Ozone Inactivation Research Articles

Gaseous ozone inactivation of Bacillus atrophaeus spores on ceramic and porcelain tiles

In this study, we investigated the ozone inactivation efficiency of Bacillus atrophaeus spores attached to various tile surfaces. Eight different types of tiles were employed, considering factors such as porosity (ceramic, porcelain), color (white, black), and glossiness (matte, glossy). Inactivation was performed by exposing the spore-loaded tiles to ozone gas for a specified duration. The inactivation efficiencies of ozone gas on different tile surfaces were compared by analyzing the colony-forming units of desorbed Bacillus atrophaeus cultured in a growth medium. Results revealed a reduction in colony counts with increasing ozone exposure time, indicating a proportional enhancement in inactivation effectiveness on ozone exposure time. After exposure to ozone gas for 30 min or longer, more than 90% of spores on each tile were inactivated. Regarding porosity, ceramic tiles exhibited slightly superior inactivation effects compared to porcelain tiles. Additionally, in terms of glossiness, glossy tiles demonstrated better inactivation effects than matte tiles. However, no significant differences were observed in inactivation effects based on the color of the tiles.

Systematic investigation and modeling prediction of virus inactivation by ozone in wastewater: Decoupling the matrix effects

Water disinfection is undoubtedly regarded as a critical step in ensuring the water safety for human consumption, and ozone is widely used as a highly effective disinfectant for the control of pathogenic microorganisms in water. Although the diminished ozone efficiencies in complex water matrices have been widely reported, the specific extent to which individual components of matrix act on the virus inactivation by ozone remains unclear, and effective methodologies to predict the comprehensive effects of various factors are needed. In this study, the decoupled impact of the intricate water matrix on the ozone inactivation of viruses was systematically investigated and assessed from a simulative perspective. The concept of "equivalent ozone depletion rate constant" (k') was introduced to quantify the influence of different species, and a kinetic model was developed based on the k' values for simulating the ozone inactivation processes in complex matrix. The mechanisms through which diverse species influenced the ozone inactivation effectiveness were identified: 1) competition effects (k' = 105∼107 M–1s−1), including organic matters and reductive ions (SO32−, NO2−, and I−), which were the most influential species inhibiting the virus inactivation; 2) shielding effects (k' = 103∼104 M–1s−1), including Ca2+, Mg2+, and kaolin; 3) insignificant effects (k' = 0∼1 M–1s−1), including Cl−, SO42−, NO3−, NH4+, and Br−; 4) promotion effects (k' = ∼−103 M–1s−1), including CO32− and HCO3−. Prediction of ozone disinfection efficiency and evaluation of species contribution under complex aquatic matrices were successfully realized utilizing the model. The systematic understanding and methodologies developed in this research provide a reliable framework for predicting ozone inactivation efficiency under complex matrix, and a potential tool for accurate disinfectant dosage determination and interfering factors control in actual wastewater treatment processes.

MnO2-based capacitive system enhances ozone inactivation of bacteria by disrupting cell membrane

The application of ozone (O3) disinfection has been hindered by its low solubility in water and the formation of disinfection by-products (DBPs). In this study, capacitive disinfection is applied as a pre-treatment for O3 oxidation, in which manganese dioxide with a rambutan-like hollow spherical structure is used as the electrode to increase the charge density on the electrode surface. When a voltage is applied, the negative-charged microbes are attracted to the electrodes and killed by electrical interactions. The contact between microbes and capacitive electrodes leads to changes in cell permeability and burst of reactive oxygen species, thereby promoting the diffusion of O3 into the cells. After O3 penetrates the cell membrane, it can directly attack the cytoplasmic constituents, accelerating fatal and irreversible damage to pathogens. As a result, the performance of the capacitance-O3 process is proved better than the direct sum of the two individual process efficiencies. The design of capacitance-O3 system is beneficial to reduce the ozone dosage and DBPs with a broader inactivation spectrum, which is conducive to the application of ozone in primary water disinfection.

The Use of Ozone Technology to Control Microorganism Growth, Enhance Food Safety and Extend Shelf Life: A Promising Food Decontamination Technology.

