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.     

Evaluation of Decolorization,Mineralization, and Toxicity Reduction of Tropaeolin O in Water by Ozonation with UV Irradiation

The combination of ozonation with UV irradiation can remove Tropaeolin O (AO6) and its by-products effectively and completely. The ozone dose affects the rate of decolorization, AO6 species removal, and dissolved organic carbon (DOC) reduction significantly. After 240 minutes of ozonation, the average DOC removal efficiency (η_DOC) for O₃ alone was about 0.79, while η_DOC for O₃/UV was 1.0. The average DOC removal rate was low at early stage of ozonation due to decolorization and low DOC. At later stage of ozonation, average DOC removal rate decreases because of the formation of persistent intermediates. The ozone consumption was consistent with η_DOC. The ratio of ozone consumption to ozone applied decreased from 14 to 12% when η_DOC < 40% because the decolorization in the early stage of the ozonation of AO6 may consume a relatively large amount of ozone. It was found that NO₂, NO, CO₂, and small amount of SO₂ was detected in the off-gas. The effective concentration (EC50) increased from 23.48% to 100%, suggesting that the toxic reduction was achieved, and O₃/UV system was superior to O₃ alone system     

Comparative study of the Effect of Oxygen and Oxygen/Ozone mixtures on the Electrochemical behaviour of different Metals

The effect of dissolved ozone on the electrochemical behaviour of heat exchanger structural materials (carbon steel, stainless steel, copper, 70:30 copper–nickel, aluminium brass and titanium grade 1) was studied to evaluate the possibility of using ozone as sole biocide in cooling water treatment. With this purpose, voltammetric and open circuit potential (OCP) against time measurements at different ozone concentrations between 0.1 and 1.2 ppm were made. Results show different electrochemical responses according to the metal characteristics and the solution composition. First, the passivity of titanium and stainless steel was not affected by ozone. A linear OCP against log time relationship was found for titanium, suggesting the growth of a barrier film in both O₂ and O₂/O₃ solutions. Mild steel does not passivate in synthetic cooling water either with O₂ or O₂/O₃ in the solution. In the presence of ozone the breakdown of passivity is facilitated and makes the repassivation difficult. Ozone enhances the dissolution of Cu₂O and the formation of Cu(II) species leading to less protective films. Both processes are strongly influenced by the pH. Finally, the dissolution of aluminium brass is higher than that of copper or copper–nickel.     

Hydroxyl Radical/Ozone Ratios During Ozonation Processes. II. The Effect of Temperature,pH, Alkalinity,and DOM Properties

The influence of temperature, pH, alkalinity, and type and concentration of the dissolved organic matter (DOM) on the rate of ozone (O₃) decomposition, O₃-exposure, ?OH-exposure and the ratio R_ct of the concentrations of ?OH and O₃ has been studied. For a standardized single ozone dose of 1 mg/L in all experiments, considerable variations in O₃-exposure and ?OH-exposure were found. This has important implications for water treatment plants regarding the efficiency of oxidation and disinfection by O₃. In oligotrophic surface waters and groundwaters, minimal calibration experiments are needed to model and control the ozonation process, whereas in eutrophic surface waters more frequent measurements of O₃ kinetics and R_ct values are required to evaluate seasonal variations.     

Ozone-Based Processes Applied to Municipal Secondary Effluents

This study analyzes the performances of 2 methods of oxidation based on ozone, namely ozonation and ozone combined with hydrogen peroxide (O₃/H₂O₂), on two biotreated municipal wastewater effluents. The main parameters monitored to evaluate the effectiveness of the processes were Chemical Oxygen Demand (COD), Dissolved Organic Carbon (DOC) and Biochemical Oxygen Demand (BOD₅). Ozonation and O₃/H₂O₂ treatment removed 44% and 48%, respectively, of the COD, after 90 min, of the secondary effluent of Calafell wastewater treatment plant (Spain). On the secondary effluent from the Grasse wastewater treatment plant (France), these same treatments (O₃; O₃/H₂O₂) achieved, respectively, a degradation of 52% and 100% of the COD after 60 min. The transferred ozone dose (TOD) during Calafell and Grasse effluents' ozonation were 122 mg·L^?1 and 77 mg·L^?1 after 90 min, respectively. A low removal of DOC was monitored during both O₃ or O₃/H₂O₂ treatments applied to Calafell wastewater, respectively 12% and 14%. Better DOC reductions were obtained on the water of Grasse treated with O₃ or O₃/H₂O₂, respectively, 48% and 60%. In addition, ammonia nitrogen was oxidized to nitrate nitrogen thus giving rise to an over ozone consumption. And finally, both processes proceeded with an increase of pH values. These results highlight the strong dependency of O₃ or O₃/H₂O₂ treatment effectiveness in terms of dissolved organic matter (DOM) removal and ozone consumption on wastewater composition (organic and inorganic substances).     

