Steady-state Concentration Of Hydroxyl Radicals Research Articles

Unraveling the multiple roles of VUV mediated hydroxyl radical in VUV/UV/chlorine process: Kinetic simulation, mechanistic consideration and byproducts formation

The application of VUV/UV/chlorine process for abatement of three representative organic contaminants, including naproxen (NPX), carbamazepine (CBZ) and iopamidol (IPM) was systematically investigated in this study with focus on the kinetic simulation, oxidation mechanisms and byproducts formation. The results demonstrated that VUV/UV/chlorine process was of outstanding efficiency with fluence-based pseudo-first-order rate constants of selected contaminants increased by 53.5–141% and 52.3–67.9% compared with UV/chlorine and VUV/UV processes, respectively. A chemical kinetic model was successfully developed to predict chlorine decay, steady-state concentrations of hydroxyl radical (•OH) and elimination of NPX, CBZ and IPM in VUV/UV/chlorine process. The modeling results suggested the VUV induced •OH could unexpectedly improve the concentrations of reactive chlorine species compared with UV/chlorine. In addition, effects of chlorine dosage, pH, natural organic matter, bicarbonate and chloride on the specific contributions of UV, •OH, chlorine radical (Cl•) and dichlorine radical (Cl2•−) to the degradation of selected contaminants were also evaluated and simulated in VUV/UV/chlorine process. The reactive sites and transformation pathways of NPX, CBZ and IPM were proposed via Fukui function analysis and UPLC-Q-TOF-MS identification. Meanwhile, the oxidation feasibility of NPX, CBZ and IPM by •OH and Cl• via single electron transfer mechanism was clarified based on theoretical thermodynamics calculation. Compared with UV/chlorine, VUV/UV/chlorine enhanced the generation of chlorate and bromate but retarded the formation of disinfection byproducts. This study first clarified the radical chemistry, contaminants transformation and byproducts formation in VUV/UV/chlorine process.

Role of Reactive Halogen Species in Disinfection Byproduct Formation during Chlorine Photolysis.

The multiple reactive oxidants produced during chlorine photolysis effectively degrade organic contaminants during water treatment, but their role in disinfection byproduct (DBP) formation is unclear. The impact of chlorine photolysis on dissolved organic matter (DOM) composition and DBP formation is investigated using lake water collected after coagulation, flocculation, and filtration at pH 6.5 and pH 8.5 with irradiation at three wavelengths (254, 311, and 365 nm). The steady-state concentrations of hydroxyl radical and chlorine radical decrease by 38-100% in drinking water compared to ultrapure water, which is primarily attributed to radical scavenging by natural water constituents. Chlorine photolysis transforms DOM through multiple mechanisms to produce DOM that is more aliphatic in nature and contains novel high molecular weight chlorinated DBPs that are detected via high-resolution mass spectrometry. Quenching experiments demonstrate that reactive chlorine species are partially responsible for the formation of halogenated DOM, haloacetic acids, and haloacetonitriles, whereas trihalomethane formation decreases during chlorine photolysis. Furthermore, DOM transformation primarily due to direct photolysis alters DOM such that it is more reactive with chlorine, which also contributes to enhanced formation of novel DBPs during chlorine photolysis.

Photogeneration and steady-state concentration of hydroxyl radical in river and lake waters along middle-lower Yangtze region, China

Hydroxyl radical (HO∙) in natural waters plays a critical role in contaminant transformation and ecosystem health. In this study, the photogeneration and steady-state concentration of HO∙ in different aquatic environments (e.g., river and lake) along the middle-lower Yangtze region, China, were evaluated. The results showed that, compared to lake samples, the river waters were characterized by lower HO∙ photoformation rate (RHO∙) (5.10–11.69 × 10−11 vs. 1.10–1.82 × 10−10 M s−1) and steady-state HO∙ concentration ([HO∙]) (1.76–3.11 × 10−17 vs. 2.50–10.33 × 10−17 M). The contribution of nitrate and nitrite to the total RHO∙ in river waters was generally higher than that in lake waters, and photolysis of nitrite exhibited contributions 1–2 times higher than those of nitrate (0–25% vs. 0–9%) irrespective of sample types. As a result, the photosensitization by chromophoric dissolved organic matter (CDOM) contributed more than 70% of the total RHO∙ for all samples except for River Ganjiang. [HO∙] among all samples was positively correlated with dissolved organic carbon (DOC) concentration, and the DOC-normalized [HO∙] was further related to the physicochemical properties of CDOM samples (e.g., aromaticity, humification, and molecular weight). The humic-like aromatic substances with low molecular weight were the controlling factors influencing [HO∙] in the studied surface waters. The results contributed to a deeper understanding of behaviors and fate of aquatic DOMs in terms of HO∙ formation and contaminant attenuation.

