309 research outputs found

    Chemistry of Ozone in Water and Wastewater Treatment

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    Even though ozone has been applied for a long time for disinfection and oxidation in water treatment, there is lack of critical information related to transformation of organic compounds. This has become more important in recent years, because there is considerable concern about the formation of potentially harmful degradation products as well as oxidation products from the reaction with the matrix components. In recent years, a wealth of information on the products that are formed has accumulated, and substantial progress in understanding mechanistic details of ozone reactions in aqueous solution has been made. Based on the latter, this may allow us to predict the products of as yet not studied systems and assist in evaluating toxic potentials in case certain classes are known to show such effects.  Keeping this in mind, Chemistry of Ozone in Water and Wastewater Treatment: From Basic Principles to Applications discusses mechanistic details of ozone reactions as much as they are known to date and applies them to the large body of studies on micropollutant degradation (such as pharmaceuticals and endocrine disruptors) that is already available. Extensively quoting the literature and updating the available compilation of ozone rate constants gives the reader a text at hand on which his research can be based. Moreover, those that are responsible for planning or operation of ozonation steps in drinking water and wastewater treatment plants will find salient information in a compact form that otherwise is quite disperse. A critical compilation of rate constants for the various classes of compounds is given in each chapter, including all the recent publications.  This is a very useful source of information for researchers and practitioners who need kinetic information on emerging contaminants. Furthermore, each chapter contains a large selection of examples of reaction mechanisms for the transformation of micropollutants such as pharmaceuticals, pesticides, fuel additives, solvents, taste and odor compounds, cyanotoxins

    Ozonation of drinking water—part II: disinfection and by-product formation in presence of bromide, iodide or chlorine,”

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    Abstract Ozone is an excellent disinfectant and can even be used to inactivate microorganisms such as protozoa which are very resistant to conventional disinfectants. Proper rate constants for the inactivation of microorganisms are only available for six species (E. coli, Bacillus subtilis spores, Rotavirus, Giardia lamblia cysts, Giardia muris cysts, Cryptosporidium parvum oocysts). The apparent activation energy for the inactivation of bacteria is in the same order as most chemical reactions (35-50 kJ mol À1 ), whereas it is much higher for the inactivation of protozoa (80 kJ mol À1 ). This requires significantly higher ozone exposures at low temperatures to get a similar inactivation for protozoa. Even for the inactivation of resistant microorganisms, OH radicals only play a minor role. Numerous organic and inorganic ozonation disinfection/oxidation by-products have been identified. The by-product of main concern is bromate, which is formed in bromide-containing waters. A low drinking water standard of 10 mg l À1 has been set for bromate. Therefore, disinfection and oxidation processes have to be evaluated to fulfil these criteria. In certain cases, when bromide concentrations are above about 50 mg l À1 , it may be necessary to use control measures to lower bromate formation (lowering of pH, ammonia addition). Iodate is the main by-product formed during ozonation of iodidecontaining waters. The reactions involved are direct ozone oxidations. Iodate is considered non-problematic because it is transformed back to iodide endogenically. Chloride cannot be oxidized during ozonation processes under drinking water conditions. Chlorate is only formed if a preoxidation by chlorine and/or chlorine dioxide has occured.

    The Impact of the Chernobyl Accident on a River/Groundwater Aquifer

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    The radionuclides 99mTc, 103Ru, 131I, 132Te, 134Cs and 137Cs, resulting from fallout from the damaged nuclear power plant at Chernobyl (USSR) were measured several times between May 2nd and 20th, 1986, in the River Glatt (ZĂĽrich, Switzerland) and in the adjacent shallow groundwater stream. Samples from the river and from different groundwater wells were filtered (0.45, 0.20, 0.05 Mm). The resulting water and the filters were assayed by 7-ray spectroscopy. For all these nuclides the main radioactivity ( > 75%) of the river water was found in the water passing the 0.05 Mm-filter. The fraction > 0.45 Mm contained the main particulate activity. Upon infiltration of river water into the groundwater stream iodine, ruthenium and tellurium are not, or only slightly sorbed, probably due to the formation of anionic or neutral species, whereas cesium is completely retained by the sediments. Particulate ( > 0.05 Mm) infiltration from the river into the groundwater is a negligible process

