Mass Transfer Coefficient Of Ozone Research Articles

Bubble-less photocatalytic ozonation with ceramic membranes and static mixers enhances the total organic carbon removal and degradation of iodinated X-ray contrast agents

Conventional bubble-based ozonation of wastewater creates several issues, e.g., the low degradation of certain micropollutants like X-ray contrast agents, mass transfer limitations due to inhomogeneous mixing, and the waste of undissolved ozone. In contrast, this work uses tubular ceramic membranes for bubble-free and bubble-less ozonation. Static mixers are placed around the membrane to enhance the radial mixing of ozone, creating homogeneous reaction conditions throughout the membrane contactor. Additionally, the ozone mass transfer significantly increases with static mixers. Furthermore, the membrane is made of a photocatalyst (TiO2) on the shell-side to improve the micropollutant degradation by photocatalytic ozonation. An ozone-stable hydrophobic treatment method is developed to use ceramic membranes as a membrane contactor for the ozonation of water. After hydrophobic treatment, the ozone mass transfer coefficient is in the order of 1.3 ⋅ 10−6 ms−1 using bubble-less operation resulting in an ozone concentration up to 4.0 mg L−1. Overall, bubble-less operation significantly increases the ozone mass transfer compared to bubble-free operation. Photocatalytic ozonation in a membrane contactor with static mixers increases the degradation of diatrizoate by 37% compared to sole ozonation in the same membrane contactor. Furthermore, this process increases the removal of total organic carbon in experiments with a water matrix consisting of four different micropollutants by 115% compared to sole ozonation.

On the geometry and material stability of tubular PVDF-TiO2 static mixer membrane contactors for photocatalytic ozonation of micropollutants

The prevention of ozone hotspots in ozonation reactors for wastewater treatment is essential for effective degradation of micropollutants without forming harmful by-products. Membrane contactors can provide a bubble-free ozonation process that is able to decrease by-product formation, e.g., bromate formation in bromide-charged wastewater. Furthermore, the geometry of the reactor influences the distribution of dissolved ozone in a membrane contactor. Turbulence promoters can significantly decrease ozone hotspots and increase ozone mass transfer into wastewater. This work presents a fabrication methodology to produce PVDF-TiO2 helical static mixer membranes using the rotation-in-a-spinneret technology. Static mixer membranes combine the functionality of a membrane contactor and a static mixer in a single component. Furthermore, the PVDF matrix is doped with TiO2 particles as photocatalyst. Thus, we present a membrane-based photocatalytic ozonation process to increase the concentration of hydroxyl radicals for degradation of micropollutants under UV radiation. Static mixer membranes increase the ozone mass transfer coefficient by 70% compared to conventional hollow fiber membranes. Furthermore, the specific photocatalytic degradation rate of methylene blue increases by 50% using static mixer membranes. However, this work also reveals a lack of long-term stability of PVDF-TiO2 membranes in the corrosive environment of photocatalytic ozonation. The molecular weight of PVDF decreases by 11% after use in photocatalytic ozonation resulting in a loss of mechanical stability of the membranes. Similar material concepts are required based on ceramic materials which avoid wetting of the porosity.

Insights into gas flow behavior in venturi aerator by CFD-PBM model and verification of its efficiency in sludge reduction through O3 aeration

The use of ozone has become a new direction in residual sludge reduction. In order to improve the mass transfer efficiency and utilization efficiency of ozone, the structure of the venturi aerator was optimized by simulating the gas flow behavior with the CFD-PBM model. The gas volume fraction slowly decreased as the inlet angle increased. Besides, the ratio of throat diameter and throat length gradually increased, increasing bubble crushing rate and breakup probability. The turbulent eddy dissipation decreased with increasing outlet angle and moved from the central region to the sidewall, reaching a maximum at the throat. Thus, the optimal parameters for the venturi aerator were determined to be an inlet angle of 15°, a ratio of throat diameter to throat length of 1 and an outlet angle of 3°. Regarding the sludge reduction effect, the sludge dissolution efficiency after treatment with an optimized venturi aerator and traditional disc aerator was 35.3 % and 28.6 %, respectively. When the ozone dosage was 100 mg/g·MLSS, the venturi aerator had a better effect on ozone utilization than the disc aerator. At an ozone inlet flow rate of 2 L/min, the mass transfer coefficient of ozone in a venturi aerator was higher than that of the disc aerator. This study demonstrates the operational feasibility of ozone combined with a venturi aerator to reduce residual sludge production.