Photo-induced phosphate release during sediment resuspension in shallow lakes: A potential positive feedback mechanism of eutrophication

Dissolved phosphate (Pi) can be released during resuspended sediments exposed to sunlight. However, the significance of this phenomenon in the process of eutrophication is not clear. In this study, the behavior of photo-induced Pi release during sediment resuspension in shallow lakes with the different trophic states was investigated. The amount of photo-induced Pi release in the sediment resuspension from Lake Liangzi, Lake Dong, Lake Tangxun and Lake Longyang in China was 0.013, 0.019, 0.032, and 0.048 mg/L, respectively, and increased as the trophic states of the lakes increased. The results of phosphorus speciation analysis showed that the phosphate monoester in the particulate phosphorus is the organic phosphorus species participated in the photochemical reaction. The steady-state concentration of hydroxyl radical (OH) in the sediment resuspension also increased along with the trophic states of lakes increased and dissolved organic matter (DOM), nitrate, and Fe3+ presented in sediment resuspension were the main photosensitizers for OH production. All these results indicate that the increase of trophic states of lakes leads to the accumulation of organic phosphorus and OH, resulting in more dissolved phosphate photo-released, which accelerate the eutrophication process in a form of positive feedback.

Photo-induced Phosphate Release from Organic Phosphorus Decomposition Driven by Fe(Ⅲ)-oxalate Complex in Lake Water

The phosphate released from organic phosphorus photo-decomposition has a significantly influence on the phosphorus levels in the water column in lakes. In order to reveal the effect of organic phosphorus photo-decomposition on phosphate level in lake water, the phosphate released from organic phosphorus photo-decomposition driven by Fe(Ⅲ)-oxalate complex under UV-Vis and sunlight irradiation was investigated in natural lake water using glyphosate as the model organic phosphorus. The effects of pH and initial concentration of Fe(Ⅲ), oxalate and glyphosate on the phosphate released from glyphosate photolysis were studied. The results showed that phosphate could be released from glyphosate degradation by Fe(Ⅲ)-oxalate complex under UV-Vis and sunlight irradiation. The concentration of phosphate reached 0.25 mg·L-1 and 0.18 mg·L-1 under UV-Vis and sunlight irradiation for 60 and 720 min, respectively. The amount of phosphate released increased with the increase of the initial concentration of Fe(Ⅲ), as well as the increasing oxalate and glyphosate concentration in lake water. However, the increase of pH could significantly inhibit this process in the reaction system. The concentration of phosphorus decreased with the addition of isopropanol, which indicated that the hydroxyl radical (·OH) was one of the main active oxygen species of Fe(Ⅲ)-oxalate complex. The rates of·OH production for Fe(Ⅲ)-oxalate/UV-Vis and Fe(Ⅲ)-oxalate/sunlight systems were 0.52×10-2 μmol·(L·min)-1 and 0.03×10-2 μmol·(L·min)-1, respectively. The steady-state concentrations of hydroxyl radical (·OH) for the Fe(Ⅲ)-oxalate/UV-Vis conditions were 4.74×10-16 mol·L-1 and 0.27×10-16 mol·L-1 for the Fe(Ⅲ)-oxalate/sunlight system.

Recent Advances and Applications in Synchrotron X-Ray Protein Footprinting for Protein Structure and Dynamics Elucidation.

