Ozonation of water containing chlorine or chloramines. Reaction products and kinetics

Ozone reacts with free aqueous chlorine when present as hypochlorite ion (OCl⁻) with a second order rate constant of 120 ± 15 M⁻¹ s⁻¹ at 20°C. About 77% of the chlorine reacts to produce Cl⁻ and 23% is oxidized to ClO⁻₃. No ClO⁻₄ is formed. Conversion of chlorine to monochloramine reduces the ozone reaction rate to 26 ± 4 M⁻¹ s⁻¹, independent of pH, NH₂Cl is transformed quantitatively to NO⁻₃ and Cl⁻ by O₃. Rate data for other chloramines are also presented. The direct reaction of ozone with chlorine accounts for a significant amount of the chlorine and ozone demand found when the two oxidants are used in combination under water works conditions.     

Rate constants of reactions of ozone with organic and inorganic compounds in water—II: Dissociating organic compounds

Rate constants of reactions of ozone with non-ionized solutes, such as aliphatic alcohols, olefins, chlorosubstituted ethylenes, substituted benzenes and carbohydrates, have been determined from the absolute rates with which ozone reacts in the presence of various concentrations of these compounds in water. They have been tested by comparison with the relative rates by which pairs of these solutes are transformed by ozone. Different experimental methods have been developed to determine such rate constants in the range from 10⁻² to 10⁵ M⁻¹ s⁻¹. Interferences between the direct reactions of ozone and reactions due to its preliminary decomposition to secondary oxidants could be eliminated. The kinetics of all the reactions studied are first order with respect to ozone and solute concentration. The rate constants of many types of organic compounds in water are of the same order of magnitude as in organic solvents. Substituted benzenes, however, react in water about 100 times faster. They obey a linear free energy relationship with p = −3.1 when based on δ_p⁺ values. Comparisons of rate constants with chemical structures of the reacting groups show that all reactions of ozone are highly selective and electrophilic. The kinetic data allow explanation of the chemical effects of ozone observed in water treatment practice.     

A quantitative investigation of the reaction of ozone with p-toluenesulfonic acid in aqueous solution as a model compound for anionic detergents

The reaction of ozone with p-toluenesulfonic acid (PTA) at initial pH 3 and 12 in aqueous solutions (25°C) has been studied at initial concentration 1 mmol l⁻¹ and ozone dose is 24 mg min⁻¹ 1. and 11 mg min⁻¹ 1. respectively. The substrate elimination follow a zero order rate law. A 98% p-toluenesulfonic acid reduction requires at least 7 mol O₃ per mol PTA, however to remove 100% PTA the consumption of ozone increases to 16 mmol O₃ per mmol PTA. At this point a 28% reduction of DOC and a 74% COD reduction was achieved.The PTA decomposition is quicker at higher ozone flow rate, but the specific ozone consumption increases also. As oxidation products the following compounds were identified and their quantitative variations as function of ozonation time were measured: methylglyoxal, acetic acid, formic acid, pyruvic acid, oxalic acid, H₂SO₄ and H₂O₂. As byproduct mesoxalic acid was identified. At pH 12 lactic acid as a further oxidation product was observed.Balances of carbon, sulfur and methyl as well of the acid equivalents indicate one or more intermediates with a sulfonic acid group. These intermediates with a proportion of about 20% disappear after 100% PTA elimination. On account of these results a reaction mechanism is discussed.     

Effect of oxidants on microalgal flocculation

The effects of chlorine, ozone and chlorine dioxide on Scenedesmus sp. cultures were studied. Algal cell viability and chlorophyll concentration decreased, and the concentration of dissolved organic substances increased with increasing applied oxidant concentration. Pretreatment with chlorine dioxide (1, 3 or 5 mg l⁻¹) or ozone (2.6, 4.6 or 8.1 mg l⁻¹) on algal cultures enhanced algal flocculation with alum, while prechlorination with 10 or 20 mg l⁻¹ increased the required dosage of alum by 15%. Scanning electron micrographs of oxidized cells revealed drastically adverse effects upon the cell surface architecture: in addition to the oxidation of noncellular organic materials, the oxidants damaged both cell surface structures and intracellular components. A model explaining the effects of the different oxidants on microalgal flocculation is suggested.     

