Sequential disinfection of cryptosporidium parvum by ozone and chlorine dioxide

A two step disinfection approach was evaluated for control of Cryptosporidium parvum using bench‐scale experiments in 0.05 M phosphate buffer at pH 8 and 22 °C. Sequential application of ozone and chlorine dioxide was evaluated where ozone was applied first followed by chlorine dioxide. Infectivity in neonatal CD‐1 mice was used to assess oocyst viability after disinfection. The sequential treatment of oocysts by ozone followed by chlorine dioxide resulted in additional inactivation of C. parvum due to the synergism of the two disinfectants. The inactivation kinetics for chlorine dioxide were modeled following preconditioning with ozone at a given level using the Integral‐Hom model which takes the disinfectant decay into account. These preliminary findings indicate that sequential disinfection with ozone followed by chlorine dioxide may have potential in controlling waterborne parasites.     

Determination of Residual Ozone or Chlorine Dioxide in Water with ACVK – an Updated Version

The determination of residual ozone or residual chlorine dioxide can be carried out with Acid Chrome Violet K (C.I. code no. 61710, formerly 6170), now available as dye for analytical use under the name of Alizarin Violet 3R (Aldrich 22, 783-8; MW 622.25). The discoloration of the dye in an NH₃-NH₄CI buffered solution of pH 8.1 to 8.5 is specific both for ozone and for chlorine dioxide without interference of chlorine, chloramines, chlorite or chlorate ions in concentrations possibly encountered in treated drinking water.

Detection limit : 0.02 mg L^?l: standard deviation : 0.01 mg L^?l are obtained both for ozone and chlorine dioxide.     

Formation of chlorite and chlorate from chlorine dioxide with Han river water

This study was designed to elucidate the behavior of chlorine dioxide in drinking water systems. Furthermore, the factors that influence the formation of chlorite, chlorate in terms of reaction time, concentration of chlorine dioxide, pH, temperature and UV irradiation were experimentally reviewed. At 20 ‡C, pH 7, 70–80% of chlorine dioxide injected was converted to chlorite and 0–10% of that was transformed into chlorate within 120 min with 2.91 mg/L of DOC. The amount of chlorite formed also increased when pH and temperature increased. As DOC content increased, the residual chlorine dioxide decreased but the amount of chlorite and chlorate were increased. These experiments revealed that chlorate was a dominant by-product under UV irradiation. The models that were obtained by the regression analysis for the formation of chlorite and chlorate from chlorine dioxide with Han River water are as follows: Chlorite (mg/L)=10^-2.20[ClO₂]^0.45[pH]^0.90[temp]^0.27[TOC]^1.04[time]^0.20, Chlorate (mg/L)=10^-2.61[ClO₂]^1.27[pH]^-0.50[temp]^1.28 [TOC]^0.31[time]^0.12     

Activation of Superoxide Ion by Reactions with Protons,Electrophiles, Secondary Amines,Radicals, and Reduced Metal· Ions

In aprotic and aqueous media the proton-induced disproportionation of superoxide ion (O⁻₂) yields a variety of reactive species (HO₂·, H₂O₂, HO⁻₂, and · OH). In aprotic media O⁻₂ rapidly degrades polychlorinated hydrocarbons (CCl₄, HCCl₃, and DDT) to oxygenated products (CCl₄ →Cl₃COO·; HCCl₃→ Cl₂C: and Cl₂C=O). Alkyl halides react more slowly (BuCl →BuOO· and BuOO⁻). Formation of O⁻₂ in the presence of methyl viologen (MV²⁺), reduced flavins, esters, and low-valent transition metal complexes results in the formation of reactive oxygenating agents and reaction mimics for oxygenases [MV⁺-OO-, 4a-hydroperoxyflavins, RC(O)OO⁻, and Zn¹¹(O₂ ·)⁺]. Kinetic data for the proton-induced disproportionation of O⁻₂ in water and the nucleophilic reactions of O⁻₂ in aprotic solvents lead to the conclusion that the latter are probably of little significance for biological oxygenation reactions.     