The need for microorganism control in the food industry has promoted research in food processing technologies. Ozone is considered to be a promising food preserving technique and has gained great interest due to its strong oxidative properties and significant antimicrobial efficiency, and because its decomposition leaves no residues in foods. In this ozone technology review, the properties and the oxidation potential of ozone, and the intrinsic and extrinsic factors that affect the microorganism inactivation efficiency of both gaseous and aqueous ozone, are explained, as well as the mechanisms of ozone inactivation of foodborne pathogenic bacteria, fungi, mould, and biofilms. This review focuses on the latest scientific studies on the effects of ozone in controlling microorganism growth, maintaining food appearance and sensorial organoleptic qualities, assuring nutrient contents, enhancing the quality of food, and extending food shelf life, e.g., vegetables, fruits, meat, and grain products. The multifunctionality effects of ozone in food processing, in both gaseous and aqueous form, have promoted its use in the food industries to meet the increased consumer preference for a healthy diet and ready-to-eat products, although ozone may present undesirable effects on physicochemical characteristics on certain food products at high concentrations. The combined uses of ozone and other techniques (hurdle technology) have shown a promotive future in food processing. It can be concluded from this review that the application of ozone technology upon food requires increased research; specifically, the use of treatment conditions such as concentration and humidity for food and surface decontamination.

Reduction of Salmonella enterica Typhimurium populations and quality of grape tomatoes treated with dry and humidified gaseous ozone

The present study was conducted to investigate the effect of humidity on the gaseous ozone inactivation of Salmonella enterica on grape tomatoes, and on the ozone-induced changes in fruit quality. Grape tomatoes were inoculated with Salmonella Typhimurium on the smooth surface and stem scar areas. The inoculated and uninoculated fruit (for quality studies) were treated for 1 h with 0, 1.59, 3.17 and 6.35 mg L−1 gaseous ozone at two humidities: ca. 4% (dry) and 90% (humidified). Salmonella survival populations were determined immediately for the inoculated fruits while appearance, off-odor, texture, firmness, color, ascorbic acid and lycopene content, oxygen radical absorbance capacity values, and total phenolic content were analyzed on the uninoculated fruit during 21 d of storage at 10 °C. Results demonstrated that, on the smooth surface, populations of Salmonella treated with 1.59, 3.17, and 6.35 mg L−1 dry ozone were reduced by 0.1, 0.6 and 3.3 log CFU fruit−1, respectively, while the corresponding humidified ozone reduced the populations by 3.2, > 4.8 and > 4.8 log CFU, respectively. On the stem scar area, 1.59, 3.17 and 6.35 mg L−1 humidified ozone treatment reduced the Salmonella populations by 1.4, 2.3 and 4.7 log CFU fruit−1, respectively, while the dry ozone treatments reduced the populations by 0.0, 0.5 and 1.9 log, respectively. On most sampling days during storage, fruit treated with 6.35 mg L−1 and, frequently, 3.17 mg L−1 dry ozone had significantly lower appearance scores, a* /b* values (redness), firmness, and ascorbic acid content than the control. When the fruit was treated with humidified ozone, the ozone-induced quality changes were negated. Our results demonstrated that, compared with dry ozone, humidified ozone had two benefits: (1) increased efficacy against Salmonella, and (2) reduced damage to fruit quality. The mechanisms for the observed phenomena are discussed in terms of water-ozone interaction and gas diffusion.

Ozone inactivation of airborne influenza and lack of resistance of respiratory syncytial virus to aerosolization and sampling processes.

Influenza and RSV are human viruses responsible for outbreaks in hospitals, long-term care facilities and nursing homes. The present study assessed an air treatment using ozone at two relative humidity conditions (RHs) in order to reduce the infectivity of airborne influenza. Bovine pulmonary surfactant (BPS) and synthetic tracheal mucus (STM) were used as aerosols protectants to better reflect the human aerosol composition. Residual ozone concentration inside the aerosol chamber was also measured. RSV's sensitivity resulted in testing its resistance to aerosolization and sampling processes instead of ozone exposure. The results showed that without supplement and with STM, a reduction in influenza A infectivity of four orders of magnitude was obtained with an exposure to 1.70 ± 0.19 ppm of ozone at 76% RH for 80 min. Consequently, ozone could be considered as a virucidal disinfectant for airborne influenza A. RSV did not withstand the aerosolization and sampling processes required for the use of the experimental setup. Therefore, ozone exposure could not be performed for this virus. Nonetheless, this study provides great insight for the efficacy of ozone as an air treatment for the control of nosocomial influenza A outbreaks.

