Mass Balance Analysis of Ozone in Conventional Bubble Contactors

Ozone transfer into potable water was studied in a commercial scale contactor. Ozone mass balances have been calculated to determine ozone utilization in the contactor. Gas and liquid flowrates, as well as inlet ozone concentrations in the gas were varied. From these data it was possible to determine the mass transfer coefficient, the ozone consumption and the transfer efficiency. Procedures for calculating the design of contactors and the optimal operating conditions are proposed.     

Gas—liquid mass transfer in pulp suspension mixing operations

The rate of mass transfer from the gas to water phases was measured in a commercial, high-shear, laboratory mixer under conditions typical of medium-consistency bleaching. The gas—liquid volumetric mass transfer coefficient, k_La, was measured using the cobalt-catalyzed sulfite oxidation technique. Suspensions of fully-bleached kraft pulp and synthetic nylon fibres were used, with mass transfer rates measured over a range of suspension compositions and mixer operating conditions. In the presence of pulp fibre, mass transfer rates were significantly reduced over the comparable water cases. The same dramatic decrease in mass transfer was not observed for the nylon suspensions, although k_La did decrease with increasing suspension concentration. Comparison of this data with that obtained from ozone bleaching experiments confirmed that at medium-consistency gas—liquid mass transfer controls ozone bleaching.     

Ozone Absorption in Water: Mass Transfer and Solubility

Mass Transfer of ozone absorbed by water in a semi-comtinuous stirred reactor is studied at the lab scale. Experimental investigation using a complete factorial scheme shows a predominant effect of agitation speed and gas flow and results in a correlation for the mass transfer coefficient, k₁a. Solubility of ozone in water is estimated by evaluation of an apparent Henry's law constant for different temperatures (20* and 50*C), pH values (2 and 7) and a t constant ionic strength (0.13).     

Mass Balance Analysis of Ozone in a Conventional Bubble Column

Ozone transfer into potable water was studied in a conventional bubble column, and ozone mass balances have been calculated to determine ozone utilization efficiencies. Liquid and gas flow rates, as well as inlet ozone concentrations in the gas phase were varied. Using these data, it was possible to determine the ozone mass transfer coefficient, ozone transfer efficiency, and ozone consumption. A model of ozone transfer was established, and procedures for calculating the optimum design parameters and operating conditions are proposed.     

Experimental Study of Ozone Generation by Negative Corona Discharge in Mixtures of N2 and O2

Ozone generation by negative DC corona discharge in N₂-O₂ mixtures has been experimentally investigated using a coaxial wire-cylinder corona reactor operating at room temperature and atmospheric pressure. The experiments have been carried out under different gas flows (15 cm³ min^?1 to 200 cm³ min^?1) and gas compositions (5% to 90% of O₂), and the effect of these parameters on the corona current, the ozone density and the efficiency of the ozone generator have been analyzed. The global rate coefficients for ozone formation and destruction have also been evaluated, and their values compared with those reported by other authors. The maximum efficiency for ozone production was found in gas mixtures with oxygen content about 70–80%.     

Ozone Side-Stream Design Options and Operating Considerations

Disinfection with ozone is achieved by CT product, where “C” is residual ozone concentration and “T” is reaction time. Ozone residual is developed after ozone gas is dissolved into the water. Ozone dissolution is most often achieved by either bubble-diffuser or side-stream ozone systems. Side-stream ozone systems are different from bubble-diffuser ozone systems in many ways: 1) Ozone addition occurs outside of the ozone contactor; 2) additional energy is used due to side-stream pump operation; 3) equipment maintenance can be completed independent of ozone contactor operation; 4) ozone contactor size and shape can have unique design features, such as pipeline contacting or shallow-depth basins. Side-stream ozonation is a treatment technique that is gaining in popularity at larger and larger plants. Ozone generators can now operate at elevated ozone concentration, which improves the economics for installing and operating side-stream processes. Two different side-stream arrangements are discussed in this paper. The arrangements differ with the presence or absence of a de-gas vessel. The de-gas vessel option is more expensive in terms of capital and operating cost, but might be the chosen option for particular contactor configurations. Issues and considerations for installing a de-gas vessel are discussed in this paper.     

