Initial Br Research Articles

Effective Inhibition of Bromate Formation with a Granular Molecular Sieve Catalyst Ce-MCM-48 during Ozonation: Pilot-Scale Study

The inhibition of bromate (BrO − ) formation during ozonation with a novel granular molecular sieve catalyst, Ce-MCM-48, was investigated in pilot-scale under simulated practical conditions by varying the initial bromide (Br − ) concentration, total organic carbon (TOC) content, aqueous ozone concentration, water pH, and hydraulic retention time (HRT). The results indicate that the inhibition efficiency of Ce-MCM-48 for BrO − formation could reach 82-90% as the initial Br − concentration varied from 200-800 μg=L under typical water treat- ment conditions: aqueous ozone concentration ¼ 2.0 � 0.1 mg=L, HRT ¼ 10 min, initial pH ¼ 7.7-7.9, and T ¼ 18 � 2°C. The extension of HRT from 10 to 20 min and pH variation in the range of 6.0-9.0 had insignificant impact on the inhibition efficiency of BrO − formation. Compared with ozonation alone, the catalytic ozonation could achieve almost the same efficiencies for TOC removal and Escherichia coli inactivation. A long-term continuous operation experiment for 33 days demonstrated that the granular catalyst Ce-MCM-48 possesses not only a high efficiency, but also a large treatment capacity for minimizing BrO − formation during the ozonation process, and thus has potential applications to water treatment. DOI: 10.1061/(ASCE)EE.1943-7870.0000585. © 2013 American Society of Civil Engineers. CE Database subject headings: Drinking water; Water treatment; Ozone; Oxidation; Case studies. Author keywords: Drinking water; Water treatment; Ozone; Oxidation; Control.

Use KMnO<sub>4</sub> to Control Bromate Formation during Drinking Water Ozonation: Influencing Factors

This formation of bromate during ozonation of polluted source water has long caused great concerns. This paper used KMnO4 to control the bromate formation during water ozonation. KMnO4 was added 10 min prior ozone to oxidize the organic pollutants. The initial Br- concentration was 1000 μg/L. The results showed that the bromate formation efficiency was low (<5%) during KMnO4-ozone oxidation. Among KMnO4 dose, ozone dose, and source water TOC, the single most important factor for bromate formation was the ozone dose. When the ozone dose was 3 mg/L or higher, the bromate concentration exceeded the national standard no matter what level of KMnO4 was used. The organic pollution level had little influence on the bromate formation.

O3/H2O2 Process for Both Removal of Odorous Algal-Derived Compounds and Control of Bromate Ion Formation

The limitation of ozonation and the applicability of ozone/hydrogen peroxide process with a source water for a water supply using a flow-through type contactor were discussed. The water sample was pre-treated in a lab and spiked with bromide ion in the concentration range from 39 to 515 μg/L, and both 2-MIB and geosmin, odorous algal-derived compounds, from 58 to 609 ng/L under the hydrogen peroxide dose of 0 to 3.7 mg/L. When the initial concentration of Br− was around 50 μg/L, the formation of BrO3 − was controlled at less than 10 μg/L at the ozone dose of 2 mg/L, however the concentration of 2-MIB was over 10 ng/L in some cases with its initial concentration of around 100 ng/L during ozonation. When the initial concentration of Br− exceeds 100 μg/L, it seems very difficult to meet the standard for drinking water quality even with the initial 2-MIB concentration of 100 ng/L. The dose of H2O2 from 0.5 to 2.3 mg/L attained the standard for drinking water quality with the initial concentrations of Br− of approximately 50 μg/L and of 2-MIB of up to 500 ng/L at the ozone dose of 2 mg/L. When the initial concentration of 2-MIB was around 100 ng/L with the initial Br− concentration of up to 200 μg/L, the H2O2 dose of 1.7 mg/L also attained the standard for drinking water quality. When the initial concentration of Br− was around 500 μg/L, although the higher dose of H2O2 was required for the control of BrO3 − formation and the increase of the initial concentration of 2-MIB requires more H2O2 dose, the higher dose of H2O2 could attain the standard for drinking water quality of BrO3 − and 2-MIB (geosmin) simultaneously.

