Investigations on Ozone Contacting by Ceramic Membranes

Ozone transfer was investigated using various oxide ceramic membranes and different process parameters. The ozone mass transfer per contactor volume through hydrophilic membranes was in the same order of magnitude as conventional bubble contacting. The pressure differential between the gaseous and aqueous phase as well as the membrane material's microstructure was found to widely determine the transfer rate. A hydrophobic coating of the membrane surface led to a considerable increase in transfer. Bubble free ozone contacting with porous ceramic is a possible approach for the ozonation of problematic wastewaters susceptible of excessive foam formation.     

Effect of Ozone as a Disinfectant on Microbial Load and Chemical Quality of Raw Wheat Germ

ABSTRACT

While raw seed sprouts can threaten consumers’ health by foodborne pathogens, thermal or chemical disinfection of sprouts may cause some negative effects; instead, ozone can be a good alternative treatment. This study investigated the effect of nine ozone treatments (2000, 4000, and 6000 ppm within 1, 2, and 4 h) on wheat germ chemical compositions and microbial flora. The results indicated that ozonation with 2000 ppm during 4 h was the optimized treatment with the greatest effect on decreasing the microbial load while it had the minimum effect on antioxidant properties, lipid oxidation, and moisture content of raw wheat germ.     

Comparison of Aqueous Ozone and Chlorine as Sanitizers in the Food Processing Industry: Impact on Fresh Agricultural Produce Quality

The effects of ozone treatment on fresh strawberry and shredded lettuce food quality were tested by varying applied ozone concentration, contact time, pH and temperature to assess ozone a potential food sanitizer. The produce quality was assessed by comparing the changes in texture firmness, browning and decolorization, oxygen consumption and carbon dioxide respiration after the post-treatment storage from 0 to 21 days. The effectiveness of ozonation on natural microfloras including mesophiles, psychotrophes, yeasts and molds, was also evaluated for the improvement in produce shelf-life. As compared to chlorine treatments, ozone treatments slightly increased the lettuce browning but substantially retarded its respiration rates and firmness deterioration even after 21 days of storage. For strawberry, no significant difference in food quality was observed between ozone and chlorine treatments. Finally, ozone treatments at the doses below 10 mg/L were found not effective in killing natural microfloras grown on the produce surfaces.     

Start-Up and Operation of the Indianapolis Ozone Disinfection Wastewater Systems

The two 125-mgd oxygen activated sludge wastewater treatment plants for the City of Indianapolis, Indiana use ozone disinfection. The process was constructed in 1983, and has maintained continuous, reliable operation since 1985. Disinfection is required at Indianapolis from April 1 through October 31. Equipment performance characteristics were evaluated during the 1985 disinfection season, and disinfection performance characteristics were optimized during the 1986 season. The evaluation documents the effect of cooling water temperatures on equipment performance, and the utilization of ozone contactor off-gas control of disinfection performance. The capital cost of both ozone systems represented about eight percent of the plants' total construction cost. The ozone system O & M cost represents about 1.9 percent and 3.7 percent of the total plant O & M cost at the Belmont and Southport plants, respectively.     

Ozone in oral surgery ‐ current status and prospects

Ozone has proved to be an effective water disinfectant for dental treatment units. Using this technique it is now possible to keep the water in a dental treatment unit low in germ count or germ‐free. Growth of germs does not occur during the routine intermissions in the daily activities of a dental office. Since ozonated water is germ‐free, it can be used in dental surgery as a coolant for burrs and for rinsing wounds. Thus, properties of ozone relevant to medicine can be utilized in the field of dental, oral and maxillomandibular surgery.     

Theoretical Analysis Of Ozone Disinfection Performance In A Bubble Column

Modelling the efficiency of ozone disinfection in a bubble column was completed using two kinetic approaches: an axial dispersion model (ADM) and a back-flow cell model (BFCM). Using these models, the effects of flow directions and mixing on disinfection performance were examined. Both models predicted the concentration profiles of dissolved ozone in water equally well. However, the BFCM could be solved much more easily than the ADM with regard to the degree of inactivation without the solution being plagued by divergence.     

