that Co/AC_w was more uniformly dispersed on the AC than Co/AC_iw. The effect of the presence of tert-butanol as radical scavenger was also studied. Higher catalytic activity was measured for Co/AC_w than Co/AC_iw. Ozone decomposition extent goes to 99% in only 3 min in the presence of Co/AC_w compared to 60% and 58% using Co/AC_iw catalyst and AC, respectively.     

Removal of Color and Organic Matter in Industrial Phosphoric Acid by Ozone: Effect on Activated Carbon Treatment

Industrial phosphoric acid at 42-45% P₂O₅ and containing organic matter (OM) in the range of 220 mg/L to 300 mg/L is treated by combined ozonation and activated carbon. Ozonation alone removes the initial dark color of the acid and eliminates the organic content. Adsorption on activated carbon alone can reduce OM levels by 80% for more than 25 g/kg P₂O₅. We find that a preozonation noticeably enhances activated carbon efficiency and reduces its specific consumption. Isoconversion curves are plotted in specific ozone and activated carbon ratio space.     

Decomposition of Dissolved Ozone in the Presence of Activated Carbon: An Experimental Study

In aqueous solutions molecular ozone (O₃) decomposes rapidly into secondary radical or ionic species such as (OH^o,, , …). This decomposition is enhanced by many factors, essentially the pH, the temperature, and the organic or inorganic compounds in the solution. The aim of this work is to study the effect of the addition of granular activated carbon on the rate of ozone decomposition in aqueous solutions containing promoter (P) and inhibitor (Q) mixtures. The activated carbon used is laboratory produced from olive stones. We found that the rate of decomposition of ozone in these conditions is described by a pseudo-first-order kinetic: . Experimental results show that adding 15 mg/L of the olive stones activated carbon (OSAC) enhances the rate constant of the P and Q controlled chain depletion by about a factor of two. We found that the decomposition increases linearly with the solid concentration (W): and that the kinetics are enhanced when the activated carbon specific area increases. We also conclude that the preozonation of the OSAC has no effect on its activity. We note that the temperature has a significant effect on the ozone decomposition rate even in the presence of OSAC. The value of the activation energy in the presence of the OSAC is lower than that obtained in homogeneous decomposition.     

臭氧/活性炭处理炼油废水的初步研究

考察了可能在实际水处理过程中影响O3 活性炭催化氧化工艺处理效果的因素 ,结果表明该工艺将臭氧的强氧化能力与活性炭的吸附、催化能力有机的结合到了一起 ,利用活性炭的催化作用来提高臭氧化的能力 ,使废水的处理效果大为改观 ,该工艺具有一定的可行性     

Modeling of Ozonation for Dissolved Ozone Dosing

Experimental research was carried out for calibration and validation of a model describing ozone decay and ozone exposure (CT), decrease in UV absorbance at 254 nm (UVA₂₅₄), increase in assimilable organic carbon concentration and bromate formation. The model proved to be able to predict these parameters on the basis of the applied ozone dosage. The experimental ozone dosages ranged from 0.4 mg-O₃/L to 0.9 mg-O₃/L for natural water with a dissolved organic carbon concentration of 2.4 mg-C/L. The UVA₂₅₄ was found to be an effective parameter for estimation of rapid ozone decay for natural water under experimental conditions tested. The experimental setup consisted of a bench-scale plug flow reactor (approximately 100 L/h) with dissolved ozone dosing.     

Ozone and Activated Carbon for Tertiary Wastewater Treatment

Preozonation of biologically or physically–chemically treated wastewater effluents, followed by passage through granular activated carbon (GAC) for tertiary wastewater treatment was studied at the Duck Creek Wastewater Treatment in Garland, Texas. Whereas the average period of operation for the GAC before exhaustion without ozone pretreatment was 70 days, pretreatment with ozone or with oxygen alone extended GAC operation to at least 480 days, withoutexhaus–tion. Effluent streams consistently metapplicable discharge standards during this period of time, without the necessity of regenerating the GAC.     

