Ozone Decay Rate Research Articles

Virus inactivation in low ozone exposure water reuse applications

In drinking water applications, an ozone exposure (Ct) based framework has been historically used to validate ozone disinfection. However, significant viral inactivation can be achieved with little to no measurable ozone exposure. Additionally, ozone exposure depends on multiple water quality variables as well as the calculation/ozone measurement method used. In this study, we evaluated alternative ozone monitoring frameworks as well as the impact of water quality variables on ozone decay kinetics and virus/coliform inactivation. Here we show that both change in UV254 absorbance and applied O3:TOC were well correlated with viral inactivation and these frameworks were resilient to changes in water quality. Both increasing temperature (12–30 ⁰C) and pH (5.5–8.4) was shown to significantly increase the ozone decay rate and decreased the resulting ozone exposure by as much as ∼90% in the case of pH. However, due to the increased reaction rate of ozone with viruses at elevated temperature and pH, there was only a minor impact (∼20% in the case of pH) in overall disinfection performance for a given O3:TOC. These frameworks were also considered for variable source water with TOC (5–11 mg/L) and TSS (1.2–5.8 mg/L). Change in UV254 absorbance or applied ozone dose (mg/L) were the strongest indicators of disinfection performance for source waters of variable TOC, however site-specific testing may be needed to apply this framework. Challenge testing with influent nitrite indicated that ozone disinfection performance is significantly impacted (>50% reduction in inactivation) in the presence of nitrite thus enforcing the importance of accounting for this value in the applied ozone dose. Multi-point ozone dissolution was investigated as an alternative ozone application method that may present a benefit with respect to overall disinfection performance especially if nitrite was present. Developing and validating these alternative monitoring frameworks and ozone application methods is imperative in water reuse applications where unnecessary elevated ozone exposure may lead to harmful byproduct formation.

Ozone Gas: Scientific Justification and Practical Guidelines for Improvised Disinfection using Consumer-Grade Ozone Generators and Plastic Storage Boxes.

We describe direct measurements of ozone concentration achievable in small enclosed containers (plastic storage boxes) for use as improvised decontamination systems for small articles such as disposable PPE (N95 masks, nitrile gloves, etc.), clothing, mail and small packages, food, and other miscellaneous articles. The emphasis is on the reliable and sustained generation of ozone gas concentrations of sufficient concentration and duration to create an effective virucidal environment to achieve more than 95% to 99% viral inactivation, based upon the data already published in the peer-review literature on this topic.
 The suggestion that ozone be used to inactivate virus is certainly not a new idea. Our objective in this report is to make clear that the necessary levels of ozone can be improvised using simple, easy-to-use, inexpensive, and widely available supplies, and that there is every theoretical and experimental reason to believe that this approach is as highly effective in viral inactivation by ozone as are the far more expensive, complex, cumbersome, and less available equivalent ozone (and other) disinfectant systems that have themselves become unavailable during times of pandemic crisis.
 Using multiple types of readily available commercial ozone generators, concentration in the tested improvised enclosure is tracked over time to assess ozone charging and decay rates, and the ozone quenching effects of items placed in the box. Generator performance is compared against published ozone dosage values for virucidal and antimicrobial activity. Bubbler and box-fan-type ozone generators were found to be effective at achieving and maintaining target concentrations of 10ppm ozone or higher, whereas automotive cigarette lighter and universal serial bus type plug in “air freshener” ozone generators could not achieve the target concentrations in these experiments. Calculations and practical guidelines for assembly and effective use of an ozone box for improvised decontamination are offered.
 The majority of this report is directed toward the scientific justification and rationale for this approach. The end of the document summarizes the findings and offers simplified designs for the construction and use of ozone boxes as an improvised method of disinfection.