Comparative disinfection of treated sewage with chlorine and ozone: Effect of nitrification

Chlorine and ozone were compared in pilot plants (capacity about 3.2 m³ h⁻¹), which were fed with the same activated sludge treated and filtered water. Together with physico-chemical analysis the water was analysed for different types of microorganisms, including vegetative bacteria (total and thermotolerant coliforms, faecal streptococci and Pseudomonas aeruginosa), bacterial spores (spores of aerobic bacteria at 37°C and sulphite reducing clostridia) and bacterial viruses (somatic coliphages and F-specific bacteriophages).The average chlorine and ozone dose were, respectively, 3.65 and 15.3 mg l⁻¹ of water, while after a contact time for both of about 25 min the average residual concentrations were 1.79 and 0.35 mg l⁻¹ of water. These residuals were measured with the DPD-method. The ammonia-N concentration varied greatly (0.06–72.0 mg l⁻¹) and was used to group the data into four classes: (1) non-nitrified water, defined as water in which nitrate-N was smaller than ammonia-N; (2) moderately nitrified water, in which nitrate-N was larger than ammonia-N and the ammonia-N was higher than 2 mg l⁻¹; (3) well nitrified water, defined as water in which ammonia-N was lower than 2 mg l⁻¹; (4) very well nitrified water, in which ammonia-N was smaller than 0.5 mg l⁻¹.This classification indicated that the concentrations of most other impurities decreased with a better nitrification. Statistical analysis of the data showed also that ozone was a better disinfectant than chlorine in the case where the disinfection is based upon their residual content. The degree of nitrification had a greater effect on chlorine disinfection than on ozone disinfection.During chlorination the total residual chlorine decreased, with better nitrification; the chlorine demand increased; the composition of the residual chlorine changed very much and the inactivation of bacterial viruses improved. The vegetative bacteria showed a varying pattern; most were inactivated in moderately nitrified water, when the dichloramine concentration was highest and false positive FAC concentration was lowest of the four classes. Reduction of bacterial spores was not observed.During ozonization other effects were indicated. Reductions of most organims increased slightly with better nitrification; only reductions of F-specific bacteriophages decreased. There was also a small decrease of bacterial spores. The treated effluent had a high ozone consumption and the inactivation of the organisms was low in relation to ozone dose and residual ozone.The bromide concentration (0.3–2.9 mg l⁻¹) effected the chemistry of chlorine and ozone and had a positive effect on chlorine and ozone disinfection of total coliforms.For most types of micoorganisms the disinfection coefficients of the Selleck model and the germicidal efficiencies could be determined.     

Ozone oxidation of pharmaceuticals, endocrine disruptors and pesticides during drinking water treatment

This study investigates the oxidation of pharmaceuticals, endocrine disrupting compounds and pesticides during ozonation applied in drinking water treatment. In the first step, second-order rate constants for the reactions of selected compounds with molecular ozone (k_O3) were determined in bench-scale experiments at pH 8.10: caffeine (650 ± 22 M⁻¹ s⁻¹), progesterone (601 ± 9 M⁻¹ s⁻¹), medroxyprogesterone (558 ± 9 M⁻¹ s⁻¹), norethindrone (2215 ± 76 M⁻¹ s⁻¹) and levonorgestrel (1427 ± 62 M⁻¹ s⁻¹). Compared to phenolic estrogens (estrone, 17β-estradiol, estriol and 17α-ethinylestradiol), the selected progestogen endocrine disruptors reacted far slower with ozone. In the second part of the study, bench-scale experiments were conducted with surface waters spiked with 16 target compounds to assess their oxidative removal using ozone and determine if bench-scale results would accurately predict full-scale removal data. Overall, the data provided evidence that ozone is effective for removing trace organic contaminants from water with ozone doses typically applied in drinking water treatment. Ozonation removed over 80% of caffeine, pharmaceuticals and endocrine disruptors within the CT value of about 2 mg min L⁻¹. As expected, pesticides were found to be the most recalcitrant compounds to oxidize. Caffeine can be used as an indicator compound to gauge the efficacy of ozone treatment.     

