Increasing Bromide Concentration Research Articles

UV-LED cocatalytic Fe3+/peroxymonosulfate process for the degradation of sulfamethoxypyridazine: Performance, mechanism and DBP formation during postchlorination

Herein, a UV-LED-catalytic Fe3+/peroxymonosulfate homogeneous advanced oxidation process (UV-LED/Fe3+/PMS) was adopted for the removal of sulfamethoxypyridazine (SMP), a commonly used sulfonamide antibiotic (SA), in water. Quenching experiments showed that SO4●–, •OH and Fe(IV) were generated in this system and contributed to the rapid removal of SMP. Generally, acidic media favored SMP degradation, and the contribution rate of active species to SMP removal was highly pH dependent. Higher light intensity and an equal Fe3+/PMS ratio (1:1) were appropriate for SMP removal. The introduction of HCO3−, NO3− and humic acid suppressed the degradation of SMP to different extents, but obvious acceleration was observed in the presence of halide ions. The transformation products were investigated, and their toxicity was also assessed. UV-LED/Fe3+/PMS was capable of controlling trichloromethane (TCM) during postchlorination while increasing the formation of dichloroacetonitrile (DCAN) and trichloronitromethane (TCNM) owing to the generation of precursors having certain functional groups. Prolonging pretreatment time had a positive effect on reducing DBP formation. The presence of humic acid increased the formation of both TCM and DCAN. Furthermore, total trihalomethanes and dihaloacetonitriles increased with increasing bromide concentration, which needs to be considered when adopting the UV-LED/Fe3+/PMS as pretreatment for the abatement of SMP.

Surface plasmon resonance of gold nanoparticle aggregates induced by halide ions

The localized surface plasmon resonance (LSPR) of metal nanoparticles is strongly dependent on geometrical and environmental factors, as well as the nanoparticle aggregation phenomena, which are exploited in a range of applications. In this work we investigate the LSPR of gold nanoparticles, produced by laser ablation in liquid (LAL), and their agglomeration induced by halides after LAL. We study the aggregation process under a range of factors like bromide concentration, temperature, and different halides. By absorption spectroscopy and electron microscopy we show that increasing bromide concentration leads to longer and more complex aggregates, with consequent red-shift and broadening of the LSPR. Simulations, in agreement with experiments, show that a red-shift of the LSPR is expected as AuNP linear chains become longer and validate this trend for different particle size and gap between particles. By using real-time absorption spectroscopy, we observe immediate growth of nanoparticles after salt addition. We also demonstrate that higher temperatures tend to suppress the aggregation process, while lower temperatures promote it. We then observe that a heavier halide like iodide tends to form a very broad LSPR indicating complex nanoparticle architectures. Finally, we show that the aggregates are disrupted by re-irradiating the colloid. These findings provide an expanded understanding into the factors ruling the aggregation phenomena, and will help developing existing applications while stimulating new ones.

Unexpected trends for the formation of chlorate and bromate during the photolysis of chlorine in bromide-containing water

Solar photolysis of free chlorine (solar/chlorine) in bromide-containing water occurs under various scenarios, such as chlorinated reservoirs and outdoor swimming pools, and the formation of chlorate and bromate is an important issue in the system. We reported unexpected trends for the formation of chlorate and bromate in the solar/chlorine system. Excess chlorine inhibited the formation of bromate, i.e., increasing chlorine dosages from 50 to 100 μM reduced the bromate yield from 6.4 to 1.2 μM in solar/chlorine at 50 μM bromide and pH 7. The yield of bromate in solar/chlorine at 100 μM chlorine and 50 μM bromide in 240 min was 18.8% of that at 50 μM bromine only. The underlying mechanism was that HOCl can react with bromite (BrO2−) to form HOClOBrO−, whose multi-step transformation finally formed chlorate as the major product and bromate as the minor product. This reaction overwhelmed the oxidation of bromite to form bromate by reactive species, such as •OH, BrO• and ozone. On the other hand, the presence of bromide greatly enhanced the formation of chlorate. Increasing bromide concentrations from 0 to 50 μM enhanced the chlorate yields from 2.2 to 7.0 μM at 100 μM chlorine. The absorbance of bromine was higher than that of chlorine, thus the photolysis of bromine formed higher levels of bromite at higher bromide concentrations. Then, bromite rapidly reacted with HOCl to form HOClOBrO− and it further transformed to chlorate. Additionally, 1 mg L−1 NOM had a negligible effect on bromate yields in solar/chlorine at 50 μM bromide, 100 μM chlorine and pH 7. This study demonstrated a new pathway of chlorate and bromate formation in the solar/chlorine system with bromide.