Perspectives on textile cleanliness – detecting human sebum residues on worn clothing

Human sebum is one of the major constituents of oily organic soils found in worn clothing. While there are methods to evaluate visible aspects of fabric cleanliness, such as stains, there is no objective method to detect skin oils transferred to the garment through contact with the human body. This research aims at establishing the feasibility of using ozone decay rates in the presence of soiled fabric samples as a metric for measuring the amount of sebum. Our central hypothesis is based on the fact that ozone is highly reactive with some of the primary compounds found in skin lipids originating from sebaceous gland secretions. Ozone decay experiments were conducted in the presence of fabric samples contaminated with known amounts of sebum and modeled using the exponential decay function. The results obtained exhibited a significant relationship between the soil add-on and the ozone decay rates. The presence of skin lipids on fabric accelerated ozone decay. It appears feasible based on our results to detect the presence of soils on garments and thus assess cleanliness using the variation of ozone decay rates.

Ozone decay rates in residential garages

Ozone is a pollutant with well-known health effects on humans. The primary source of ozone inside buildings is ozone in outdoor air that enters buildings by infiltration, natural ventilation, or mechanical ventilation. For infiltration, ozone is transported from outdoors to indoors through inadvertent openings in the building envelope, some of which connect occupied and unoccupied spaces of the building. For example, ozone may enter buildings through garages, attics and crawl spaces that are connected directly to the occupied space.In this study, ozone decay rates were determined for twelve residential garages with a range of sizes, level of attachment to the occupied space, and clutter. Air exchange rates for garages were measured to have a mean of 0.47 (±0.18) hr−1. The mean ozone decay rate in these garages was 2.7 (±1.1) hr−1, a value comparable to previous data for occupied space ozone decay rates. There were differences in ozone decay rates between one-car and two-car garages, which seemed to be correlated with the volume/area ratio. Using these and previously published data, it was concluded that, under normal conditions, ozone penetration through garages to the occupied space is not a significant pathway. However, there are some conditions for which garages may be a major pathway for ozone entry into homes. One example of this is when both the garage door and the door connecting the garage to the occupied space is opened for a long period of time.

Plasmas ozone inactivation of Legionella in deionized water and wastewater.

The results show that ozone concentration determination using ultraviolet spectrophotometry (UV-2450) at 258nm is easier than using indigo method at 600nm. A strong linear relationship was found between purge time and O3 concentration in deionized water. Ozone concentration can be predicted in deionized water. A higher O3 flow rate or lower temperature led to a higher O3 concentration. Ozone concentration was stable in 60min, so that ozone self-decomposition could be ignored at ozone concentrations below 0.4mgL-1. A higher temperature led to a higher inactivation efficiency and rate, and that a lower temperature led to a lower ozone decay rate and inactivation efficiency even if ozone solubility increased when temperature decreased. The fastest inactivation rate occurred before c0t = 165μgL-1s, but the inactivation rate decreased after c0t = 165μgL-1s with tail phenomena. The tail phenomena were clearly observed and may be caused by oxidization of lipopolysaccharides (LPS), cell membrane, etc. The activation energy Ea = 55,404 ± 0.3Jmol-1 were obtained for Legionella inactivation with ozone in deionized water. Ozone maximum decay rate was positively proportional to COD concentration. COD impacted on ozone concentration seriously. Higher COD concentration resulted in higher ozone decay rate. COD could result in ozone concentration decrement rapidly to a steady value in 5s. Higher initial ozone concentration resulted in higher germ inactivation rate. Higher initial COD concentration resulted in lower Legionella inactivation efficiency. COD was easier to react with ozone than Legionella. The relationship among the initial COD concentrations COD0, the initial O3 concentration c0, and the O3 contact time t necessary for a 99.999% reduction of Legionella in wastewater can be expressed in some equations. O3 disinfection time t necessary for a 99.999% reduction of Legionella can be predicted by Eqs. (10) and (11). Graphical abstract ᅟ.

