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.     

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.     

Laboratory Simulation of the Effect of Ozone and Monochloramine on Biofilms in Drinking Water Mains

Cultivated on cement surfaces to simulate growth on cement mortar lined drinking water mains was investigated in a laboratory biofilm reactor. The biofilms were subsequently exposed to ozone and monochloramine. Inactivation of biofilm bacteria by ozone was found to be a non-linear function of the ozone dose, and the results provided a more rational basis for determining conditions for ozone disinfection of water mains. Results further suggest that monochloramine might be an effective disinfectant for biofilms on pipe walls. Microbiological observations indicated that monochloramine is a non-selective disinfectant compared to ozone.     

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.     

An Assessment of the Benefits Afforded by the Continuous Versus Intermittent Operation of Ozone for Drinking Water Treatment

Stricter regulation by OFWAT has encouraged water companies to optimize all stages of the water treatment process. This work reviews the ozonation process, in order to evaluate the benefits and disadvantages of continuous versus intermittent ozone operation. Two Advanced Water Treatment Works (AWTW) were surveyed, Farmoor AWTW, Which involves traditional (chemical) treatment processes, and Kempton Park AWTW, which incorporates slow sand filter sandwich? beds. Both reviews indicated that continuous ozone operation would result in an optimized solution based on dependability of ozone plant, reliability of water quality and cost efficiency.     

Ozone Concentration and Temperature Effects on Disinfection Kinetics

The cysts of the nonpathogenic soil and water amoeba, Naegleriagruberi strain (NEG), were inactivated using aqueous ozone in batch reactors at controlled temperatures (5–30°C) at pH 7. The semi-log plots of survival ratio vs. time consisted of an initial shoulder followed by a linear portion. The log-log plots of ozone concentration against time for 99 percent inactivation were essentially linear. The relationship between the overall inactivation rate and absolute temperature was well expressed by the Arrhenius theory. An empirical relationship was developed between the extent of cyst inactivation, ozone dose, temperature, and contact time.     

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.     

Development Of An Ozone Disinfection Contactor Using A Physical Scale Model

This paper presents the design of a 1/5 scale model study of a five-stage counter-current ozone disinfection contactor. The selection of appropriate scaling laws is discussed and model test runs are presented and compared with the preliminary rule-of-thumb design. Simple modifications to the internal baffle design were tested leading to improved residence time characteristics.     

Wastewater Disinfection by Ozone: Influence of Water Quality and Kinetics Modeling

Wastewater disinfection by ozone was investigated at pilot scale on different effluents. The organic matter (COD and TOC) was shown to have the biggest influence on the ozone demand of the effluents. Disinfection of fecal indicators could be modeled as the reaction on a double population. The presence of more resistant microorganisms results in the need for higher treatment doses and a tertiary filtration when the effluent has to meet the stringent Title 22 standard. Eventually, the high virucidal power of ozone makes it very attractive when viruses are targeted.     

Disinfection of Seawater: Application of UV and Ozone

Ozone and ultraviolet technologies are proposed as potential disinfecting agents for seawater. Ozone doses were applied in the range 0.38 to 4.89 mg O₃ L^?1. They permit to observe a complete disinfection as well as UV doses superior to 320 J L^?1. Impacts of both processes on organic matter were also studied. UV absorbances were reduced in both cases but in higher proportion using ozone (up to 50% removal). Total organic carbon was slightly reduced by UV radiation, and ozonation achieves up to 10% mineralization. Ozone reaction proceeds with biochemical oxygen demand increase. Seawater ozonation, in addition, leads to the formation of residual oxidants that show an inhibitory effect on autochthonous microorganisms.     

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.     

Design And Efficiency Of Ozone Contactors For Disinfection

One commercial contact chamber which is designed for ozone disinfection has been tested for the following : determination of residence time distribution (RTD), measurement of dissolved ozone concentrations in water, and measurement total plate counts. Disinfection is achieved but this type of reactor is not ideal, due to dispersion of the residence time distribution. As these bubble contactors do not behave like plug flow reactors, it is possible to improve the hydrodynamics of ozone contactors with the use of static mixers. Experiments with ozone static mixers have been conducted.     