Modeling Hydrodynamics And Mass Transfer Parameters In A Continuous Ozone Bubble Column

A computer model based on the establishment of mass balance equations and on the model of fluids flow “stirred tank in series” was developed in order to calculate the ozone transfer coefficient k_La and kinetic constant k_c of ozone consumption by water. On the basis of experimental data, the correlation for gas holdup ε_g and bubble diameter d_vs, were proposed and used to calculate the specific interfacial area a. The liquid-phase mass transfer coefficient k_L for ozone was evaluated from a and the k_La data.     

After a Decade of Development: A Profile of Municipal Drinking Water Plants Utilizing a Sidestream Injection Process

The technology of rapid ozone mass transfer followed by degasification, the GDT? Process, was first introduced in 1995 Mazzei, A.L., Meyer, R. and Bollyky, L.J. . Proceedings International Ozone Association Pan American Group Conference. “Mass Transfer of High Concentration Ozone with High Efficiency Injectors and Degassing Separators”, November, Cambridge, MA [Google Scholar] by Mazzei et al. At the time of introduction, municipal ozone installations utilized a low concentration, air-fed ozone gas as a disinfectant in atmospheric contact basins fitted with fine bubble diffusers (FBD). Over the past decade, air- fed ozone has given way to highly concentrated, oxygen-fed ozone. The change to concentrated oxygen feed gas has increased concerns about the corrosive effects of high finished water dissolved oxygen (DO). Water treatment plants using oxygen fed ozone have reported finished water DO levels in excess of 20 mg/L, with some plants resorting to air sparging at the back end of the contact basin to restore finished water to atmospheric gas levels.

However, the evolution to oxygen feed gas has also produced significant cost benefits. Operating an ozone generator on oxygen increases its ozone production; reducing the size and capital cost of the generator needed to meet ozone output requirements. The use of a concentrated gas stream has also led to the development of side stream injection systems, which move the gas mixing out of the atmospheric basin and into the upstream pipeline (Neemann, 2002 Neemann, J. . The Use of Injectors and Nozzles for Sidestream Ozone Addition. Proceedings AWWA Water Quality Technology Conference.  [Google Scholar]), resulting in a more compact contact basin design. Municipal water plants not having a CT requirement have streamlined one step further, by eliminating the ozone contact basin in favor of a sidestream injection Process. This paper reviews the technology of the GDT? sidestream injection process and introduces 2 municipal water treatments plant (WTP) installations utilizing this process to remediate taste and odor compounds and as a method to reduce finished water dissolved oxygen concentrations.     

旋转微气泡反应器强化臭氧降解水中对硝基苯酚

臭氧氧化技术在水处理系统中具有良好的应用前景,但实际应用中受到臭氧传质及氧化选择性的限制。故本研究以对硝基苯酚废水为研究对象,采用一种新型旋转微气泡反应器,通过多孔陶瓷填料的旋转将臭氧气泡尺寸破碎至微米级别,实现对废水降解过程的强化,同时本研究还进一步考察了操作条件对臭氧传质过程和臭氧分解产生羟基自由基过程的影响规律。实验结果表明,提高反应器转速和气体流量可以加快臭氧传质和羟基自由基产率,同时提高溶液pH也可以提高羟基自由基产率进而提高对硝基苯酚的去除率。与其他操作变量相比,反应器转速的影响最为明显,说明改善臭氧气泡流体力学行为能有效地提高对硝基苯酚的去除效果,体现反应器强化臭氧体系的可行性。此外,二甲亚砜的加入抑制了对硝基苯酚的去除,说明臭氧的间接氧化方式是降解对硝基苯酚的一种重要途径。本研究结果为旋转微气泡反应器在臭氧氧化降解过程中开发及应用提供合理指导。     

