Belgian Experiences in the Ozonization of Water

After reviewing the uses of ozone in the preparation of drinking water, high purity water for Pharmaceuticals industries, and swimming pools throughout Belgium, a discussion of technological developments made at the Tailfer plant (serving Brussels) concerning the uses of ozone is presented. These subjects include analytical and monitoring techniques developed for ozone, procedures for ozone contacting employed at this plant, treatment of ozone contactor off–gases, and the use of oxygen–enriched process gas to produce supplemental amounts of ozone required periodically. Capital and operating cost data are presented.     

Catalytic ozonation of humic acids with Fe/MgO

Humic acids were degraded by ozone at room temperature in a stirred tank reactor and a fixed bed reactor with Fe/MgO catalysts. Experimental results show that the ozonation with Fe/MgO induced a significant reduction in UV absorbance of humic acids as compared to ozone alone. Fe/MgO was the most efficient catalyst to degrade humic acids in the presence of ozone. GPC (gel permeation chromatography) showed that the humic acids with high molecular weight could be severely decomposed into organic compounds with low molecular weight on the Fe/MgO catalyst, indicating that humic acids could be catalytically decomposed. The continuous reaction experiments with the palletized catalysts supported that humic acids can be removed by catalysis as well as adsorption.     

Ozonation of Humic Substances: Effects on Molecular Weight Distributions of Organic Carbon and Trihalomethane Formation Potential

Four different sources of humic substances were studied to determine the effects of ozonation on molecular weight-distributions, based on dissolved organic carbon (DOC) and trihalomethane formation potential (THMFP). Solutions of two soil-derived fulvic acids and a one soil-derived humic acid, as well as dissolved organic matter (DOM) associated with a natural water source were studied. Both gel permeation chromatography (GPC) and ultrafiltration (UF) were employed to define apparent molecular weight (AMW). Applied ozone doses ranged from 2.0 to 2.5 mg O₃/mg DOC. Overall samples of untreated and ozonated waters, as well as individual molecular weight fractions, were characterized according to DOC, UV absorbance, and THMFP. Ozonation resulted in a significant disappearance of higher AMW material with a corresponding increase in lower AMW material. Although little overall reduction in DOC concentration was observed, significant overall reductions in UV absorbance and THMFP levels were observed.     

Formaldehyde Formation During Ozonation Of Drinking Water

Partial oxidation of natural organic material during ozonation produces oxygenated by-products of low molecular weight. Formaldehyde, being the most common oxygenated by-product of ozone, is considered to be a problematic compound by the water industry due to its potential adverse health effects. This research attempts to provide specific information on the effects of water quality parameters, specifically, pH and alkalinity, the structure of humic material, and the operational parameters, e.g., ozone dosage and contact time, on generation of formaldehyde. The results showed that ozonation caused almost an immediate formation of formaldehyde, which reached a peak value, and then started to decrease with continued ozonation. Ozonation of aqueous fulvic acid produced higher concentrations of formaldehyde compared to other types of humic material. Formaldehyde formation was suppressed by high bicarbonate levels, and enhanced at higher pH. Formaldehyde accumulation was more dramatic at low ozone dosages.     

Destruction of Ozone Off–Gas by Thermal Catalytic Method

In the operation ofozone treatment plants, one will have to deal with ozone inthe off–gas exhaust air. In higher concentrations in the exhuast air, ozone has the unpleasant property of being detrimental to plant, animal and man.

The normal ozone concentration inambient air should not be more than 1/10of the MAK–value. Insmall treatment plants inEurope the small amount of ozone off–gas can be diluted with atmospheric airso that itis permitted to be discharged into the outside air. For larper plants there isthe choice between a thermal and catalytic ozone destruction, or a process that combines both. In the Lengg Waterworks the exhaust air of the reaction chamber was passed through a thermal destruction systen. From the granular activated carbon (GAC) filters theair was passed into the atmosphere untreated. It was ascertained that during GAC back–washing 1200 PPtl ozone were in the exhaust air. This ozone concentration was much too high.     