Making Full Use of the Oxidizing Equivalents in Bromate in the Selective Oxidation of Thiols, Sulfides, and Benzylic/Secondary Alcohols into Disulfides, Sulfoxides, and Aldehydes/Ketones

The oxidation of thiols to disulfides was achieved in high yields with 6:1 mol ratio of thiol to NaBrO3, while the oxidation of sulfides and benzylic/secondary alcohols to the corresponding sulfoxides and aldehydes/ketones was successfully undertaken with 3:1 mol ratio of substrate to NaBrO3. These ratios correspond to the minimum theoretical requirement of NaBrO3. The reactions were conducted at 0−30 °C, depending upon substrate, and were initiated with catalytic amounts of H+ and Br− (initial Br−/BrO3− = 1:3.5 for thiol oxidation and 1:8 for sulfide and alcohol oxidation). Further, regeneration and reuse of the spent reagent in the aqueous effluent was demonstrated.

Potential Proton‐Release Channels in Bacteriorhodopsin

The protein bacteriorhodopsin pumps protons across a bacterial membrane; its pumping cycle is triggered by the photoisomerization of a retinal cofactor and involves multiple proton-transfer reactions between intermittent protonation sites. These transfers are either direct or mediated by hydrogen-bonded networks, which may include internal water molecules. The terminal step of the proton-transfer sequence is the proton release from a pocket near Glu194 and Glu204 to the extracellular bulk during the transition from the L to the M photointermediate states. The polar and charged side chains connecting these two regions in the crystal structures show no structural changes between the initial bR state and the L/M states, and no intermittent protonation changes have been detected so far in this region. Based on biomolecular simulations, we propose two potential proton-release channels, which connect the release pocket to the extracellular medium. In simulations of the L photointermediate we observe bulk water entering these channels and forming transient hydrogen-bonded networks, which could serve as fast deprotonation pathways from the release pocket to the bulk via a Grotthuss mechanism. For the first channel, we find that the triple Arg7, Glu9, and Tyr79 acts as a valve, thereby gating water uptake and release. The second channel has two release paths, which split at the position Asn76/Pro77 underneath the release group. Here, water molecules either exchange directly with the bulk or diffuse within the protein towards Arg 134/Lys129, where the exchange with the bulk occurs.

Simulation of neutron-physical processes in the surface layer of a fuel kernel

A large change in the structure, density, and chemical and phase composition occurs in nuclear fuel with deep burnup, and an edge zone is formed. Simulation of the formation of an edge zone in a fuel kernel of thermal reactors will make it possible to suggest ways to decrease its influence on the characteristics of a fuel element. In the present work, the neutron-physical processes occurring in the peripheral layer of a fuel kernel are simulated. The distribution of nuclear reaction rates along the radius of a fuel pellet is calculated using the SCALE-4.3, MCNP-4B, and UNK computer programs. The radial dependence of the local breeding ratio is calculated. It is shown that for fresh fuel BR > 1 for fissile nuclei in a 100 µm thick layer, while the initial BR averaged over a pellet is no more than 0.5. The volume energy distribution in a 100 µm thick peripheral layer is 30% higher than the average value over a pellet. A combined pellet, where the central part possesses the standard enrichment (4–5% 235U) and the peripheral layer contains less than 0.7% 235U, is proposed to decrease the influence of the edge zone on the properties of fuel.