Catalytic decomposition and mass transfer of aqueous ozone promoted by Fe-Mn-Cu/γ-Al2O3 in a rotating packed bed

This study investigated catalytic decomposition and mass transfer of aqueous ozone promoted by Fe-Mn-Cu/γ-Al2O3 (Cat) in a rotating packed bed (RPB) for the first time. The results showed that the value of the overall decomposition rate constant of ozone (Kc) and overall volumetric mass transfer coefficient (KLa) are 4.28 × 10−3 s−1 and 11.60 × 10−3 s−1 respectively at an initial pH of 6, β of 40, CO3(g) of 60 mg·L−1 and QL of 85 L·h−1 in deionized water, respectively. Meanwhile, the Kc and KLa values of Fenhe water are 0.88 × 10−3 s−1 and 2.51 × 10−3 s−1 lower than deionized water, respectively. In addition, the Kc and KLa values in deionized water for the Cat/O3-RPB system are 44.86% and 47.41% higher than that for the Cat/O3-BR (bubbling reactor) system, respectively, indicating that the high gravity technology can facilitate the decomposition and mass transfer of ozone in heterogeneous catalytic ozonation and provide some insights into the industrial wastewater.

Degradation of Methyl Orange by ozone microbubble process with packing in the bubble column reactor

ABSTRACT The performance of the ozone microbubble(MB) process for the degradation of Methyl Orange (MO) in a bubble column reactor with added packing was investigated. The highest decolorization efficiency of 96.04% was achieved by the ozone MB process with packing, which was 10.17% and 62.02% higher than that of the ozone MB process without packing and the ozone millimeter bubble(MLB) process, respectively while keeping other operating parameters the same. In addition, the saturation gas holdup, ozone mass transfer coefficient, and decolorization rate constant of the ozone MB process with packing were 15.32%, 0.260 min−1, and 0.027 min−1, respectively, which were much better than those of the ozone MB process without packing and the ozone MLB process. The study also suggested that within a certain porosity range, the types of packings did not affect the performance of the ozone MB process in the degradation of MO. Moreover, the optimum operating conditions were initial concentration of MO of 30 mg/L, initial pH of 3, circulating liquid flow of 75 L/h, and ozone dosage of 0.56 mg/L. The decolorization efficiency was 99.28% within 120 min.

Degradation of Bisphenol A by ozonation in rotating packed bed: Effects of operational parameters and co-existing chemicals

Bisphenol A (BPA), a typical endocrine disrupting chemical, widely exists in water and threatens human health. The degradation of BPA by ozone in water is limited by the gas-mass transfer due to the low solubility of ozone. In this study, a rotating packed bed (RPB) was employed to create a high gravity environment to intensify the ozone mass transfer and BPA degradation. The effects of operational parameters (rotation speed of RPB, pH of the solution, ozone concentration, BPA concentration, gas volumetric flow rate and liquid volumetric flow rate) on BPA degradation efficiency and overall volumetric mass transfer coefficient of ozone were investigated. The results show that RPB effectively promoted the ozone mass transfer and BPA degradation and can be used for the ozonation of micropollutants that have fast reaction rates with ozone. Quenching experiments suggest that both ozone and HO∙ participated in BPA degradation from acidic to alkaline environments. In addition, the effects of co-existing chemicals on BPA degradation efficiency were studied. The addition of H2O2 or Cl− had no obvious impact on BPA degradation; the addition of HCO3− is beneficial for BPA degradation while the addition of fulvic acid suppressed the degradation. These results indicate that the pH value, which affects the reaction rate between ozone and BPA, is a major factor to be considered during the ozonation of BPA in RPB.