Investigation of an Ozone Membrane Contactor System

Ozone mass transfer rates were determined for nine expanded porous Teflon membranes that had different pore size, thickness, and pore volume, a nonporous Teflon membrane, and a PVDF membrane. The mass transfer coefficient was 7.6 ± 0.5 × 10^?5 m/s at Re of 2000 for all membranes tested even though pore sizes ranged from 0.07 to 6 μm and thickness from 0.076 to 0.25 mm. Mass transfer increased with liquid side Reynolds number. Therefore, it is likely that ozone mass transfer is liquid phase controlling and not membrane limited. For a hypothetical case of 4000 m³/d and 2 mg/L ozone transferred, plate and frame membrane and hollow fiber contactors are approximately one and two orders of magnitude smaller, respectively, than fine-bubble diffusers.     

Destruction of Helminth (Ascaris suum) Eggs by Ozone

Based on the properties of ozone as a strong germicidal agent, the inactivation kinetics or disintegration of Ascaris suum eggs in water were studied. Ozone was applied in synthetic samples, the concentration of dissolved ozone in the liquid phase was typically between 3.5 to 4.7mg/L, pH 5, 9. The value of 90% inactivation (t₉₀) obtained was at 1 h, the remaining 10% being inactivated in 2 h. A linear correlation between the logarithm of bacterial or yeast concentration (N) and contact time was found, being the linear significant correlation coefficient (r of 0.95). That 2-log inactivation occurred at a CT value near 4.7mg/min/L. The best reduction percentage was of 99.00 in 120min. It therefore could be demonstrated that ozone indeed induces effects on the helminth eggs.     

Antibacterial Effect of Gaseous and Aqueous Ozone in Root Canals Infected by Enterococcus Faecalis

The present study evaluated the antibacterial effects of aqueous and gaseous ozone in human root canals infected with Enterococcus faecalis. Infected root canals were divided into two control groups (saline, sodium hypochlorite) and three experimental groups (manual or ultrasonic technique of aqueous and, gaseous ozone). Disinfection procedures were performed, remaining microbial colonies were counted and data were evaluated. Sodium hypochlorite showed the highest antibacterial effect on root canals infected with Enteroccous faecalis. Moreover, aqueous ozone with ultrasonic technique appear to be more influential than aqueous ozone with manual technique and gaseous ozone.     

A Study of Ozone Formation on the Surfaces of Electrodes

It had been previously thought that ozone production occurred in gaseous space, especially the space between electrodes. However, based on our research, we believe that may only be one of the ozone-producing processes. In this study, we aimed to confirm that a third body, which is present at the interface between oxygen gas and a metal electrode, works to compose ozone. Ozone was not observed in pure oxygen (400x10^?6 Nm³/min flow rate) when electrical discharge was supplied after approximately 6 months. The concentration of ozone increased (approximately 0.07 ppm) when nitrogen (approximately 20x10^?6 Nm³/min flow rate) was added to a gas-mixing chamber. A third body was required to produce ozone when an oxygen molecule and an oxygen atom collided. The same phenomenon was observed on the surface of a copper anode. A simulation confirmed this. Using an industrial ozone generator which utilized ceramic dielectrics and expanded metal electrodes, an increase in the temperature of the cooling water led to a proportional decrease in ozone concentration. After changing from the titanium electrode to a nickel electrode and an antimony electrode, we observed the difference in the enthalpy changes which were calculated using van't Hoff's formula. The antimony electrode increases the efficiency of the ozone generator to produce ozone. We have come to believe that ozone can be composed on the surface of a metal electrode.     

Water Disinfection of Dental Units using Ozone – Microbiological Results after 11 Years and Technical Problems

Water disinfection in dental treatment units using ozone and hydrogen peroxide/silver ion were compared for a period of 11 years. Water from nine treatment units was microbiologically examined in a total of 240 tests. Eight treatment units using peroxide disinfection regularly exceeded the limits stipulated by water purity regulations, and Pseudomonas aeruginosa was detected at 154 water outlets. However, hardly any of the water specimens taken from the treatment unit using ozonated water disinfection showed bacteria. Four technical problems to using ozonated water were found during this eleven year period. The use of hydrogen peroxide necessitated 48 basic disinfections.     

Ozone Disinfection of Sewage in a Static Mixer Contacting Reactor System on a Plant Scale

Results of our earlier laboratory study on ozone contacting systems in a continuous flow mode identified that the ozone disinfection process is limited by the mass transfer rate (7). The main controlling factor is the mass transfer efficiency rather than the contact time of the contactor in determining the effect of disinfection. By applying these concepts, we suggested a new ozone disinfection technique of using a static mixer as the contactor to substitute for a conventional bubble column designed with contact time.     