Synchrotron X-ray Footprinting is a powerful in situ hydroxyl radical labeling method for analysis of protein structure, interactions, folding and conformation change in solution. In this method, water is ionized by high flux density broad band synchrotron X-rays to produce a steady-state concentration of hydroxyl radicals, which then react with solvent accessible side-chains. The resulting stable modification products are analyzed by liquid chromatography coupled to mass spectrometry. A comparative reactivity rate between known and unknown states of a protein provides local as well as global information on structural changes, which is then used to develop structural models for protein function and dynamics. In this review we describe the XF-MS method, its unique capabilities and its recent technical advances at the Advanced Light Source. We provide a comparison of other hydroxyl radical and mass spectrometry based methods with XFMS. We also discuss some of the latest developments in its usage for studying bound water, transmembrane proteins and photosynthetic protein components, and the synergy of the method with other synchrotron based structural biology methods.

Correlating the chemical and spectroscopic characteristics of natural organic matter with the photodegradation of sulfamerazine

The role of aquatic natural organic matter (NOM) in the removal of contaminants of emerging concern has been widely studied. Sulfamerazine (SMR), a sulfonamide antibiotic detected in aquatic environments, is implicated in environmental toxicity and may contribute to the resistance of bacteria to antibiotics. In aquatic systems sulfonamides may undergo direct photodegradation, and, indirect photodegradation through the generation of reactive species. Because some forms of NOM inhibit the photodegradation there is an increasing interest in correlating the spectroscopic parameters of NOM as potential indicators of its degradation in natural waters.Under the conditions used in this study, SMR hydrolysis was shown to be negligible; however, direct photolysis is a significant in most of the solutions studied. Photodegradation was investigated using standard solutions of NOM: Suwannee River natural organic matter (SRNOM), Suwannee River humic acid (SRHA), Suwannee River fulvic acid (SRFA), and Aldrich humic acid (AHA). The steady-state concentrations and formation rates of the reactive species and the SMR degradation rate constants (k1) were correlated with NOM spectroscopic parameters determined using UV–vis absorption, excitation-emission matrix (EEM) fluorescence spectroscopy, and proton nuclear magnetic resonance (1H NMR).SMR degradation rate constants (k1) were correlated with steady-state concentrations of NOM triplet-excited state ([3NOM∗]ss) and the corresponding formation rates (3NOM*) for SRNOM, SRHA, and AHA. The efficiency of SMR degradation was highest in AHA solution and was inhibited in solutions of SRFA. The steady-state concentrations of singlet oxygen ([1O2]ss) and the SMR degradation rate constants with singlet oxygen (k1O2) were linearly correlated with the total fluorescence and inversely correlated with the carbohydrate/protein content (1H NMR) for all forms of NOM. The total fluorescence and EEMs Peak A were confirmed as indicators of 1O2 formation. Specific ultraviolet absorbance at 254 nm (SUVA254) and aromaticity showed potential correlations with the steady-state concentrations of hydroxyl radical ([HO]ss) and the corresponding formation rates (HO).

Reductive and oxidative degradation of iopamidol, iodinated X-ray contrast media, by Fe(III)-oxalate under UV and visible light treatment

Iopamidol, widely employed as iodinated X-ray contrast media (ICM), is readily degraded in a Fe(III)-oxalate photochemical system under UV (350 nm) and visible light (450 nm) irradiation. The degradation is nicely modeled by pseudo first order kinetics. The rates of hydroxyl radical (OH) production for Fe(III)-oxalate/H2O2/UV (350 nm) and Fe(III)-oxalate/H2O2/visible (450 nm) systems were 1.19 ± 0.12 and 0.30 ± 0.01 μM/min, respectively. The steady-state concentration of hydroxyl radical (OH) for the Fe(III)-oxalate/H2O2/UV (350 nm) conditions was 10.88 ± 1.13 × 10−14 M and 2.7 ± 0.1 × 10−14 M for the Fe(III)-oxalate/H2O2/visible (450 nm). The rate of superoxide anion radical (O2−) production under Fe(III)-oxalate/H2O2/UV (350 nm) was 0.19 ± 0.02 μM/min with a steady-state concentration of 5.43 ± 0.473 × 10−10 M. Detailed product studies using liquid chromatography coupled to Q-TOF/MS demonstrate both reduction (multiple dehalogenations) and oxidation (aromatic ring and side chains) contribute to the degradation pathways. The reduction processes appear to be initiated by the carbon dioxide anion radical (CO2−) while oxidation processes are consistent with OH initiated reaction pathways. Unlike most advanced oxidation processes the Fe(III)-oxalate/H2O2/photochemical system can initiate to both reductive and oxidative degradation processes. The observed reductive dehalogenation is an attractive remediation strategy for halogenated organic compounds as the process can dramatically reduce the formation of the problematic disinfection by-products often associated with oxidative treatment processes.