Optimization of Ozonation Process for Disinfection of Dental Unit Waterlines Using Response Surface Methodology

ABSTRACT

The reduction of microbial contamination in dental unit waterlines (DUWLs) appears to be necessary because of a potential risk of infections in immunocompromised patients and medical staff, which are regularly exposed to water and aerosols generated from DUWLs. In the present study, the qualitative and quantitative microbial contamination of water in DUWLs were determined and the conventional biomedical diagnostic tests were applied to identify microorganisms. A 3-level, 2-factor central composite design was utilized to investigate the effects of chief operating parameters and optimize ozone disinfection conditions. Also, the activity of three disinfectant (ozone, NaOCl, and peracetic acid) in microbial decontamination of DUWLs were compared. The results indicated that Microbacterium laevaniformans were the most prevalent genera (21%) among both Gram-negative and positive species in all samples. Regression analysis illustrated the good fit of the experimental data to the predicted model with R² and R²_adj correlation coefficients of 0.988 and 0.980, respectively. Moreover, under the optimal circumstances (Ozone concentration = 1.2 ppm and reaction time = 13.5 min) the disinfection efficiency was 97.52%. The results also revealed that ozone was effective disinfectant to reduce prevalent genera (with the removal of 93.75%, 92.57% and 96.15% of Pseudomonas aeruginosa, Microbacterium ?laevaniformans, and Alcaligenes faecalis, respectively) and already formed biofilms under optimum conditions. Based on achieved results, ozone was highly effective on microbial decontamination compared to peracetic acid and NaOCl disinfectant and can be used for disinfection of DUWLs.     

Improvement of Ozone Oxidation and Disinfection Design

For a long timei the aim of ozonation has been the improvement of the organoleptic qualities of treated water. Disinfection! and particularly virus inactivationi also has been a reason for introducing ozonation steps in the treatment line of a potable water treatment plant. Other purposes of ozonation then have been developed in different fields of application, such as iron and manganese removal, micropollutants oxidation, urban wastewater disinfection! coagulant and flocculant aids, and improvement of biological treatment. During the last few years, numerous studies have been concerned either with the kinetics of ozonation reactions, or the modelling of contact systems. A better fit between these two factors should be found.     

Ozone Disinfection of Vibrio Vulnificus in Artificial Seawater

Disinfection experiments were performed using Vibrio vulnificus exposed to ozonated artificial seawater (ASW). Residual oxidant concentration was monitored using a modified neutral KI test. Inactivations of V. vulnificus cultures were performed in 500 mL flasks containing ozone-treated seawater. The laboratory scale trials reduced numbers of V. vulnificus an average of 8 log units after 240 seconds with an initial oxidant concentration of 5.3 mg/L. Ozone is a very effective bactericidal (Blogoslawski et al., 1975) and viricidal agent (Englebrecht and Chain, 1985; Farooq and Akhaque, 1983), and is able to degrade toxins (Blogoslawski et al., 1979; Thurberg, 1975). Ozone gas is one of the most powerful oxidizing gases known. When ozone comes in contact with bacteria it can react directly to inactivate the organism. When ozone comes in contact with the constituents of seawater it reacts with bromide ion to form hypobromous acid, hypobromite ion and bromate ion (Haag and Hoign6, 1984) which are stable and effective disinfecting agents.     

Evaluation of Empirical Process Design Relationships for Ozone Disinfection of Water and Wastewater

A research program was undertaken to examine the dose-response of Escherichia coli ATCC 11775 in ozone demand-free phosphate buffer solution and in a high quality secondary wastewater effluent with a total organic carbon content of 8 mg/L and a chemical oxygen demand of 26 mg/L. The studies were conducted in benchscale batch reactors for both water types. In addition, studies using secondary effluent also were conducted in a pilot-scale, semi-batch reactor to evaluate scale-up effects. It was found that the ozone dose was the most important design parameter in both types of water. Contact time was of some importance in the ozone demand-free water and had no detectable effect in the secondary effluent.

