Ozone Mass Transfer Research Articles

Ozonation of guaiacol solution in a rotating packed bed

As a building block of lignins, guaiacol represents a large number of mono- and dimethoxy phenols found in bio-oil derived from soft- or hardwood, respectively. During lignin degradation by ozone-based processes, the intermediate product guaiacol is also oxidized by ozone. Traditionally, ozonation of organic wastewater is carried out in a bubble column. This study employed a rotating packed bed that used high rotating speed to enhance ozone mass transfer rate for guaiacol degradation. The effects of guaiacol initial concentration, ozone feed rate, rotating speed, and solution pH on the residual guaiacol concentration, residual chemical oxygen demand (COD) and total organic carbon (TOC) were experimentally measured. The experimental results show that the guaiacol, COD, and TOC degradation rates increase with increasing initial concentration, ozone feed rate, rotating speed, or solution pH. A kinetic model has been developed to predict the residual guaiacol concentration, residual COD and TOC satisfactorily.

Development of a tool, using CFD, for the assessment of the disinfection process by ozonation in industrial scale drinking water treatment plants

Foreseen standards regarding microorganism content for drinking water require assessment of the capability of existing plants to reach the upcoming requirements. This paper presents the development of a tool to assess this capability in a commonly encountered key step of water disinfection: ozonation. In this paper, this tool is applied to the test case of an ozonation channel of the Belgian drinking water producer Vivaqua. This tool is based on a mathematical model of the momentum and mass transport phenomena in an ozonation channel. The gas–liquid flow is coupled to ozone mass transfer and kinetics describing the ozone and microorganisms concentrations decay. The degradation of Bacillus subtilis spores, as a representative of resistant microorganisms, is implemented in the model. The model takes explicitly into account the bubble size variation and its impact on mass transfer. Bubbles sizes and kinetics parameters are estimated based on dedicated experiments. The model is partially validated by comparing simulations results, obtained using computational fluid dynamics, to experimental residence time distributions, residual ozone concentration and Bacillus subtilis spores degradation efficiency measurements obtained on the studied ozonation channel. It is shown that, at the industrial scale, bubble diameter variation has a significant impact on ozone concentration in the liquid at the reactor exit. Using the tool, it is also shown that, the ozonation channel of Vivaqua can be used to achieve degradation of resistant microorganisms but only with its maximal flow rate and concentration of ozone injection. Moreover, at low operating temperature, some microorganisms that present latency towards reaction with dissolved ozone might hardly be destroyed.

Kinetics and mass transfer of atrazine ozonation

The kinetics of the atrazine oxidation in aqueous solution by ozone was studied under different initial pH conditions and in the presence of a hydroxyl radical scavenger at pH 2.8. It was verified that the process took place mainly through radical reaction, even in acid medium. Therefore, a relatively high value of 26.4 L/(mol.s) for the rate constant of the direct reaction between molecular ozone and atrazine was found. After 10 minutes of oxidation, the degradation of the herbicide was more effective for pH 10.30 than for pHs 6.25 and 2.80. The mass transfer of ozone from the gas phase to the liquid phase was strongly affected by the oxygen flowrate and to a lesser extent by the stirring speed.

The modelling of ozone mass transfer in static mixers using Back Flow Cell Model

Static mixers are efficient devices successfully used in water and wastewater treatment such as water ozonation for disinfection and oxidation. The growing interest in new ozone generators delivering high ozone concentrations at low gas flow rates has made static mixers an excellent choice for dissolving ozone into water. However it is still a challenging issue when there is a need to design static mixers for their best process performance. A modelling tool is then required to aid with static mixer design, especially for ozonation processes. In this study, Back Flow Cell Model (BFCM), which is a two-parameter model, was used to simulate at steady state ozone mass transfer from the gas phase to water in Kenics static mixer. Mass transfer resistance developed in the liquid phase controlled the process and was described by a volumetric mass transfer coefficient k l a. The model parameters, number of cells ( N) and back flow ratio ( α), were determined from RTD tracer studies and did not change significantly with the gas-to-liquid volumetric flow rate ratios ( Q G / Q L ). The model was validated with experimental data and was found to be able to accurately predict the gas and liquid concentrations at the outlet of the mixer alongside ozone transfer efficiency. The BFCM was found reliable, accurate and simple to use. It also offers advantage of being flexible and simple to implement over other models and can be used for efficient static mixer design for ozonation processes.