Method for Making Higher Concentration Ozone than Supplied O3 Derived from Condensing Process Using Ozone Storage under the Same Conditions

We have been researching ozone storage using a silica gel that functions as an adsorbent. We found that ozone stored in silica gel was, once released, higher in concentration than the original ozone that was produced by an ozone generator powered by an electrical discharge. Additionally, this method of storage led to an increase in ozone concentration without the need for any additional energy. When ozone was stored in silica gel, it changed from a gaseous state to a liquid state via a vapor state in narrow capillaries according to Kelvin's law. When ozone was desorbed, it was concentrated depending on the changing of the form from a liquid state to a gaseous state via a supercritical fluids state in the narrow capillaries.     

Effects of Ozonation on Molecular Weight Distribution of Humic Substances and Coagulation Processes – A Case Study: The Úzquiza Reservoir Water

In this article the influence of preozonation on the effectiveness of NOM removal via coagulation processes will be studied (focusing on the influence of the calcium hardness) as well as changes in MW (molecular weight) distribution of humic substances caused by ozonation. Additionally, THMFP removal in both ozonation and preozonation-coagulation processes is assessed. Three different types of water have been used in this study: a natural water from the Úzquiza Reservoir (Burgos, Spain), a synthetic water prepared using natural fulvic acids extracted from the Úzquiza Reservoir and a synthetic water prepared using a commercially supplied humic acid. Molecular weights of humic substances were determined using high-performance size exclusion chromatography (HPSEC); average molecular weights calculated for the unozonated humic substances are 4500 Da for the commercial humic acids and 1000 Da for the natural fulvic acids extracted from the Úzquiza Reservoir. Preozonation shifted the molecular weight distribution of humic substances (both humic and fulvic acids) towards lower average molecular weight values. For the natural water from the Úzquiza Reservoir (with low levels of calcium hardness and hydrophobic fraction (humic substances) being the main fraction of NOM), preozonation has a negative effect on the effectiveness of the coagulation process for NOM removal: the percentages of TOC removal via coagulation decrease with increasing ozone dosage; the maximum TOC removal (33%) is achieved for the unozonated water. Also for this water, ozonation reduced 5–25% of THMFP with ozone doses varying from 0.25 to 2.5 mg O₃/L. A preferential THMFP removal, that is to say, higher reduction in THMFP (43%) relative to TOC (28%) is achieved by the coagulation-flocculation process; this also occurs when preozonation is used, independently of ozone dosage.     

Influence of Ozonation Conditions on Aldehyde and Carboxylic Acid Formation.

The influence of ozonation conditions (i.e. ozone dose and contact time) on the aldehyde and carboxylic acids formation was studied on a pilot scale. The data derived from changes in the molecular weight distribution of natural organic matter (NOM) and the concentration of residual ozone can be applied to a selection of the optimum ozonation conditions. The results confirm the relative ease with which ozone reacts with the organic matter. The short contact time (4–6?min) appeared to be sufficient for the reaction. The higher molecular weight (1600?D) fraction of NOM seems to be slightly more reactive to ozone than the lower molecular weight fraction (500?D). It was also observed that carboxylic acids had been formed at much higher quantities than aldehydes. Two differently acting groups of aldehydes were identified. The concentration of the first one (i.e. formaldehyde, acetaldehyde) strongly depends on ozone dose, while the concentration of the second group of aldehydes (i.e. glyoxal, methylglyoxal) seems to be relatively independent of the ozone dose.     

Verification of Ozone Clusters (O6 & O9)

The use of silica gel for the storing of ozone was investigated. The ozone gas that was discharged from the silica gel was found to be different from normal ozone which is generated by the ozone generator that makes ozone with electric discharge. Ozone clusters could be synthesized by this method, which detaches ozone from silica get without requiring any additional energy. These ozone clusters didn't decompose at room temperature and atmospheric pressure over a half-day. We confirmed that the cluster was heavier than a heavy standard gas, the presence of clusters with an analysis using GC/MS, and the existence of ozone clusters by the bonding energy using a computer simulation by MOPAC.     

