A Novel Electrochemical Technique to Monitor Metal Release in Drinking Water Due to Internal Corrosion of Distribution Pipes

Results of a pioneering study, concerning the development of a new technique far on-line monitoring of copper concentration in drinking water, are presented and discussed. The technique is based on the use of a surrogate parameter, represented by the electrochemical potential, to measure the amount of copper released in drinking water because of corrosion. The most representative findings, resulting from laboratory and field studies, are described, highlighting the potentiality of the proposed technique. Experimental data are used to verify the relationship between the electrochemical potential and the copper concentration derived from a mathematical model, shortly presented, which describes the corrosion process taking place during water stagnation in contact with a metal surface

Probing the Mechanism of NOM Chlorination Using Fluorescence: Formation of Disinfection By-Products in Alento River Water

Experiments with Alento River water (a drinking water source in the province of Salerno, Italy) showed that considerable amounts of disinfection by-products, primarily chloroform and haloacetic acids, form in that water upon chlorination. The total yield of haloacetic acids was almost twice as high as that of chloroform. Chlorination also caused significant changes in the intensity of NOM fluorescence and the position of the emission band. To quantify the latter, the wavelength that corresponds to the position of the emission band at its half-intensity (λ0.5) was employed. Chlorination caused the λ0.5 values to decrease, while the THMs and HAAs concentrations were linearly correlated with the corresponding λ0.5 values. The strength of correlations between DBP concentrations and λ0.5 values indicates that the latter parameter can be employed in studies of DBP formation in drinking water

Alterazione della Sostanza Organica Naturale e Formazione di Sottoprodotti in Acque Disinfettate con Clorammine

Vengono riportati i risultati di una ricerca sperimentale finalizzata a monitorare la formazione dei sottoprodotti della disinfezione in acque superficiali trattate con clorammine. Le concentrazioni e la tipologia delle singole specie individuate vengono analizzate per comprendere i possibili meccanismi cinetici di produzione dei diversi composti. I risultati ottenuti per acque di provenienza diversa caratterizzate da uno stesso valore di concentrazione di carbonio organico, vengono confrontati e discussi. Le modifiche indotte dal disinfettante sulla sostanza organica naturale in forma disciolta vengono seguite attraverso l’esame delle misure di assorbanza e fluorescenza

Changes of the corrosion potential of iron in stagnation and flow conditions and their relationship with metal release

This study examined the behavior of corrosion potential (Ecorr) of iron exposed to drinking water during episodes of stagnation and flow. These measurements showed that during stagnation episodes, Ecorr values decrease prominently and consistently. This decrease is initially rapid but it becomes slower as the stagnation time increases. During flow episodes, the Ecorr values increase and reach a quasi-steady state. Experiments with varying concentrations of dissolved oxygen showed that the decrease of Ecorr values characteristic for stagnation is likely to be associated with the consumption of dissolved oxygen by the exposed metal. The corrosion potential of iron and its changes during stagnation were sensitive to the concentrations of sulfate and chloride ions. Measurements of iron release showed that both the absolute values of Ecorr measured prior to or after stagnation episodes were well correlated with the logarithms of concentrations of total iron. The slope of this dependence showed that the observed correlations between Ecorr values and Fe concentrations corresponded to the coupling between the oxidant consumption and changes of Fe redox status. These results demonstrate that in situ Ecorr measurements can be a sensitive method with which to ascertain effects of hydrodynamic conditions and short-term variations of water chemistry on metal release and corrosion in drinking water. This approach is valuable practically because Ecorr measurements are precise, can be carried out in situ with any desired time resolution, do not affect the state of exposed surface in any extent and can be carried out with readily available equipment

In Situ Examination of the Protonation Behavior of Fulvic Acids Using Differential Absorbance Spectroscopy

The effects of pH changes on the absorbance spectra of fulvic acids, which constitute a major part of natural organic matter (NOM) were examined based primarily on the example of standard Suwannee River fulvic acid (SRFA). Differential absorbance spectra of SRFA generated at varying pH values were determined to be rich in features that are absent in the conventional spectra. Analysis of the differential absorbance revealed the existence of two predominant types of pH-active chromophores which produced features that emerged in the pH ranges associated with carboxylic and phenolic functional groups of fulvic acids. Comparison of the differential absorbance spectra of SRFA and those of the fraction of hydrophobic acids of South Platte River fulvic acid show the existence of differences indicative of fulvic acids’s site-specificity. The evolution of the pH-differential spectra of fulvic acids was in accord with predictions made based on the NICA-Donnan theory. These results show that pH-differential absorbance spectroscopy can be used to quantify in situ the protonation and site-specificity of fulvic acids

Modelling NOM Halogenation in Bromide-Containing Waters

A kinetic model capable of simulating by-products formation in bromide-containing waters during disinfection processes is presented in this paper. The model is based on two parallel sequences of incorporation and oxidation reactions induced by bromine or chlorine reacting with NOM. Each sequence starts from a different type of NOM functionality that has its own set of specific reaction rate. Decay reactions of NOM and halogenated intermediates are assumed to follow a first order kinetic, while DBP generation reactions are simulated introducing so-called splitting coefficients. This approach allows obtaining explicit expressions for DBP species. Model’s results are compared with experimental data obtained for coastal seawater samples. Comparison of the data confirm the model’s ability to predict DBPs formation with high precisio

