1,720,981 research outputs found
Modelling Disinfection By-Products formation in bromide-containing waters
No full textA 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 natural organic matter (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 disinfection by-product (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 seawater samples. Comparison of the data confirm the model’s ability to predict DBPs formation with high precision
Probing the Mechanism of NOM Chlorination Using Fluorescence: Formation of Disinfection By-Products in Alento River Water
No full textExperiments 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
Formation of Disinfection By-Products and Applicability of Differential Absorbance Spectroscopy to Monitor Halogenation in Chlorinated Coastal and Deep Ocean Seawater
No full textFormation of disinfection by-products (DBPs) in chlorinated coastal (CS) and deep ocean (sampled at a 1500-m depth) seawater (DO) was explored using conventional chromatographic methods and differential absorbance spectroscopy. It was determined that trihalomethanes (THMs) predominated by bromoform, haloacetonitriles and haloacetic acids (HAA) form in chlorinated seawater. The yield of identified DBPs, especially THMs, was higher in CS, while in DO seawater the relative contribution of HAAs was almost four times higher than that of THMs. The fraction of consumed chlorine incorporated into the identified DBPs in DO natural organic matter (NOM) was much lower than that for coastal marine NOM, which was also more active in forming brominated DBPs. The kinetics of seawater chlorination was relatively rapid, and high levels of DBPs were released within the first 20–30 min of reaction. The kinetics of THMs and HAAs release could be approximated using a logarithmic function of reaction time. Absorbance measurements showed that chlorination caused the absorbance of DO and CS to decrease at wavelengths >250 nm. The features of the differential absorbance spectra of chlorinated seawater were close to those reported for drinking water, but their intensity was lower. The concentrations of CHBr3, CHBr2Cl and CHBrCl2 formed in CS and DO chlorinated at varying chlorine doses and reaction times were well correlated with the corresponding — ΔA272 and/or — ΔA405 values. (The differential absorbance at 405 nm can be measured in the presence of residual chlorine). These results show that differential absorbance provides a number of sensitive surrogate parameters that can be used to monitor and quantify the formation of halogen-containing DBPs in seawater
Monitoraggio dei Sottoprodotti della Disinfezione in Acque Potabili Soggette a Clorazione e ad Ozonizzazione
No full textIl lavoro presenta I risultati di una ricerca sperimentale condotta per investigare le possibilità di utilizzo di misure spettrofotometriche per il monitoraggio dei sottoprodotti della disinfezione di acque destinate a scopo potabile, nel caso di impiego di cloro ed ozono. Dopo una rapida disamina dei sottoprodotti normalmente individuati nei processi di disinfezione e dei presunti meccanismi di formazione degli stessi, viene mostrata l’esistenza di forti correlazioni tra l’assorbanza differenziale di luce ultravioletta e la concentrazione delle singole specie di composti alogenati volatili, nel caso della clorazione, nonché dei principali composti ossidati, in particolare delle aldeidi totali, nel caso dell’ozonizzazione. Viene altresì mostrato come tali correlazioni siano legate alla fenomenologia dei processi in gioco, tanto da poter considerare la misura dell’assorbanza differenziale quale parametro surrogato per conoscere la concentrazione delle diverse specie di sottoprodotti
A Novel Electrochemical Technique to Monitor Metal Release in Drinking Water Due to Internal Corrosion of Distribution Pipes
No full textResults 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
Alterazione della Sostanza Organica Naturale e Formazione di Sottoprodotti in Acque Disinfettate con Clorammine
No full textVengono 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
In Situ Examination of the Protonation Behavior of Fulvic Acids Using Differential Absorbance Spectroscopy
No full textThe 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
Use of spectroscopic indicators for the monitoring of bromate generation in ozonated wastewater containing variable concentrations of bromide
Full text linkTime-resolved monitoring of bromate and other by-products formed into effluents treated with ozone or advanced oxidation processes in wastewater treatment plants (WWTPs) is time-consuming and expensive. This study examined whether concentrations of bromate formed in wastewater after ozonation in the presence of widely varying bromide levels (from ca. 0.7–21.2 mg/L) can be quantified based on measurements of changes in optical properties (differential UV absorbance (ΔUVA), spectral slopes, total or regional fluorescence) of the ozonated samples. Batch ozonation was carried out using a secondary effluent produced at a major wastewater treatment plant located in the Metropolitan Seattle Area. The tests involved raw and bromide-spiked samples treated with ozone doses from 0.1 to 1 mg O3/mg DOC. Measurements of the absorbance at 254 nm (UVA254), fluorescence and bromate concentrations were performed on the treated samples. In the ozonated wastewater the concentration of bromate increased approximately linearly, from 10 mg/L) tended to inhibit the generation of bromate. Relative reduction of UVA254 and total fluorescence (TF) were found to be good predictors of bromate generation. Specifically, exponential curves could adequately fit the non-linear relationships found to exist between the concentrations of bromate and the relative reductions of the UV254 and TF, for any initial bromide concentrations used in this study. Little formation of bromate was found to occur for reduction ranges for UVA254 and TF of 30–40% and 70–80% respectively. Conversely, rapid increases in bromate generation were observed when the decrease of UVA254 or TF exceeded these threshold values
Effects of chlorination on the fluorescence of seawater: Pronounced changes of emission intensity and their relationships with the formation of disinfection byproducts
No full textChlorination of coastal (CS) and deep ocean (DO) seawater was accompanied by a prominent decrease (of up to 70%) of the intensity of its emission which was measured using a 315 nm excitation wavelength. Deconvolution of the emission spectra of CS and DO seawater showed that these spectra comprised three Gauss-shaped bands. The intensities of two of these bands decreased rapidly as the halogenation proceeded. For both DO and CS seawater, two stages of changes of their fluorescence were observed. The first stage in which the relative changes of the fluorescence intensity (ΔF/F) were between zero to 0.30 and 0.40 was not accompanied by the release of individual disinfection byproduct (DBP) species. For ΔF/F values above the corresponding thresholds, the relative changes of fluorescence intensity were well correlated with the concentrations of individual DBP species such as trihalomethanes and haloacetonitriles. R2 values for CHBr3, CHBr2Cl and CHBrCl2 formed in DO seawater were 0.83, 0.80 and 0.68, respectively while for CS seawater, the corresponding R2 values were 0.91, 0.93 and 0.92. The presented data demonstrate that the intrinsic chemistry of DBP formation and dissolved organic matter (DOM) halogenation in seawater can be well quantified based on the examination of changes of its fluorescence. This approach can also be employed for practical monitoring of changes of properties of marine DOM and generation of DBPs in desalination, marine aquaculture and other processes
Modelling NOM Halogenation in Bromide-Containing Waters
No full textA 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
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