Effect of Ozone on Inactivation of Purified Pepper Mild Mottle Virus and Contaminated Pepper Seed

Pepper mild mottle virus (PMMoV) is a major viral pathogen of pepper (Capsicum spp.). PMMoV is readily mechanically transmitted and is seed transmissible. Trisodium phosphate (TSP) treatment is commonly used to reduce the level of viable PMMoV in contaminated seed. Ozone is efficacious in disinfecting fungal-contaminated seed and disrupting bacterial and viral pathogens on various substrates. The purpose of this study was to evaluate efficacy of ozone and chemical treatment on PMMoV viability. Treated pepper seed infectivity was evaluated via bioassay with Nicotiana benthamiana. Symptoms of PMMoV infection were not observed in bioassays of TSP-treated seed. Sufficient viable PMMoV remained on ozone-treated seed to cause infection, which was confirmed by ELISA. Neither treatment affected seed germination. Ozone treatment of purified PMMoV was assessed to determine the extent, if any, of PMMoV inactivation by ozone. At the low PMMoV concentration (0.01 mg/ml), 14-h ozone exposure eliminated infectivity as determined by N. benthamiana bioassays with ELISA confirmations. At the higher PMMoV concentration (0.1 mg/ml), ozone treatment was insufficient to prevent infection. Ozone inactivation of purified PMMoV was quantified via bioassay using the local lesion host N. glutinosa and quantitative real-time PCR. Ozone exposure reduced lesion counts and PMMoV concentration, and PMMoV degradation increased with exposure time. Although PMMoV infection was eliminated at the low PMMoV concentration, bioassays using naturally infected seed and purified PMMoV preparations at relatively higher concentrations demonstrated that ozone is not efficacious as a standard treatment to sufficiently reduce levels of infective PMMoV in contaminated pepper seed. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Kinetics of Inactivation of Waterborne Enteric Viruses by Ozone.

Ozone is an effective disinfectant against all types of waterborne pathogens. However, accurate and quantitative kinetic data regarding virus inactivation by ozone are scarce, because of the experimental challenges associated with the high reactivity of ozone toward viruses. Here, we established an experimental batch system that allows tailoring and quantifying of very low ozone exposures and simultaneously measuring virus inactivation. Second-order ozone inactivation rate constants (kO3-virus) of five enteric viruses [laboratory and two environmental strains of coxsackievirus B5 (CVF, CVEnv1, and CVEnv2), human adenovirus (HAdV), and echovirus 11 (EV)] and four bacteriophages (MS2, Qβ, T4, and Φ174) were measured in buffered solutions. The kO3-virus values of all tested viruses ranged from 4.5 × 105 to 3.3 × 106 M-1 s-1. For MS2, kO3-MS2 depended only weakly on temperature (2-22 °C; Ea = 22.2 kJ mol-1) and pH (6.5-8.5), with an increase in kO3-MS2 with increasing pH. The susceptibility of the selected viruses toward ozone decreases in the following order: Qβ > CVEnv2 > EV ≈ MS2 > Φ174 ≈ T4 > HAdV > CVF ≈ CVEnv1. On the basis of the measured kO3-Virus and typical ozone exposures applied in water and wastewater treatment, we conclude that ozone is a highly effective disinfectant for virus control.

Inactivation efficiency of Escherichia coli and autochthonous bacteria during ozonation of municipal wastewater effluents quantified with flow cytometry and adenosine tri-phosphate analyses

Inactivation kinetics of autochthonous bacteria during ozonation of wastewater effluents were investigated using cultivation-independent flow cytometry (FCM) with total cell count (TCC) and intact cell count (ICC) and intracellular adenosine triphosphate (ATP) analysis. The principles of the methods including ozone inactivation kinetics were demonstrated with laboratory-cultured Escherichia coli spiked into filtered and sterilized wastewater effluent. Both intracellular ATP and ICC decreased with increasing ozone doses, with ICC being the more conservative parameter. The log-inactivation levels (−log(N/N0) of E. coli reached the method detection limits for FCM (∼3) and ATP (∼1.7) at specific ozone doses of ≥0.5 gO3/gDOC. During ozonation of four real wastewater effluents, the log-inactivation of autochthonous bacteria with FCM ICC was 0.3–1.0 for 0.25 gO3/gDOC and increased to 1.1–2.1 for 0.5 gO3/gDOC, but remained at a similar level of 1.5–2.8 for a further increase of the specific ozone doses to 1.0 and 1.5 gO3/gDOC. The FCM data also showed that autochthonous bacteria were composed of communities with high and low ozone reactivity. The inactivation levels measured with intracellular ATP were reasonably correlated to ICC (r2 = 0.8). Overall, FCM and ATP measurements were demonstrated to be useful tools to monitor the inactivation of autochthonous bacteria during ozonation of municipal wastewater effluents.