The Control of Brominated By-products and the Removal of Organic Pollutants during the Ozone/Hydrogen Peroxide Treatment of Secondary Effluent

This study aims to establish appropriate conditions to control the formation of bromate ion and brominated organic compounds during the O₃/H₂O₂ treatment of the secondary effluents of sewage. When the H₂O₂/O₃ mole ratio of injection was above 0.5 and the dissolved ozone concentration was below 0.1 mg/L, bromate ion formation was controlled, and treatment purposes such as the reduction of estrogenic activity or organic matter were completed. The formation of TOBr and individual brominated organic compounds during O₃/H₂O₂ treatment was also completely controlled.     

Combination of Ozone with Activated Carbon as an Alternative to Conventional Advanced Oxidation Processes

The objective of this study was to compare the efficiency of O₃/granular activated carbon (GAC) to enhance ozone transformation into ·OH radicals, with the common advanced oxidation processes (O₃/OH^?, O₃/H₂O₂). The results obtained with model systems under the given experimental conditions showed that the system O₃/OH^? (pH 9) and O₃/H₂O₂ (pH 7, [H₂O₂] = 1·10^?5 M) are more efficient than O₃/GAC (pH 7, [GAC] = 0.5 g/L) to enhance ozone transformation into ·OH radicals. However, in Lake Zurich water the O₃/GAC process has a similar efficiency as O₃/H₂O₂ for ozone transformation into ·OH radicals. The results also show that the presence of GAC during Lake Zurich water ozonation leads to (i) removal of hydrophilic and hydrophobic micropollutants, (ii) reduction of the concentration of CO₃ ^2?/HCO₃ ^?, and (iii) decrease of the concentration of dissolved organic carbon (DOC) present in the system.     

The Impact of Traces of Hydrogen Peroxide and Phosphate on the Ozone Decomposition Rate in “Pure Water”

To obtain an idea of the magnitudes of the ozone loss rates r_O3 in practical applications of ozone, an overall determination of the ozone decay profiles and rate constants was carried out in four different systems. These systems resemble different conditions for industrial application of ozone and the peroxone process, such as in the field of micro electronics, drinking water purification, disinfection, etc. Therefore, the behavior of ozone was monitored in the pH range from 4.5 to 9.0, in pure water and phosphate buffered systems in absence and presence of small amounts of hydrogen peroxide (10^?7 M to 10^?5 M H₂O₂). First the reproducibility of the ozone decay profiles was checked and from the various kinetic formalism tests, the reaction order 1.5 for the ozone decay rate has been selected. As expected, hydrogen peroxide increases the decay rates. In pure systems, added concentrations of 10^?7M H₂O₂ already cause a remarkable acceleration of the ozone decay in the acidic and neutral pH range compared to the pure systems. However for alkaline pH conditions almost no effect of the low hydrogen peroxide concentrations was noticed. Contradictory to literature data, in the absence of hydrogen peroxide, ozone displays faster decays in the buffered systems of low ionic strength of 0.02 compared to pure water. This acceleration is more pronounced for acidic pH conditions. Low concentrations of phosphate may indeed accelerate the ozone decay in the presence of organic matter. Adding H₂O₂ concentrations below 10^?5M to phosphate buffered solutions has a negligible effect on the ozone decay rate compared with pure water systems, except for pH 7. It appears that phosphate masks the effect of hydrogen peroxide below 10^?5 M as tested here. Thus the application of AOP's by adding low concentrations of hydrogen peroxide is not well feasible in the presence of phosphate buffers in pure water systems.     