Comparative Analysis of Ozone and Ultrasound Effect on the Elimination of Giardia spp. Cysts from Wastewater

Giardia spp. is a flagellate protozoan that presents two evolution forms, cysts and trophozoites. Cysts are resistant to chlorine, the most employed disinfectant agent in the treatment of water. For this reason, new techniques for the disinfection of waters that contain this parasite are necessary. This work evaluated the efficiency of the disinfection by ozone and ultrasound individually and simultaneously upon wastewater. The data obtained showed that after application, ozone, ultrasound, and combined techniques induced a significant elimination of Giardia spp. cysts. Furthermore, this effect was more accentuated when the two techniques were applied simultaneously.     

Principles of Ozone Oxidation and Disinfection Design

The efficiency of ozone for different purposes can be determined by different laboratory tests. It is necessary to use a specific test for each aim of ozonation. Consequently, the design of commercial ozone–water contact systems can be determined in relation with the purpose of ozonation: virucide effect, oxidation of pollutant, clarification improvement or wastewater disinfection.     

The Development Of An Ozone Contact Tank Simulation Model

Anglian Water (AW) operates ozone facilities as a treatment stage at all its surface water sources. The main ozone treatment stage takes place after filtration in multi-compartment concrete ozone contactors. These have two stages of ozone gas injection via ceramic bubble diffusers and two decay stages.

To enable AW to gain a better understanding of the contact tank performance, a computer simulation model incorporating Computational Fluid Dynamics and ozone process modeling was developed in conjunction with AEA Harwell. The model was calibrated using site data from Alton WTW. The results were used to improve the tank design and to optimize the ozone dose; this resulted in improved performance and a significant reduction in ozone dose.     

Effect of Ozone Treatment on the Reduction of Chlorpyrifos Residues in Fresh Lychee Fruits

The effect of ozone on the reduction of chlorpyrifos residue in lychee cv. Chakapat (Litchi chinensis Sonn.) was studied. Lychee fruits were dipped in the solution of chlorpyrifos at a concentration of 10 mg L^?1 for 10 min. Then, they were exposed to ozone gas (O₃) at concentrations of 80, 160, 200, 240 mg L^?1 and dipped in ozone-containing water, at concentrations of 2.2, 2.4, 3.4 and 3.2 mg. L^?1 for 10, 20, 30 and 60 min, respectively. Both ozone gas and ozone-containing water reduced pesticide residue in lychee, but exposure to ozone gas for 60 min was most effective. When lychee fruits were stored at 25 °C for 6 days, both processes did not show significant differences in weight loss, total soluble solids (TSS) and titratable acidity (TA). However, ozone-containing water decreased the eating quality of lychees after storage, compared with the ozone-fumigated groups.     

Effect of Ozone and Peroxone on Helminth Hymenolepis nana Eggs

In this study the effect of ozone and peroxone on the structure of Hymenolepis nana eggs at different pH (5, 7 and 10) was evaluated. Experiments were conducted with an ozone dose of 1.1 mg/min for 60 min; peroxone tests were done with the same conditions of ozonation process plus 0.33 mL of 33% hydrogen peroxide. Studies with scanning and transmission electron microscopy did not show ultrastructural changes after the treatment with ozone and peroxone at pH 5 and 7, but at pH 10 the eggs lost their external layer, making them more vulnerable.     

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.     

Multistage Ozone Treatment of Dye Waste

An ozonation technology to treat lightly loaded effluents from dye manufacturing processes has been developed. The process uses airgenerated ozone and countercurrent contactors. An intermediate step is included to eliminate OH-radical scavengers and slowly reacting oxidized species from the liquid phase.

A study of ozone efficiency and yield concerning the reduction of TOC and COD levels is presented. The biological degradability.of treated water is discussed. A design and rating calculation procedure for countercurrent contactors is presented. Various waste treatment strategies using separation processes and ozone are discussed briefly. A cost estimate to treat a typical dye effluent in two stages on industrial scale is included.     

Experimental Investigation on the Microbial Inactivation of Domestic Well Drinking Water using Ozone under Different Treatment Conditions

The effect of ozonation on the microbial activities of domestic well drinking water was investigated, and the influence of the treatment conditions such as pH, temperature, ozone dose, and contact time was elucidated by comparing removal efficiencies. The results revealed that the disinfection of the microorganisms was related to an increase in contact time and thereby increases in Ct values with ozone. Higher ozone doses led to a large amount of microbial inactivation. The addition of hydroxyl and hydronium ions contributed greatly to the destruction of any microorganism in both acidic and basic mediums, achieving 25–88% efficiencies.