Modification of glassy carbon electrode with multi-walled carbon nanotubes and iron(III)-porphyrin film: Application to chlorate, bromate and iodate detection

In this study, multi-wall carbon nanotubes (MWCTs) is evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on iron-porphyrin. 5,10,15,20-Tetraphenyl-21H,23H-porphine iron(III) chloride (Fe(III)P) adsorbed on MWCNTs immobilized on the surface of glassy carbon electrode. Cyclic voltammograms of the Fe(III)P-incorporated-MWCNTs indicate a pair of well-defined and nearly reversible redox couple with surface confined characteristics at wide pH range (2-12). The surface coverage (Γ) and charge transfer rate constant (k_s) of Fe(III)P immobilized on MWCNTs were 7.68 × 10⁻⁹ mol cm⁻² and 1.8 s⁻¹, respectively, indicating high loading ability of MWCNTs for Fe(III)P and great facilitation of the electron transfer between Fe(III)P and carbon nanotubes immobilized on the electrode surface. Modified electrodes exhibit excellent electrocatalytic activity toward reduction of ClO₃⁻, IO₃⁻ and BrO₃⁻ in acidic solutions. The catalytic rate constants for catalytic reduction of bromate, chlorate and iodate were 6.8 × 10³, 7.4 × 10³ and 4.8 × 10² M⁻¹ s⁻¹, respectively. The hydrodynamic amperometry of rotating-modified electrode at constant potential versus reference electrode was used for detection of bromate, chlorate and iodate. The detection limit, linear calibration range and sensitivity for chlorate, bromate and iodate detections were 0.5 μM, 2 μM to 1 mM, 8.4 nA/μM, 0.6 μM, 2 μM to 0.15 mM, 11 nA/μM, and 2.5 μM, 10 μM to 4 mM and 1.5 nA/μM, respectively. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantages of this sensor. The obtained results show promising practical application of the Fe(III)P-MWCNTs-modified electrode as an amperometric sensor for chlorate, iodate and bromate detections.     

The Evaluation Of Ozonation and Chlorination On Disinfection By-Product Formation for a High-Bromide Water

High-bromide raw water was ozonated or chlorinated with and without hydrogen peroxide to study the effect of the disinfectants on the disinfection by-product (DBP) formation. Less bromate was formed when ozonation was made at the ambient pH of 5.8 as compared to ozonation at pH 7, showing the effectiveness of pH reduction in controlling the bromate formation. When chlorine dose was 1 mg/L instead of 2.3 mg/L, the trihalomethane formation was 50 μg/L instead of >100 μg/L, and the proportional distribution of the trihalomethanes was similar. The use of ozone for this water could provide good results in respect of the DBP formation.     

Formation of Bromate Ion Through a Radical Pathway in a Continuous Flow Reactor

The contribution of ozone and hydroxyl radical to the formation of bromate ion was investigated in a continuous flow reactor. Experiments were conducted under a wide range of ozone dose (0.7 ～ 3.8 mgL), pH (6.5 ～ 8.5), and t-butanol concentration (0 ～ 0.5 mM). The formation of bromate ion was found to depend on radical reaction pathway, because the amount of bromate ion formed increased with pH and decreased with t-butanol, a radical scavenger, even when dissolved ozone concentrations were almost the same. In fact, the amount of bromate ion formed was reduced by 90% in the presence of t-butanol. Furthermore, the formation of bromate ion occurred even when dissolved ozone was not significantly detected in the presence of organic matter (TOC of 1 mgCL). The second-order reaction rate constant of hydroxyl radical with bromide ion, k _HO,Br^? of 1.7 × 10⁹ (M^?1s^?1), was obtained on the assumption that the reactions of bromide ion and t-butanol with hydroxyl radical were competitive with each other in the presence of t-butanol and that the formation of bromate ion depended on the reaction of bromide ion with hydroxyl radical. Therefore, it is concluded that the reaction of bromide ion with hydroxyl radical dominated in the overall reaction from bromide ion to bromate ion in the continuous flow reactor.     

Bromate Ion Analysis By Ion Chromatography

Bromate ion occurs during ozonation of bromide-containing waters. The current WHO guideline for bromate ion is 25 μg/L. Bromate analysis in drinking waters can be performed by various techniques. However, given the commonly low concentrations of bromate ion found in drinking waters, the classical methods do not fit for bromate analysis in most cases.

A specific conductimetric method with anion suppression which enhances analyte detection by lowering the eluent conductivity is described in this paper for low bromate level analysis. Three eluents have been tested in order to have the best signal to noise ratio. Some other parameters likely to interfere in bromate ion detection (nitrate and sulfate in particular) are also investigated. Taking into account the results of three interlaboratory trials between six European laboratories, a 2 μg/L detection level for bromate can be established.     

Inhibition of Nano-Metal Oxides on Bromate Formation during Ozonation Process

Simulation studies in pure water were conducted to investigate the effect of nano-metal oxides on bromate (BrO₃^?) formation as catalysts and the catalytic mechanism. Results indicated that compared to ozonation alone, both nano-SnO₂ and nano-TiO₂ could inhibit the formation of bromate during ozonation process. The inhibition efficiency of BrO₃^? formation by nano-TiO₂ enhanced with the increasing of ozone dosage and the decreasing of nano-TiO₂ dosage, Br^? concentrations and the pH value. Possible BrO₃^? minimization mechanism was that nano-TiO₂ accelerated the decomposition of the dissolved O₃ into OH radicals, which rapidly generated H₂O₂, and reduced HOBr/OBr^? to Br^?.     

