Ozone Decay Research Articles

Ozonation of haloacetic acid precursor using phenol as a model compound: effect of ozonation by-products

The formation pattern of haloacetic acids (HAAs) was investigated using phenol as a model precursor of HAAs, and the oxidation by-products formed from phenol ozonation, such as hydroquinone, catechol, glyoxal, glyoxylic acid and oxalic acid, were also chlorinated to measure the HAAs formation potential (HAAFP). Of these, phenol showed the highest reactivity with chlorine, yielding the most HAAFP. Even though HAAFP of the tested by-products was lower than that of phenol, it was confirmed that all by-products can act as the precursor of HAAs. Regarding the ozonation of phenol-containing water, the efficiency of ozone in controlling HAAs can be reduced by the formation of oxidation by-products. When comparing conditions for pH 7 and 3, the ozonation for pH 7 was more effective in removing the overall HAA precursors than the ozonation for pH 3. This result was attributed to complete oxidation by the production of the secondary oxidant, such as the OH radical (OH·) from ozone decay, and ionization of phenol.

The Use of para-Chlorobenzoic Acid (pCBA) as an Ozone/Hydroxyl Radical Probe Compound

Since OH· radicals cannot be measured directly during an ozonation process, para-chlorobenzoic acid (pCBA) has been used recently as an OH· radical probe compound during ozonation based on its very slow direct reaction with ozone and fast reaction with OH· radicals. However, in experiments of this study it was shown that pCBA accelerated ozone decay. Furthermore, the formation of hydrogen peroxide was observed during this process. The formed H2O2 increases the decomposition of aqueous ozone and leads to enhanced formation of OH· radicals. The chain reaction therefore changes to HO2 − ion initiated decay of ozone instead of hydroxide ion, OH−. Thus, an error in applying pCBA as a probe compound in low scavenger containing waters is likely to occur if the scavenging rate of pCBA makes up more than 5% of the total scavenging rate.

Evaluating Magnetic Ion Exchange Resin (MIEX)® Pretreatment to Increase Ozone Disinfection and Reduce Bromate Formation

Magnetic ion exchange resin, known by its commercial name (MIEX®) provides one pretreatment alternative that could maximize ozonation disinfection while decreasing bromate formation in bromide-containing waters. During a 5-week pilot study, the MIEX® process removed up to 30 % of the dissolved organic carbon (DOC) and reduced ultraviolet absorbance at 254 nm (UV 254) by up to 60%. When MIEX® pretreated water was ozonated, ozone decay rates were reduced, increasing the CT achieved by 40% to 65%. The increased disinfection capability reduced the transferred ozone dosages required for Cryptosporidium inactivation by 15% to 25% and bromate formation by 35%.

The Impacts of New CT Requirements for Designing Ozone Systems for Cryptosporidium Inactivation

The impacts of new CT requirements for ozone disinfection of Cryptosporidium are evaluated using a desktop CT disinfection analysis. The analysis is applied to the design of new and upgraded ozone systems for two water treatment plants in Virginia. The results indicate that the feasibility of ozone disinfection of Cryptosporidium is dependent on ozone demand and decay characteristics of the water supply and may not be feasible for water supplies with moderate to high ozone decay rates. The CT analysis is a useful design procedure to evaluate the benefit-cost tradeoffs of using ozone to achieve alternative disinfection goals.

Determination of Ozone Emission from a Domestic Air Cleaner and Decay Parameters using Environmental Chamber Tests

A methodology has been established to quantify the ozone emission rate from electronic air cleaners, as well as the ozone decay parameter. Three different portable ionisation-type air cleaners were used in the experiments. A stainless steel environmental chamber with volume size 6.4m3 (1.6×2×2m) was employed in the study. The leakage rate of the chamber was measured to be 0.0042h-1 by a tracer decay gas test. The ozone growth curve within the chamber was used to quantify the ozone emission rate of the air cleaner and the ozone decay parameter. The emission rate and the decay parameter were determined by the initial slope and the equilibrium state of the growth curve simultaneously, and the technique of least squares fitting was introduced in the data analysis. The ozone emission rates and the decay parameters of Air Cleaner I, II, and III were found to be 119.4±15.6, 77.6±5.4, and 1092.3±112.5ppbh−1 and 2.59×10−1±0.03, 1.68×10−2± 0.001 and 9.48×10−2±0.01h−1, respectively. The wide range of the emission rates was believed to relate to the individual designs of the air cleaners. The variation in decay parameters obtained from the measurements was tentatively associated with the level of VOCs in the sampling environment.

Ozone monitoring in a Mediterranean forest using diffusive and continuous sampling.

