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.     

The Disinfecting Action of Ozonated Water and of Hydrogen Peroxide/Silver Ions In Vitro

An in-vitro comparison was made between the disinfecting action of ozonated water and hydrogen peroxide/silver ion preparations using the “Quantitative suspension” test and Pseudomonas aemginosa. No microorganisms could be detected immediately after contact between ozonated water and the pseudomonadeae. In the case of the peroxide preparation, however, its action corresponded to that of aqua bidestillata (control experiment) and no disinfection had taken place. The use of hydrogen peroxide preparations in dental units for microbiological and toxicological reasons should therefore be reconsidered.     

The influence of the water heater in dental chairs on the ozone concentration in the water used

Water heaters in dental chairs serve to heat water to about body temperature in order to make it more comfortable for the patient. This leads to a reduction in ozone concentration of 40–50%, as shown in laboratory experiments and also at dental chairs. In the event that evidence is found of positive biological effects in oral surgery on using relatively high ozone concentrations in water (5–10 μg/ml) then water heaters should not be used.     

Application of Combined Ozone–Hydrogen Peroxide for the Removal of Aromatic Compounds from a Groundwater

Nitro and chlorobenzene compounds, which are widely used in dye industries, have been associated recently with groundwater contamination. Because of their potential toxicity and for taste and odor considerations, three main actions were undertaken to solve the problem. First, to follow the advance of pollution toward the wells, samples were collected automatically and analyzed using GC-MS. Results indicate that o-chloronitrobenzene was the main pollutant in concentrations ranging from 10 to 2000μg/L. Second, to monitor the drinking water quality, an on-line spectrophotometer was used to measure the optical density at 254 nm at the inlet and outlet of the plant. Third, the feasibility of using the O₃/H₂O₉ combination was determined at a 450 L/h pilot plant. Reduction of concentrations of chloronitrobenzenes from 1900 μ/L to less than 20 μg/L could be reached by the application of 8 mg O3/L and 3 mg H2O9/L with a 20-minute contact time. To avoid an eventual bacterial egrowfn in the network due to biodegradability of the oxidation by-products, sand and GAC filtration were tested after oxidation. An evaluation of the costs of these different treatments is also presented.     

Removal of Natural Organic Matter from Groundwater Using Advanced Oxidation Processes at a Pilot Scale Drinking Water Treatment Plant in the Central Banat Region (Serbia)

To improve water quality, a pilot-scale evaluation into upgrading the conventional treatment process was conducted. By following DOC content, UV₂₅₄ absorbance, SUVA and by-products formation, three oxidative pre-treatments were evaluated: pre-ozonation (2.2 g O₃/m³); O₃/H₂O₂ process (2.2 g O₃/m³; H₂O₂:O₃ = 1:2) and O₃/H₂O₂ process (2.2 g O₃/m³; H₂O₂:O₃ = 2:1). The second pre-treatment gave the best results, with a final average DOC content of 0.9 mg C/L, UV₂₅₄ absorbance of 0.06 cm^?1 and the lowest THMFP of 130 μg/L. UV₂₅₄ absorbance can serve as a proper indicator for predicting THM and HAA formation, yielding a correlation coefficient ≥ 0.90.     

The Installation of GAC and Ozone Surface Water Treatment Plants In Anglian Water,UK

The surface water treatment plants in Anglian Water are being upgraded in order to more reliably meet the requirements of the EEC Drinking Water Directive. Ozone and additional GAC filtration capacity are being installed at 11 waterworks treating river and reservoir water, with capacities ranging from 11 to 360 ML/d. The installations and reasons for the plant designs are discussed.     

Criteria for the Selection of the Feed Gas For Ozone Generation

This paper brings together the requirements and experiences of the supplier of ozone generating equipment and the user of this equipment. The technical requirements of the ozone generator on the feed gas, the main characteristics of the system alternatives, the on-site experience and the development of criteria for future applications are described. The particular application of ozone and the quantities required are detailed to provide a full understanding of the background and environment of the case study and its demands on the system selection. The evolution from an air fed system to an oxygen fed system is outlined. This paper describes the joint evaluation of the choice of feed gas for the Purton Water Works by Bristol Water Plc and Ozonia using the experience gained at the Littleton Works and the technical assessment during the pre-contract stage of the Purton Treatment Works Development Scheme.     

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.     

Influence of Carbonate on the Ozone/Hydrogen Peroxide Based Advanced Oxidation Process for Drinking Water Treatment

The influence of carbonate on the ozone/hydrogen peroxide process has been investigated. Carbonate radicals, which are formed from the reaction of bicarbonate/carbonate with OH radicals, act as a chain carrier for ozone decomposition due to their reaction with hydrogen peroxide. The efficiency of bicarbonate/carbonate as a promoter for the radical-based chain reaction in presence of hydrogen peroxide has been calibrated and compared to a well-known chain promoter (methanol) and an inhibitor (tert-butanol). Relative to tert-butanol, the hydrogen peroxide induced ozone decomposition is accelerated by bicarbonate/carbonate. Relative to methanol, bicarbonate/carbonate in presence of hydrogen peroxide is less effective as a promoter under comparable experimental conditions.     

The Influence of H2O2 in Ozonation Treatment: Experience of the Water Supply Service of Florence,Italy

This paper reports on the use of ozone in the Water Supply Service of Florence (Italy). The addition of hydrogen peroxide at the end of ozonation treatment has proved particularly efficient for controlling bromates and brominated organic byproducts. Significant differences regarding the formation of oxygenated organic compounds were not observed.     

Seawater Ozonation of Bacillus subtilis Spores: Implications for the Use of Ozone in Ballast Water Treatment

The potential of ozone for disinfection of ships’ ballast water was investigated using Bacillus subtilis spores as an indicator. The effects of pH, presence of iron, and bacterial strain on disinfection efficacy in seawater, under simulated ballast conditions, were investigated. Ozone dosages of 9 mg/L (pH 7) and 14 mg/L (pH 8.2) and 24 h contact achieved a 4-log inactivation with the various oxidant residuals formed. Iron surface at a ratio to water of 9 m²/m³ impaired the oxidant residuals and the disinfection of spores. Different strains of B. subtilis resulted in different CT values. Ozone does not seem to be a good choice for the control of spore-forming organisms in ballast water, but may be suitable for the control of other species.     

Combination of Ozonation and the Fenton Processes for Landfill Leachate Treatment: Evaluation of Treatment Efficiency

Single processes such as ozonation, ozone/hydrogen peroxide, Fenton and several combined treatment schemes were applied for leachate collected from a waste disposal site. The implementation of combined Fenton and ozonation processes resulted in the highest chemical oxygen demand removal (77% from initial value) among all the treatment methods applied, while biodegradability improvement was observed during the Fenton pre-treatment only. Some decrease of chemical oxygen demand was obtained during the single ozonation or combined schemes including ozone resulting in slight if any biodegradability improvement. The addition of hydrogen peroxide to ozonation did not enhance chemical oxygen demand, dissolved organic carbon or biochemical oxygen demand removal compared to ozone alone. Ferric chloride coagulation used as a pre-treatment stage did not improve subsequent chemical oxygen demand removal by ozonation or the Fenton processes. Taking into account the effective chemical oxygen demand, dissolved organic carbon removal and biodegradability improvement the single Fenton process seems to be a preferable treatment method for the leachate treatment. Some reduction in toxicity to Daphnia magna was observed after the application of the studied treatment methods.