Formation characteristics of disinfection byproducts from four different algal organic matter during chlorination and chloramination

Algal organic matter (AOM) has become an important precursor of disinfection byproducts (DBPs) in multiple drinking water sources. In this study, the formation of DBPs during chlorination and chloramination of AOMs from four algal species (Microcystis aeruginosa, Chlorella vulgaris, Scenedesmus obliquus, and Cyclotella sp.) under different conditions (disinfectant doses 4.0–8.0 mg/L as Cl2, pH 6.0–8.0, and bromide 0–1.0 mg/L) were simultaneously investigated. Some common and specific characteristics of DBP formation have also been identified. The yields of total DBPs from the four AOMs were 3.28 × 102–6.00 × 102 and 1.97 × 102–3.70 × 102 nmol/mg C during chlorination and chloramination, respectively. The proportions of haloacetic acids (HAAs) in total DBPs were approximately ≥50%. Increasing disinfectant doses or pH only enhanced the yields of trihalomethanes (THMs) during chlorination but enhanced the yields of THMs, HAAs and dihaloacetonitriles (DHANs) during chloramination. Increasing bromide concentrations enhanced THM yields but decreased HAA yields during chlorination and chloramination, in addition to the shift from chlorinated DBPs to brominated DBPs. The DHAN yields of the four AOMs slightly decreased with bromide levels during chlorination, whereas different AOMs showed different trends with bromide levels during chloramination. During chlorination, C. vulgaris and S. obliquus AOMs generated higher THM and DHAN yields (at 4.0–5.0 mg/L as Cl2) than the other AOMs. During chloramination, M. aeruginosa AOM generated higher THM and HAA yields than the other AOMs (at 0.1 mg/L bromide). Cyclotella sp. AOM had the highest THM-bromine substitution factors during chlorination and the highest DHAN-bromine substitution factors during both chlorination and chloramination (at 0.1 mg/L bromide).

Multivariate experimental design provides insights for the optimisation of rechloramination conditions and water age to control disinfectant decay and disinfection by-product formation in treated drinking water

The stability of drinking water disinfectant residuals is known to be influenced by multiple variables. To evaluate the effects of various influencing variables on disinfectant stability, a multivariate analysis of chloramine decay and associated disinfection by-products (DBPs) formation was investigated in a series of bench-scale experiments. Of nine water quality variables previously identified, monochloramine dose, pH, and bromide concentration were selected as key water quality variables based on previous investigations and modelling. Co-effects of these key variables on monochloramine decay and formation of 33 halogenated and nitrogen-containing DBPs were investigated using response surface experimental design.Rechloramination conditions, including monochloramine dose, pH and bromide concentration, were optimised via a 3-factorial multivariate analysis of monochloramine stability in post-treatment drinking water. Effects of influencing variables on disinfectant decay and DBP formation were assessed and graphically presented as response surfaces with minimal experiments using Doehlert matrix experimental design compared to other multivariate experimental designs. Concentrations of trihalomethanes (THMs), haloacetic acids (HAAs), and N-nitrosamines were found to increase with water age, whereas opposite phenomenon was observed in the net production of haloacetonitriles (HANs). Increasing pH was found to stabilise monochloramine but it could cause DBP speciation to shift. Furthermore, increasing bromide concentration elevated Br-DBP formation. In bromide-containing water, pH = 7.8–8.0 should be considered as higher pH increases Br-THMs formations and lower pH increases formations of Br-HAAs and Br-HANs. However, water age or pH has insignificant impacts on DBP formation after significant monochloramine decay or at low initial monochloramine dose.These findings indicate that effective combined control measures to maintain monochloramine stability should include the application of high monochloramine dose (>1.5 mg-Cl2.L−1) under conditions of moderate to high pH (pH = 7.8–8.0) and minimal bromide concentration. This study provides relevant insights to water utilities aiming to design effective disinfectant residual management strategies for controlling monochloramine decay and DBP formation.