Ambient ozone was measured in a forest in Castelporziano (Italy) characterised by the prevailing presence of Holm-oak trees (Quercus ilex L.) from June to November 2003. Two methods for measuring ozone were used: long-term monitoring using diffusive samplers at three heights within the canopy, and continuous monitoring at two heights using the UV method. Results for one week mean ozone levels above and below the canopy from the diffusive samplers were compared to those obtained using the automatic analyser at the same levels. A good correlation between the two sampling techniques was found. Continuous monitoring showed a daily cycle with a midday maximum and a nocturnal minimum. While the forest floor consistently had the lowest ozone concentration, there were no differences during most daytime hours. The midday maximum is clearly due to downward mixing with O3-rich air from above. The night-time ozone decay within the canopy is the result of dry deposition of O3 and most likely due to reaction with biogenically produced NO. AOT40 within and above the canopy mostly exceeded the critical levels.

Inactivation of Cryptosporidium parvum with ozone in treated drinking water

Cryptosporidium parvum oocyst disinfection experiments were performed using ozone at bench-scale in batch reactors. The water matrix was filter effluents collected from a full-scale facility in different seasons but with similar water quality. Cell tissue culture (FDM-MPN) was used to assess the viability of C. parvum oocysts. The disinfection kinetics showed no significant difference in waters from different seasons. The simple Chick–Watson model was found to be the best fit model for MPN data in combination with first-order-plus-demand ozone decay kinetics. The CT value for 99% inactivation was determined to be 19.5 mg-min l −1 at 15°C when pooling data together, which was larger than values reported in other studies.

Disinfectant decay and disinfection by-products formation model development: chlorination and ozonation by-products

Comprehensive disinfectant decay and disinfection by-product formation (D/DBP) models in chlorination and ozonation were developed to apply to various types of raw and treated waters. Comparison of several types of models, such as empirical power function models and empirical kinetic models, was provided in order to choose more robust and accurate models for the D/DBP simulations. An empirical power function model based on dissolved organic carbon and other parameters (Empirically based models for predicting chlorination and ozonation by-products: haloacetic acids, chloral hydrate, and bromate, EPA Report CX 819579, 1998) showed a strong correlation between measured and predicted trihalomethane (THM) and haloacetic acid (HAA) formation for raw waters. Internal evaluation of kinetic-based models showed good predictions for chlorine decay and THM/HAA formation, but no significant improvements were observed compared to the empirical power function model simulations. In addition, several empirical models for predicting ozone decay and bromate (ozonation disinfection by-product) formation were also evaluated and/or developed. Several attempts to develop kinetic-based and alternative models were made: (i) a two-stage model (two separate decay models) was adapted to ozone decay and (ii) an ozone demand model was developed for bromate formation. Generally, internal evaluation of kinetic-based models for ozone decay showed significant improvements, but no significant improvements for the simulation of bromate formation were observed compared to the empirical power function model simulations. Additional efforts were performed to reduce the gaps between specific models and their actual application. For instance, temperature effects and configuration of ozone contactors were considered in actual application.

The effects of dissolved organic matter on the decomposition of di-n-butyl phthalate by ozone/hydrogen peroxide process

The effects of the dissolved organic matter (DOM) on the ozone decay and the di-n-butyl phthalate (DBP) decomposition during ozone/hydrogen peroxide (O3/H2O2) process were investigated (DBP-d4 was used instead of DBP). Four surface waters, two secondary municipal sewage effluents (SMSEfs) and Suwannee river natural organic matter were used as DOM. The ozone decompositions in the DOM solutions were separated by instantaneous ozone consumption and slower ozone decay. The effect of H2O2 addition on the ozone decay was clearly observed at slower ozone decay. Ozone decomposition rate at slower ozone decay increased linearly with H2O2 dose. DBP-d4 was exponentially decreased with ozone consumption. Ozone consumption required to decompose 90% of DBP-d4 ((deltaO3)90%) in SMSEFs was higher than those in surface waters. The (deltaO3)90% per DOC of DOM values were from 22 to 23 micromole/mgC for SMSEFs and from 10 to 17 micromole/mgC for surface waters. The (deltaO3)90% values were correlated to specific ultraviolet absorbance at 254 nm (SUVA254) for surface waters.

Numerical Simulation of Bromate Formation during Ozonation of Bromide

The purpose of this study is to develop a kinetic model that links O\d3 decomposition reactions from the TFG ozone decay model with recognized Br\u- oxidation reactions, secondary \Dp9e\N OH reactions, and H\d2O\d2 reactions in order to improve O3 decay and bromate formation prediction capabilities under multiple water quality conditions. The model was compared with experimentally measured ozone decomposition and final bromate concentration data sets provided by two researchers. The data sets included varying pH (6.5–8.5), initial hydrogen peroxide (0–1 mM), and initial bromide concentration (0.1–1 mM). Model verification was carried out by sensitivity analysis of the rate constants and then optimization of the most sensitive rate constants using the method of least squares. Model predicted ozone decay data was analyzed and compared with measured ozone decay data using \iR-squared statistic for linear regression model. The model predicted final bromate concentration is analyzed by comparing it with the residual Δ (%) between experimental and model results. The TFG model was effectively tested for multiple data sets and it was found that model prediction was a success both for ozone decay (regression coefficients >0.95 for all experimental conditions but one) and bromate prediction with residual of less than 100% for all experimental conditions except low peroxide dose (<20 μm).