Chlorination of bromide-containing waters: Enhanced bromate formation in the presence of synthetic metal oxides and deposits formed in drinking water distribution systems

Bromate formation from the reaction between chlorine and bromide in homogeneous solution is a slow process. The present study investigated metal oxides enhanced bromate formation during chlorination of bromide-containing waters. Selected metal oxides enhanced the decay of hypobromous acid (HOBr), a requisite intermediate during the oxidation of bromide to bromate, via (i) disproportionation to bromate in the presence of nickel oxide (NiO) and cupric oxide (CuO), (ii) oxidation of a metal to a higher valence state in the presence of cuprous oxide (Cu₂O) and (iii) oxygen formation by NiO and CuO. Goethite (α-FeOOH) did not enhance either of these pathways. Non-charged species of metal oxides seem to be responsible for the catalytic disproportionation which shows its highest rate in the pH range near the pK_a of HOBr. Due to the ability to catalyze HOBr disproportionation, bromate was formed during chlorination of bromide-containing waters in the presence of CuO and NiO, whereas no bromate was detected in the presence of Cu₂O and α-FeOOH for analogous conditions. The inhibition ability of coexisting anions on bromate formation at pH 8.6 follows the sequence of phosphate >> sulfate > bicarbonate/carbonate. A black deposit in a water pipe harvested from a drinking water distribution system exerted significant residual oxidant decay and bromate formation during chlorination of bromide-containing waters. Energy dispersive spectroscopy (EDS) analyses showed that the black deposit contained copper (14%, atomic percentage) and nickel (1.8%, atomic percentage). Cupric oxide was further confirmed by X-ray diffraction (XRD). These results indicate that bromate formation may be of concern during chlorination of bromide-containing waters in distribution systems containing CuO and/or NiO.     

Nongenotoxic Mechanisms Involved in Bromate-Induced Cancer in Rats

Risk assessments for bromate (BrO₃-) in drinking water are based on linear extrapolation from the total incidence of tumors in male rats. The only genotoxic effects that might result from carcinogenic doses of BrO₃- in vivo are the formation of 8-oxodeoxyguanosine (8-oxoG) in deoxyribonucleic acid (DNA) and the production of micronuclei. The mutations in tumors are consistent with the 8-oxoG adduct, and both effects are nonlinear with respect to dose. Treatment of rats with BrO₃- resulted in bromination of protein tyrosines. The accumulation of these proteins in the kidney appeared to contribute to kidney cancer in male, but not female, rats. BrO₃- increased the rate of apoptosis (programmed cell death) in the kidneys of rats of both sexes, an effect associated with increasing expression of antiapoptotic genes and proteins. Consequently, suppression of apoptosis is a likely mechanism for BrO₃- induced kidney cancer. More limited data suggest nongenotoxic modes of action for thyroid tumors and mesotheliomas. If these data are confirmed, linear extrapolation of risk to low doses is inappropriate.     

Survey of Seawater Intrusion in the Pearl River Basin and Modeling Bromate Formation during Ozonation of the Raw Water

Bromate formation has been identified as a significant barrier in the application of ozone during water treatment the downstream region of the Pearl River Basin that contains high levels of bromide. Seawater intrusion will increase bromide concentration in the inshore surface water. In this study, seawater intrusion in the Pearl River Basin was surveyed and modeling bromate formation during ozonation of the raw water affected by seawater intrusion was studied. Bromate formation models were developed to simulate the effects of the characteristics of water quality and the operating parameters of treatment processes on bromate formation during preozonation process and postozonation process. The results show that the downstream of the Pearl River Basin is affected seriously by seawater intrusion and the bromide mainly comes from seawater. Some empirical models were developed to estimate the concentration of bromate in ozonated surface raw water affected by seawater intrusion during the treatment process.     

Threshold Levels for Bromate Formation In Drinking Water

Ozone is a sufficiently strong oxidant to cause the oxidation of bromide ion and formation of bromate ion. In this study, bromate ion formation in a wide variety of drinking water sources was analyzed, with bromate ion formed in all sources under drinking water treatment conditions. Threshold levels for pH, bromide ion concentration, and ozone dose were found to be source-specific. Two non-linear empirical models were developed to predict bromate ion formation; these models are easy to use and require only several water quality and treatment variables. The models were tested against several literature data and a good simulation was found in other bench-scale tests, whereas the model tended to under-predict bromate ion formation in pilot-scale and full-scale programs.     

Ozone-Bromine Treatment – Water Treatment in Public Pools without Chlorine: A New Standard?

The central task of the rules and regulations governing water treatment in public swimming pools is to provide guidelines, the compliance with which leads to completely hygienic water. For this purpose, DIN 19643 “Treatment of Water of Swimming Pools and Baths” applies in Germany. To date, this standard has prescribed the chlorination of water. In a therapeutic pool introduced here, water was treated without chlorine. The water quality was observed as part of a long-term study over the course of three years. During the entire period, no germs were detected in the filtrate of the system, not even unspecific CFU germs. The treatment presented here is detailed from both theoretical and practical viewpoints. The treatment uses the oxidation power of ozone to form hypobromous acid as a disinfectant in water containing bromide. A crucial aspect of the treatment is the possible formation of bromate. It is shown that the formation of bromate can be suppressed very effectively. Further bromine-based by-products were monitored. Unpleasant by-products as known from the chlorination were not found. The treatment, known as ozone-bromine Treatment, demonstrates new ways to treat water in public swimming pools and should now be incorporated into the German DIN 19643. It is to be expected that this will also be reflected in the national standards of other countries.