Enhancement of bromate formation by pH depression during ozonation of bromide-containing water in the presence of hydroxylamine

This work investigated the fate of bromate formation during ozonation in the presence of hydroxylamine (HA). Results indicated that pH depression, as a commonly feasible control strategy for bromate formation during ozonation, unexpectedly enhanced the bromate formation during ozonation in the presence of HA. A dramatically high level of bromate was observed at acidic pH in the ozone/HA process. The scavenging experiments demonstrated the essential role of OH produced in the reaction of ozone with HA in bromate formation. In the process, OH mainly oxidizes bromide to Br, which is further oxidized by ozone and eventually converts to bromate. Further investigations suggested that the unexpected enhancement on bromate formation by pH depression can be mainly ascribed to the pH-dependent ozone decay, OH exposures and formation rate of Br. As pH decreased from 7 to 5, the reduced OH scavenging capacity of HA led to higher OH exposures, which contributed to the enhancement of bromate formation. As pH decreased from 5 to 3, the enhanced formation rate of Br largely augmented the formation of bromate. In addition, the ozone decay slowed down by pH depression provided more available ozone for the oxidation of the formed Br to bromate. The enhanced effect of pH depression on bromate formation was still observed in the real water samples in the ozone/HA process. Accordingly, pH depression might be avoided to control the bromate formation during ozonation in the presence of HA.

SOA in newly decorated residential buildings

Secondary organic aerosols (SOA) are products of the reaction of reactive organic gases (ROGs) and ozone. Most SOA are in the nanometer or submicron range, and thus SOA may be harmful to human health. Concentrations of ROGs may be high in newly decorated rooms, which may result in high SOA concentrations, especially during seasons with high ozone concentration. The objective of this study was to investigate the concentrations of SOA and the extent to which SOA contribute to indoor PM2.5 concentrations in newly decorated residential buildings. We measured concentrations of ROGs in 24 rooms of eight newly decorated (within the preceding three months) residential buildings in Beijing, China. Using previously measured indoor ozone decay rates, air change rates, and corresponding monitored ozone concentrations, we estimated the indoor ozone concentrations for the newly decorated rooms. Subsequently SOA concentrations were calculated using an aerosol mass fraction (AMF) model. We further estimated the fractions of SOA concentrations in indoor PM2.5. The SOA concentrations in 18 of the rooms ranged from 0.88 to 18.18 μg/m3, contributing to between 3.77% and 78.57% of indoor PM2.5 concentrations. The other six rooms had much lower SOA concentrations, less than 0.1 μg/m3, contributing to less than 0.39% of indoor PM2.5 concentrations. The results indicate that the concentrations and contribution of SOA in most newly decorated residential rooms are much higher than those in rooms with long-term occupancy, while some newly decorated rooms can still have low SOA concentrations.

Deethylatrazine as a more appropriate hydroxyl radical probe compound during ozonation: Comparison with the widely used p-chlorobenzoic acid

This study proposed deethylatrazine (DEA) as the OH probe compound during ozonation and compared with the widely used p-chlorobenzoic acid (pCBA) for the first time. Results showed the ozone decay was not affected by DEA, but largely accelerated by pCBA as compared to the control. The DEA degradation was exclusively attributed to OH formation from ozonation of the tested waters, while pCBA was partially degraded by OH formation from the pCBA-derived propagation reactions. In synthetic waters with different OH scavenging capacities, the ozone decay rates with DEA were almost consistent with the control. The ozone decay rates with pCBA remained consistent with the control only in the synthetic waters with high OH scavenging capacities. For the synthetic waters with low OH scavenging capacities, pCBA led to higher ozone decay rates and OH exposures, and thus gave overestimated Rct values. The two OH probe compounds were also investigated in four authentic waters with different OH scavenging capacities. DEA exhibited no detectable effect on the ozone decay in all four authentic waters as compared to the control. The enhancing effects of pCBA on the ozone decay and OH formation were observed in the tap and reservoir water, which led to an overestimation of Rct as compared to the presence of DEA. In the ground water and wastewater, similar values were observed in ozone decay rates and Rct for the presence of pCBA and DEA. Thus, the use of pCBA as the OH probe compound should be carefully examined or avoided to prevent its interrupts in determining the Rct during ozonation of waters with different OH scavenging capacities. DEA is a more appropriate OH probe compound during ozonation.