Establishing Surrogate–Virus Relationships for Ozone Disinfection of Wastewater

Abstract Safe reuse of wastewater requires high levels of pathogen inactivation. Ozone is a very effective disinfectant for viruses and has distinct benefits over other forms of disinfectants, in that it increases the clarity of water and can oxidize some chemical contaminants in water. However, because of the combination of high ozone demand of most wastewaters and rapid reaction with viruses, determination of ozone dose in wastewater and recycled water treatment is not well defined. While various surrogates are used as indicator organisms for human pathogenic viruses in water reuse practice, much less is known about the relationship between surrogates and human pathogenic viruses for ozone disinfection in wastewater. In this study, the ozone inactivation dose response of several surrogates (Escherichia coli, coliphage T1, T4, PRD-1, ΦX174, and MS2) and human pathogenic viruses (poliovirus 1, echovirus 11, coxsackievirus B5, and adenovirus 2) were compared for the first time in secondary effluent wastewa...

Microorganism Inactivation by Ozone Dissolved in Aqueous Solution: A Kinetic Study Based on Bacterial Culture Lipid Unsaturation

Physiological solutions ozonated are widely used in the medical field (dentistry and surgery) as an effective bactericide. In this investigation, the inactivation of Escherichia coli and Pseudomonas aeruginosa by ozone dissolved in physiological solution was studied. There is a poor knowledge of the inactivation efficiency of this solution for different bacteria. The efficiency of the microorganisms’ inactivation was evaluated by the total unsaturation of lipids measured by the so-called Double Bond Index (DB-index). This is a sensitive analysis to evaluate the quantity of carbon-carbon double bonds (>C=C<) available in organic and biological samples, with high efficiency and in a short time. DB-index results were compared with the quantity of colony forming units (CFU) available in the culture. Three experimental systems were evaluated to determine the relationship between the DB-index variable and the microorganism’s inactivation: 1) using BHI agar as a culture medium to evaluate the dynamic growing curve when the ozone dissolved was dosed over the strain’s surface; 2) using a glucose solution (5%) as culture media and keeping the ozone concentration constant, which was dissolved in different physiological solutions, to observe the effects of solvent type over the bacteria growth; and, 3) using a glucose solution (5%) as culture media, and physiological solution of NaCl (0.9%) as a dissolved media for ozone at different concentrations. From the experimental data, a model of the ozone inactivation of each pathogen was built to obtain the inactivation kinetics. The model obtained showed a correlation between the CFU behavior and DB-index to each bacteria, since Pseudomona aeruginosa was more resistant to being oxidized than Escherichia coli.

Phage MS2 Inactivation in Pure and Filtered Water: Effect of Pseudo-Kinetics and Other Factors

This article reports results of studies on the effects of pH, temperature, particulate matter, organic matter, and ions on the phage MS2 inactivation in pure water and actual water samples. Organic matter and pH as well as the presence of Br− and I− ions strongly affected the ozone inactivation of MS2, whereas temperature and particulate matter had minimal effects. Moreover, the nitrogen from ammonia had a negligible effect on ozone inactivation. The delayed Chick–Watson model provided the most suitable description of MS2 inactivation by ozone. The equation of the inactivation rate was also obtained, which was well correlated with the measured results.

Ozone inactivation of infectious prions in rendering plant and municipal wastewaters

Disposal of tissues and organs associated with prion accumulation and infectivity in infected animals (designated as Specified Risk Materials [SRM]) is strictly regulated by the Canadian Food Inspection Agency (CFIA); however, the contamination of wastewater from slaughterhouses that handle SRM still poses public concern. In this study, we examined for the first time the partitioning of infectious prions in rendering plant wastewater and found that a large proportion of infectious prions were partitioned into the scum layer formed at the top after gravity separation, while quite a few infectious prions still remained in the wastewater. Subsequently, we assessed the ozone inactivation of infectious prions in the raw, natural gravity-separated and dissolved air flotation (DAF)-treated (i.e., primary-treated) rendering plant wastewater, and in a municipal final effluent (i.e., secondary-treated municipal wastewater). At applied ozone doses of 43.4–44.6mg/L, ozone was instantaneously depleted in the raw rendering plant wastewater, while a greater than 4-log10 inactivation was achieved at a 5min exposure in the DAF-treated rendering plant wastewater. Prion inactivation in the municipal final effluent was conducted with two levels of applied ozone doses of 13.4 and 22.5mg/L, and a greater than 4-log10 inactivation was achieved at a 5min exposure with the higher ozone dose. Efficiency factor Hom (EFH) models were used to model (i.e., fit) the experimental data. The CT (disinfectant concentration multiplied by contact time) values were determined for 2- and 3-log10 inactivation in the municipal final effluent treated with an ozone dose of 13.4mg/L. Our results indicate that ozone could serve as a final barrier for prion inactivation in primary- and/or secondary-treated wastewaters.