Energy Conversion and Temperature Dependence in Ozone Generator Using Pulsed Discharge in Oxygen

A detailed reaction kinetic model consisting of 10 species and 63 reactions is developed to investigate the energy conversion and temperature dependence in an ozone generator using oxygen pulsed discharge. The energy conversion ratios of total electric energy converted into reaction heat, heat carried by gas and heat loss to ambient, namely η_reaction, η_gas and η_loss, are obtained for the first time. The ratio of reaction heat η_reaction decreases substantially with increasing specific energy and inlet gas temperature, which represents how much energy is utilized effectively to synthesize ozone. Correspondingly, η_loss and η_gas increase gradually. η_reaction declines from 55.4% to 27.7% at inlet gas temperature of 298 K when specific energy changes from 0.06 J/cm³ to 0.78 J/cm³. The detailed reaction pathway including the degree of transformation among species for ozone formation is also obtained via kinetics simulation. Meanwhile, sensitivity analysis and rate-of-production analysis for the four most important species O₃, O, O(1D) and O₂(b¹∑) obtained from the reaction pathway are executed to understand quantitatively the temperature dependence of sensitivity coefficient and production rate for each individual reaction. The production rate of ozone via the most important ozone generation reaction O+O₂+O₂ = > O₃+O₂ increases linearly with the increase of gas temperature, as well as the destruction rates of ozone via the most important ozone decomposition reactions O₃+O₃ = > O₂+O₂+O₂ and O₃ + O = > O₂(b¹∑)+O₂.     

Concerning the Radical Character of Superoxide. The H—O Bond Energy of HO−2

The strength of the H-O bond in H⁻O₂ should be a good indicator of the chemical reactivity of superoxide, O⁻₂, as a hydrogen atom abstractor. This quantity can be calculated if the electron affinity of HO₂ is known. A recent experimental determination of the electron affinity of HO₂ [V. M. Bierbaum, R. J. Schmitt and C. H. DePuy, J. Am. Chem. Soc., 103 , 6262–6263 (1981)] gave that value as 27.4 ± 0.2 kcal mol⁻¹. The H-O bond energy of HO⁻⁻₂ can then be calculated from that value to be approximately 66 kcal mol⁻¹. Various theoretical methods may also be used to approximate the value of the electron affinity of HO₂. These methods generally give values in accord with the experimental result. Based on the low H—O bond energy of 66 kcal mol⁻¹ for HO⁻₂, superoxide is expected to be relatively unreactive, comparable to iodine atoms but less reactive than bromine atoms or HO₂ and much less reactive than chlorine atoms or hydroxyl radicals. Based on our analysis, we predict that superoxide can only react as a hydrogen atom abstractor with substrates that contain relatively weak bonds to hydrogen such as hydroxylamine or hydroquinones.     

A Study of Ozone Generation by Negative Corona Discharge Through Different Plasma Chemistry Models

The Steady radial distribution of chemical species in a wire‐to‐cylinder ozone generator filled with pure oxygen has been computed by applying four different plasma chemistry models of increasing complexity. The most complete model considers ten species (e, O₂ ⁺, O₂ ^?, O₃ ^?, O^?, O₂, O₂(¹Δ_g), O₂(¹∑_g ⁺), O and O₃) and 79 reactions, including ionization by electron impact, electron attachment and detachment, electron-ion recombination, charge transfer, etc. The chemical model is coupled with the electrical model through Poisson's equation. The spatially averaged ozone density has been computed as a function of the current intensity and compared with the experimental values obtained by UV spectroscopy.     

Ozonation and Advanced Oxidation of Wastewater: Effect of O3 Dose,pH, DOM and HO•-Scavengers on Ozone Decomposition and HO• Generation

The decomposition of ozone in wastewater is observed starting 350 milliseconds after ozone addition. It seems not to be controlled by the autocatalytic chain reaction, but rather by direct reactions with reactive moieties of the dissolved organic matter (DOM). A larger ozone dose increases ozone consumption prior to 350 milliseconds but decreases the rate of ozone decomposition later on; this effect is predicted by a second-order kinetic model. Transferred Ozone Dose (TOD) is poorly correlated with ozone exposure (= ∫[O₃]dt) indicating that TOD is not a suitable parameter for the prediction of disinfection or oxidation in wastewater. HO^? concentrations (> 10^?10 M) and R_ct (=∫[HO^?]dt/∫[O₃]dt > 10^?6) are larger than in most advanced oxidation processes (AOP) in natural waters, but rapidly decrease over time. R_ct also decreases with increasing pre-ozonation doses. An increase in pH accelerates ozone decomposition and HO^? generation; this effect is predicted by a kinetic model taking into account deprotonation of reactive moieties of the DOM. DOC emerges as a crucial water quality parameter that might be of use to normalize ozone doses when comparing ozonation in different wastewaters. A rapid drop of absorbance in the water matrix—with a maximum between 255–285 nm—is noticeable in the first 350 milliseconds and is directly proportional to ozone consumption. The rate of absorbance decrease at 285 nm is first order with respect to ozone concentration. A kinetic model is introduced to explore ozone decomposition induced by distributions of reactive moieties at sub-stoichiometric ozone concentrations. The model helps visualize and comprehend the operationally-defined “instantaneous ozone demand” observed during ozone batch experiments with DOM-containing waters.     