    Quantitative structure–activity relationships (QSARs) for the transformation of organic micropollutants during oxidative water treatment

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    Various oxidants such as chlorine, chlorine dioxide, ferrateVI, ozone, and hydroxyl radicals can be applied for eliminating organic micropollutant by oxidative transformation during water treatment in systems such as drinking water, wastewater, and water reuse. Over the last decades, many second-order rate constants (k) have been determined for the reaction of these oxidants with model compounds and micropollutants. Good correlations (quantitative structure–activity relationships or QSARs) are often found between the k-values for an oxidation reaction of closely related compounds (i.e. having a common organic functional group) and substituent descriptor variables such as Hammett or Taft sigma constants. In this study, we developed QSARs for the oxidation of organic and some inorganic compounds and organic micropollutants transformation during oxidative water treatment. A number of 18 QSARs were developed based on overall 412 k-values for the reaction of chlorine, chlorine dioxide, ferrate, and ozone with organic compounds containing electron-rich moieties such as phenols, anilines, olefins, and amines. On average, 303 out of 412 (74%) k-values were predicted by these QSARs within a factor of 1/3–3 compared to the measured values. For HO reactions, some principles and estimation methods of k-values (e.g. the Group Contribution Method) are discussed. The developed QSARs and the Group Contribution Method could be used to predict the k-values for various emerging organic micropollutants. As a demonstration, 39 out of 45 (87%) predicted k-values were found within a factor 1/3–3 compared to the measured values for the selected emerging micropollutants. Finally, it is discussed how the uncertainty in the predicted k-values using the QSARs affects the accuracy of prediction for micropollutant elimination during oxidative water treatment

    Oxidation of iodide and iodine on birnessite (δ-MnO2) in the pH range 4-8

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    The oxidation of iodide by synthetic birnessite (δ-MnO2) was studied in perchlorate mediain the pH range 4-8. Iodine (I2) was detected as an oxidation product that was subsequently further oxidized to iodate (IO3). The third order rate constants, second order on iodide and first order on manganese oxide, determined by extraction of iodine in benzene decreased with increasing pH (6.3-7.5) from 1790 to 3.1 M2 s1. Both iodine and iodate were found to adsorb significantly on birnessite with an adsorption capacity of 12.7 mM/g for iodate at pH5.7. The rate of iodine oxidation by birnessite decreased with increasing ionic strength, which resulted in a lower rate of iodate formation. The production of iodine in iodide-containing waters in contact with manganese oxides may result in the formation of undesired iodinated organic compounds (taste and odor, toxicity) in natural and technical systems. The probability of the formation of such compounds is highest in the pH range 5-7.5. For pH 7.5, iodide is not oxidized to a significant extent

    Oxidative Transformations of Contaminants in Natural and in Technical Systems

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    In this paper, we present case studies of oxidative transformations of contaminants by oxidants which are relevant in natural and in technical systems. These oxidants are reactive oxygen species (ROS), manganese(III,IV), iron(III), and molecular dioxygen (O2). Regarding ROS, we discuss i) their concentrations and their efficiencies as oxidants in natural waters and in water treatment, ii) reactions occurring in bromide-containing waters in the presence of ROS, iii) role of iron in the formation of ROS, and iv) quantitative structure-activity relationships (QSAR) of reactions of ROS with contaminants. Concerning MnIII and MnIV as oxidants, we present experimental studies on the oxidation of anilines by δ-MnO2. With respect to oxidative transformation of the hydrophilic organic contaminants ethylenediaminetetraacetate (EDTA) and nitrilotriacetate (NTA), we show that these organic complexing agents are efficiently oxidized by FeIII and O2, respectively, if catalyzed by light (for the oxidation of EDTA by FeIII and by enzymes (for the oxidation of NTA by O2)

    IODO-Disinfection By-Products: An Emerging Concern

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