Influence of Seasonal Variation of Water Temperature and Dissolved Organic Matter on Ozone and OH Radical Reaction Kinetics During Ozonation of a Lake Water

ABSTRACTThis study used key description parameters of the ozonation process in lake water samples over a 1-year period to better understand the influence of seasonal variations in water quality such as water temperature and dissolved organic matter on ozone decomposition and OH radical formation and reaction kinetics. The parameters were the initial ozone demand (IOD), ozone decay rate constant after the IOD (ksec), ratio of OH radical exposure to the ozone exposure (RCt), and ratio of ozone consumption to the OH radial exposure multiplied by the second-order rate constant for the reaction of the OH radical with an OH radical probe compound (Ω). The seasonal variations in water quality had the most significant influence on RCt (39–64%), followed by ksec (35–38%), Ω (27–34%), and IOD (11–25%) for the raw lake water and sand-filtered water in which the numbers inside parentheses indicate the percent standard deviation of the measured values for 1 year. For the oligotrophic-type lake water, the seasonal variation in water temperature (6–26 °C) had the most significant influence on the ksec, RCt, and Ω. The Ω was newly found to be inversely related with water temperature, possibly due to the temperature-dependent OH radical yield from ozone decomposition. This implies that the OH radical oxidation capacity during ozonation can be significantly influenced by the temperature due to the varying ozone decomposition rate and the intrinsic OH radical yield. This study also demonstrated the Ω is a useful, alternative parameter to the RCt for describing or predicting OH radical exposure from ozone consumption especially when the ozone decay is rapid or varies over time such as the initial ozonation phase of natural water or wastewater where a considerable OH radical exposure takes place.

Obtaining Real-Time Kinetic Parameters on Ozone Decay from a Full-Scale Ozone Contactor Using the Axial Dispersion Reactor Model

Ozone decay kinetic parameters, including fast ozone demand ([D]0), ozone decay rate constant (kD), and rate constant for ozone reaction with ozone demand (kR), are required for a numerical simulation targeting the design and operational optimization of an ozone contactor. The kinetic parameters of ozone decay and dispersion number were obtained from a full-scale ozone contactor for the axial dispersion reactor model simulation. The sensitivity analysis showed that the influence of kR was minor and the constant 13 L mg−1 min−1 for kR was suitable for carrying out simulations for sand-filtered raw water without measuring it. Curve fitting with on-site ozone concentrations and the ADR simulation results using a trial-and-error method could successfully provide kinetic parameters on ozone decay (i.e., kD and [D]0). Using these real-time kinetic parameters, we successfully predicted the CT, residual ozone, C. parvum log inactivation, and bromate formation. Compared to a method based on the CSTR in series, this method could provide more accurate CT and residual ozone for an ozone contactor with horizontal meandering flow and low dispersion number.