The Influence of Ozone,Oxygen and Chlorine on Biolocical Activity on Biological Activated Carbon

A laboratory study was conducted into the effects of the treatment of activated sludge effluent with different oxidants on the biodegradability of the organic substances. It was found that, under the experimental conditions described, ozone increased the biodegradability, whereas chlorine had no apparent significant effect. The effect of continuous oxidative pretreataent of activated sludge effluent on microbial populations and the biological activated carbon used subsequently in the process also was studied. It was found that ozone, particularly at a dosage of about 5 mg/L promoted biological activity, while chlorine and oxygen (in addition to the dissolved oxygen already in the effluent) had no significant effect on the biological population size.     

Evaluation of Solubility and the Gas-Liquid Equilibrium Coefficient of High Concentration Gaseous Ozone to Water

Solubility and the gas-liquid equilibrium coefficient of gaseous ozone to water were examined under higher concentrations of supplied gaseous ozone up to 100 mg/L. The experimental and modeling approach was employed to evaluate the gas-liquid equilibrium coefficients and mass transfer of ozone. The gas-liquid equilibrium coefficients were evaluated as 0.35, 0.31 and 0.25 (mg/L-liquid)/(mg/L-gas) at 15, 20 and 30 °C, respectively. These gas-liquid equilibrium coefficients are applicable for the wide concentration range of supplied ozone gas up to 100 mg/L. The calculation result by a model which has terms of the mass transfer of ozone, the gas-liquid equilibrium coefficient and the rate of ozone self-decomposition, was examined and had a good agreement with the experimental data over the wide range of temperatures, pHs, inorganic carbon concentrations and supplied ozone gas concentrations. The rate of ozone self-decomposition evaluated separately from this study was employed for the calculation. We can conclude that absorption of gaseous ozone to water is expressed by the three terms mentioned above when the rate of ozone self-decomposition is evaluated properly. In sensitive analysis, we elucidated that the rate of ozone self-decomposition affected strongly on the concentration of dissolved ozone at steady-state under higher concentration of supplied gaseous ozone.     

A Study of the Physical and Chemical Processes Active in Ozone Generation by Carbon Dioxide Fed Corona Discharges

Ozone generation in both positive and negative corona discharges DC corona, both operated in glow regime, feed by dry CO₂ has been studied. Higher ozone concentrations were observed in negative corona discharges. Ozone formation was found to be strongly dependent upon both the flow rate of the gas and on the radius of the outer electrode. The physical characteristics of the discharge were monitored through measurement of the discharge current. Small increases in the gas flow rate were observed to cause a significant increase in the discharge current of a negative corona discharge but little/no effect was observed in positive corona.     

Soft-Sensor of Ozone Concentration in Ozone Generation System

The soft-sensor of ozone concentration is introduced. Six secondary variables are chosen in the soft-sensor model. The model is built based on the radial basis function neural network and its parameters are confirmed by the Gradient-descent algorithm. The model is implemented on the basis of the monitoring system that is necessary for ozone generation; thus, it requires no additional hardware cost. The response time of the model is less than 0.6 seconds. The experimental results indicate that the relative errors of the soft-sensor are less than 5%.     

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.     

Ozone Cleaning of Fouled Poly(Vinylidene) Fluoride/Carbon Nanotube Membranes

This research demonstrates for the first time that ozone is an effective cleaning agent for polyvinylidene fluoride (PVDF) membranes fouled by natural organic matter (NOM). Bare PVDF membranes as well as PVDF impregnated with CNTs (pristine (CNTs–P) and oxidized (CNTs–O)) at 0.3% mass membranes were used. Three different methods were investigated for cleaning the fouled membranes including; A: 10-min cleaning by pure water, B: 5-min water followed by 5-min ozonated water, and C: 10-min fully ozonated water. It was found that the application of fully ozonated water for 10 min was very effective to reinstate the flux to almost its original value of unfouled membrane. The CNTs–P/PVDF membrane exhibited the highest fouling with a total fouling ratio of 81%, while for the bare PVDF and the CNTs–O/PVDF membranes, the fouling ratios were 76% and 74%, respectively. The full ozonated water cleaning method gave the highest removal of fouling leaving the lowest irreversible fouling on the membrane as compared to the other cleaning methods. On the other hand, the highest removal of NOM fouling was obtained for CNTs–O/PVDF membranes indicating that fouling on CNTs–O/PVDF membrane was less bound than the other membranes. Contact angle measurements of the fouled membranes showed that all membranes exhibited increased contact angles due to the NOM deposition but after cleaning, particularly with ozonated water, the membrane contact angles returned to almost their original values. FTIR analysis of the membranes corroborated the results obtained.     