Comparison of UV and UV/chlorine system on degradation of 2,4-diaminobutyric acid and formation of disinfection byproducts in subsequent chlorination

• UV/chlorine system showed extremely excellent performance in degrading DAB. • C-C bond and C-N bond fracture were the main reactions of DAB degradation by UV. • RCS produced by UV/chlorine system preferentially attacked amino groups on DAB. • N-DBPs had great formation potential when UV/chlorine was used as pretreatment. • THMs were more prone to bromine substitution than HANs. 2,4-diaminobutyric acid (DAB) is a common non-protein amino acid with extremely high neurotoxicity in water environment, posing a serious threat to human health and animal welfare around the world. Therefore, it is necessary to take appropriate measures to remove it. In this paper, degradation of DAB in UV and UV/chlorine system were studied, and transformation pathways of DAB were preliminarily proposed based on the identified transformation products. Moreover, formation of disinfection byproducts (DBPs) during post-chlorination under different conditions were also discussed. The results indicated that the presence of reactive substances in UV/chlorine system significantly promoted the degradation of DAB, but more DBPs and their precursors were produced at the same time. UV irradiation time, pH and Cl 2 /N affected the formation of DBPs during post-chlorination to various degrees. Notably, precursors of carbonaceous DBPs were mainly formed during UV irradiation, while those of nitrogenous DBPs were mainly formed during UV/chlorine system. In the presence of bromide, brominated DBPs were the absolute dominant species, while formation of chlorinated DBPs were inhibited. Furthermore, total trihalomethane and total haloacetonitrile increased with increasing bromide concentration. Overall, special attention should be paid to DBP formation when selecting UV or UV/chlorine system as pretreatment to eliminate DAB.

Effect of copper oxide on monochloramine decomposition in bromide-containing waters

Copper oxide (CuO), a common corrosion product found in copper pipes, has been shown to catalyse the decay of different oxidants in drinking water, including chlorine, bromine, iodine, and chlorine dioxide. However, its impact on monochloramine (NH2Cl), a disinfectant commonly used in long distribution system worldwide is still unknown. In this study, the effect of CuO on NH2Cl decay in the absence or presence of bromide was investigated. Results showed that in the presence of CuO and the absence of bromide, NH2Cl slightly decayed under acidic conditions. When bromide was present in NH2Cl solutions, the total oxidant concentration (sum of the different bromo-chloro-amines) was significantly decreased by CuO. This was primarily due to the degradation of bromochloramine (NHBrCl) by CuO which was evidenced by membrane inlet mass spectrometry. The decomposition rate of the total oxidant was similar for different CuO dosages (0.02–0.2 g/L) but increased with increasing bromide concentration (0–80 μM) and decreasing pH (6.5–8). An apparent second-order rate constant of 0.73 M−1 s−1 was determined with respect to NH2Cl and bromide concentrations for a CuO concentration of 0.05 g/L. Our findings suggest that, during water transportation in copper pipes or in distribution systems where copper oxide is present, special attention should be given to the stability of chloramines when bromide-containing waters are chloraminated.

Formation of haloacetic acids from different organic precursors in swimming pool water during chlorination

Haloacetic acids (HAAs) were reported to be the most abundant category of DBPs in swimming pool water. In this study, the formation of HAAs from different organic precursors in swimming pool water, including UV filters, human body fluids, and natural organic matter (NOM), during chlorination was examined, and the effects of chlorine dose and halide concentrations on the formation of HAAs were evaluated. The results show that the total HAA yields from benzophenone-3 (BP-3) and Suwannee River humic acid (SRHA) were the highest among the nine organic precursors, and the yields of dichloroacetic acid and bromochloroacetic acid were higher than that of the other HAA species. In all the chlorinated samples of different organic precursors, longer chlorination time enhanced HAA formation. Both chlorine dose and bromide concentration significantly affected the formation of HAAs from BP-3 and SRHA during chlorination. With the increasing chlorine dose, the total HAA yields from SRHA and BP-3 significantly increased. Besides, the proportion of trihaloacetic acids (THAAs) rose while that of dihaloacetic acids (DHAAs) and monohaloacetic acids (MHAAs) declined with the increasing chlorine dose. With the increasing bromide concentration, HAA formation from SRHA increased while that of BP-3 decreased. The bromine incorporation factor (BIF) of the formed MHAAs, DHAAs and THAAs from SRHA and BP-3 both increased with the increasing bromide concentration in the following order: BIFDHAAs > BIFTHAAs > BIFMHAAs, indicating that bromine was easier to be incorporated into DHAAs rather than MHAAs or THAAs. Moreover, bromide promoted the formation of Br-HAAs.