Ozonation of pyrene in aqueous solution

The reaction of pyrene with ozone was studied in aqueous solution at low (10–200 μg l⁻¹) substrate concentration and with ozone concentrations (5 mg l⁻¹) approximating to those used in potable water treatment. Degree of reaction and the formation of polyaromatic/aromatic reaction products were assessed using a technique of solvent extraction and derivatisation with gas chromatographic (GC), gas chromatographic-mass spectrometric (GC-MS), high performance liquid chromatographic (HPLC) and u.v. spectrometric analysis of extracts. A freeze drying/derivatisation technique with GC and GC-MS analysis was employed for the isolation/identification of short chain polar aliphatic reaction products. Substantial destruction of pyrene was recorded within 1 min of reaction with ozone. Polyaromatic/aromatic compounds did not persist; reaction products are likely to be short chain polar aliphatic compounds. Products of this type were isolated but not identified in the study.     

Mechanism and kinetics of cyanide ozonation in water

The rate of oxidation by ozone of potassium cyanide into cyanate has been measured in alkaline aqueous solutions buffered at a pH of 11.8 and a temperature of 20°C. The initial cyanide concentration has mostly been 100 g m⁻³. Under these conditions the reaction rate can within the experimental error be described by an equation which is of first order in ozone and independent of the cyanide concentration. The reaction rate is so large that the conversion is limited by mass transfer. Mass balances show that one mole of ozone oxidizes one mole of cyanide.The oxidation of cyanide is part of a reaction sequence similar to the ozone decomposition mechanism. For both reactions, cyanide oxidation and ozone decay, mechanisms are proposed. The kinetics predicted for the ozone decay are in agreement with experimental data from the literature.The mechanism proposed for the cyanide oxidation predicts a reaction rate equation given by: with

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. This equation has been supported by experimental evidence.     

Rate constants of reactions of ozone with organic and inorganic compounds in water—III. Inorganic compounds and radicals

Second-order rate constants for reactions of ozone with 40 inorganic aqueous solutes are reported. Included are compounds of sulfur (e.g. H₂S, H₂SO₃, HOCH₂SO₃H), chlorine (e.g. Cl⁻, HOCl, NH₂Cl, HClO₂, ClO₂), bromine (e.g. Br⁻, HOBr), nitrogen (e.g. NH₃, NH₂OH, N₂O, HNO₂) and oxygen (e.g. H₂O₂), as well as free radicals (e.g. O₂⁻, OH^•). Most of these compounds exhibit an increase in rate constant with increasing pH corresponding to their degree of dissociation. Rate constants are based on ozone consumption rates measured by conventional batch-type or continuous-flow methods (10⁻³-10⁺⁶ M⁻¹ s⁻¹ range) and determinations of stoichiometric factors. Also listed are data determined by pulse-irradiation techniques using kinetic spectroscopy (10¹⁰ M⁻¹ s⁻¹ range). Additional literature data are reviewed for completeness. Results are discussed with respect to water treatment and environmental processes.     

Passive reduction of human exposure to indoor ozone

Reactive building materials offer an opportunity to provide indoor air cleaning with minimal energy use. Laboratory and test house experiments provide evidence that indoor ozone concentrations can be diminished by activated carbon (AC) and unpainted gypsum wallboard (GWB) panels. These two materials are highly reactive with ozone and produce few byproducts. When measured in a 14.2 m³ stainless-steel chamber, the mean deposition velocities to the materials were 5.3 m h^-1 for AC and 2.4 m h⁻¹ for GWB for a variety of airflow and relative humidity conditions. The ozone decay rates for both the materials were also measured in an unoccupied 34.5 m³ bedroom under various mixing conditions. In this case, ozone removal increased relative to background by 27–100% with a 4.4 m² panel of a reactive material placed on one wall of the bedroom. The ozone decay rate for the bedroom increased over background by approximately 2–3 h⁻¹ for GWB and 2–7 h⁻¹ for AC. Application of a mass balance model for a typical home demonstrates that effectiveness for ozone removal depends weakly on the air exchange rate and strongly on the panel material, panel area, and mixing conditions. An ozone removal effectiveness of over 80% is possible with sufficient panel area and positioning that provides elevated air speeds near the panels.     