Use of modified flotation cell as ozonation reactor to minimize mass transfer limitations

A novel approach based on high turbulence zones to minimize mass transfer limitation in ozonation and catalytic ozonation processes was investigated. A modified flotation cell (MFC), was used as a reactor because this device is widely used for application where three phases (solid-liquid-gas) must interact. Hydrodynamic parameters such as stirring rate, bubbles production and ozone dispersion were evaluated as well as the catalyst load, ozone mass flow, and catalyst reuse. The results show that by increasing the stirring rate in MCF, the ozone mass transfer coefficient enhanced. Under the best operating condition, complete caffeine degradation and mineralization of 57% is achieved in 20 min. It was demonstrated that the kinetic regime of ozonation for caffeine degradation in MFC was moderated, whereas in other reactors, this kinetic regimen is diffusional and even very slow. The ozone bubbles produced and dispersed have diameters between 1.32 and 1.98 mm. It was identified by using the scavenger that hydroxyl radical is generated in catalytic ozonation, and it is a key species for caffeine degradation and mineralization.

Solubilization and stabilization for prolonged reactivity of ozone using micro-nano bubbles and ozone-saturated solvent: A promising enhancement for ozonation

The enhanced ozonation treatment by a combination of micro-nano bubbles (MNBs) and ozone-saturated solvent (e.g. acetic acid (HAc)) was investigated. The solubility, decomposition rate of ozone, and reactive oxygen species (ROSs) in various concentrations of HAc with/without MNBs were examined, and these synergetic effects were verified by the enhanced removal of p-chlorophenol (4-CP). The results showed that MNBs promoted the solubility and mass transfer coefficient (KLa) of ozone in both deionized (DI) water and HAc solution by 2.03–2.26 and 2.30–3.68 times respectively compared with normal millibubbles. Addition of a certain amount (0.5–5%) of HAc can further benefit the ozonation process. The ozone solubility was about four times larger in 5% HAc solution compared with that in DI water (0%), while the former KLa was 3.91-fold higher. The average half-lives of ozone were prolonged by 1.39–3.52 times in 0.5–5% HAc solutions to water alone. This was attributed to the inhibited chain reaction by scavenging the hydroxyl radical (OH) in the presence of HAc and thus retarded OH-catalyzed ozonolysis. The detection of ROSs showed that the concentrations of hydrogen peroxide (H2O2) and OH were up to 39.53 ± 4.10 and 70.17 ± 3.09 μg/L in the hybrid system. The ROSs led to that 48.15–77.55% of 4-CP were removed by ozonation with MNBs in 30 min, and 9.50–29.40 percent improvements were achieved in the HAc solutions than in the DI water. These results indicate that the combination of ozone with MNBs and HAc could enhance the removal of 4-CP effectively. This study illustrated the solubilization and stabilization effect for prolonged reactivity of ozone using MNBs and ozone-saturated solvent together.

The progressive steps for TPH stripping and the decomposition of oil refinery sludge using microbubble ozonation

Total petroleum hydrocarbons (TPH) in activated petroleum waste sludge (PWS) hindered the disintegration of sludge, and microbubble ozonation (MB-O3) was explored to separate the TPH and solids particle, enhance the decomposition of PWS, and improve the efficiency of ozonation. The maximum solubilization of PWS reached to approximately 41.9% at an ozone dose of 5.40 gO3/gTS, two times higher than the control one. The ozone mass transfer coefficient of kLa increased from 0.1101 min−1 to 0.2293 min−1 in MB-O3, resulting in the formation of a higher concentration of 1.29 μg/L hydroxyl radicals. The medium diameter sharply declined from 38.6 μm to 17.5 μm, and more porous surface of sludge flocs was observed, indicating that MB-O3 destroyed the water-oil-gel structure and contributed to the stripping of TPH. The soluble chemical oxygen demand was released by 390% with respect to initial value (from 764 to 3740 mg/L) and acetic acid was the predominant component with yield of 590 ± 7.1 mg/L, which could be served as an additional carbon source. This study provides an efficient approach to achieve sludge disposal and simultaneous enhance the stripping of total petroleum hydrocarbons from oil refinery sludge.