Case Report Vestibular Rehabilitation Decreases Fall Risk and Improves Gaze Stability for an Older Individual with Unilateral Vestibular Hypofunction

Partial or total unilateral vestibular loss is the third most common cause of peripheral vestibular dysfunction. Dysfunction of one or both of the vestibular mechanisms can manifest physically as abnormalities of posture, balance, and/or visual acuity. This case report describes physical therapy examination and individualized intervention with vestibular rehabilitation for a patient with unilateral vestibular hypofunction. The patient was an 80-year-old male with electronystamographically confirmed unilateral vestibular loss of 98.3%. He demonstrated altered balance and gaze stability classifying him as having an increased risk for falling. After 5 weeks of individualized vestibular rehabilitation, the patient significantly decreased his fall risk from 11 to 20 of 24 on the Dynamic Gait Index. His gaze stability also improved from a 4 to 1 line disparity with dynamic visual acuity testing. The patient also had a decrease in perceived disability on the Dizziness Handicap Inventory from 30/100 at evaluation to 12/100 at discharge. Individualized vestibular rehabilitation decreased fall risk and improved gaze stability for a patient with significant unilateral vestibular hypofunction.

Formation of brominated products in irradiated titanium dioxide suspensions containing bromide and dissolved organic carbon

We report the irradiation of TiO 2 suspensions containing Br - and dissolved organic carbon (DOC). In the absence of DOC, we found no evidence for the formation of BrO 3 - upon irradiation of 1 g L - 1 P25 suspensions with UV light for initial Br - concentrations up to 10 mg L - 1 . In the presence of DOC (Lake Hohloh, Germany and salicylic acid), we found no evidence for the formation of either BrO 3 - or trihalomethanes (THMs). However, small amounts of adsorbable organic halogen (AOX) were formed at high bromide concentrations ( 3 mg L - 1 ). When irradiating P25 suspensions containing bromide and 2,4-dihydroxybenzoic acid (DHBA, high bromoform formation potential), we observed the formation of significant amounts of bromoform (up to 10 μ g L - 1 ). Bromoform appeared only after the DHBA had been degraded.

Bacteriorhodopsin photocycle at cryogenic temperatures reveals distributed barriers of conformational substates

The time course of thermal reactions after illumination of 100% humidified bacteriorhodopsin films was followed with FTIR spectroscopy between 125 and 195 K. We monitored the conversion of the initial photoproduct, K, to the next, L intermediate, and a shunt reaction of the L state directly back to the initial BR state. Both reactions can be described by either multiexponential kinetics, which would lead to apparent end-state mixtures that contain increasing amounts of the product, i.e., L or BR, with increasing temperature, or distributed kinetics. Conventional kinetic schemes that could account for the partial conversion require reversible reactions, branching, or parallel cycles. These possibilities were tested by producing K or L and monitoring their interconversion at a single temperature and by shifting the temperature upward or downward after an initial incubation and after their redistribution. The results are inconsistent with any conventional scheme. Instead, we attribute the partial conversions to the other alternative, distributed kinetics, observed previously in myoglobin, which arise from an ensemble of frozen conformational substates at the cryogenic temperatures. In this case, the time course of the reactions reflects the progressive depletion of distinct microscopic substates in the order of their increasing activation barriers, with a distribution width for K to L reaction of approximately 7 kJ/mol.

Translating Thomas Mann

Tief ist der Brunnen der Vergangenheit, he writes, and looks at the sen tence, clears his throat, and grins as he feels the tide beginning to well up behind the six words. It is the onset of that thorough and entire throat-clearing which he will later call simply Hoellenfahrt, Passage to Hell, the fifty page introduction to his longest book. It is truly a passage to hell for the innocent reader. Deep is the well of the past, I write, and my troubles begin, for my translation has killed the melody. Brunnen has two syllables, Vergangenheit, the German word for past, has four, and the line is a loose iambic pentameter. But meter is less worrisome than the music of association. For Brunnen can mean one of two things, well but also spring, and so it carries the burble of a running stream in its initial br and its trippling n's, even when it stands, as it does here, for a partially filled shaft of still water, sunk into an arid hill above Hebron in Canaan, while Vergangenheit expresses the com plexity of completed process, not our blunt and noncommittal past; gangen means gone, and the entire four-syllable package something like finished-having-gone-itude. His next three sentences are each as long as the one I've just written, and he is only warming up, for his second page has no periods in it at all; unlike Faulkner's monsters, though, this one has grammatical bones and indeed, an articulated ceremonial structure; it is an invocation, an incantation to Joseph, and gives the writer, composing it, that surge of self-admiration, those passionate yet mischievous giggles that will cause him to write, later, to a friend, that he has never enjoyed as much as this work of playful science, as he calls his biblical epic, allud ing, almost certainly, to Nietzsche's joyful wisdom, which is, in turn...