Absorption of NO x into Nitric Acid Solution in Rotating Packed Bed

Absorption of NO x into nitric acid solutions was studied in the presence of ozone by using a rotating packed bed (RPB) contactor. The influences of operating parameters, such as high gravity number, amount of ozone, gas velocity, liquid spray density and inlet concentration of NO x , on the removal efficiency of NO x were investigated, among which the high gravity number and ozone amount are more important. Ozone was introduced to oxidize HNO 2 to HNO 3 to prevent the decomposition of HNO 2 in the liquid phase. The high gravity number presents the effective external force for enhancing the mass transfer of ozone from gas phase to liquid phase. Under the experimental condition, the removal efficiency of NO x is higher than 90% and the concentration of nitric acid product exceeds 45%.

Decomposition of excess sludge in a membrane bioreactor using a turbulent jet flow ozone contactor

We have investigated the decomposition of excess sludge generated in a membrane bioreactor using a turbulent jet flow ozone contactor (TJC), which induced both hydrodynamic cavitation and ozonation reactions. We monitored the effects of various TJC operating parameters on the properties of the sludge, including the particle sizes, the particle size distribution, and the levels of soluble COD, total COD, and mixed liquor suspended solids. The TJC enhanced the degree of sludge reduction while consuming less energy, relative to conventional ozonation treatment systems, because of the synergic effects of hydrodynamic cavitation and ozonation. The hydrodynamic cavitation generated in the TJC increased the ozone mass transfer efficiency, which in turn promoted the rate of disintegration and solubilization of the sludge particles.

Ozone mass transfer in an ozone–water contacting process with Shirasu porous glass (SPG) membranes—A comparative study of hydrophilic and hydrophobic membranes

Ozone absorption into water in a bubble-free ozone–water contacting process was investigated with tubular hydrophilic and hydrophobized Shirasu porous glass (SPG) membranes having uniform pores to gain a better understanding of the membrane's role in the ozone transfer. The surface of SPG membranes was hydrophobized by chemical modification with an organosilane having a fluorocarbon functional group. At a water flow rate of 8 dm 3 min −1, corresponding to a Reynolds number of 820, the overall mass transfer coefficient, K L based on water phase for the hydrophobized membrane with a mean pore diameter of 0.51 μm was 1.2 × 10 −5 m s −1, which was much larger than the K L value of 2.1 × 10 −6 m s −1 for the hydrophilic membrane with the same diameter. The main resistances to ozone transfer for the hydrophilic and hydrophobized membranes were in the membrane and in the water phase boundary layer, respectively. Under the same conditions, the mass transfer coefficient in the hydrophilic membrane, k M was 2.9 × 10 −6 m s −1, which was four orders of magnitude lower than that of the hydrophobized membrane because of the presence of water in the pores. The higher K L values at water flow rates were ascribed to an enhanced turbulence on the membrane surface. Due to an increase in the length of the pores filled with water, the K L value for the hydrophilic membrane increased with an increase in the membrane thickness, while the K L value for the hydrophobized membrane was independent of the membrane thickness because of the gas-filled pores. The K L value was unaffected by the membrane pore diameter for both membranes.

