Use of spectroscopic indicators for the monitoring of bromate generation in ozonated wastewater containing variable concentrations of bromide

Time-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

Formation of Pb(III) Intermediates in the Electrochemically Controlled Pb(II)/PbO 2

The formation of lead dioxide PbO(2), an important corrosion product in drinking water distribution systems with lead-bearing plumbing materials, has been hypothesized to involve Pb(III) intermediates, but their nature and formation mechanisms remain unexplored. This study employed the electrochemical (EC) method of rotating ring disk electrode (RRDE) and quantum chemical (QC) simulations to examine the generation of intermediates produced during the oxidation of Pb(II) to PbO(2). RRDE data demonstrate that PbO(2) deposition and reduction involves at least two intermediates. One of them is a soluble Pb(III) species that undergoes further transformations to yield immobilized PbO(2) nanoparticles. The formation of this intermediate in EC system is mediated by hydroxyl radicals (OH(•)), as was evidenced by the suppression of intermediates formation in the presence of the OH(•) scavenger para-chlorobenzoic acid. QC simulations confirmed that the oxidation of Pb(II) by OH(•) proceeds via Pb(III) species. These results show that Pb(III) intermediates play an important role in the reactions determining transitions between Pb(II) and Pb(IV) species and could impact lead release in drinking water

Adsorption/membrane filtration as a contaminant concentration and separation process for mixed wastes and tank wastes. 1998 annual progress report

'This report describes progress through May, 1998, which is a little past mid-way through the second year of a three-year project. The goal of the research is to develop a treatment system for the separation of contaminants in low-organic Hanford tank wastes into various sub-groups that are relatively easy to treat further to yield products that are amenable to final disposal. The main target contaminants are Sr and Cs, although heavy metals and actinide-group elements are also targets. Effort during the first half-year of the project was devoted primarily to development of experimental and analytical techniques that could be used to test and quantify the treatability of Sr and Cs in the extremely complex matrix of the tank wastes. The treatment technologies to be tested for isolation of Sr from other waste constituents included adsorption of Sr onto various mineral solids and membrane separation of particulate from dissolved Sr. The proposed technology for treating Cs was electrochemically controlled, reversible binding of the Cs to hexacyanoferrates. Results obtained during the remainder of the first year suggested that hematite (a-Fe{sub 2}O{sub 3}) and iron-oxide-coated sand (IOCS) were the best adsorbents for Sr among the oxides tested, and work during the second project year followed up on that result.

Monitoraggio dei Sottoprodotti della Disinfezione in Acque Potabili Soggette a Clorazione e ad Ozonizzazione

Il 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

Formation of Disinfection By-Products and Applicability of Differential Absorbance Spectroscopy to Monitor Halogenation in Chlorinated Coastal and Deep Ocean Seawater

Formation 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

Modelling Disinfection By-Products formation 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 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