Inactivation of E. coli and B. subtilis spores in ozonized cassava starch

In the present study, the efficacy of ozone inactivation of B. subtilis spores and E. coli in cassava starch was evaluated. Cassava starch with 18 and 30% moisture content was processed with ozone at concentrations of 40-118 ppm and exposure times of 15-120 minutes. The processing at 113 ppm/120 minutes (maximum exposure level to ozone evaluated) at 18% of moisture content did not cause significant reduction of B. subtilis spores and caused the reduction of only 2 decimal of E. coli. On the other hand, when the ozonation process was carried out for 120 minutes at 30% of moisture content, 3.6 decimal reduction of B. subtilis was achieved at 40 ppm of ozone and total B. subtilis load reduction (>5 log cycles) was observed at 118 ppm of ozone. Similarly, total E. coli load reduction (>7 log cycles) was achieved at 40 ppm of ozone exposure for 60 minutes. Therefore, the results indicate that the ozone efficacy against microorganisms in cassava starch was mainly dependent on the sample moisture content and to ozone concentration and exposure time. Moreover, it was observed that ozone is a promising technology to reduce microbial counts in dried food.

Kinetics of ozone inactivation of infectious prion protein.

The kinetics of ozone inactivation of infectious prion protein (PrP(Sc), scrapie 263K) was investigated in ozone-demand-free phosphate-buffered saline (PBS). Diluted infectious brain homogenates (IBH) (0.01%) were exposed to a predetermined ozone dose (10.8 ± 2.0 mg/liter) at three pHs (pH 4.4, 6.0, and 8.0) and two temperatures (4°C and 20°C). The inactivation of PrP(Sc) was quantified by determining the in vitro destruction of PrP(Sc) templating properties using the protein misfolding cyclic amplification (PMCA) assay and bioassay, which were shown to correlate well. The inactivation kinetics were characterized by both Chick-Watson (CW) and efficiency factor Hom (EFH) models. It was found that the EFH model fit the experimental data more appropriately. The efficacy of ozone inactivation of PrP(Sc) was both pH and temperature dependent. Based on the EFH model, CT (disinfectant concentration multiplied by contact time) values were determined for 2-log10, 3-log10, and 4-log10 inactivation at the conditions under which they were achieved. Our results indicated that ozone is effective for prion inactivation in ozone-demand-free water and may be applied for the inactivation of infectious prion in prion-contaminated water and wastewater.

Ozone inactivation of resistant microorganisms: Laboratory analysis and evaluation of the efficiency of plants

In this work, the ozone inactivation of resistant microorganisms is studied and a method to assess the efficiency of a drinking water plant to inactivate resistant microorganisms using ozone is proposed. This method aims at computing the fraction of resistant microorganisms that are not inactivated at the exit of an ozonation step by evaluating the duration of the lag phase of the ozone inactivation of these microorganisms and the contact time distribution of these microorganisms with the ozone in the step. To evaluate the duration of the lag phase of the ozone inactivation of resistant pathogenic microorganisms, an experimental procedure is proposed and applied to Bacillus subtilis spores. The procedure aims at characterizing the ozone inactivation kinetics of B. subtilis spores for different temperature and ozone concentration conditions. From experimental data, a model of the ozone inactivation of B. subtilis spores is built. One of the parameters of this model is called the lag time and it measures the duration of the lag phase of the ozone inactivation of B. subtilis spores. This lag time is identified for different temperature and ozone concentration conditions in order to establish a correlation between this lag time and the temperature and ozone concentration conditions. To evaluate the contact time distribution between microorganisms and the ozone in a disinfection step of a drinking water plant, a computational fluid dynamics tool is used. The proposed method is applied to the ozonation channel of an existing drinking water plant located in Belgium and operated by Vivaqua. Results show that lag times and contact times are both in the same order of magnitude of a few minutes. For a large range of temperatures and ozone concentrations in the Tailfer ozonation channel and for the highest hydraulic flow rate applied, a significant fraction of resistant microorganisms similar to B. subtilis spores is not inactivated.