Assessing the role of different dissolved organic carbon and bromide concentrations for disinfection by-product formation using chemical analysis and bioanalysis.

Concerns regarding disinfection by-product (DBP) formation during drinking water treatment have led water utilities to apply treatment processes to reduce the concentration of DBP precursor natural organic matter (NOM). However, these processes often do not remove bromide, leading to high bromide to dissolved organic carbon (DOC) ratios after treatment, which can increase the formation of more toxic brominated DBPs. In the current study, we investigated the formation and effect of DBPs in a matrix of synthetic water samples containing different concentrations of bromide and DOC after disinfection with chlorine. Trihalomethanes and haloacetic acids were analysed by chemical analysis, while effect was evaluated using in vitro bioassays indicative of the oxidative stress response and bacterial toxicity. While the addition of increasing bromide concentrations did not alter the sum molar concentration of DBPs formed, the speciation changed, with greater bromine incorporation with an increasing Br:DOC ratio. However, the observed effect did not correlate with the Br:DOC ratio, but instead, effect increased with increasing DOC concentration. Water samples with low DOC and high bromide did not exceed the available oxidative stress response effect-based trigger value (EBT), while all samples with high DOC, irrespective of the bromide concentration, exceeded the EBT. This suggests that treatment processes that remove NOM can improve drinking water quality, even if they are unable to remove bromide. Further, iceberg modelling showed that detected DBPs only explained a small fraction of the oxidative stress response, supporting the application of both chemical analysis and bioanalysis for monitoring DBP formation.

Surface composition of MAPb(IxBr1−x)3 (0 ≤ x ≤ 1) organic-inorganic mixed-halide perovskites

Organic-inorganic halide perovskites have been used as light absorbers in photovoltaic cells. The energy band gap of these perovskites can be tuned by mixing various halides at different concentrations. In this work, mixed iodide-bromide perovskite films at various concentrations were deposited on fluorine-doped tin oxide glass substrates via a spin coating technique. The films were characterized using X-ray diffraction (XRD), ultraviolet-visible spectroscopy and synchrotron-radiation photoemission spectroscopy. The XRD results suggest that the lattice spacing decreased with increasing bromide concentration, which also relates to an increase in the energy band gap. The mixed halide films showed less crystallinity than that of pure halide films. The photoemission results showed that the iodide concentration at the surface was higher than expected. This could have been due to the higher solubility of iodide perovskite in the dimethylformamide solvent than that of bromide perovskite. These results suggest that the energy levels at the surface of the films can be different from those of the bulk material.

The influence of bromide on the degradation of sulfonamides in UV/free chlorine treatment: Degradation mechanism, DBPs formation and toxicity assessment

The degradation of sulfonamides (SAs) in the presence of bromide during the UV/free chlorine process was investigated in this study. The reactions followed pseudo first-order kinetics. With increasing bromide concentrations of 1, 5, 10–20 µM, the degradation rate was gradually raised. The contribution of different reactive species has been calculated. The degradation products and DBPs formed by SAs were determined. The mechanisms of the degradation of SAs in the presence of bromide included hydroxylation, cleavage of the pyrimidinyl group, and bromine and chlorine electrophilic addition. The concentration of brominated disinfection by-products, including DBCM, TBM and DBAN, increased with increasing bromide dosage and degradation time, while 1, 1, 1-TCP and 1, 1-DCP decreased. In an acute toxicity test, the inhibition rate decreased in the first 5–10 min then increased after 10 min degradation when 10 µM Br− was added to the system. The initial decrease may due to the formation of low toxicity substances after the cleavage of the pyrimidinyl group, while the subsequent increase may be attributable to the increased formation of DBPs.