Preliminary studies on the leaching of some trace metals from kitchen faucets

Preliminary studies were carried out on the leaching of copper, zinc, chromium, cadmium and lead from eight kitchen faucets by samples of raw, filtered and distributed Ottawa water, a sample of well water and deionized water containing 2 mg l⁻¹ aqueous fulvic acid. Leaching was effected by allowing the test solutions to stand in the inverted faucets for two successive 24-h periods. Concentrations of the metals found in the leachates were copper: first leaching, 0.12–28.0 mg l⁻¹, second leaching, 0.08-3.54 mg l⁻¹; zinc: first leaching, 0.13-10.25 mg l⁻¹, second leaching, 0.06-2.85 mg l⁻¹; chromium: first leaching, < 1.0 × 10⁻³ − 0.395 mg l⁻¹, second leaching, < 1.0 × 10⁻³−0.032 mg l⁻¹; cadmium: first leaching, < 0.05 × 10⁻³−0.01 mg l⁻¹, second leaching, < 0.05 × 10⁻³−4 × 10⁻³ mg l⁻¹; and lead: first leaching, < 0.2−110.0 mg l⁻¹, second leaching, < 0.2−82.0 mg l⁻¹. The faucets containing lead-soldered copper joints released high concentrations of lead, particularly in the case of leaching with the aqueous fulvic acid solution. Under the conditions of the present investigations it is indicated that in some cases the concentrations of metals leached could lead to intakes in excess of the maximum permissible limits for these metals. However, further investigations will be required to determine the possible contribution of these faucets to metal intake under normal usage.     

Sorption and accumulation of cadmium in the sediment of the Tama River

Cadmium contents in the water and the sediment samples collected from the Tama River and several branches were measured. Cadmium (above 0.005mgl⁻¹) was detected in only four of the water samples, while the sediment samples showed cadmium content of 1.0–9.8 μg g⁻¹ dry sediment. Cadmium concentration in the sediments of the main stream was correlated against ignition loss of the samples and it was found that 1 g of ignition loss (organic matter) corresponded to 35 μg of cadmium.The batch adsorption experiment in the laboratory using an aqueous solution of cadmium for 14 sediment samples with a higher concentration of cadmium indicated that the amount adsorbed by the sediment is highly dependent on the ignition loss. The amount adsorbed on unit mass of ignition loss q_IL could be correlated by a Freundlich-type equilibrium relation as where C is the equilibrium concentration in the aqueous phase ranging between 7 × 10⁻³ and 10 mg l⁻¹, while k_IL and n are equilibrium constants.The adsorption rate measurement showed that the intraparticle diffusion coefficient of cadmium in the sediment was about 1.1 × 10⁻⁶ cm²s⁻¹, which is of a reasonable order of magnitude assuming the pore diffusion mechanism inside the particle.The results suggest that suspended solid particles of high organic content in flowing water contribute significantly to the transport of cadmium along the river.     

Quality aspects of ozonisation

Only at relatively low initial values of colour, taste and organic compound content, ozonisation can lead to a quality of drinking water that meets the requirements. In combination with other processes ozone can give a considerable reduction when removing colour and taste from strongly polluted surface water (60 and 75% respectively). One often needs artificial recharge or coagulation before applying ozonisation and carbon filtration after ozonisation. The organic compound content is reduced by ozone to only a small extent (10% of the TOC). In many of the cases investigated a dosage of more than 2 to 2.5 mg 1⁻¹ ozone seems to bring about no further effect. Yet, for the colour reduction of ground water from the isle of Ameland there appeared to be indications of a dosage of 5 mg 1⁻¹ ozone being optimal. The optimal dosage for other types of water is still to be investigated.     

Mass transfer and reaction kinetics in the ozone/tap water system

The mass transfer and the reaction kinetics of ozone in tap water were examined. The contacting system was a well-mixed reactor with perpendicular jets. The ozone residual range was the lowest detectable range. A simple mathematical model was proposed to describe the mechanism of the ozone in the reactor and was checked over the range of water flow rates from 2.170 to 3.080 l min⁻¹, gas flow rates from 0.667 to 1.333 l min⁻¹ and different temperature conditions. The proposed model describes quite accurately the mass-transfer behavior in the reactor and determines the operational parameters which control the reactor operation. There is a linear relationship between the ozone feed rate and ozone residual. Zero order kinetics best describe the autodecomposition of ozone in plain tap water. The mass transfer coefficient is about 1.14 min⁻¹. Without use of agitation, there is a large decrease in the value of the mass transfer coefficient, to about 0.250 min⁻¹. The magnitude of the reactor rate constant is between 0.05 and 0.13 mg min⁻¹ l.     

Hyperconcentrated cultures of Scenedesmus obliquus: A new approach for wastewater biological tertiary treatment?