Spectroscopic in situ examination of interactions of rare earth ions with humic substances

This study utilized the methods of fluorescence quenching and differential absorbance to probe in situ the extent and the nature of the interactions between rare earth ions (REIs) and humic substances. Experiments were conducted with the standard Suwannee river humic acid (SRHA) in the presence of varying amount of lanthanum, europium and terbium. The data of differential absorbance showed that the mechanism of SRHA-metal complexation was largely the same for all the examined REIs. In all cases several discrete bands whose properties were discerned via numerical decomposition of the differential spectra absorbance were observed. Their nature was examined based on the comparison of the experimental data and those of NICA-Donnan modeling carried out for Eu3þ. The observed effects suggested that the changes of SRHA absorbance induced by REIs binding are likely to be caused by a bathochromic shift of the absorbance bands associated with such chromophores. The intensity of the Gaussian band with a maximum at 387 nm was observed to be proportional to the total concentration of SRHA-bound REIs. The data obtained in this study demonstrate the existence of complex yet quantifiable changes of the spectroscopic properties of humic species in the presence of REIs and their utility to quantify modes of interactions in such systems

Effects of organic matter - Aluminium oxide interactions on Eu(III) speciation

International audienceInteractions between Natural Organic Matter (NOM) and mineral surfaces modify the properties of both reacting phases. It also alters the behaviour of metal ions such as radionuclides in the environment. Here, we focus on the influence of the interactions between humic substances, major NOM components, and some minerals of soils (metal oxides and clays) on the speciation of europium (III), chosen for its analogy with trivalent actinides. To understand the binding of metal ions, proton binding must first be considered. Potentiometric titrations of both organic matter and mineral suspensions are realized before and after their interactions, to study variations of their reactivity. To be closer to environmental conditions (i.e. low DOC concentrations), a new approach must be considered to characterize organic matter reactivity. Spectrophotometric titrations and UV-vis spectra of NOM [1] are used to estimate changes in reactivity with the help of differential absorbance spectra variations of the solution as function of pH. The correlation between the two methods of characterization of NOM is quite good, and it is used to determine the changes of the organic matter properties after adsorption onto the mineral surfaces, in order to better describe the binding of radionuclides in a ternary system. The speciation of Eu(III) in presence of NOM or oxide surface is also studied by time resolved laser fluorescence spectroscopy (TRLFS). [1] Dryer, Korshin & Fabbricino (2008) Environ. Sci. Technol. 42, 6644-6649

Using spectrophotometric titrations to characterize humic acid reactivity at environmental concentrations

International audiencePotentiometric titration is a common method to characterize dissolved organic matter (DOM) reactivity. Because of the sensitivity of pH electrodes, it is necessary to work with very high DOM (>1 g/L) concentrations that are unrealistic compared to those found in natural waters (0.1 to 100 mg/L). To obtain proton binding data for concentrations closer to environmental values, spectroscopic titration methodology is a viable alternative to traditional potentiometric titrations. Spectrophotometric titrations and UV−visible spectra of a diluted solution of purified Aldrich humic acid (5 mg$_{DOC}$/L) are used to estimate changes in proton binding moieties as function of pH and ionic strength after calculation of differential absorbance spectra variations. After electrostatic correction of spectrophotometric data, there is a linear operational correlation between spectrophotometric and potentiometric data which can be used as a transfer function between the two properties. Spectrophotometric titrations are then used to determine the changes of humic acid protonation after adsorption onto $\alpha$-alumina

Effects of charging on the chromophores of dissolved organic matter from the Rio Negro basin

This study demonstrates that the deprotonation of dissolved organic matter (DOM) originating from a small creek characteristic for DOM-rich waters located in the Rio Negro basin can be quantified based on measurements of pH effects on its absorbance spectra. The method was ascertained by the data of Near-Edge X-Ray Absorbance Spectroscopy (NEXAFS), potentiometric titration to quantify the structural and compositional differences between the colloidal and hydrophobic fractions that contribute 91% of black-water creek DOM. Changes in the absorbance spectra of the DOM fractions caused by deprotonation quantified via numeric deconvolution which indicated the presence of six well-resolved Gaussian bands in the differential spectra. The emergence of these bands was determined to be associated with the engagement of carboxylic and phenolic functionalities and changes of inter-chromophore interactions in DOM molecules. Interpretation of the data based on the NICA-Donnan approach showed that behavior of DOM chromophores was consistent with results of potentiometric titrations. Similar trends were observed for changes of the spectral slope of the DOM absorbance spectra in the range of wavelengths 325e375 nm (DSlope325e375). The behavior of DSlope325e375 values was modeled based on the NICA-Donnan approach and correlated with potentiometrically-estimated charge