Chlorination of bromacil: Kinetics and disinfection by-products

Bromacil, a nonselective uracil compound, is applied to field crops, such as citrus and pineapple, to control annual and perennial grass weeds. In this study, the degradation kinetics and effects of influencing factors on the formation of disinfection by-products (DBPs) during bromacil chlorination were investigated. The reaction between chlorine and bromacil followed second-order kinetics, and the degradation kinetic model for bromacil chlorination was established. The rate constants of the reactions between bromacil and HOCl and ClO− were calculated as 4.33 (±1.40) × 101 and 3.21 (±0.47) × 102 M−1 s−1, respectively. The presence of Br− in water resulted in the formation of HOBr and accelerated the rate of bromacil degradation during chlorination. The rate constant was calculated as 6.34 (±0.09) × 104 M−1 s−1 for the reaction between bromacil and HOBr at 25 °C. The apparent second-order rate constant (kapp) increased with increase in temperature and pH, and the activation energy was calculated as 37.83 kJ/mol using the Arrhenius equation. Because the structure of bromacil comprises bromine atoms, brominated DBPs, including dibromochloromethane (DBCM) and bromodichloromethane (BDCM), formed abundantly during bromacil chlorination. The formation of bromoform (BF), BDCM, and DBCM increased with the reaction time, whereas the formation of chloroform (CF) increased until day 4 and then decreased. The yields of all the detected DBPs increased with the increase in pH from 5 to 8. With increasing bromide concentration, the formation of CF and BDCM gradually decreased, where as that of BF considerably increased, resulting in relatively stable bromine utilization factor in the bromide to chlorine ratio of 0.00–0.10 during bromacil chlorination.

The interplay between natural organic matter and bromide on bromine substitution

This study examined the interplay between bromide and DOM characteristics, described with SUVA254, in terms of formation and speciation of selected DBPs [trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetonitriles (HANs)] during chlorination under various water treatment conditions. Cytotoxicity evaluations were also conducted based on the types and amounts of DBPs formed and their corresponding cytotoxicity index values. The results showed that the formation of THMs and HAAs increased as the specific UV absorbance at 254 nm (SUVA254) of the waters increased; however, there was no clear trend for HANs. THM and HAN formation increased with increasing bromide levels, while there was no bromide effect on the HAA formation. Lower HAA5 (monochloroaceticacid, monobromoaceticacid, dichloroaceticacid, trichloroaceticacid, dibromoaceticacid) to HAA9 (monochloroaceticacid, monobromoaceticacid, dichloroaceticacid, trichloroaceticacid, dibromoaceticacid, bromochloroaceticacid, bromodichloroaceticacid, dibromochloroaceticacid, tribromoaceticacid) ratios, independent of SUVA254, were observed with increasing bromide levels. Bromine substitution factor (BSF) values were in the order of BSFDHAN > BSFTHAA > BSFTHM ≈ BSFDHAA. BSF values for all class of DBPs decreased with increasing SUVA254. TOX formation increased with increasing SUVA254 without an impact of bromide concentration. UTOX/TOX ratios were higher in treated low SUVA254 waters than raw waters having higher SUVA254 values, and they decreased with increasing initial bromide concentration in all sources. Increasing bromide concentration from 0.5 μM to 10 μM elevated the calculated cytotoxicity index values of waters. Despite their much lower (approximately ~10 times) formation as compared to THMs and HAAs, HANs controlled the calculated cytotoxicity of studied waters.

Degradation kinetics and disinfection by-product formation of chlorimuron-ethyl during aqueous chlorination

Abstract The degradation kinetics of chlorimuron-ethyl during chlorination was analyzed, and the effects of the influencing factors of pH, bromide and ammonium concentrations and reaction temperature on degradation kinetics were evaluated. Regarding degradation kinetics, the chlorination of chlorimuron-ethyl followed second-order kinetics, first-order kinetics when the chlorine concentration was changed, and first-order kinetics when the chlorimuron-ethyl concentration was changed. The apparent second-order rate constant was calculated, which significantly decreased increasing pH. The rate constant of the reaction between chlorimuron-ethyl− and HOCl was calculated as 3.25 (±1.14) × 103 M−1 min−1, and under the acid-catalyzed condition, the rate constant significantly increased to 6.41 (±1.62) × 107 M−1 min−1. The degradation rate of chlorimuron-ethyl decreased with increasing bromide (at pH 5.5–7.0) and ammonium concentrations (≤6 μM). Chlorimuron-ethyl chlorination is an endothermic reaction, with an activation energy estimated as 22.46 kJ mol−1 using the Arrhenius equation. During chlorimuron-ethyl chlorination, chloroform was the major volatile degradation product during chlorimuron-ethyl chlorination, and its concentration increased with the increasing reaction time and pH level. The distribution of disinfection by-products (DBPs) formed at different solution pH levels was quite distinct. In the presence of bromide, the concentration and species of brominated DBPs increased with the increasing bromide concentration. Notably, carcinogenicity and mutagenicity of brominated DBPs were higher than their chlorinate analogs.