Process Control For Ozonation Systems: A Novel Real-Time Approach

For real-time control of ozonation processes in water works, a sequencing batch reactor was constructed to measure the ozone decay rate constant (kO3) in short time intervals of about 15 min. The batch reactor is filled during the production process, immediately after dissolving ozone in water by a static mixer. On the basis of kO3 and the initial ozone concentration ([O3]0), and the experimentally determined ratio of the concentrations of •OH radicals to ozone (Rct), the degradation of micropollutants in ozone reactors (modeled as Continuously Stirred Tank Reactors - CSTRs) were calculated for compounds with known reaction rate constants with ozone and •OH radicals. Calculated degradation of atrazine, iopromide, benzotriazole and acesulfame are in good agreement with measured data. For acesulfame the following rate constants were determined in this study at 20 oC: reaction rate constant with ozone = 88 M−1s−1, reaction rate constant with •OH radical = 4.55 × 109 M−1s−1. For the ozone reaction an activation energy of 35 kJ/mol was determined. Similarly to micropollutants, the relative inactivation of microorganisms (N/N0) can be calculated based on the inactivation rate constant for ozone and if applicable the lag phase. The pI-value (= −logN/N0) was introduced and implemented in the process management system to calculate online the log inactivation of reference microorganisms such as B. subtilis spores. The system was tested for variation of pH (6.5–8.5), DOC (1.2–4.2 mg/L) flowrate 3.2–12 m3/h and temperature (5.7–9 oC). Furthermore, a given pI-value, e.g. 1 for a 1-log inactivation of B. subtilis spores, can be set as control parameter in the process management system. The ozone gas flow is then adjusted until the set pI-value is reached. The process control concept was validated with B. subtilis spores. Generally, a good agreement was found between calculated and measured inactivation data. It was also demonstrated, that a constant ozone residual may lead to insufficient disinfection or overdosing of ozone. The new process control concept for ozonations based on onsite measurement of the ozone decay rate constant and the pI-value allows to assess disinfection and degradation processes quantitatively in real-time.

Investigation on the pyrolysis of cow bone as a catalyst for ozone aqueous decomposition: Kinetic approach

In this study, the feasibility of using pyrolysis of cow bone (PCB) as a catalyst for ozone aqueous decomposition was investigated. PCB, a new catalyst prepared under laboratory conditions, was used for ozone aqueous decomposition in a fluidized bed reactor (FBR) with liquid recirculation using a pump. The catalytic effect of PCB and the relevant parameters of this heterogeneous catalyst on ozone decomposition were investigated. The chemical composition of PCB samples was analyzed by X-ray fluorescence (XRF), which showed that the PCB was composed of CaO, P2O5, MgO, SiO2, Na2O, K2O and MnO. Results of ozone aqueous decomposition indicated that ozone decay rates, for both self and heterogeneous ozone decomposition, accelerated with increasing the pH of the solution. A first-order kinetic model fit the self and heterogeneous decays of ozone the best. tert-Butyl alcohol (TBA) was employed as a radical scavenger during the experiments. In heterogeneous catalytic ozone decay, results indicated that the ozone decay rate was less affected by TBA at an alkaline pH. The contribution of a radical reaction mechanism on the ozone decay rate was subsequently determined. Results showed that the ozone decay rate increased due to surface catalyzed radical reactions. At pH values higher than the pH of the point of zero charge (pHPZC) of the PCB, ozone interactions with strong Lewis acids (LA) on metal oxide surface sites of the PCB, as well as rates of aqueous ozone decay, increased. These findings suggested that the ozone decomposition reaction mainly took place on the PCB surface and that the surface chemistry of the PCB played a key role in the performance of the catalytic process.

A case study on the automatic ozone dose control system based on the ozone decay rate in a full-scale advanced water treatment plant

Recently, a growing concern about algae-origin taste and odor in drinking water made it possible to introduce ozone and granular activated carbon (GAC) processes to large-capacity (more than 300,000 m3/d) water treatment plants in the Han River area in South Korea. Especially, concerning the ozone process, the ozone residual of ozone contactor effluent may affect on the biological destabilization, poor physical properties of the following GAC process and operators’ health due to high ozone gas concentration in GAC contactor. Therefore, maintaining an optimal ozone dose based on the ozone demand is essential to the operation of the ozone process. The Koyang Advanced Water Treatment Plant (KAWTP) has been utilizing a new type of ozone control method since July 2009, which automatically calculates required ozone dosed based on the instantaneous ozone demand (ID) and the ozone decay rate constant (Kc ). The ID and the first-order Kc values are calculated based on the measured dissolved-ozone concentrations fr...