Research Note: Penetration of Ozone Gas Across the Shell of Hen Eggs

Increasing evidence indicates that ozone gas is effective against Salmonella on and within shell eggs. However, information on the penetration of ozone across egg shell is limited. In this study, whole hen egg shells, filled with indigotrisulfonate solution (OD₆₀₀ ～1), were exposed to ozone gas (12–14% wt/wt O₃ in O₂) at 1.5 liters/min and atmospheric pressure for ≤ 40 min with appropriate controls. Ozone penetrated the shells over time (r²?=?0.9974) causing indigo decoloration and increasing its transmittance from 16 to 28% after gas exposure for 40 min. This study confirms ozone penetration through egg shell using a simple qualitative technique.     

Ozone Treatment in Cooling Water Systems

Ozone treatment for preventing the biofouling in cooling water systems is investigated.

In the fresh water system, the separating effect of the ozonated water on the microorganisms such as the sphaerotilus and the zoogloea which adhere to the piping and form the slime is recognized. When the ozonated water is supplied intermittently to the piping without stopping the flow of the cooling water, a constant volume of cooling water can be maintained. At the velocity of 1 m/sec, the amount of metal corrosion produced by the ozonated water is reduced on the mild steel, increased on the copper and does not change on the cast iron, when compared with that produced by the water containing no ozone.

In the seawater system, since many substances are oxidized by the ozone, the same treatment as that in the fresh water system cannot be applied. However, if the seawater in the cooling system can be replaced with ozone-containing air intermittently once a week, the adhesion of organisms such as barnacles and mussels to the piping can be prevented without having a bad influence on the other living oceanic organisms.     

Performance of a hydro-filter — Mass transfer coefficient and gas-liquid interfacial area

An experimental study of the effect of operating conditions on the performance of a hydro-filter (marble-bed scrubber) has been conducted. The overall volumetric mass transfer coefficient, K_Ga, remains constant while the gas flow rate changes in the stable operating regions but increases sharply in the region above the loading point, corresponding to a sharp increase in the total pressure drop of the hydro-filter. Since the gas flow is turbulent and the liquid flow is laminar under the present experimental conditions, the value of K_Ga is strongly dependent on the flow conditions of the liquid and its properties, while those of the gas have less effect. The performance of a hydro-filter as a mass transfer device is shown to be superior to other types of scrubbers although its main drawback is large pressure drop.     

Effect of Chemical Reaction and Mass Transfer on Ozonation of the Azo Dyes Reactive Black 5 and Reactive Orange 96

Ozonation of wastewater containing azo dye has been studied to evaluate the enhancement of ozone mass transfer from O₂O₃ gas into water with the presence of chemical reactions in a bubble column reactor. Experiments were performed at different initial dye concentrations and at various gas flow rates. C.I. Reactive Black 5 (RB 5) and C.I. Reactive Orange 96 (RO 96) have been chosen as representative model substances being found in wastewater from textile-finishing wastewater. Results show that the rate of ozone mass transfer increases with increasing initial dye concentration and gas flow rate. Consequently, an enhancement factor E for ozone mass transfer with chemical reaction could be calculated which increases with dye concentration. The chemical reaction between ozone and dye enhanced the mass transfer within the liquid film of the gas liquid boundary. The greatest enhancement factor for wastewater containing RO 96 of 2050 mgL^?1 is E = 15.4 compared with E = 9.1 for RB 5 of 3800 mgL^?1, both for gas flow rates of 19 Lh^?1. For lower gas flow rates, higher enhancement factors were observed, particularly for RO 96.     

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.     