The role of effluent nitrate in trace organic chemical oxidation during UV disinfection

Most conventional biological treatment wastewater treatment plants (WWTPs) contain nitrate in the effluent. Nitrate undergoes photolysis when irradiated with ultraviolet (UV) light in the 200–240 and 300–325 nm wavelength range. In the process of nitrate photolysis, nitrite and hydroxyl radicals are produced. Medium pressure mercury lamps emitting a polychromatic UV spectrum including irradiation below 240 nm are becoming more common for wastewater disinfection. Therefore, nitrified effluent irradiated with polychromatic UV could effectively become a de facto advanced oxidation (hydroxyl radical) treatment process. UV-based advanced oxidation processes commonly rely on addition of hydrogen peroxide in the presence of UV irradiation for production of hydroxyl radicals. This study compares the steady-state concentration of hydroxyl radicals produced by nitrate contained in a conventional WWTP effluent to that produced by typical concentrations of hydrogen peroxide used for advanced oxidation treatment of water. The quantum yield of hydroxyl radical production from nitrate by all pathways was calculated to be 0.24 ± 0.03, and the quantum yield of hydroxyl radicals from nitrite was calculated to be 0.65 ± 0.06. A model was developed that would estimate production of hydroxyl radicals directly from nitrate and water quality parameters. In effluents with >5 mg-N/L of nitrate, the concentration of hydroxyl radicals is comparable to that produced by addition of 10 mg/L of H2O2. Nitrifying wastewater treatment plants utilizing polychromatic UV systems at disinfection dose levels can be expected to achieve up to 30% degradation of some micropollutants by hydroxyl radical oxidation. Increasing UV fluence to levels used during advanced oxidation could achieve over 95% degradation of some compounds.

Selective aerobic oxidation of para-xylene in sub- and supercritical water. Part 1. Comparison with ortho-xylene and the role of the catalyst

The selective, continuous, aerobic oxidations of para-xylene (pX) and ortho-xylene (oX) were performed in an identical fashion in supercritical water. The xylenes were oxidized without a catalyst and with hydrobromic acid, cobalt(II) and manganese(II) bromide catalysts. The conversions and yields to phthalic acid (OA) from oX were always significantly higher than those for terephthalic acid (TA) from pX. The formation of CO2 was significantly higher for pX than oX despite the higher conversions to oX. These results are unexpected because the literature teaches that thermal and catalytic decarboxylation is much higher for OA than TA. The superior yields from oX are consistent with a lower steady-state concentration of hydroxyl radicals, OH˙ due to the internal, concerted attack of the peroxides with the oX methyl group. This mechanism forms the phthalide directly from o-tolualdehyde (oTOL) which is consistent with the observation that ortho-toluic acid (OTA) is much lower in oX than para-toluic acid, PTA, in pX oxidation. This mechanism also lowers the steady-state concentration of aromatic acids consistent with the observed lower benzoic acid and CO2 yields. Overall, the results suggest that the metal catalysts can play more than one role, thereby opening up the opportunity for discovering new catalytic synergies which are explored in our next paper, Part 2 of this series.