Algal cultures of Scenedesmus obliquus at low concentrations (0.1–0.2 g dry wt l⁻¹) provide adequate biological tertiary treatment of wastewaters. This research was aimed at studying the possibility of increasing the system performance by using hyperconcentrated cultures of S. obliquus (up to 2.6 g dry wt l⁻¹) at the laboratory scale. The algal culture grown on secondary effluent was first chemically flocculated with chitosan (30 mg l⁻¹) and decanted; the sedimented culture (5 g dry wt l⁻¹) was then resuspended in secondary effluent to obtain algal suspensions at various concentrations, the performance of which was compared to that of a control culture (0.13 g dry wt l⁻¹). The rate of exhaustion of nitrogen (N-NH₄⁺) was proportional to the algal concentration and a complete removal could be obtained within 15 min (at 2.6 g dry wt algae l⁻¹); this result compares favorably to the 2.5 h or so required by the control culture. The unit uptake rate for nitrogen (N-NH₄⁺) had a tendency to increase with the algal concentration, whereas that of phosphorus (P-PO₄³⁻) showed the opposite relationship. Considering the results obtained, it appears that hyperconcentrated algal cultures have a high potential for the tertiary treatment of wastewaters; a significant reduction of pond surface for large scale operations can be anticipated.     

Removing metals from waste solutions with low rank coals and related materials

Ion exchange media were produced by contacting brown coal, peat or wood sawdust with a solution of calcium hydroxide, preferably as an aqueous slurry of lime. The resultant calcium loading on the media, which ranged up to 8% for sawdust, 12% for peat and to 19% for brown coal, was exchanged for many metals in solution.Preliminary work showed the method to be amenable to extraction of copper, nickel, chromium, cadmium, lead, zinc, mercury, cobalt, silver, iron, manganese, vanadium, germanium, gallium, aluminium, antimony and uranium. For most of the metals more than 99% was removed from I g 1⁻¹ solutions.In more detailed work, confined to calcium loaded brown coal and solutions having metal concentrations more typical of industrial operations, minimum residual metal concentrations of 0.0005 mg l⁻¹ mercury; 0.02 mg 1⁻¹ copper; 0.02 mg 1⁻¹ zinc; <0.05 mg l⁻¹ cadmium; 0.1 mg 1⁻¹ lead and 0.2 mg l⁻¹ manganese were obtained. These results compare favourably with those reported for other relevant processes and there might be operational advantages in the method.The method can be applied either by agitating the calcium loaded media in the solution and then filtering, or by passing the solution through packed beds of the media. Where appropriate, dilute solutions can be up-graded for re-use by stripping the metals from the media which can also be re-used. Alternatively, the loaded media can be combusted and the metals recovered from the residues.The method might be applicable to mine drainage and to effluents from metallurgical processing and electroplating, but more work is required to assess costs.It is suggested that the method is environmentally preferable to other common effluent treatment procedures because it enables collection and recycling of heavy metal pollutants.     

Note on a rapid and sensitive method for the determination of anionic detergents in natural waters at the ppb level

A rapid and sensitive method for the determination of anionic detergents in natural waters is developed using atomic absorption spectrophotometry and his (ethylenediamine) copper(II) ion. The method is suitable for a concentration range of 0–50 μg1⁻¹ (ppb), but its applicability can be extended up to 15 μg ml⁻¹. The limit of detection is 0.3 μg l⁻¹.     

The manual determination of ammonia in fresh waters using an ammonia-sensitive membrane-electrode

The use of a commercially-available ammonia-sensitive membrane-electrode for the manual determination of ammonia in discrete samples of fresh water has been investigated and the analytical procedure is described. The electrode is simple and convenient to use, and a sample can be analyzed in a few minutes. For normal routine analysis, the lower limit of determination is approximately 0·1 mg N 1⁻¹ though smaller concentrations can be measured. The relative standard deviation of analytical results varied from approximately 10 to 3 per cent as ammonia concentration increased from 0·1 to 4 mg N 1⁻¹. Results for samples of river water agreed well with those obtained by absorptiometric methods of analysis; the electrode responds to amines but otherwise appears to be essentially specific for ammonia. Use of the electrode will be advantageous in a number of applications, and it also has good potential for the on-line analysis of fresh waters.     