Ozonation of dye wastewater by membrane contactor using PVDF and PTFE membranes

This work aimed to study the decolorization of dye wastewater by ozonation membrane contacting process. Three different dyes, i.e., Direct red 23, Acid blue 113 and Reactive red 120 were selected to be used in this work. The effects of operating parameters which were gas and liquid velocity, liquid phase temperature, dye auxiliary reagents were investigated along with the mass transfer study. Membranes used in this work were PVDF and PTFE hollow fiber membranes. The ozone mass transfer performance and long term performance in ozonation by these two different types of membrane were studied. In addition, decolorization performance and kinetic study of ozonation in the batch system with various operating parameters and dye types were investigated. From the results, the ozone mass transfer increased with increasing liquid velocity, liquid phase temperature, and with the presence of Na 2CO 3. On the contrary, the ozone flux was not influenced by gas velocity. PVDF membrane provided higher ozone flux than PTFE, but PTFE membrane gave more stable and higher flux than PVDF for a long operation period. The ozone flux of different types of dye was in the following order: Direct red 23 > Reactive red 120 > Acid blue 113. Conversely, the decolorization performance of Acid blue 113 was higher than those of Direct red 23 and Reactive red 120. Kinetic analysis showed that decolorization of dyes followed the first order kinetics and the rate constants were in the following order: Acid blue 113 > Reactive red 120 > Direct red 23.

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.

Ozone Mass Transfer in a Recirculating Loop Semibatch Reactor Operated at High Pressure

AbstractThe effects of water flow rate, mixing, gaseous ozone concentration, inlet gas flow rate, temperature, and pH on ozone hydrodynamics at high pressure were studied. Varying the cross flow rate had only a slight influence on the ozone mass transfer rates, indicating that sufficient mixing in the reactor was attained at the low flow rates used. The addition of an inline static mixer had a negligible effect on aqueous ozone concentrations in the reactor, suggesting that mixing was sufficient without the mixer. The ozone mass transfer increased with increasing gaseous ozone concentration and with the inlet gas flow rate. The dissolved ozone concentration decreased with increasing pH due to the greater rate of ozone decomposition at higher pH. Increasing the temperature resulted in a decrease in the ozone mass transfer. A model to describe the ozone mass transfer was developed. Good agreement between the model predictions and the experimental data was achieved.

Removal of phenolic compounds present in olive mill wastewaters by ozonation

The aim of this work is to study a pre-treatment process of olive mill wastewaters based on ozonation. The efficiency of the process depends on the removal of pollutants and on ozone mass transfer performance. In order to choose an appropriate gas/liquid contactor, the rate constants of three phenolic compounds (gallic acid, p-hydroxybenzoic acid and p-coumaric acid) were determined by using competition kinetic model. These constants, obtained at pH 5, were found to be high (from 3.8 × 10 4 L/mol s to 2.9 × 10 5 L/mol s), inducing a diffusion controlled regime (Ha > 3). Thus, to obtain an efficient ozonation process, gas/liquid contactor should be adapted to this regime. An ejector was chosen as gas/liquid contactor. In a first time, treatment of synthetic effluent containing the three phenolic compounds was performed to evaluate efficiency of the process. Experimental conditions were chosen to obtain a diffusion controlled regime (Ha > 3). It appeared that this gas/liquid contactor permits obtaining complete and fast removal of pollutants with a very efficient ozone mass transfer (up to 90% during removal of phenolic compounds). So, this process was used to perform the ozonation treatment of olive mill wastewaters from Sfax (Tunisia). It was proved to be very efficient: up to 80% of phenolic compounds were removed and ozone mass transfer reached 95% during this oxidation.

Kinetic Study of Pressurized Ozonation Reactor of Tap Water

A developed pressurized pilot scale ozonation system with the volume of 28 L was designed to simulate the field operating condition by transferring premixed ozone and tap water into this system under the influence of three system pressure (1, 2 and 3 kgf/cm2), seven initial pH (5, 6, 6.5, 6.8, 8, 8.5, 9). The system was running in a continuous mode and with only initial pH adjustment to study the dissolution, self-decomposition and mass transfer of ozone in these conditions. The effects of the operating pressure and pH on ozone dissolution concentration, ozone decomposition rates and the liquid phase overall mass transfer coefficients (KLa) were determined quantitatively. The data show the calculated average ozone decomposition rates for pH increase from 5 to 9 are 9.01E-7 to 2.64 E-6 mol/L-min by using mole balance equation at the system pressure 2 kgf/cm2. The calculated average of KLa at the pseudo-steady state are 0.039 min−1 and 0.069 min−1 for pH less 6.5 and greater than 6.8, respectively.