Setting maximum emission rates from ozone emitting consumer appliances in the United States and Canada

A Monte Carlo analysis of indoor ozone levels in four cities was applied to provide guidance to regulatory agencies on setting maximum ozone emission rates from consumer appliances. Measured distributions of air exchange rates, ozone decay rates and outdoor ozone levels at monitoring stations were combined with a steady-state indoor air quality model resulting in emission rate distributions (mg h−1) as a function of % of building hours protected from exceeding a target maximum indoor concentration of 20 ppb. Whole-year, summer and winter results for Elizabeth, NJ, Houston, TX, Windsor, ON, and Los Angeles, CA exhibited strong regional differences, primarily due to differences in air exchange rates. Infiltration of ambient ozone at higher average air exchange rates significantly reduces allowable emission rates, even though air exchange also dilutes emissions from appliances. For Houston, TX and Windsor, ON, which have lower average residential air exchange rates, emission rates ranged from −1.1 to 2.3 mg h−1 for scenarios that protect 80% or more of building hours from experiencing ozone concentrations greater than 20 ppb in summer. For Los Angeles, CA and Elizabeth, NJ, with higher air exchange rates, only negative emission rates were allowable to provide the same level of protection. For the 80th percentile residence, we estimate that an 8-h average limit concentration of 20 ppb would be exceeded, even in the absence of an indoor ozone source, 40 or more days per year in any of the cities analyzed. The negative emission rates emerging from the analysis suggest that only a zero-emission rate standard is prudent for Los Angeles, Elizabeth, NJ and other regions with higher summertime air exchange rates. For regions such as Houston with lower summertime air exchange rates, the higher emission rates would likely increase occupant exposure to the undesirable products of ozone reactions, thus reinforcing the need for zero-emission rate standard.

Ozone application in water sources: effects of operational parameters and water quality variables on ozone residual profiles and decay rates

Systematic ozonation tests were conducted by means of a mobile pilot plant. Water source 1 was a low turbidity stream with very low solids content and very low turbidity, apparent color and alkalinity. Water source 2 was reservoir water with higher turbidity, solids content and alkalinity than source 1. The ozone plant was a counter-current contactor composed of four columns in series. Variations in contact time, in the feed gas concentration (in terms of percent by weight of ozone) and in splitting of the total applied ozone dosage between columns 1 and 2 were tested. Concentration - time (CT) products were calculated and decay coefficients K were estimated from experimental data. The relative importance of water quality and certain operational parameters with regard to CT products and ozone decay was assessed. Total CT values seemed to increase with: (a) total applied ozone dosage, (b) percent by weight of ozone in the feed gas to the bubble contactor, (c) increasing contact time and (d) higher water quality, with regard to turbidity, apparent color, total organic carbon and particle counts. As the total applied ozone dosage was increased, the more important the contact time and ozone dosage configuration became for the total CT value. The apparent first order ozone decay rate constant (K) decreased with increasing total applied ozone dosage. The contact time appeared to exert a much stronger influence on total CT values than on K values, particularly so as the total applied ozone dosage was increased.

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.

OZONE DISINFECTION OF FISH HATCHERY WATERS: PILOT PLANT RESULTS, PROTOTYPE DESIGN AND CONTROL CONSIDERATIONS

For over two years, ozone pilot plant studies have been conducted examining the efficacy of disinfecting makeup water entering the Dworshak National Fish Hatchery at Orofino, Idaho. The major pilot plant equipment consisted of a 1.12 kg/day Union Carbide Ozone Generator and contacting column. Plate counts for total bacteria were taken at various points in the pilot plant. Similar plate counts were taken from existing ultraviolet disinfection equipment. Also monitored were ozone residual levels entering and within the recycle system, ammonia, nitrate, nitrite, total organic nitrogen, suspended solids, turbidity and biochemical oxygen demand. Analysis of the plate counts shows ozone consistently provides more effective disinfection of the makeup water than the existing ultraviolet system. Nitrite levels after ozonation show a significant decrease, while nitrate levels increased. Ozone disinfection of recycle water was also satisfactorily demonstrated. Additionally, batch studies indicate ozone effectively destroyed algae. The pilot work established Dworshak ozone requirements to disinfect both makeup and recycle water. Experimental ozone demand, residual ozone removal rates, and ozone decay rates make it possible to design equipment and controls that will protect the fish from unsafe ozone concentrations. An ozone disinfection system preliminary design for a typical recycle fish hatchery is presented.