Use Of Static Mixer For Oxidation And Disinfection By Ozone

Ozone is used in drinking water treatment as a biocide, as an oxidant and as a pretreatment in order to improve the performance of subsequent processes. Increasing concern over the quality of drinking water has led to a number of new stringent regulations in the control of chemical and microbiological contaminants. Disinfection deals with the concept of “CT”, which is the need to maintain a certain minimum concentration for a given time. Under ideal laboratory conditions, it is 0.4 mg O₃/L for 4 min. In practice, since the method for the CT determination has not been finalized by the EPA, “T” can be the minimum detention time of 90% of total flow, and “C” can be a measured ozone residual at the outlet of cells of the contactor. New standards for micropollutants in drinking water imply an optimization of the ozonation step, by improving the ozone transfer from gas to water, and the control of the detention time as well as ozone residual within the contactor.

All these considerations have led us to use static mixers to transfer ozone into water. This process enables us to control the ozone concentration in water and detention time. It is a very simple system, with very low maintenance requirements due to the lack of moving parts. Civil engineering is minimized. A pilot scale study is presented here. It took place at the Méry-sur-Oise water treatment plant, on a pilot plant working at 8-12 m³/h. It is composed of a static mixer for the transfer of ozone from gas to liquid, linked to an air lift to separate gas from liquid, providing ozonated water.

The optimization of transfer was achieved by studying the impact of water flow, gas flow and ozone concentration in the gas. It is possible to reach 90% of transfer in less than 15 s. Headloss (ΔP) across the mixer is a function of gas and water flows and remains economically very acceptable as 0.15 bar for 12 m³/h.

Atrazine removal was studied using a static mixer, an air lift and a contact pipe 80-m long, providing an optimum contact time phase, working as a plug flow reactor. Ozone and H₂O₂/O₃ treatments were compared. The maximum reduction of atrazine concentrations (e.g., for an infinite contact time) is a function of the amount of transferred ozone, but H₂O₂ influences the kinetics of the reaction. In the presence of H₂O₂ with a ratio of H₂O₂ to O₃ of 0.4 w/w, maximum elimination is reached in 2 min 30 s.

The effect of such treatments on environmental bacteria also was followed. A counting of total germs at 20°C showed a decrease of 1- to 3-logs 10 after 1 min 30 s of contact time for about 2 mg/L of transferred ozone. No significant difference between treatments with or without H₂O₂ was shown. The same conclusions were obtained from heterotrophic plate counts (37°C) and epifluorescence countings.     

Gas—liauid mass transfer in three-phase stirred tank reagors: Newtonian and non-newtonian fluids

Gas—liquid mass transfer has been investigated in gas—liquid-solid three-phase stirred tank reactors with Newtonian and non-Newtonian liquids. Volumetric mass transfer coefficients and gas hold-ups were measured in a 0.2 m i.d. stirred tank reactor and the effects of low-density polymeric particles (ρ_s, =1030 and 1200 kg/m³; up to 15 vol%) on gas—liquid mass transfer were examined. The volumetric mass transfer coefficients in water were found to decrease due to the presence of solid particles at constant impeller speed and superficial gas velocity. On the other hand, solids loading led to higher mass transfer rates in non-Newtonian carboxymethyl cellulose aqueous solutions. Our previously proposed model for mass transfer in gas—liquid two-phase systems was extended to gas—liquid—solid three-phase systems. Reasonable agreement was found between the predictions of the proposed model and the experimental data.     

Ozone Production Influenced by Increasing Gas Pressure in Multichannel Dielectric Barrier Discharge for Positive and Negative Pulse Modes

This paper describes the influence of gas pressure on the conversion of O₂ to O₃ and the ozone production efficiency in a multichannel dielectric barrier discharge (DBD) reactor utilizing positive and negative pulses. Results show that conversion of O₂ to O₃ is continuously enhanced by the increase of gas pressure (0.1–0.24 MPa) while the rising speed of oxygen conversion with the increasing gas pressure at fixed specific input energy is reduced above 0.15 MPa. The maximum ozone generation efficiency is increased with increasing gas pressure (0–0.2 MPa) while positive pulse exhibits higher energy efficiency. The maximum ozone generation efficiency is suppressed with further increase of gas pressure (0.2–0.24 MPa) while no significant difference in ozone generation efficiency is observed for two unipolar pulse modes. Results also show that 0.2 MPa is the optimal working gas pressure to obtain the maximum ozone generation efficiency and increasing gas pressure would lead to remarkable increase of ozone generation efficiency for ozone production at high energy densities in multichannel DBD.     