Influence parameters in the ozonation of phenol wastewater treatment using bubble column reactor under continuous circulation

The ozonation of phenol wastewater treatment system has been investigated with effective mass transfer between gas and liquid phase in a bubble column reactor. The designed bubble column reactor was investigated for increasing the rate of mass transfer of ozone, the rate of oxidation of phenol in the solution, the solubility and decomposition rate of ozone in the distilled water were also studied at different flow rates. The decomposition rate constants were calculated based on pseudo first order kinetics. The oxidation of phenol was investigated in order to provide the overall reaction rate constant for the reaction between ozone and phenol at 25 °C. The influence of the operating parameters like initial phenol concentration, ozone flow rate and pH for the destruction of phenol by ozonation were studied. The pseudo first order rate constant was depending on the initial concentration of phenol solution. A comparison of TOC removal percentage between bubble column reactor and bubble diffuser using ozonation were reported.

Mass transfer of ozone in purified water

Mass transfer of ozone in purified water

Modeling Ozone Mass Transfer in Reclaimed Wastewater

Ozone mass transfer in reclaimed water was evaluated at pilot scale to determine mass-transfer characteristics and reaction kinetics and to assess the use of oxygen as a surrogate to measure this process. Tests were conducted in a 40-L/min pilot plant over a 3-year period. Nonsteady-state mass-transfer analyses for both oxygen and ozone were performed for superficial gas flow rates ranging from 0.13m/min to 0.40m/min. The psi factor, which is the ratio of volumetric mass-transfer coefficients of ozone to oxygen, was determined. The decrease in oxygen transfer rate caused by contaminants in reclaimed water was only 10 to 15% compared to tap water. A simple mathematical model was developed to describe transfer rate and steady state ozone concentration. Ozone decay was modeled accurately as a pseudo first-order reaction between ozone and ozone-demanding materials.

Application of ozonation membrane contacting system for dye wastewater treatment

The aims of this work are to investigate the ozone mass transfer in the hollow fiber membrane contactor for ozonation of dye solution and to study the effect of dyeing auxiliary reagents on decolorization performance. Effects of hydraulic retention time (HRT) in the system and membrane on color removal were also investigated in the continuous ozonation membrane contacting system. Dye used in this experiment was C.I. Reactive Red 120 (RR 120) and sodium carbonate (Na 2CO 3) and sodium chloride (NaCl) were used as additives. It was found that the ozone flux increased with increasing liquid velocity for water and dye solution as a liquid phase. Change in gas velocity did not influence the ozone flux. Therefore, the main mass transfer resistance for ozonation in membrane contactor was in liquid phase for both cases. The presence of Na 2CO 3 in the dye solution resulted in increasing the ozone flux, conversely, the ozone flux decreased when NaCl was added. Decolorization performance by ozone was inhibited when Na 2CO 3 existed in the dye solution. For ozonation membrane contacting system, the dye color removal performance increased with increasing HRT of the system. Additionally, decolorization of dye solution increased with decreasing HRT in the membrane module.

Mass Transfer of Ozone in a Novel In Situ Ozone Generator and Reactor

A porous tubular reactor that also served as an electrode for ozone generation was studied in this research to determine the effects of in situ ozone generation on mass transfer and reaction rates. Experimental data over a range of gas flow rates and ozone generation rates gave KL a values in the range 0.77–1.14 min−1 . These values are more than double the values typically reported for bubble columns, and about 30% higher than that for packed beds. The specific power requirement for the laboratory-scale in situ reactor is an order of magnitude lower than that for bubble columns and stirred tank reactors that are used for ozone dissolution. A compartments-in-series fluid flow model was developed to describe the reactor system, and this model provides a good comparison to the experimental data for dissolved ozone and off-gas concentrations in the reactor. Sensitivity analyses indicate that the dissolved and off-gas ozone profiles are most sensitive to the gas–liquid partition coefficient and the overall ma...