Pilot-scale data confirmed the results obtained at bench-scale for the secondary effluent. Regression analysis of the logarithm of the E. coli response on the logarithm of the utilized ozone dose revealed that there was lack-of-fit using the model form which has been used frequently for the design of wastewater disinfection systems. This occurred as a result of a marked tailing effect of the log-log plot as the ozone dose increased and the kill increased. It was postulated that this was caused by some unknown physiological differences within the E. coli population due to age or another factor.     

Enhancement of Wastewater Disinfection Efficiency in Full-Scale Ozone Bubble-Diffuser Contactors

Tracer and disinfection tests were performed with the ozone bubble-diffuser contactors at the Belmont and Southport Advanced Wastewater Treatment Plants operated by the City of Indianapolis, Department of Public Works. The objective of the study was to develop a better understanding for the role of hydrodynamics and contactor design on the disinfection efficiency achieved in these contactors. Tracer tests were performed at varying gas and wastewater flow rates. The results indicated that high backmixing occurred within each chamber of the over-under ozone bubble-diffuser contactor trains. The addition of three baffles to one of the contactor trains resulted in a decrease in overall contactor backmixing. Low contactor backmixing was observed at high wastewater flow rates combined with high or medium gas flow rates for both the modified and original trains. Monitoring of effluent fecal coliform concentrations for both the original and modified contactor trains revealed lower average concentrations in the modified train effluent as compared to the original train.     

Ozone Application for Postharvest Disinfection of Tomatoes

Ozone is an effective alternative for the postharvest treatment of fruits and vegetables. The purpose of this study was to evaluate the ozone application in gaseous or aqueous phases for postharvest disinfection of tomatoes (Lycopersicon esculentum Mill) cultivar FA-180. Fruits harvested at the breaker stage were exposed to ozone concentrations of 25 and 45 mg m^?3 for 2 h per day during 16 days, at non-controlled temperature and relative humidity. Exposure to ozone during storage extends the shelf-life of tomatoes, besides preserving its sensory attributes. Mature tomatoes, inoculated with Escherichia coli ATCC 25922, were washed with ozonated water containing 0.5 to 1.0 mg L^?1 during 15 to 30 min. To achieve an adequate disinfection, 1 mg L^?1 and 15 min are recommended. The disinfection with ozonated water was effective.     

Start-Up and Optimization of the Ozone Disinfection Process At the Sebago Lake Water Treatment Facility

The purpose of the ozone process at the Sebago Lake Water Treatment Facility (SLWTF) is to meet the disinfection requirements of the Surface Water Treatment Rule with ozone and without filtration. The start-up experience is presented including initial operating strategies to meet disinfection requirements. An ozone system performance test conducted during the first month of plant operation is described and the results are reviewed. The initial and proposed activities of an ozone optimization project are discussed.     

Advanced Treatment For Municipal Wastewater Reuse In Agriculture. III - Ozone Disinfection

Results of a pilot (100 m³/h) investigation on ozone disinfection of municipal tertiary effluents for reuse in agriculture carried out at West Bari (S. Italy) treatment plant are presented. Among dosages, contact times and advanced treatment schemes investigated it was demonstrated that ozone disinfection results in the achievement of the WHO microbial guideline (1,000 CFU/100ml for Fecal Coliforms) for unrestricted wastewater reuse in agriculture of both clarified and clarified-filtered municipal secondary effluents; it is very effective towards Pseudomonas aeruginosa, rather effective towards Giardia lamblia and substantially ineffective towards Cryptosporidium parvum and it forms limited amount of DBP (approx. 350 ppb of total aldehydes). O&M costs amount to 37 Euro/1000m³.