Optimization and Control of Ozonation Plant Using Raw Water Characterization Method

This study was undertaken to devise an innovative method for optimization and control of ozone dosage in drinking water ozonation treatment plants. The method is based upon a specifically-conceived analytical procedure, which can accurately measure the ozone decomposition rate. This was found to consist of two apparent phases: an instantaneous ozone demand (ID) phase and a relatively slower ozone decay (pseudo first-order rate constant, kc) phase. Those parameters, ID and kc were measured in a demonstration plant by the testing procedure in order to characterize raw water and process water, and utilized an Automatic Ozone Control Unit (ACU) to optimize preozonation (with parameter, ID) and postozonation (with parameter, kc).

Innovative reactor technology for selective oxidation of toxic organic pollutants in wastewater by ozone

Ozonation can be a suitable technique for the pre-treatment of wastewater containing low concentrations of toxic or non-biodegradable compounds that cannot be treated with satisfactory results when only the traditional, less expensive biological techniques are applied. In this case, the oxidation process has to be made as efficient as possible, in order to reduce the coats of ozone addition and use. An efficient oxidation process with ozone can be obtained by focusing the oxidation with ozone selectively on the direct oxidation of toxic pollutants and to minimize ozone losses due to the decay of ozone in water. Supported by data of the rate constants of the reactions involved, a mathematical model was developed. It quantifies the ozone consumption by the process, and the share of ozone consumption by undesired side reactions, in several different reactor systems. Results obtained with this model indicate that a plug flow reactor (PFR) will be the most efficient design for the oxidation reactor. As an alternative, the cascaded tank reactor system (CTR), in which the ozone feed may be realized with less practical problems, might be considered. The traditional continuous flow stirred tank reactor (CFSTR) is shown to be the least efficient system.

Effect of pH and Importance of Ozone initiated Radical Reactions In Inactivating Bacillus subtilis Spore

The effect of pH on the inactivation of Bacillus subtilis spores with ozone in a batch reactor was examined in association with the role of OH radicals. The exact effect OH radicals have on ozone inactivation of microorganism is not well understood, although a direct reaction of molecular ozone has sometimes been emphasized. This study reports a novel observation that the presence of OH radicals plays a significant role in microbial inactivation. Considering the dependence of the ozone decay rate on pH, the observed C¯ T values for achieving a 2 log inactivation using the modified Chick-Watson model was 40 % lower at pH 8.2 compared to that at pH 5.6. In the presence of OH radical scavengers (tert-butanol), the observed change of C¯ T with pH was within 10%. This difference could be explained by the significant role of OH radicals.

Development of measurement equipment of half life of ozone

In the present research, a new measurement method and the mechanism of half-lifetime τ (h) of ozone decay is proposed. Ozone is generated by such electric discharge as a silent or surface discharge and has a strong oxidation power and is widely used for air or water purification. But to determine the dosage of ozone, it is necessary to know the half-lifetime of ozone decay τ in air and/or water [1]. Ozone decay is found to change in a logarithmic way. Through the measurements of the ozone concentration x (g/m 3) with time t, the half-lifetime of ozone decay, τ, is estimated [2].

Femtosecond dissociation of ozone studied by the Auger Doppler effect

A Doppler-type shift in the kinetic energy of atomic Auger electrons emitted after fast dissociation of O3 molecules is observed. The resonant Auger spectrum from the decay of repulsive core-excited states reflects both the early molecular ozone decay and that from excited dissociation fragments. The kinetic energy of the fragment is manifested as an energy shift of the atomic Auger lines when the measurement is made under certain conditions. We report measurements of the energy-split atomic fragment emission lines arising from dissociation on a time scale comparable to the core-hole lifetime. For the O 1s–σ* states the kinetic energy release amounts to several electron volts. We report measurements for excitation of both the terminal and central oxygen 1s electrons. A simple kinematic model for extracting a lower limit for the kinetic-energy release is presented and is compared with the result of a Born–Haber cycle, which may be seen as an estimate of the maximum energy release.