Études des transformations des formes du carbone, azote, phosphore, soufre et des principaux éléments minéraux au cours de la mesure de la demande totale en oxygene—III transformation des formes du soufre

Previous experiments carried out with the laboratory TOD meter Ionics 225 of the DOW Chèmical made it possible (after a high temperature catalytic action) to characterize the stable forms of organic and inorganic carbon and nitrogen (NH₄⁺, NO₂⁻, NO₃⁻), and the principal cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) in the course of the total oxygen demand (TOD) measurement.The object of this study is firstly to compare the oxidation capability of different techniques of organic pollution (particularly the COD and TOD) in relation to the constituent elements of the organic matter C, N, P, S, and to calculate the possible interferences of the inorganic compounds at the time of TOD test.These investigations warrant the application of this technique to measure the amount of organic pollution in relatively mineralized conditions (Industrial wastewater, sea-water…). The present publication is concerned more with the study of the transformation of the organic and inorganic sulphur forms (S²⁻, SO₃²⁻. SO₄²⁻) in the course of the TOD measurement.The study of the oxidizability of the organic sulphur compound type C_xH_yO_zS, made it possible to establish a specific relation with a ratio of 0–50 mg of organic sulphur l⁻¹, between the oxygen demand of this element [TOD (S)] and its concentration (TOD (S) = 0.97 [S]).These tests showed a partial oxidation of the sulphur to SO₂ and SO₃ as the literature claimed. On the other hand, the oxidation of the same compounds during the COD tests varies greatly and although it is not possible to establish a correlation between these two measurements, as applies in the case of organic nitrogen, nevertheless these experiments showed a greater reliability of the TOD compared with the COD in the oxidation of organic matter in general. We then carried out experiments on the different mineral forms of sulphur in order to distinguish the possible effects and to recommend simple improvements.A relative study on sulphate ions had been carried out with standard solutions which have the same TOD (the basic TOD is obtained using potassium phthalate acid) and the same increasing concentration of the salt M₂SO₄ type. The experiments showed that the basic TOD decreases when the concentration of sulphate ions is increased (Fig. 3). Therefore, the interference is negative and taking into consideration the specific oxygen demand of the cation, we can propose an evaluation of this interference (ΔTOD (SO₄²⁻) = 0.203 [SO₄²⁻]). The same experiments have been conducted with a salt of M₂SO₃ type and similar results obtained (Fig. 5).The specific interference of the sulphite ion is negative and can be estimated by the following equation (ΔTOD (SO₃²⁻) = 0.132 [SO₃²⁻]). In both cases, we have to note that the transformation of these inorganic anions occurs between those relative to the theoretical dissociation reaction corresponding to the appearance of the oxide SO₂ and SO₃. For sulphurous on the contrary, the interference is positive and therefore corresponds to an extra oxygen demand (Fig. 8).The experiments were conducted directly with the M₂S salts (M representing K or Na) in aqueous solution.The evaluation of this interference had been made in the consideration of two concentration ranges of the sulphurous ions (0–35 mg S²⁻ l⁻¹): TOD (S²⁻) = 0.4 [S²⁻] and (35–100 mg S²⁻ l⁻¹): TOD (S²⁻) = 1.2 [S²⁻] − 30.Therefore this study confirms a better oxidation of the organic matter by TOD test in comparison with COD test.But sulphate and sulfite have a negative interference in the TOD measurement, whereas sulphurous is positive.The evaluation model of these interferences allows a correction to be made of the TOD value or to verify TOD measurement of organic pollution obtained by this technique.     

Disinfection of viruses in sewage by ozone

The action of ozone on poliovirus was examined employing two different methods. In the first, the filtered sewage together with a virus inoculum was added to a buffer solution which contained known concentrations of ozone. The most outstanding finding was the complete disappearance of the ozone immediately after the addition of the effluent. At the same time, there was a rapid reduction in virus titer. However, after the initial reduction, the virus titer remained unchanged. The degree of virus inactivation was dependent on ozone concentration and on the amount of organic matter in the effluent. With increased ozone concentration and decreased organic matter, a larger percentage of viruses were inactivated. With the second method, ozone was bubbled into filtered sewage containing a virus inoculum. Inactivation of the virus started after a lag period of about 30 s. even before ozone residual in the sewage was detected. Inactivation of 99.999% of the virus was obtained when the ozone residual was about 0.6 mg l⁻¹. In similar experiments performed with buffer instead of sewage, the entire process took place at a much faster rate. When ozone concentrations reached about 1.0 mg l⁻¹. 99.999% of the virus was inactivated. In conclusion, ozone was found to be a very potent viral disinfectant, even in contaminated water.