Experimental Investigations On Production Of Excited Ozone Species From A Silent Discharge Ozone Generator

Ozone decomposition kinetics are investigated together with the influence of energy input to an ozone generator. Decomposition is considered in a solid bed reactor, a gas phase reactor and a bubbling reactor. Ozone is produced at the same concentration and gas flow rate using two methods: 1) from the generator at a higher power giving higher ozone concentration, then ozone is diluted by oxygen before entering the decomposition reactor, and 2) at a lower power without dilution.     

Ozone: A Means of Stimulating Biological Activated Carbon Reactors

To reduce the formation of chlorination byproducts in drinking water, the European strategy consists in developing techniques for the removal of organic matter. No chlorine is added to the water until the end of the treatment line, allowing a great reduction of the chlorine dose applied. Delaying the chlorination also improves the biological assimilation of organics within the filters. Identification of the basic properties (i.e., molecular weight, biodegradability) of the molecules which react with chlorine shows that the combination of ozone and biological activated carbon (BAC) filtration is an efficient and economical technique for the removal of these undesirable byproducts. More and more, drinking water suppliers are faced with the worrisome problem of chlorinated byproducts. This concern was prompted largely by the degradation of raw waters. Chlorinated byproducts are caused by the effect of chlorine on organic matter dissolved in water.     

Pyruvic Acid Removal from Water by the Simultaneous Action of Ozone and Activated Carbon

Activated carbon (AC) has been used to catalyze the ozonation of pyruvic acid in water. Pyruvic acid conversions were found to be 9 and 37% after 90 min of single ozonation and single adsorption with 40 gL^?1 AC, respectively, while 82% was reached at the same conditions during the AC catalytic ozonation. Also, for similar conditions, mineralization reached values of 67% in the AC catalytic ozonation against hardly 5% in the non-catalytic experiment. The process likely develops through both adsorption of ozone and pyruvic acid on the AC surface and generation of hydroxyl radicals that eventually is the responsible oxidizing species. Rate constants for both non-catalytic ozonation and AC-Ozone catalytic surface reaction, at 20°C and pH 7.5, were found to be 0.025 min^?1 and 87.9 Lg^?1s^?1, respectively. For AC concentrations higher than 2.5 gL^?1 gas-liquid mass transfer of ozone constituted the limiting step. At lower concentrations, internal diffusion plus surface reaction controlled the process rate.     

Evaluation of the Catalytic Effect of the Ozone/Carbon Nanotube (O3/CNT) Process Using para-Chlorobenzoic Acid (pCBA)

The catalytic effects and mechanisms of the ozone/carbon nanotube (O₃/CNT) process using para-chlorobenzoic acid (pCBA) were evaluated. To use pCBA as an O₃-resistant OH? probe compound in a pure water system at pH 7, an adequate amount of scavenger was needed. During the O₃/CNT process, a synergetic catalytic effect by OH? generation on the CNT surface could be evaluated in the condition of excess tert-butyl alcohol (TBA) concentration. The OH? radicals were generated and existed on both the bulk phase and CNT surface. The OH-ct values of the CNT surface and bulk phase in the O₃/CNT process for 10 min were 2.1 × 10^?5 and 2.5 × 10^?5μ M·s, respectively. In modifying CNT evaluation, the catalytic effects were the most apparent in the following order: CNT treated with acid then heat (CNT-T), original untreated CNT (CNT-O), and CNT treated with an acid (CNT-A).