The Application of Ozone in Semiconductor Cleaning Processes: The Solubility Issue

The solubility of ozone in aqueous solutions expressed as a pseudo-Henry’s law coefficient for ozone, is measured over a pH range of 1 to 8, and temperature range of 15 to 45°C in the presence of several additives: HCl, HAc (Ac is acetate), NaAc, and NaOH. The value of was found to be a function of temperature, pH, and nature of the anion. The pseudo-Henry’s law coefficient is maximal at low pH and decreases with rising pH of the aqueous solution. The addition of chloride enhances the ozone decay rate and thus decreases the solubility below pH 2 while the addition of acetic acid/acetate results in an increase of for The solubility enthalpy for ozone is found to be equal to For applications of ozone in semiconductor cleaning processes, knowledge of the dependence of on pH, temperature, gas phase concentration, and additive is important in order to achieve optimized cleaning conditions. © 2001 The Electrochemical Society. All rights reserved.

Characterization of raw water for the ozone application measuring ozone consumption rate

This study was conducted to illustrate an ideal method for characterizing natural waters for ozonation processes in drinking water treatment plants. A specific instrument designed with the flow injection analysis (FIA) technique enabled us to measure accurately the ozone decomposition rate, which was found to consist of two stages: the instantaneous ozone consumption stage and the slower ozone decay stage. The ozone consumption rate was measured at the initial and secondary stages by determining certain parameters called the instantaneous ozone demand (ID) and the pseudo first-order decay rate constant ( k c). Using the OH ·-probe, the yield of OH · per consumed ozone was also measured to determine its potential to produce OH · for the oxidation of micropollutants during the ozonation process. The ozone consumption of the ID values was significant in most natural waters, and substantial amounts of OH · were found to generate during the instantaneous ozone consumption stage. This study also investigated the effects of particulates, ozone doses, and sequential ozone injection on ozone decomposition kinetics and OH · formation yield.

Ozone emission rate testing and ranking method using environmental chamber

Ionization-based air cleaners can emit high concentrations of ozone. With the aim to limit the ozone concentration below the standard value in actual use conditions, we propose a standard procedure for testing and ranking the ozone emission of air cleaners. It is demonstrated by testing 27 samples of air cleaners that ozone emission rate can be measured in an airtight environmental chamber, by applying a generation-decay model to the concentration increase curve. The results indicate that deposition velocities v d on chamber wall surfaces need to be better characterized so that the ozone emission of a tested product could be characterized by a three-parameter model. The model takes into account actual room sizes and surface material deposition effects to predict ozone concentrations in indoor applications. This procedure accounts for ozone decay effect in an explicit manner and allows using alternative testing chamber sizes other than as specified in the current Underwriters Laboratory standard.

Integrated modelling of ozonation processes in water treatment

This paper presents the formulation of an integrated Back Flow Cell Model (IBFCM) for ozonation processes by incorporating together the contactor hydrodynamics, mass transfer, ozone decay in water, microbial inactivation, and disinfection by-products formation to describe the significance of their interrelated nature in determining the overall process performance. It also summarizes the experimental procedures that could be used to quantify the characteristic parameters for each process component. The model applicability was then illustrated by comparing the predictions with the experimentally observed dissolved ozone profiles. Further analysis was made to demonstrate the model application for predicting the disinfection efficiency and disinfection by-products formation simultaneously. From these analyses, it was also found that during the ozonation of natural waters, the ozone decay could not be described by the simple first order rate expression.

Rate constants and activation energies for ozonolysis of isoprene methacrolein and methyl-vinyl-ketone in aqueous solution: Significance to the in-cloud ozonation of isoprene

Rate constants and activation energies for the reactions of ozone with isoprene, methacrolein, and methyl-vinyl-ketone in aqueous solution have been determined at temperatures from 5 to 30°C, using the stopped-flow-technique and monitoring ozone decay. The rate constants at 25°C and the activation energies have been found to be 4.1 (±0.2) × 105 M−1 s−1 and 19.9 (±0.5) kJ mol−1 for isoprene, 2.4 (±0.1) × 104 M−1 s−1 and 23.9 (±0.5) kJ mol−1 for methacrolein, and 4.4 (±0.2) × 104 M−1 s−1 and 18.0 (±0.5) kJ mol−1 for methyl-vinyl-ketone. A UV spectrum of a transient intermediate with a lifetime of about 15 s formed during the ozonation of isoprene was obtained in the range 220 to 300 nm. It rises steadily toward 220 nm. It is suggested that the spectrum can be attributed to the two unsaturated Criegee-intermediates (carbonyl oxides), which would conceivably be stabilized by resonance. Lifetime considerations indicate that the oxidation of isoprene and its first-generation reaction products, methacrolein and methyl-vinyl-ketone, by ozone and OH in the aqueous phase of a cloud environment play only a minor role compared to homogeneous gas-phase processing. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 182–190, 2001