Complementary uses of chlorine dioxide and ozone for drinking water treatment

Application of both chlorine dioxide (ClO₂) and ozone (O₃) at a single drinking water treatment plant is rare in the United States but not in other countries. European utilities that use both oxidants commonly add ozone at one or more points prior to filtration and then apply ClO₂ after filtration. In this mode, the oxidant demand is considerably reduced prior to ClO₂ addition, thus reducing the ClO₂ requirement for maintaining a concentration of 0.1 mg/L to 0.2 mg/L in the distribution system. The combined use of ClO₂ and O₃ has merit in many situations, but the way in which the oxidants are sequenced (e.g. pre‐ozonation followed by ClO₂ treatment or vice versa) is critical in terms of finished water quality. The objectives of this paper are: (1) to review the most common water‐treatment goals associated with ClO₂ and O₃, and (2) to discuss the potential consequences and benefits of applying both oxidants at various points in the treatment train.     

Influence of presence of tannic acid on removal of sodium dodecylbenzenesulphonate by O3 and advanced oxidation processes

BACKGROUND: The objective of the present investigation was to determine the role of the tannic acid (TAN) component of organic matter dissolved in water, in the removal of sodium dodecylbenzenesulphonate (SDBS) by ozone and by O₃/H₂O₂, O₃/granular activated carbon (GAC) and O₃/powdered activated carbon (PAC) advanced oxidation processes. RESULTS: Low doses of TAN (1 mg L^?1) during SDBS ozonation cause (i) an increased ozone decomposition rate and (ii) an increased SDBS removal rate. The SDBS removal rate with ozone in the presence of TAN was reduced when HCO₃^? ions were added. A rise in TAN concentration increased the SDBS removal rate, with a linear relationship between added TAN and the removal rate. SDBS was removed more effectively by O₃/GAC, O₃/PAC and O₃/H₂O₂ systems in the presence of TAN. CONCLUSIONS: Results obtained indicated two mechanisms involved in the generation of HO^· radicals by the O₃/TAN interaction: (i) direct generation of HO^· radicals from the reaction between ozone and TAN, and (ii) increased generation of O₂^?· radicals in the medium, enhancing the transformation of ozone into HO^· radicals by different radical reactions. In O₃/GAC and O₃/PAC systems, HO^· radicals are mainly generated in the O₃/TAN interaction, which is a homogeneous reaction with fast kinetics, whereas the O₃/GAC and O₃/PAC interactions are in a heterogeneous phase with much slower kinetics, and are therefore not competitive in the generation of HO^· radicals. Copyright © 2008 Society of Chemical Industry     

Oxidation of Nitrites in Mine Waters

A major component in the disinfection cost of mine water is the oxidation of microbiologically formed nitrite ion, which can be effectively oxidized by ozone (at close to the stoichiometric ratio of 3.4 mg O₃ per mg nitrite–snitrogen. The injudicious use of oxidizing disinfectants in the mine water may be implicated n i nitrite ion buildup. Laboratory batch reactor experiments show that 3 to 12 mg Cl₂/L and 3 to 11 mg CIO₂/L can inhibit nitrite ion oxidation by Nitrobacter. This inhibitive effect has not been observed for ozone.     

Enterococcus sp. Inactivation by Ozonation in Natural Water: Influence of H2O2 and TiO2 and Inactivation Kinetics Modeling

This article presents the results about the disinfectant power of treatments based on the application of ozone (578 mg O₃ h^?1) and ozone combined with TiO₂ (1 g L^?1) and H₂O₂ (0.04 mM) on Enterococcus sp., a bacteria indicator used in the control of water quality. The results show that all the ozone-based treatments under study achieve the inactivation of Enterococcus sp. solution in natural water. Moreover, the combination of ozone with H₂O₂ or TiO₂ lightly improves the inactivation of Enterococcus sp. compared to the ozonation. However, the treatment with O₃, H₂O₂ and TiO₂ is less effective than the use of O₃, O₃/H₂O₂ or O₃/TiO₂. Finally, the primary mathematical models are applied (Hom, biphasic and Mafart) and they adequately describe the disinfection kinetics of the ozonation treatments studied for Enterococcus sp.     