Intensifying ozonation treatment of municipal secondary effluent using a combination of microbubbles and ultraviolet irradiation.

Ozonation treatment of municipal secondary effluent is complicated by the low solubility of ozone and inefficient production of hydroxyl free radicals from ozone decomposition. To resolve these problems, this study investigated methods for intensifying ozonation treatment, using a combination of microbubbles and ultraviolet (UV) irradiation (UV/MBO). The high efficiency of the method was illustrated by treating river water containing refractory components derived from secondary effluent in a wastewater treatment plant. The results showed that the ozone mass transfer coefficient in a microbubble system was an order of magnitude compared with a conventional macrobubble system at the initial stage. The amount of ·OH generated during the treatment was quantified using a fluorescent probe analysis. The amount of ·OH in the UV/MBO system was almost 2-6 times more than the amount found with conventional ozonation using macrobubbles (CO), CO with UV irradiation (UV/CO), and microbubble ozonation (MBO) units. The UV/MBO system achieved chemical oxygen demand (COD), UV254, and UV400 removal performance rates of up to 37.50%, 81.15%, and 94.74% respectively. These levels were 2-36% higher than those in other systems. The coupling UV/MBO treatment significantly reduced all five categories of substances according to EEM spectra and fluorescence regional integration. The distribution of fractions with different molecular weights (MW) was altered and the UV254 of MW (< 500Da) increased by 15.8%. The biodegradability of the water was significantly improved, as indicated by the TOC/UV254. This is ascribed to the enhanced degradation of refractory organics in the water. The combination of the UV/microbubble technique with ozonation could provide an efficient approach for advanced wastewater treatment. Graphical abstract.

Synergistic effect of microbubbles and activated carbon on the ozonation treatment of synthetic dyeing wastewater

Abstract The performance of catalytic microbubble (MB) ozonation using a commercial granular activated carbon (AC) as catalyst in synthetic acid red 3R wastewater treatment was more efficient than that of coarse bubble (CB) and MB ozonation alone. The ozone mass transfer coefficient, ozone decomposition coefficient, decolorization rate constant, TOC removal rate constant, and ozone reaction efficiency achieved in catalytic MB ozonation were 0.253 min−1, 0.093 min−1, 0.342 min−1, 0.0242 min−1 and 0.128 mg(TOC removed)/mg(ozone consumed), respectively. The average ozone utilization efficiency in catalytic MB ozonation was as high as 98.3%. The synergistic effect of collapsing ozone MBs and catalytic activity of AC enhanced hydroxyl radicals ( OH) oxidation in catalytic MB ozonation which provided about 75% of oxidative capacity for TOC removal, even at a low pH. The enhanced OH oxidation was crucial for the mineralization of acid red 3R in catalytic MB ozonation where some OH scavengers could make TOC removal less efficient, especially Na2CO3. In addition, the catalytic activity of this commercial AC seemed stable after five recycling cycles. UV–Vis spectra and GC–MS analyses indicated that acid red 3R was oxidized-degraded by a pathway of azo bond cleavage, formation of naphthalene- and benzene-type compounds, further generation and final mineralization of small organic acids, which initially reduced the pH and increased the value again during catalytic MB ozonation. Therefore, the catalytic MB ozonation with commercial granular AC was a promising solution for wastewater treatment by ozonation process.