Efficient Decomposition of Trichloroethylene (TCE) in Groundwater by Ozone-Hydrogen Peroxide Treatment

It was verified that the ozone-hydrogen peroxide treatment (O₃/H₂O₂) was very effective for decomposing trichloroethylene (TCE) in groundwater. The reaction efficiency of O₃/H₂O₂ was 40% better than that of ozone treatment by using a diffuser type reactor and the optimum operating conditions were also revealed by laboratory-scale experiments and computer simulations. Taking these results into consideration, the 2-port ozone injection method using an ejector-type reactor was investigated to decompose TCE more rapidly and efficiently, and it was revealed that the ozone dose necessary for satisfying the Japanese water quality standard for drinking water (0.03mg/L) by the 2-port ozone injection method was 13% less than that by the conventional 1-port ozone injection method under the condition of the same amount of ozone injected. Also, the effectiveness of the 2-port injection method was proved by a sequential plant-scale experiment for about 40 days.     

Bromate Formation in Ozone and Advanced Oxidation Processes

Both the direct ozone reaction and the indirect hydroxyl radical reaction are important in ozonation of drinking water. This article investigates the effectiveness of ozone versus the advanced oxidation process of ozone coupled with hydrogen peroxide in the formation of bromate. The investigation was conducted on a pilot scale at various H₂O₂:O₃ dose ratios of 0.1, 0.2, and 0.35 at different times of the year. The results of this study show a reduction in bromate with the addition of hydrogen peroxide to an ozone system versus ozone alone. It was also observed that bromate increased with increased H₂O₂:O₃ ratios; however, concentrations were still lower than those in the ozone only system.     

An On-Site Cooling Tower Treated by Stand-Alone Low-Concentration Dissolved Ozone

We report on an on-site 500 RT cooling tower ozone treatment process, in which chemicals other than ozone itself were completely eliminated. Ozone in an amount leading to less than 0.1 ppm of dissolved ozone was continuously introduced via side-stream injection into the circulating water returning from the chiller. The ozonated water was initially made to flow from the distributor to the filler in order to eliminate the growth of algae, and then to the chiller to reduce the corrosion and the fouling in the water. Positive ions such as Ca⁺² and Mg⁺² in the circulating water were precipitated by chelating them with carboxylic acids formed by the oxidation of organic compounds. We observed that using an ozone dosage of 0.1 ppm resulted in a colony-forming unit (CFU) less than 2 × 10³ /mL. With that well-controlled CFU, corrosion controlling and scale reducing were achieved as well.     

Effects Of Ozone-Hydrogen Peroxide Combination On The Formation Of Biodegradable Dissolved Organic Carbon

The effects of ozone and ozone/hydrogen peroxide on BDOC formation were studied with the “Ozotest” method, a laboratory technique that permits the assessment of oxidation efficiency. Oxidation treatments were performed on river water and sand filter effluent samples. Ozone consumption, reduction of UV absorbance, and BDOC formation were monitored during the experiments. The ratio of 0.35-0.45 mg H₂O₂ per mg O₃ used to degrade pesticides also was optimal for the oxidation of organic matter. BDOC formation versus ozone dose curves with ozone alone or ozone/peroxide system were similar. BDOC formation was optimum at an applied ozone dose of 0.5-1 mg O₃/mg C (contact time = 10 min). The ozone/peroxide system yielded lower BDOC values than ozone alone, a phenomenon related to differences in byproducts generated by the two oxidative systems. Moreover, reduction of the concentration of DOC was higher with ozone/hydrogen peroxide than with ozone alone. For both oxidant systems, BDOC formation occurred during the first minute of treatment.     

Assessment of the Efficacy of Intermittent Ozone Disinfection

An example of intermittent disinfection occurs in dental-unit water systems (DUWS), which are disinfected only for a specified time per each day. The efficacy of intermittent ozonation was evaluated using a laboratory-scale, membrane-based ozone disinfection system (MBODS), which delivers bubbleless dissolved ozone to the DUWS. A new tool - the weighted Ct value, or C_w, - was applied to interpret heterotrophic plate counts (HPC) data. To achieve the American Dental Association's (ADA's) criterion (<200 CFU/mL), the required ozone dosage was C_w > 0.07 mg–O₃/L. However, even the highest ozone dosage (C_w > 0.130 mg/L) allowed biofilm HPC to persist at over 10⁴ CFU/cm². Although a higher C_w killed planktonic and biofilm bacteria more thoroughly, it also generated more biodegradable dissolved organic carbon (BDOC). Thus, this research illustrates the inherent trade-off of intermittent ozonation: a higher C_w kills more bacteria during the ozonation period, but creates more BDOC that fosters biofilm regrowth when ozonation is off.     