Research Note: Measurement of Ozone via an Indirect Gas Chromatography Method

Gas chromatography was used to measure the ozone concentration in oxygen produced by an ozone generator. In this indirect method, the ozone reacts with the coating of the capillary column and produces carbon dioxide, which is then detected. The primary methods of calibration for this technique were based on a wet-chemistry process and absorption of ultraviolet light. This finding also is important if the primary reason for using gas chromatography is detection of carbon dioxide, as artificially high readings of carbon dioxide would be measured in the presence of ozone. The method was tested for ozone concentrations of 3–70?mg/L but the method should also be applicable to higher concentrations.     

Ozone Yields from Oxygen Irradiated at 193 nm

The use of ArF laser radiation at wavelength 193 nm to generate ozone from various pressures of oxygen gases was investigated. Kinetic results were interpreted from molecular spectroscopy and dynamics points of view. The 193 nm radiation can dissociate both oxygen molecules and ozone to produce oxygen atoms. This is an essential process in ozone generation. In this investigation, we focused on the mechanisms that ozone dissociates into three oxygen atoms or vibrationally excited oxygen molecules. The above mechanisms imply a potential process to improve the efficiency of ozone generation.     

Ozonation and Precipitation for Treatment of Bleachery Effluents from Pulp Mills

Results from precipitation of an oxygen/peroxide-bleachery effluent from pulp mills with and without preozonation are presented. Reductions in DOC levels by about 60% were achieved at the pH optimum of 5.5 at an AI/D0C ratio of 0.25 g/g. Increasing alum dosages did not improve the elimination. Ozonation at pH 2 reduced COD, DOC, UV and color levels, while under alkaline conditions an increase of color could be obtained. This effect, based on a polymerization of organics, could be improved at low ozone dosages, by reducing the ozone dosage rate, elevating the pH up to 11 and diluting the wastewater. However, the shift towards high and low molecular weight fractions indicated competing degradation reactions, which counteract a suggested improvement of precipitation by preozonation.     

The Treatment of Spa Water with Ozone Produced by UV Light

Some North American manufacturers are selling devices which produce ozone from UV radiation, which is pumped or sucked into spas, presumably to disinfect the water, without having to use chlorine. To test this claim, a private spa used by two people at least once a day was equipped with a UV radiation unit and an ozone (generating by UV) unit. Bacterial analyses were conducted during experiments carried out using chlorine alone, ozone generated by UV radiation, unit and an ozone (generating by UV) unit. Bacterial analyses were conducted during experiments carried out using chlorine alone, ozone generaed by UV radiation, and ozoen in combination with UV radiation.

Heterotrophic plate counts, and counts of Staphyiococcus aureus and Pseudomonas aeruginosa were lowest when using chlorine, next lowest when using ozone #x002B; UV radiation, and highest when using UV-generated ozone. It is concluded that insufficient dissolved ozone is present for a sufficient reaction time to effect disinfection of these organisms by ozone generated by UV radiation. The fact that the odor of ozone was present above the spa water indicates that contacting also was inefficient.     

Optimal Sizing of a DBD Ozone Generator Using Response Surface Modeling

Dielectric barrier discharge (DBD) reactors used as ozone generators are well known today and widely used for water treatment and air disinfection. The purpose of this article is to propose an experimental procedure based on the response surface modeling in order to optimize the geometrical dimensions of the cylindrical shape ozone generator, i.e., the discharge gap and the electrodes length. Because an effective ozone generator is expected to give high ozone concentration with a minimum of power requirements, the applied high voltage was associated with the geometrical parameters to carry out a composite centered faces design. Obtained results indicate that for an efficient ozone generator, length of the electrodes needs to be optimized while the discharge gap should be minimized.     

Improvement and Optimization of the A. H. Weeks Water Treatment Plant Processes,Windsor, ON,Canada

After the ozone system was implemented at the A.H.Weeks Water Treatment Plant in June 2001, the plant was monitored to evaluate the effects that ozone had on the plant operation and filtered water quality. Filter performance showed an improvement since ozone was applied. Longer filter run time and lower filtered water turbidity and particle count were achieved. Average treated water turbidity was 0.07 NTU for the year before ozone was applied and 0.05 NTU for the year after ozone was applied. An optimization process was conducted to improve the operation. The benefits of the ozone system optimization resulted in more consistency in meeting performance objectives. Ozone generator power requirement was decreased while ozone generator efficiency was increased. Overdosing of ozone quenching agent was less frequent. Reduction in total operational cost was also observed for the year ozone was applied.     