Degradation kinetics and DBP formation during chlorination of metribuzin

Abstract A common nitrogen-containing herbicide, metribuzin, was studied for the effect of pH, bromide and ammonium concentrations as well as temperature on its degradation kinetics and disinfection by-product (DBP) formation during chlorination. Metribuzin chlorination can be well described by a second-order kinetic model, and the rate constants of the acid-catalyzed and HOCl oxidizing charged metribuzin (metribuzin + ) were calculated as 7.72 (±0.90) × 10 8 M −2 min −1 and 8.22 (±4.00) × 10 3 M −1 min −1 , respectively. Metribuzin degradation rate increased with increasing bromide concentration or decreasing ammonium concentration. A kinetic model of metribuzin chlorination in the presence of bromide and ammonium, respectively, was developed in this study, and the rate constant for the reaction of HOBr and metribuzin + was calculated as 2.44 (±2.30) × 10 5 M −1 min −1 . Moreover, the formation and distribution of chlorinated DBPs were analyzed. Chloroform was the major volatile degradation product with the molar yield of 0.86% under the circumneutral condition, and its formation increased gradually with the increase of reaction time and pH. However, the formation of dichloroacetonitrile, 1,1-dichloro-2-propanone, 1,1-trichloro-2-propanone and trichloronitromethane climbed up and then declined with increasing reaction time and pH. The formation of brominated DBPs increased with increasing bromide to chlorine molar ratio, especially for dibromochloromethane. The rate constants of metribuzin chlorination increased with increasing temperature, and the activation energy was estimated as 22.83 kJ mol −1 . In sum, special attention should be paid during metribuzin chlorination at alkaline conditions, especially in the presence of bromide, which would cause the formation of more toxic brmoninated DBPs than their chlorinated analogs.

Characteristics of molecular weight distribution of dissolved organic matter in bromide-containing water and disinfection by-product formation properties during treatment processes

The characteristics of dissolved organic matter (DOM) and bromide ion concentration have a significant influence on the formation of disinfection by-products (DBPs). In order to identify the main DBP precursors, DOM was divided into five fractions based on molecular weight (MW), trihalomethane formation potential and haloacetic acid formation potential were determined for fractions, and the change in contents of different fractions and total DBPs during treatment processes (pre-chlorination, coagulation, sand filtration, disinfection) were studied. Moreover, the relationship between bromide concentration and DBP generation characteristics in processes was also analyzed. The results showed that the main DBP precursors were the fraction with MW <1kDa and fraction with MW 3−10kDa, and the DBP's generation ability of lower molecular weight DOM (<10kDa) was higher than that of higher molecular weight DOM. During different processes, pre-chlorination and disinfection had limited effect on removing organics but could alter the MW distribution, and coagulation and filtration could effectively remove organics with higher MW. For DBPs, trihalomethanes (THMs) were mainly generated in pre-chlorination and disinfection, while haloacetic acids (HAAs) were mostly generated during pre-chlorination; coagulation and sand filtration had little effect on THMs but resulted in a slight removal of HAAs. In addition, the results of ANOVA tests suggested that molecular sizes and treatment processes have significant influence on DBP formation. With increasing bromide concentration, the brominated DBPs significantly increased, but the bromine incorporation factor in the processes was basically consistent at each concentration.

Factors affecting THM, HAN and HNM formation during UV-chlor(am)ination of drinking water

This study investigated the effect of several factors on the formation of disinfection byproducts (DBPs) including trihalomethanes (THMs), haloacetonitriles (HANs) and halonitromethanes (HNMs) during UV-chlor(am)ination of the water collected after filtration unit in a drinking water treatment plant. In general, THM formation was higher during UV-chlorination while HAN and HNM formation were higher during UV-chloramination. Higher Medium pressure (MP) UV dose resulted in more DBP formation. The value of pH affected DBP formation differently. THMs decreased with increasing pH during UV-chlorination but remained stable during UV-chloramination. HNMs increased as pH increased from 5 to 7 but decreased as pH further increased to 9 during UV-chlorination. On the other hand, HNM formation decreased with increasing pH during UV-chloramination. However, pH had little impact on HAN formation. The nitrate concentration had negligible impact on the formation of THM, HAN and HNM during both UV-chlor(am)ination. Increasing bromide concentration improved THM and HAN formation, decreased HNM formation, and shifted DBPs to more brominated species in the three categories. MP UV irradiation enhanced the formation of DBPs compared to low pressure UV during both UV-chlor(am)ination, especially for nitrogenated DBPs.