Ozonation and Advanced Oxidation of Wastewater: Effect of O3 Dose,pH, DOM and HO•-Scavengers on Ozone Decomposition and HO• Generation

The decomposition of ozone in wastewater is observed starting 350 milliseconds after ozone addition. It seems not to be controlled by the autocatalytic chain reaction, but rather by direct reactions with reactive moieties of the dissolved organic matter (DOM). A larger ozone dose increases ozone consumption prior to 350 milliseconds but decreases the rate of ozone decomposition later on; this effect is predicted by a second-order kinetic model. Transferred Ozone Dose (TOD) is poorly correlated with ozone exposure (= ∫[O₃]dt) indicating that TOD is not a suitable parameter for the prediction of disinfection or oxidation in wastewater. HO^? concentrations (> 10^?10 M) and R_ct (=∫[HO^?]dt/∫[O₃]dt > 10^?6) are larger than in most advanced oxidation processes (AOP) in natural waters, but rapidly decrease over time. R_ct also decreases with increasing pre-ozonation doses. An increase in pH accelerates ozone decomposition and HO^? generation; this effect is predicted by a kinetic model taking into account deprotonation of reactive moieties of the DOM. DOC emerges as a crucial water quality parameter that might be of use to normalize ozone doses when comparing ozonation in different wastewaters. A rapid drop of absorbance in the water matrix—with a maximum between 255–285 nm—is noticeable in the first 350 milliseconds and is directly proportional to ozone consumption. The rate of absorbance decrease at 285 nm is first order with respect to ozone concentration. A kinetic model is introduced to explore ozone decomposition induced by distributions of reactive moieties at sub-stoichiometric ozone concentrations. The model helps visualize and comprehend the operationally-defined “instantaneous ozone demand” observed during ozone batch experiments with DOM-containing waters.     

Dynamic Performance of Ozonation Treatment for Nonionic Surfactants (Polyoxyethylene Alkyl Ether) in a Bubble Column Reactor

The ozonation of a nonionic surfactant, Sannonic SS-90 (polyoxyethylene alkyl ether), which is one of polyoxyethylene nonionic surfactants, in water has been investigated using a bubble column. The effects of initial nonionic surfactant concentration, ozone gas flow rate, inlet ozone concentration in the gas-phase, liquid-phase temperature and hydrogen peroxide dose on decomposition of Sannonic SS-90 were systematically examined. The decomposition rate of Sannonic SS-90 decreased with the increase in the initial surfactant concentration and increased with increasing ozone flow rate and temperature. It was found that the rate of Sannonic SS-90 mineralization was weakly dependent on the gas-phase inlet ozone concentration in the range of the gas-phase inlet ozone concentration in this study. The oxidation rate increased with increasing concentration of H₂O₂, reached a maximum value and then decreased with further increasing of H₂O₂ concentration. The dynamic performance of the ozonation in a semi-batch bubble column was simulated using a mathematical model based on a tanks-in-series model. Reasonable agreement between the present experimental data and the simulated results was found.     

Pilot-Scale Evaluation of Ozone vs. Peroxone for Trihalomethane Formation

Both the direct ozone reaction and the indirect hydroxyl radical reaction are important in the ozonation of drinking water. This paper investigates the effectiveness of ozone versus ozone coupled with hydrogen peroxide (peroxone) with respect to trihalomethanes formation. The investigation was conducted on a pilot-scale at various H₂O₂:O₃ dose ratios of 0.1, 0.2, and 0.35 and change in peroxide addition point (pre- and post-ozonation). It was observed that the addition of peroxide, either before or after ozonation, increased trihalomethane concentrations and that increasing H₂O₂:O₃ increased trihalomethane concentrations. In comparing the addition point of peroxide, addition prior to ozonation better controlled trihalomethane formation than after ozonation.     