All-optical switching characteristics in bacteriorhodopsin and its applications in integrated optics

We experimentally and theoretically investigated the optical switching characteristics of bacteriorhodopsin (bR) at lambda=633 nm using the pump-probe method. A diode-pumped second harmonic YAG laser (lambda=532 nm which is located around the maximum initial Br state absorption) was used as a pumping beam and a cw He-Ne laser (lambda=633 nm which is around the peaks of K and O states) was used as a probe. Due to the nonlinear intensity induced excited state absorption of the K, L, M, N, and O states in the bR photocycle, the switching characteristics are sensitive to the intensity of the probe and pump beams. Based on this property, we have demonstrated an all-optical device functioning as 11 kinds of variable binary all-optical logic gates.

Transient absorption and photovoltage study of‘ self-assembled bacteriorhodopsin/polycation multilayer films

A series of organized (PDAC/PM) n (poly(diallyldimethylammonium chloride)/purple membrane) multilayer films were prepared by alternate adsorptions of positively charged PDAC polyelectrolyte and negatively charged purple membrane (PM). The kinetics of the photocycle of bacteriorhodopsin (bR) in PM was studied by flash photolysis and transient photovoltage methods. Although the orientation of the adsorbed bR depends on the pH of the PM suspension, the kinetics of the photo-induced reaction cycle in dehydrated films is independent of the deposition pH. In dry (PDAC/PM) n films the decay of the M intermediate to the initial bR state is multiexponential and delayed to several minutes for both orientations. A simultaneous two-exponential decay in millisecond time domain was observed at red wavelengths. The source of the red-shifted absorption is suggested to be the C 610 intermediate of the cis photocycle of bR.

Atomic structural changes of a Br-chemisorbedSi(111)−7×7surface under 10–150 eV electron impact

Electron-stimulated desorption from Br-chemisorbed $\mathrm{Si}(111)\ensuremath{-}7\ifmmode\times\else\texttimes\fi{}7$ surfaces was investigated by scanning tunneling microscopy. Irradiating these surfaces with electrons field emitted from the tip of the scanning tunneling microscope induced various desorption behaviors depending on the initial Br coverage and electron energy. At low Br coverage, Br atoms desorb but no atomic changes occur on the Si surface. At saturation coverage, Si adatoms as well as Br atoms desorb to a large extent. The cross section of Br atom desorption first increases near 15 eV and then increases by orders of magnitude with electron energy up to 150 eV. The cross section of adatom desorption, in contrast, is much less dependent on the electron energy in this energy region. These desorption behaviors are discussed from the viewpoint of electronic excitation at the Br-chemisorbed Si(111) surface.

Atomic-Layer Etching and Electron-Stimulated Desorption of Br-Chemisorbed Si(111) Surfaces.

Atomic-layer etching and electron-stimulated desorption of Br-chemisorbed Si(111)-7×7 surfaces were investigated by scanning tunneling microscope. In a Br2 dose of 100 L, most of the Si adatoms are saturated with Br atoms, while the 7×7 structure is completely retained. In further Br2 doses up to 400 L, most of the Si adatoms are etched, and the underlying rest-atom layer is imaged during the tip scanning at a sample bias of +3 V. Irradiating Br-chemisorbed surfaces with the field-emitted electrons from an STM tip, which was farther away from the sample than at usual observation, induced various desorption behavior depending on the initial Br coverage and electron energy. At low Br coverage, Br atoms desorb but no atomical changes on the Si surface occur. At saturation coverage, Si adatoms as well as Br atoms desorb remarkably. The cross section of Br atom desorption first increases near 15 eV and then increases by orders of magnitude with an electron energy up to 150 eV. The cross section of adatom desorption, in contrast, is much less dependent on the electron energy in the above energy region. The desorption behavior is discussed in terms of electronic excitation at the Br-chemisorbed Si(111) surface.