Modelling Industrial Wastewater Ozonation In Bubble Contactors. 2. Scale-up From Bench To Pilot Plant

A kinetic model constituted by ozone mol balance equations both in the gas and in the water phases and a total mole balance equation has been applied to predict concentrations of dissolved ozone, C_o3, ozone partial pressure at the reactor outlet, P_(o3)0, and remaining chemical oxygen demand, COD, for the ozonation of two industrial wastewaters released from distillery and tomato processing plants.

Kinetic equations for ozone absorption rate present in the model were derived from the application of film theory to an irreversible gas-liquid reaction. Parameters involved in the model, reaction rate and mass transfer coefficients, Henry's law constant, etc., were estimated from bench-scale experiments. The model was applied to ozonation in bubble contactors of height/diameter ratio equal to that of the bench scale contactor and to a pilot plant bubble column of a height/diameter ratio about 3.6 times higher.     

Experimental Study of Oxygen Mass Transfer Coefficient in Bubble Column with High Temperature and High Pressure

The volumetric gas‐liquid mass transfer coefficient, k_Lα, for oxygen was studied by using the dynamic method in slurry bubble column reactors with high temperature and high pressure. The effects of temperature, pressure, superficial gas velocity and solids concentration on the mass transfer coefficient are systemically discussed. Experimental results show that the gas‐liquid mass transfer coefficient increases with the increase in pressure, temperature, and superficial gas velocity, and decreases with the increase in solids concentration. Moreover, k_Lα values in a large bubble column are slightly higher than those in a small one at certain operating conditions. According to the analysis of experimental data, an empirical correlation is obtained to calculate the values of the oxygen volumetric mass transfer coefficient for a water‐quartz sand system in two bubble columns with different diameter at high temperature and high pressure.     

Enhancement of Ozone Mass Transfer by Stainless Steel Wire Mesh and Its Effect on Hydroxyl Radical Generation

ABSTRACT

In order to improve the mass transfer efficiency of ozone in water, stainless steel wire mesh (SSWM) corrugated structure was packed into a microbubble ozone reactor to enhance the mass transfer efficiency. The results showed that the SSWM/O₃ system could effectively improve the mass transfer efficiency. When the concentration of ozone in the liquid phase reached a stable state, it was about 21 mg/L, which was about 14% higher than that of ozone alone; the apparent mass transfer coefficient (K_La) was 0.7255 min^?1, which was about 51% higher than that by ozone alone systems. The hydroxyl radicals in the SSWM/O₃ system were more generated than that of ozone alone. After 6 min of operation, the concentration of hydroxyl radicals increased by 60 µmol/L compared with that in ozone alone system. The Chemical Oxygen Demand (COD) removal efficiency of biologically treated leachate by SSWM/O₃ system was about 10% higher than that of ozone alone system after 120 min of reaction. The effects of pressure, temperature, ozone inlet concentration, and flow rates on the ozone concentration in the liquid phase and the generation of hydroxyl radicals were also investigated. The results indicated that reactor pressure has little effect on ozone concentration in liquid phase, but increasing pressure helps to generate ·OH; ozone concentration and ·OH generation in liquid phase increase with the increase of inlet ozone concentration and flow rate; ozone concentration in the liquid phase decreases with the increase of temperature, but ·OH generation increases with the increase of temperature. Our results indicate that the system consisting of SSWM and microbubble column reactor is an efficient process for the intensification of ozone-based advanced oxidation processes.