Countercurrent gas/liquid flow and mixing: Implications for water disinfection

Experimental and numerical results are presented from investigations into the hydrodynamics of a bench scale bubble column reactor. Countercurrent bubble column reactors are most commonly used in water disinfection for effecting mass transfer of ozone to the aqueous phase. In the reactor column used in this study, gas is introduced at the bottom of the column via a spherical diffuser and water is introduced to the top of the column through a manifold packed with glass spheres. Residence time distribution (RTD) studies were conducted for a range of gas flow rates chosen to span the dispersed flow bubble regime. A multiphase computational fluid dynamics (CFD) model was used to simulate the flow in the bubble column and to gain insights into the fluid dynamics of countercurrent flow bubble columns. The CFD model accurately predicted trends in mixing. Use of CFD in bubble column design and scale-up thus may yield better designs than those based on empirical relations.

Enhanced treatment of practical textile wastewater by microbubble ozonation

In this paper, microbubble technology was employed to increase the mass transfer rate of ozone and enhance the ozone oxidation of practical textile wastewater. Experiments were performed using a microbubble generator and a bubble contactor, which is commonly used in ozonation system, for comparison. The microbubble generator produced a milky and high intensity microbubble solution, which could reach a higher oxygen transfer rate at a lower input gas flow rate. A volumetric oxygen transfer rate (VOTR) of 0.086–0.413 kg/m 3 h and a total mass transfer coefficient of 0.1072–0.4859 min −1 were obtained at airflow rates of 0.02–1.5 dm 3/min. During the ozonation of practical textile wastewater by using the microbubble system, the input ozone could be almost completely utilized, and the rate of decolorization and organic reduction were much faster than those of the bubble contactor. For the practical textile wastewater tested, the time required for 80% removal of color was about 140 and 280 min by ozone microbubble and conventional bubbles, respectively. The chemical oxygen demand (COD) removal efficiency in the microbubble system was higher by 20%. The results revealed that in addition to the enhancement of the mass transfer of ozone, microbubbles could improve the oxidation of actual textile wastewater.

Combined photolysis and catalytic ozonation of dimethyl phthalate in a high-gravity rotating packed bed

In this study, a high-gravity rotating packed bed (HGRPB) was used as a catalytic ozonation reactor to decompose dimethyl phthalate (DMP), an endocrine disrupting chemical commonly encountered. The HGRPB is an effective gas–liquid mixing equipment which can enhance the ozone mass transfer coefficient. Platinum-containing catalyst (Pt/-Al 2O 3) of Dash 220N and ultra violet (UV) lamp were combined in the high-gravity ozonation (HG-OZ) system to enhance the self-decomposition of molecular ozone in liquid to form highly reactive radical species. Different combinations of HG-OZ with Dash 220N and UV for the degradation of DMP were tested. These include HG-OZ, HG catalytic OZ (HG-Pt-OZ), HG photolysis OZ (HG-UV-OZ) and HG-UV-Pt-OZ. The result indicated that all the above four ozonation processes result in significant decomposition of DMP and mineralization of total organic carbon (TOC) at the applied ozone dosage per volume of liquid sample of 1.2 g L −1. The UV and Pt/γ-Al 2O 3 combined in HG-OZ can enhance the TOC mineralization efficiency ( η TOC) to 56% (via HG-UV-OZ) and 57% (via HG-Pt-OZ), respectively, while only 45% with ozone only. The process of HG-UV-Pt-OZ offers the highest η TOC of about 68%.