Photochemistry of adsorbed molecules: Part XX: Photodissociation and photoreaction in CH 3Br/CaF 2(111) at 193 nm

Methyl photofragments from the 193 nm photodissociation of CH 3Br adsorbed on CaF 2(111) were studied by angularly resolved time-of-flight mass spectrometry. The translational energy distributions, P( E T′), of the CH 3 photofragments showed evidence of four pathways, depending on the coverage. The pathways were termed ‘direct’ (DIR), ‘indirect(1′)’ [IND(1′)], ‘indirect(1)’ [IND(1)] and ‘indirect(2)’ [IND(2)] in order of decreasing peak E T′. The DIR methyl P( E T′) peaked at 2.4 eV, with a full-width at half-maximum (FWHM) of 0.6 eV, corresponding closely to that reported for gas-phase CH 3 (peak=2.5 eV, FWHM=0.5 eV). The P( E T′) of this DIR pathway was consistent with CH 3 escaping directly without collisions. For these DIR methyls the angular distribution, P( θ′), reflected the prior BrC bond direction at the various coverages. The DIR P( θ′) indicated a change in the alignment of BrCH 3 with increasing coverage, from one in which the Br–C axis was initially roughly parallel to the surface plane (0.25 ML), to one with the Br–C axis along the surface normal (0.5 and 2 ML), and finally to one with the Br–C axis 23° from the surface normal (7 ML). The IND(1′) and IND(1) methyls, despite an energy loss of 0.7 and 1.3 eV, respectively, in a strong inelastic encounter, both exhibited similar energy and angular distributions to the DIR component. We propose that the IND(1) pathway is due to the occurrence of an ‘intralayer’ exchange reaction ( C H 3+BrCH 3′→CH 3Br+C H 3′ ) in one layer, and in the case of the IND(1′) pathway the same process occurring in ‘interlayer’ collisions, since IND(1′) methyls were only observed at ∼2 ML coverage. This methyl-exchange reaction has been invoked previously to explain a similar inelastic pathway observed for photorecoiling CH 3 coming from CH 3Br on LiF(001), NaCl(001) and MgO(001). The IND(2) pathway was characterized by a broader P( E T′) than the other three pathways, and a broad P( θ′) (cos n θ ′, n=1.7–3.8), peaking at the surface normal. These attributes of P( θ′) for IND(2) are characteristic of strongly inelastic encounters in which memory of the initial BrC bond direction is lost.

The vibrational predissociation of HeBr 2: a wavepacket study

We present a theoretical study of the vibrational predissociation of the Van der Waals complex HeBr 2, using a time-dependent quantum mechanical approach with a symplectic integrator propagator, for total angular momentum J = 0. This method gives not only vibrational predissociation lifetimes, resonance energies and rotational product distributions but also information on the dynamics of the system. A comparison is made with time-independent and experimental results, for initial Br 2 excitation level v=8, 10, 12, and good agreement is found.

Effect of the arginine-82 to alanine mutation in bacteriorhodopsin on dark adaptation, proton release, and the photochemical cycle.