Influence of presence of tannic acid on removal of sodium dodecylbenzenesulphonate by O3 and advanced oxidation processes

BACKGROUND: The objective of the present investigation was to determine the role of the tannic acid (TAN) component of organic matter dissolved in water, in the removal of sodium dodecylbenzenesulphonate (SDBS) by ozone and by O₃/H₂O₂, O₃/granular activated carbon (GAC) and O₃/powdered activated carbon (PAC) advanced oxidation processes. RESULTS: Low doses of TAN (1 mg L^?1) during SDBS ozonation cause (i) an increased ozone decomposition rate and (ii) an increased SDBS removal rate. The SDBS removal rate with ozone in the presence of TAN was reduced when HCO₃^? ions were added. A rise in TAN concentration increased the SDBS removal rate, with a linear relationship between added TAN and the removal rate. SDBS was removed more effectively by O₃/GAC, O₃/PAC and O₃/H₂O₂ systems in the presence of TAN. CONCLUSIONS: Results obtained indicated two mechanisms involved in the generation of HO^· radicals by the O₃/TAN interaction: (i) direct generation of HO^· radicals from the reaction between ozone and TAN, and (ii) increased generation of O₂^?· radicals in the medium, enhancing the transformation of ozone into HO^· radicals by different radical reactions. In O₃/GAC and O₃/PAC systems, HO^· radicals are mainly generated in the O₃/TAN interaction, which is a homogeneous reaction with fast kinetics, whereas the O₃/GAC and O₃/PAC interactions are in a heterogeneous phase with much slower kinetics, and are therefore not competitive in the generation of HO^· radicals. Copyright © 2008 Society of Chemical Industry     

Simulation Of Ozone Transfer In Water. Comparison With A Pilot Unit

A computer simulation of a bubble column is established to determine the residual ozone concentration in the air and the dissolved ozone residual in the water. This study is aimed to improve the control of ozonation systems, both technically and economically.

The program is based on mass balances along the contact column, which take into account the ozone consumption due to both the self-decomposition and the reactions with organic compounds contained in the water. The experimental measurements allow quantification of the ozone concentration in the air at the inlet and outlet of the pilot unit, as well as the dissolved ozone concentration at different heights along the column. A relation between the transfer coefficient, k_La, and the superficial velocity of the ozonated air is established. It is specific to the diffusion characteristics of the pilot unit. The k_La then is reintroduced in the program.

The calculated and the measured values are shown to be similar regarding the transfer yields, the dissolved ozone concentrations at the pilot unit outlet and the profiles of dissolved ozone concentrations along the contact column. Using the program, the influence of the most important parameters of ozonation on the transfer (treatment rates, initial ozone concentration in the air, pH and organic content of the water, k_La values) have been simulated.     

The Effect of Gaseous Diluents on Ozone Generation from Oxygen

Ozone generation in a negative corona discharge has been experimentally investigated using both a pure oxygen and in binary mixtures of oxygen with several gases. The concentration of ozone (O₃) in such mixtures is found to be dependent both on the input energy density η, dissipated in unit volume of gas mixture and on the type and the concentration of the additives. The experimentally measured dependencies of ozone concentration on the input energy density (O₃) = f(η) have been fitted using the Vasiliev–Kobozev–Eremin formula and the specific rate coefficients for ozone formation K_f and ozone decomposition K_d have been calculated. Using Ar, N₂ or CO₂ as admixtures, an increase in the specific rate coefficient for ozone generation was observed for increasing concentrations of added gaseous impurity into oxygen. In contrast, admixtures with SF₆ or CCl₂F₂ caused a substantial reduction of K_f values. The absolute values of ozone concentration at constant input energy density were observed to decrease with decreasing concentrations of oxygen in all mixtures.     

Preliminary Results on Ozonation Enhancement by a Perfluorinated Bonded Alumina Phase

A preliminary study was undertaken in order to determine the efficiency of ozonation in the presence of perfluorooctylalumina (PFOA) for the removal of organic substances from aqueous solutions by ozone. PFOA was synthesized by reacting hydrated alumina with pentadecafluorooctanoic acid. A monomolecular layer of non-polar perfluorinated alkyl chains, orientated away from the surface of alumina, capable of dissolving ozone and organic molecules, was obtained. The efficiency of ozonation alone and ozonation in the presence of PFOA or Al₂O₃ was compared. PFOA was found to significantly enhance the degradation level of organic substances in comparison with ozonation alone. Al₂O₃ did not show any catalytic activity.