Mass Transfer Coefficient of Ozone in a Bubble Column

The effect of flow rate of ozone-containing gas and pH on the mass transfer coefficient of ozone through water in a bubble column reactor has been studied. Ozone was generated from air using a corona discharge ozone generator. The flow rate of air was varied from 2 to 5 L min-1, while pH was varied from 4 to 10. The gas containing ozone was bubbled to the reactor containing 1.5 L of 2% KI solution. The temperature was set at 28±1ºC. The concentration of ozone was determined using titrimetric method every 5 minutes. The results show that the concentration of ozone increases with time, and it reaches a steady-state concentration after 30 minutes of ozonation. The gas flow rate and pH apparently affect both the concentration and the kLa. The highest kLa of 2.1 X 10-2 s-1 is obtained at pH 4 with a gas flow rate of 4 L min-1.

Coefficient of ozone mass transfer during its interaction with an aqueous solution of formic acid in a bubble column reactor

A way of determining the coefficient of ozone mass transfer between the gas phase and liquid aqueous phase using a test compound (formic acid) is described. The values of ozone mass transfer coefficient (in aqueous solutions of 0.1–0.55 М HClO4 and 0–1 М НСООН, and in 0.75 М H2SO4, 0.125 М KHSO4, and 0–2 М НСООН) are determined along with the rate constants of the reaction of О3 with undissociated НСООН molecules and formate ions at 21 ± 1°С.

Mathematical model involving chemical reaction and mass transfer for the ozonation of dimethyl phthalate in water in a bubble column reactor

AbstractThis research investigated the establishment of a mathematical model for the ozonation of dimethyl phthalate (DMP) through the analysis of the mass transfer and reactions in a semi-batch bubble column reactor. Negative step tracer experiments were conducted with ozone as a tracer, which indicated that the gas phase is perfectly well mixed at the gas flow rate of 400 mL/min. Based on the results from ozone absorption experiments the mass transfer coefficient of ozone was determined to be 0.0054 s

Removal of dimethyl phthalate from water by ozone microbubbles

ABSTRACT This work investigates the removal of dimethyl phthalate (DMP) from water using ozone microbubbles in a pilot plant of 20 dm3 capacity. Experiments were performed under various reaction conditions to examine the effects of the initial concentration of DMP, pH of the medium, ozone generation rate, and the role of H2O2 on the removal of DMP. The DMP present in water was effectively removed by the ozone microbubbles. The removal was effective in neutral and alkaline media. Increase in the initial concentration of the target pollutant negatively affected its removal efficiency. The removal efficiency dramatically increased from 1% to 99% when the ozone generation rate was increased from 0.28 to 1.94 mg s−1 at pH 7. The total organic carbon measurements revealed that a complete mineralization of DMP was achieved within 1.8 ks at the high ozone feed rate. The use of t-butyl alcohol as the hydroxyl radical scavenger confirmed that the reaction between the target organic compound and ·OH radical dominated over its direct reaction with ozone. The reaction between DMP and ozone followed an overall second-order kinetics. The volumetric mass transfer coefficient of ozone in the reacting system and the enhancement factor increased with increasing initial concentration of DMP. Very low values of Hatta number were obtained at all initial concentrations of DMP and pH, which show that the mass transfer resistance was small.

Removal of diethyl phthalate from water by ozone microbubbles in a pilot plant

Ozone microbubbles (OMBs) were used to remove diethyl phthalate (DEP) from water in a pilot plant. The removal of DEP and the mineralization efficiency were investigated under various reaction conditions. The removal of DEP by OMBs was very effective at the high pH and high ozone generation rates. Almost complete mineralization of DEP could be achieved at the high pH. The contribution of OH was computed by using a hydroxyl radical scavenger (i.e. t-BuOH). In neutral and alkaline media, the reaction of DEP with OH dominated over its direct reaction with ozone. The overall oxidation reaction fitted a second-order kinetic model. The overall rate constant and the volumetric mass transfer coefficient of ozone slightly increased with increasing pH. The results indicate that the OMBs were efficient in terms of the reduction of concentration of DEP and its complete mineralization.