Energy conversion and temperature dependence in ozone generator fed by synthetic air

A homogenous chemical kinetic model consisting of 21 species and 118 reactions is applied to investigate energy conversion and its temperature dependence in ozone generator fed by synthetic air. The portion of electric energy converted into reaction heat, gas heating and heat loss to surroundings (by convection) in terms of the total electric energy input, the conversion ratios η_reaction, η_gas, and η_loss, are obtained. The detailed reaction pathway including the degree of transformation among species for ozone production is also obtained via simulation of the reaction kinetics. In addition, sensitivity analysis and rate-of-production analysis for the three foremost species O₃, O, and N₂(A) are performed to understand quantitatively the temperature dependence of sensitivity coefficient and production rate for each individual reaction. η_reaction shows a steep rise at low specific energy, but then suffers a gradual decrease at high specific energy. η_loss has a contrary behavior. And η_gas increases steadily with the increase of specific energy. The η_reaction peak of 35.1% is achieved at specific energy of 0.17 J/cm³ at the conditions under investigation. Additionally, inlet gas temperature only has a small effect on energy conversion. Moreover, high gas temperature in discharge gap is confirmed to be not favorable for ozone formation from the view of reaction heat. The sensitivity coefficients of reactions with electron participation are sensitive to gas temperature. O+O₂+O₂→O₂+O₃ and O+O₂+N₂→N₂+O₃ account for about 70% and 30% of generated ozone respectively at the given conditions. And e+O₂→e+O+O, N₂(A)+O₂→N₂O+O, and N₂(A)+O₂→O+O+N₂ are responsible for about 51.3%, 14.7%, and 32.0% of oxygen atom, respectively.     

Kinetic Modeling of Ozone Generation via Dielectric Barrier Discharges

A mathematical model combining chemical kinetic and reactor geometry is developed for ozone synthesis in dry O₂ streams with a wire-tube dielectric barrier discharge (DBD) reactor. Good agreement is found between the predicted ozone concentrations and experimental data. Sensitivity analysis is conducted to elucidate the relative importance of individual reactions. Results indicate that the ground-state oxygen atom is the most important species for O₃ generation; however, ozone generation will be inhibited if the O atom is overdosed. The excited species, that is, O(¹ D) and O₂(b ¹Σ), can decompose O₃ and suppress ozone synthesis. The model developed is then applied to modify the original DBD reactor design for the enhancement of ozone yield. With a thinner dielectric thickness, more than 10% increase of ozone concentration is achieved.     

The Mortality of Nematodes in Drinking Water in the Presence of Ozone,Chlorine Dioxide,and Chlorine

ABSTRACT

Nematodes are among the organisms most commonly found in treated water. Although they are believed to be harmless, colonization of nematodes by pathogenic bacteria may transform them into harmful contaminants of the drinking water. Thus, efficient disinfectants must be applied to inactivate and remove nematodes. In the present study, nematode inactivation using different concentrations of ozone, chlorine dioxide, and chlorine for different exposure times are described. Three different disinfection models were tested. Based on experimental data, the best statistically significant relationship between mortality of nematodes in probits (Y), concentrations of disinfectants mg/L (C), and the exposure times in minutes (t) was established as Y = a*log(C) + b*log(t) + c. The estimated values of regression coefficients a, b, and c were 6.89, 0.76, and 1.13 for ozone, 0.66, 1.23, and 5.28 for chlorine dioxide and 1.59, 0.92, and 3.06 for chlorine, respectively. Comparison of the predicted LC(90) molar concentrations of the investigated disinfectants, chlorine dioxide, ClO₂, was found to be the most effective disinfectant, followed by ozone, O₃, while chlorine, Cl₂, was the least efficient disinfectant for inactivation of nematodes.     

Inactivation of cryptosporidium at 1°c using ozone or chlorine dioxide

Inactivation of cesium chloride purified, bovine‐derived C. parvum oocysts was studied at bench‐scale using ozone or chlorine dioxide at 1°C. Experiments were conducted in 200 mL of 0.05 M phosphate buffer using a temperature controlled water bath. Animal infectivity using neonatal CD‐1 mice was used for evaluation of oocyst viability after treatment. The results showed that while the parasite could be killed at 1°C, the level of effort was substantially higher than that found at 22°C. An ozone Ct product (final residual and contact time product) of 7.2 to 15 mg‐min./L at pH 6.9 and 1°C resulted in an inactivation of 0.7 to 1.3 log‐units. This was about one‐third to one‐fifth of that observed at room temperature using a similar Ct product. A chlorine dioxide Ct product of 120 to 135 mg?min./L at pH 6.0 and 1°C resulted in an inactivation of 0.5 to 0.6 log‐units. This was about one‐fourth the kill observed at 22°C using a similar Ct product.     