Ozone inactivation of norovirus surrogates on fresh produce.

Preharvest contamination of produce by foodborne viruses can occur through a variety of agents, including animal feces/manures, soil, irrigation water, animals, and human handling. Problems of contamination are magnified by potential countrywide distribution. Postharvest processing of produce can involve spraying, washing, or immersion into water with disinfectants; however, disinfectants, including chlorine, have varying effects on viruses and harmful by-products pose a concern. The use of ozone as a disinfectant in produce washes has shown great promise for bacterial pathogens, but limited research exists on its efficacy on viruses. This study compares ozone inactivation of human norovirus surrogates (feline calicivirus [FCV] and murine norovirus [MNV]) on produce (green onions and lettuce) and in sterile water. Green onions and lettuce inoculated with FCV or MNV were treated with ozone (6.25 ppm) for 0.5- to 10-min time intervals. Infectivity was determined by 50% tissue culture infectious dose (TCID(50)) and plaque assay for FCV and MNV, respectively. After 5 min of ozone treatment, >6 log TCID(50)/ml of FCV was inactivated in water and ∼2-log TCID(50)/ml on lettuce and green onions. MNV inoculated onto green onions and lettuce showed a >2-log reduction after 1 min of ozone treatment. The food matrix played the largest role in protection against ozone inactivation. These results indicate that ozone is an alternative method to reduce viral contamination on the surface of fresh produce.

Extrinsic control parameters for ozone inactivation ofEscherichia coliusing a bubble column

To investigate the effect of extrinsic control parameters for ozone inactivation of E. coli in a bubble column. Ozone inactivation of Escherichia coli ATCC 25922 in Tryptic Soya Broth was examined. The parameters studied included temperature (ambient, 20, 25 and 30 degrees C), exposure time (up to 30 min), gas flow rate (0.03, 0.06, 0.12, 0.25, 0.5 and 0.75 l min(-1)) and concentration level (five different levels). The efficacy of ozone treatment was a function of the parameters investigated and optimum control parameters of flow rate (0.12 l min(-1)), temperature (ambient) and ozone concentration (75 microg ml(-1)) resulted in a t(d5) (time required to achieve 5 log reduction) of 20 min. Optimum control parameters of gas flow rate, ozone concentration and temperature are reported for E. coli inactivation within a bubble column. In 2001, the FDA approved use of ozone as a direct additive to food and in 2004, issued guidelines for the use of ozone in liquid systems. However, these guidelines highlighted gaps in the literature for ozonation of liquid foods. This study provides useful information regarding optimum extrinsic control parameters for E. coli inactivation in liquid media using a bubble column to ensure microbiological safety.

Combined Ozone and Ultraviolet Inactivation of Escherichia coli

The kinetics of Escherichia coli inactivation using ozone and ultraviolet (UV) radiation, separately and simultaneously, was evaluated at 25°C in buffered (pH 6.0, 7.0 and 8.0), demand-free media. While ozone was found to be a stronger disinfectant than UV radiation, using both simultaneously was more effective than using them individually. Inactivation kinetics was pseudo first-order for the three treatment processes, while the disinfection rate was a linear function of the disinfectant dose. The synergism observed in microbial inactivation when the disinfectant processes were combined was illustrated by estimates of kinetic model parameters. This synergy was attributed to the generation of hydroxyl radicals via ozone photolysis. Subsequently, dosage calculations, as based on disinfectant level and exposure time, indicated that the simultaneous use of UV and ozone could substantially reduce their individual doses.

Effect of Micro-Mixing Conditions on Predictions of Cryptosporidium Inactivation in an Ozone Contactor

The U.S. EPA is considering segregated flow analysis as an alternative calculation method to determine Cryptosporidium parvum inactivation credit in continuous-flow ozone contactors in drinking water treatment facilities. A computer method is presented in which C. parvum inactivation in the reactive flow segment of a hypothetical ozone contactor with a pre-determined residence time distribution is calculated based on the assumption of either completely segregated or completely micro-mixed flow. In a series of computer simulations using typical ozonation conditions in a water treatment facility, inactivation predicted assuming complete segregation was 0.3 to more than 2.0 log greater than that predicted assuming complete micro-mixing, depending on the level of back-mixing, ozone decomposition rate and inactivation level. CFSTR-in-series model predictions of inactivation were between those of segregated flow analysis and micro-mixed analysis. It was concluded that segregated flow analysis calculations may result in significant over-prediction of C. parvum inactivation credit in ozone contactors and should be used with caution.