Response Surface Methodology Applied to Ozone Generation

In this work, a strategy is presented to optimize the ozone generation by response surface methodology. A dielectric barrier discharge ozone generator was developed in which it is possible to control electrical current frequency and gas flow entering the generator. Response surface methodology was used to identify ozone generator optimum operational conditions, that is, those that permit considerable ozone productivity and high concentration of ozone gas.     

Medium frequency pulse train ozone generation

In this paper an ozone generation system that uses square bipolar pulses at 1900 Hz frequency (carrier signal) modulated with low frequency square wave is presented. The optimization of the carrier was done by sweeping the frequency from 500 to 2400 Hz and the duty cycle from 20 to 100 %, obtaining the best results at 1900 Hz and 80 % respectively. The experiment was done using a corona discharge generator with glass dielectric, 2 mm gap, water‐cooling at 26 °C and oxygen as the feed gas. Different levels of ozone production were obtained by changing the duty cycle of the modulator signal. The modulator signal works on a discrete way with whole numbers of pulses. The priority of the pulse polarity can be set so the beginning of the pulses may be either positive or negative. A dead time between pulse trains is always present with a minimum value of 10% of the modulator signal. The dead time contributes to the generator cooling because no energy is applied.

A comparative study between the proposed system and a 60 Hz traditional source generator shows an increase in the ozone concentration and ozone production rate, as well as a reduction of the voltage required to produce the corona discharge by using a pulse train at medium frequency.     

Investigations on the Effect of Ozone as a Disinfectant of Egg Surfaces

The feasibility of gaseous ozone to reduce the number of microorganisms on the shell surface, of Salmonella Enteritidis (S.E.) in particular, of avian hatching eggs was investigated. Shell eggs were externally contaminated with S.E. to contain either 10²–10⁴ or 10⁵–10⁶ cfu/shell. Subsequently, the eggs were exposed to several ozone concentrations ranging from 0.5% to 5% wt/wt in combination with two relative humidities (< 30, > 70%) at room temperature. Exposure times varied between 20 minutes and 24 hours. A complete inactivation of 10²–10⁴cfu S.E./egg shell was reached by using an ozone concentration of 1% (wt/wt) for 120 min. Considering higher concentrations of S.E. on the shell ozone treatment caused approximately a 6 log₁₀ reduction. This demonstrates that gaseous ozonation is suitable for applications in hatcheries provided that high-power ozone generators are available. The parameters should be verified in large ozone cabinets.     

Higher Oxidation State Responsible for Ozone Decomposition at Room Temperature over Manganese and Cobalt Oxides: Effect of Calcination Temperature

The heterogeneous catalytic decomposition of ozone was investigated over unsupported manganese and cobalt oxide at room temperature. All catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption (Brunauer–Emmet–Teller method), H₂-temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic activity test indicated that these oxides had a good activity on ozone conversion meanwhile the catalysts remained highly active over time under reaction conditions. The treated temperature of the catalyst had a significant impact on the performance of ozone abatement and the samples treated at lower temperature showed higher activity. The surface area decreased obviously when developing the calcination temperature and H₂-TPR results demonstrated that much higher oxidation state of metal ions and active oxygen species were maintained on the surface under low treated temperature. XPS analysis showed that there were higher oxidation states of metal ions (Mn⁴⁺ and Co³⁺) and adsorbed oxygen species on the surface of catalysts treated at lower temperature, both of which play a significant role in ozone decomposition. However, the activity of manganese oxide was higher than that of cobalt oxide and the possible reason for this phenomenon was discussed.     

Technological parameters that influence the production of ozone in A .D. C. Corona discharfe

Experiments using dry oxygen in a wire–to–cylinder ozone generator, submitted to D.C. corona discharges show that technological parameters (diameter and composition of wire and cylinder, length of cell, gas flow and transit time of the gas) greatly influence ozone production. The cell geometry to be used depends on the polarity of the D.C. voltage applied to the wire and, for a predetermined design, the maximum ozone production rate will be obtained by seeking the most suitable gas flow. Lining up a series of optimized cells can give significant results.