Bactericidal Effectiveness of O3, O3/H2O2 and O3/TiO2 on Clostridium perfringens

The purpose of this research is to evaluate the bactericidal capacity of different Advanced Oxidation Treatments (AOTs) based on ozone: ozone, ozone/hydrogen peroxide and ozone/titanium dioxide on a wild strain of Clostridium perfringens, a fecal bacterial indicator in drinking water. The dose of ozone consumed ranges from 0.6 mg L^?1 min^?1 to 5.13 mg L^?1 min^?1 depending on the process and on the sample. In the treatments combined with O₃, H₂O₂ dose utilized is 0.04 mM and TiO₂ dose, 1 g L^?1. In order to evaluate the influence of natural organic matter and suspension solids over the disinfection rate, treatments are performed with two types of water – natural water from Ebro River (Zaragoza, Spain) and NaCl solution 0.9%. To achieve 4 log units of inactivation, 3.6 mg O₃ L^?1 is necessary in O₃ treatment, 4.25 mg O₃ L^?1 in O₃/TiO₂ system and 2.7 mg O₃ L^?1 in O₃/H₂O₂ after processing the natural water. In NaCl solution, to get the same inactivation, 0.42 mg O₃ L^?1 is necessary in O₃ treatment, 1.15 mg O₃ L^?1 in O₃/TiO₂ system and 0.06 mg O₃ L^?1 in O₃/H₂O₂ process. Even though the three treatments studied have a high bactericidal activity due to the number of surviving bacteria decreases to non-detectable levels, O₃/H₂O₂ is the most effective system for eliminating C. perfringens cells in a lower contact time, followed by O₃ and finally O₃/TiO₂ system.     

Examination of in situ Generation of Hydroxyl Radicals and Ozone in a Flow-through Electrochemical Reactor

Generation of hydroxyl radicals and ozone in a low ionic strength influent (0.001 M Na₂SO₄) treated in a continuous flow electrochemical (EC) reactor equipped with a cobalt-promoted lead dioxide anode was examined using p-chlorobenzoic acid (pCBA) and indigotrisulfonate (ITS) probes. EC generation of hydroxyl radicals via the oxidation of water was determined to precede that of ozone. OH· current yields were affected virtually solely by the current density, with almost negligible effects of variations of pH and carbonate concentrations. Absolute values of the current yields of EC generated OH· radicals were close to 1.0% for current densities > 30 mA/cm². The EC generation of ozone was suppressed in the presence of organic species, primarily due to the interception of OH· radicals that react with oxygen to form ozone. Apparent kinetic constants of major reactions associated with the EC generation of ozone were determined based on a steady-state model of an EC-controlled continuous flow reactor.     

Bicarbonate Effect in the Ozone-UV Process in the Presence of Nitrate

Ozonation and advanced oxidation processes (AOP) are very efficient methods for the destruction of refractory organic matters. These virtues have always been related to the production of hydroxyl radicals HO^?, which are extremely powerful and non-selective oxidants. In this study, the O₃-UV process is used as an AOP, where hydroxyl radicals are generated from the photodecomposition of ozone by short wavelength ultraviolet radiation. The obtained results indicated a weak scavenging effect of tert-butanol proving that hydroxyl radicals and ozone are not the only oxidants existing in the medium. Moreover, bicarbonate, known for a long time as effective HO^? radical scavengers, does not slow down the oxidation of benzoic acid, but surprisingly increases it. Chlorides significantly decrease the degradation of organic compounds through their reaction with HO^? radicals to produce chlorine. Carbonate radicals, nitrate and nitrogenated species as peroxynitrite/?peroxynitrous acid are involved in the oxidative mechanisms.     

Kinetics of MIB and Geosmin Oxidation during Ozonation

Ozonation is an effective means for oxidation of two common earthy/musty odorants (MIB and geosmin) in drinking waters. Second order constants were experimentally determined between the two odorants with ozone and hydroxyl radicals (HO^?). Geosmin was oxidized faster than MIB. Under most surface water treatment conditions, hydroxyl radical mediated reactions dominate over ozone reactions during MIB or geosmin oxidation. MIB and geosmin oxidation increases with greater ozone dose, higher pH, higher temperature or addition of H₂O₂.