The pH dependence of the rate constant of dark adaptation (thermal isomerization from all-trans- to 13-cis-bR) drastically changes when Arg82 of bacteriorhodopsin is replaced by an alanine. In the wild type (WT) the rate decreases sharply between pH 2.5 and pH 5. In R82A the sharp decrease is shifted to pH > 7. This correlates with the shift in the pK of the purple-to-blue transition from pH 2.6 in the wild type to pH 7.2 in the mutant (in 150 mM KCl). We propose that the same group that controls the purple-to-blue transition, namely, Asp85, catalyzes dark adaptation. The rate of dark adaptation in the R82A mutant is proportional to the fraction of protonated Asp85, indicating that dark adaptation occurs when Asp85 is transiently protonated. Thermal isomerization is at least 2 x 10(3) times more likely when Asp85 is protonated (blue membrane) than when it is deprotonated (purple membrane). The pH dependence of dark adaptation in the WT can be explained by a model in which the rate of dark adaptation in the WT is also proportional to the fraction of protonated Asp85 and that the pK of Asp85 depends on some other group, X, which deprotonates (or moves away from Asp85) with pK9 and causes the shift in the pK of Asp85 from 2.6 to 7.2. The quantum yield of light adaptation is at least an order of magnitude less in R82A as compared to the WT. The rise time of M formation is very fast in R82A and, unlike the WT, pH independent (1 microsecond versus 85 and 6 microseconds in the WT at pH 7 and 10, respectively). The activation energy of the L to M transition is 6.9 kcal/mol versus 13.5 kcal/mol in the WT. Thus the loss of a positive charge in the active site greatly increases the rate of light-induced deprotonation of the Schiff base. In the R82A mutant, the M decay at pH > 8.8 is much faster than the recovery of initial bR, which suggests a decrease in the rate of back-reaction from N to M. In a suspension of R82A membranes the rate of proton release as measured by the pH-sensitive dye pyranine is delayed by at least 20-fold (in 2 M KCl), while the uptake of protons did not change much (12 ms in the WT versus 8 ms in R82A).(ABSTRACT TRUNCATED AT 400 WORDS)

Relationship of proton uptake on the cytoplasmic surface and reisomerization of the retinal in the bacteriorhodopsin photocycle: An attempt to understand the complex kinetics of the pH changes and the N and O intermediates

In the bacteriorhodopsin photocycle the recovery of the initial BR state from the M intermediate occurs via the N and O intermediates. The molecular events in this process include reprotonation of the Schiff base and the subsequent uptake of a proton from the cytoplasmic side, as well as reisomerization of the retinal from 13-cis to all-trans. We have studied the kinetics of the intermediates and the proton uptake. At moderately low pH little of the N state accumulates, and the O state dominates in the reactions that lead from M to BR. The proton uptake lags behind the formation of O, suggesting the sequence N(0)<==>O(0) + H+ (from the bulk)-->O(+1)-->BR+H+ (to the bulk), where the superscripts indicate the net protonation state of the protein relative to BR. Together with a parallel study of ours at moderately high pH, these results suggest that the sequence of proton uptake and retinal reisomerization depends on pH: at low pH the isomerization occurs first and O accumulates, but at high pH the isomerization is delayed and therefore N accumulates. Although this model contains too many rate constants for rigorous testing, we find that it will generate most of the characteristic pH-dependent kinetic features of the photocycle with few assumptions other than pH dependency for protonation at the proton release and uptake steps.

Measurement of THM and Precursor Concentrations Revisited: The Effect of Bromide Ion

In the absence of bromide ion (Br−), method 5710B from Standard Methods is adequate for measuring trihalomethane (THM) precursor concentrations, provided a free available chlorine (FAC) residual of 3 mg/L is maintained at the end of incubation, and method 5710E from Standard Methods is appropriate for predicting THM concentrations at the consumer's tap. In the presence of Br−, method 5710B is adequate for measuring THM precursor concentrations provided only total precursor is desired. Because the initial Br−/average FAC dosage molar ratio influences bromine substitution, THM species concentrations cannot be predicted using method 5710B. Instead, method 5710E must be used. This is particularly important when evaluating THM precursor removal unit processes when the use of method 5710B may indicate greater bromine substitution in the unit process effluent than in the influet.

Br2 adsorption on GaAs(110) and surface etching at low temperature.

The adsorption and reactivity of Br 2 on GaAs (110) was studied in the temperature range of 25≤T≤300 K with photoemission spectroscopy. Initial Br 2 adsorption was dissociative at all temperatures with Br bonding to both As and Ga. Thermally activated etching was observed after warming up a surface with condensed Br 2 multilayers. AsBr 3 formation was evident at 50-100 K but this species desorbed for T≥150 K