Catalytic ozone aqueous decomposition promoted by natural zeolite and volcanic sand

Chemical oxidation using ozone in the presence of appropriate catalysts offers an attractive option for removing poorly biodegradable pollutants. However, the effect of such catalysts on ozone aqueous decomposition is not well documented. This study compares experimental results on ozone aqueous decomposition promoted by zeolite and volcanic sand. These are two low costs natural materials identified as suitable catalysts for heterogeneous ozonation. The effects of pH (2–8) and free radical scavengers (acetic acid) on the dissolved ozone decay rate are evaluated at laboratory scale. Results show that the ozone decay rate increases in the presence of natural materials tested here. Under alkaline conditions, the effect of free radical scavengers on ozone self-decomposition is significantly reduced when such materials were present, particularly in the case of volcanic sand. Results suggest that ozone aqueous decomposition in the presence of zeolite and volcanic sand take place mainly on the natural material surface. The presence of metal oxides in zeolite and volcanic sand might catalyse ozone decomposition into more active radicals, thus enhancing the oxidation of organic pollutant.

The Impact of Traces of Hydrogen Peroxide and Phosphate on the Ozone Decomposition Rate in “Pure Water”

To obtain an idea of the magnitudes of the ozone loss rates rO3 in practical applications of ozone, an overall determination of the ozone decay profiles and rate constants was carried out in four different systems. These systems resemble different conditions for industrial application of ozone and the peroxone process, such as in the field of micro electronics, drinking water purification, disinfection, etc. Therefore, the behavior of ozone was monitored in the pH range from 4.5 to 9.0, in pure water and phosphate buffered systems in absence and presence of small amounts of hydrogen peroxide (10−7 M to 10−5 M H2O2). First the reproducibility of the ozone decay profiles was checked and from the various kinetic formalism tests, the reaction order 1.5 for the ozone decay rate has been selected. As expected, hydrogen peroxide increases the decay rates. In pure systems, added concentrations of 10−7M H2O2 already cause a remarkable acceleration of the ozone decay in the acidic and neutral pH range compared to the pure systems. However for alkaline pH conditions almost no effect of the low hydrogen peroxide concentrations was noticed. Contradictory to literature data, in the absence of hydrogen peroxide, ozone displays faster decays in the buffered systems of low ionic strength of 0.02 compared to pure water. This acceleration is more pronounced for acidic pH conditions. Low concentrations of phosphate may indeed accelerate the ozone decay in the presence of organic matter. Adding H2O2 concentrations below 10−5M to phosphate buffered solutions has a negligible effect on the ozone decay rate compared with pure water systems, except for pH 7. It appears that phosphate masks the effect of hydrogen peroxide below 10−5 M as tested here. Thus the application of AOP's by adding low concentrations of hydrogen peroxide is not well feasible in the presence of phosphate buffers in pure water systems.

Synergistic Evaluation of Ozone and UV at the Coquitlam Source for Enhanced DBP Control and Cryptosporidium Inactivation

A study was performed for the GVRD to select the ozone dose that results in a higher UVT (UV Transmittance) and reduced DBP formation potential, at the most economical life cycle costs of ozone and UV treatment. The GVRD treats its Coquitlam source with ozone, to meet Giardia and virus inactivation requirements. Currently, the Coquitlam Facility does not meet Cryptosporidium inactivation requirements (3-log). Because the ozone dosage required for Cryptosporidium inactivation is cost prohibitive, UV treatment was selected to provide for adequate log inactivation. Based on pilot and full-scale test results, a model was developed to predict the ozone treated water UVT, which was applied to historical water quality data to evaluate life cycle costs of ozone and UV treatment. In addition, the dosage necessary for control of DBPs, the change in ozone decay rate with increases in pH, and the impact of three quenching chemicals on treated water UVT were evaluated.