Relationship between acceleration of hydroxyl radical initiation and increase of multiple-ultrasonic field amount in the process of ultrasound catalytic ozonation for degradation of nitrobenzene in aqueous solution

The synergetic effect between ozone and ultrasound can enhance the degradation of nitrobenzene and removal efficiency of TOC in aqueous solution, and the degradation of nitrobenzene follows the mechanism of hydroxyl radical (OH) oxidation. Under the same total ultrasonic power input condition, the degradation rate of nitrobenzene (kNB), the volumetric mass transfer coefficient of ozone (kLa), and the initiation rate of OH (kOH) increases with introduction of additional ultrasonic field (1–4) in the process of ozone/ultrasound. The increasing amount of ultrasonic fields accelerates the decomposition of ozone, leading to the rapid appearance of the maximum equilibrium value and the decrease in the accumulation concentration of ozone in aqueous solution with the increasing reaction time. The increase in mass transfer of gaseous ozone dissolved into aqueous solution and the acceleration in the decomposition of ozone in aqueous solution synchronously contribute to the increase of kLa. The investigation of mechanism confirms that the increasing amount of ultrasonic fields yields the increase in cavitation activity that improves the mass transfer and decomposition of ozone, resulting in acceleration of OH initiation, which determines the degradation of nitrobenzene in aqueous solution.

Experimental Investigation on Ozone Mass Transfer Coefficient Enhanced by Electric Field in Liquid Phase

In order to improve the efficiency of ozone mass transfer in liquid phase, the method enhanced by electric field was put forward. The effect on ozone mass transfer was investigated from voltage, electrode spacing and gas flow rate. The result showed that ozone concentration in water and the total mass transfer coefficient increased correspondingly with the increase of the voltage, and ozone concentration in water and the total mass transfer coefficient increased correspondingly with increase of the electrode spacing in the range from 1 to 3 cm, and ozone concentration in water increased correspondingly with increase of the gas flow rate, but the total mass transfer coefficient reduced correspondingly.

Removal of Ammonia from Water by Ozone Microbubbles

Ammonia is a major source of water pollution. One of the most common methods for removal of ammonia from water is oxidation. In this work, ozonation of ammonia using microbubbles was studied in a pilot plant. The experimental results indicate that ozone microbubbles were quite effective in oxidizing ammonia. Oxidation of ammonia was effective at high pH and high ozone generation rates. Ozonation was found to occur by direct reaction of ozone with ammonia at the higher pH. However, the hydroxyl radicals were also involved at the lower pH. Bromide ions acted as a catalyst in the ozonation process, and a faster rate of oxidation of ammonia and lower yield of nitrate was observed. The volumetric mass transfer coefficient of ozone in water was determined. It increased with the increasing rate of ozone generation and the pH of the medium.

Estimation of mass transfer coefficient in ozone absorption by linear least square fitting and Simplex search methods

For physical ozone absorption without reaction, two parametric estimation methods, i. e. the common linear least square fitting and non-linear Simplex search methods, were applied, respectively, to determine the ozone mass transfer coefficient during absorption and both methods give almost the same mass transfer coefficient. While for chemical absorption with ozone decomposition reaction, the common linear least square fitting method is not applicable for the evaluation of ozone mass transfer coefficient due to the difficulty of model linearization for describing ozone concentration dissolved in water. The nonlinear Simplex method obtains the mass transfer coefficient by minimizing the sum of the differences between the simulated and experimental ozone concentration during the whole absorption process, without the limitation of linear relationship between the dissolved ozone concentration and absorption time during the initial stage of absorption. Comparison of the ozone concentration profiles between the simulation and experimental data demonstrates that Simplex method may determine ozone mass transfer coefficient during absorption in an accurate and high efficiency way with wide applicability.