Broad-spectrum antimicrobial photocatalysis mediated by titanium dioxide and UVA is potentiated by addition of bromide ion via formation of hypobromite

Antimicrobial photocatalysis involves the UVA excitation of titanium dioxide (TiO2) nanoparticles (particularly the anatase form) to produce reactive oxygen species (ROS) that kill microbial cells. For the first time we report that the addition of sodium bromide to photoactivated TiO2 (P25) potentiates the killing of Gram-positive, Gram-negative bacteria and fungi by up to three logs. The potentiation increased with increasing bromide concentration in the range of 0–10mM. The mechanism of potentiation is probably due to generation of both short and long-lived oxidized bromine species including hypobromite as shown by the following observations. There is some antimicrobial activity remaining in solution after switching off the light, that lasts for 30min but not 2h, and oxidizes 3,3′,5,5′-tetramethylbenzidine. N-acetyl tyrosine ethyl ester was brominated in a light dose-dependent manner, however no bromine or tribromide ion could be detected by spectrophotometry or LC–MS. The mechanism appears to have elements in common with the antimicrobial system (myeloperoxidase+hydrogen peroxide+bromide).

Formation of iodinated trihalomethanes after ferrate pre-oxidation during chlorination and chloramination of iodide-containing water

Iodinated disinfection by-products (I-DBPs) are responsible for taste and odor issues, and more toxic than their brominated and chlorinated analogs. Ferrate salt (Fe(VI)) is green, efficient and multifunctional in drinking water treatment. Iodinated trihalomethanes (I-THMs) formation of iodide containing water pretreated by ferrate during chlorination/chloramination was investigated in this paper. The results indicated that I-THMs can be reduced significantly by ferrate pre-oxidation due to the oxidation of iodide to iodate. During chlorination, no detectable I-THMs were found at pH < 8 after ferrate pre-oxidation. However, I-THMs formation increased significantly at pH 8–9. I-THMs formation decreased drastically with increasing ferrate dosage and no detectable I-THMs were found at high ferrate dosage (>2 mg/L). The presence of high bromide concentration could restrain the transformation from iodide to iodate during ferrate pre-oxidation. However, no obvious changes in the amount and speciation of I-THMs were observed with increasing bromide addition. The yield of I-THMs was within 15 ± 2 µg/L when bromide addition varied. During chloramination, compared to the samples without bromide, the formation of I-THMs was restrained too. However, increasing bromide concentration in chloraminated solutions would lead to significant increase in the I-THMs formation and could contribute to the changes in speciation. The yield of I-THMs increased from 16.11 µg/L to 33.28 µg/L when bromide concentration is 25 µM and 100 µM, respectively. Ferrate pre-oxidation can be employed to reduce the I-THMs formation in drinking water treatment for iodide-containing water.

Estimating Potential Increased Bladder Cancer Risk Due to Increased Bromide Concentrations in Sources of Disinfected Drinking Waters

Public water systems are increasingly facing higher bromide levels in their source waters from anthropogenic contamination through coal-fired power plants, conventional oil and gas extraction, textile mills, and hydraulic fracturing. Climate change is likely to exacerbate this in coming years. We estimate bladder cancer risk from potential increased bromide levels in source waters of disinfecting public drinking water systems in the United States. Bladder cancer is the health end point used by the United States Environmental Protection Agency (EPA) in its benefits analysis for regulating disinfection byproducts in drinking water. We use estimated increases in the mass of the four regulated trihalomethanes (THM4) concentrations (due to increased bromide incorporation) as the surrogate disinfection byproduct (DBP) occurrence metric for informing potential bladder cancer risk. We estimate potential increased excess lifetime bladder cancer risk as a function of increased source water bromide levels. Results based on data from 201 drinking water treatment plants indicate that a bromide increase of 50 μg/L could result in a potential increase of between 10(-3) and 10(-4) excess lifetime bladder cancer risk in populations served by roughly 90% of these plants.