Quantification of singlet oxygen and hydroxyl radicals upon UV irradiation of surface water

We measured the formation rate and the steady-state concentration of hydroxyl radicals and of singlet oxygen upon irradiation of lake water. There is controversy about the importance of singlet oxygen in the environmental photochemistry, but here we show that the steady-state concentration of 1O2 under irradiation can be higher by about two orders of magnitude compared to the hydroxyl radical. The higher occurrence of singlet oxygen in surface waters is mainly due to a higher rate of formation, because the transformation rate constants of 1O2 (collision with the solvent) and of ·OH (reaction with dissolved compounds) are comparable.

Disinfection of Secondary Effluents Using Tin Oxide Anodes

Direct current applied to a tin oxide anode submersed in water has the potential to generate hydroxyl radicals, a strong chemical oxidant. Tin oxide anode systems, which may represent a viable alternative disinfectant, were investigated for the disinfection of secondary effluents. Coliform bacteria in the effluent were effectively inactivated in a bench-scale tin oxide disinfection system. The number of anodes in the tin oxide disinfection system influenced the steady-state concentration of hydroxyl radicals and, consequently, the contact time necessary to achieve a specified dose. The life expectancy of the anodes was greater than 30 days and no appreciable loss of tin was observed over a 5-day period. A preliminary estimate of the capital and operating costs of a pilot- or full-scale tin oxide disinfection system designed to meet a discharge requirement of 23 most probable number/100 mL at a 3 785-m3/d (1-mgd) facility was comparable to UV and chlorination/dechlorination facilities. Based on this preliminary assessment, tin oxide disinfection systems are a promising alternative disinfectant for secondary effluents.

Hydroxyl Radical/Ozone Ratios During Ozonation Processes. I. The Rct Concept

The ozonation of model systems and several natural waters was examined in bench-scale batch experiments. In addition to measuring the concentration of ozone (O3), the rate of depletion of an in situ hydroxyl radical probe compound was monitored, thus providing information on the transient steady-state concentration of hydroxyl radicals (√OH). A new parameter, Rct , representing the ratio of the √OH-exposure to the O3-exposure was calculated as a function of reaction time. For most waters tested, including pH-buffered model systems and natural waters, Rct was a constant value for the majority of the reaction. Therefore, Rct corresponds to the ratio of the √OH concentration to the O3 concentration in a given water (i.e. Rct = [√OH]/[O3]). For a given water source, the degradation of a micropollutant (e.g. atrazine) via O3 and √OH reaction pathways can be predicted by the O3 reaction kinetics and Rct .

Formation of hydroxyl radical (·OH) in illuminated surface waters contaminated with acidic mine drainage

Formation rates and steady-state concentrations of hydroxyl radical (·OH) in illuminated surface water samples collected in west-central Indiana that receive acidic mine drainage runoff are reported. Formation rates for ·OH in samples were measured by the addition of 1 × 10−3 M benzene prior to illumination in order to effectively scavenge all of the ·OH formed, thereby yielding phenol. The ·OH formation rates were calculated from the measured phenol formation rates. Steady-state concentrations of ·OH were measured by the addition of 5 × 10−7 M nitrobenzene to the samples prior to illumination. Estimated sunlight ·OH formation rates range from 16 μM h−1 to 265 μM h−1. Estimated sunlight steady-state ·OH concentrations range from 6.7 × 10−15 to 4.0 × 10−12 M. Both the formation rates and steady-state concentrations for ·OH are thus two to three orders of magnitude higher than values reported in the literature for other sunlit surface water samples. Due to the very high rates of formation and steady-state concentrations for ·OH in these samples, we conclude that aqueous-phase reactions involving ·OH represent a significant pathway by which organic pollutants in illuminated surface waters receiving acidic mine drainage runoff may be consumed.

FORMATION OF HYDROXYL RADICAL (⋅OH) IN ILLUMINATED SURFACE WATERS CONTAMINATED WITH ACIDIC MINE DRAINAGE

Formation rates and steady-state concentrations of hydroxyl radical ({sup {sm_bullet}}OH) in illuminated surface water samples collected in west-central Indiana that receive acidic mine drainage runoff are reported. Formation rates for {sup {sm_bullet}}OH in samples were measured by the addition of 1 {times} 10{sup {minus}3} M benzene prior to illuminate in order to effectively scavenge all of the {sup {sm_bullet}}OH formed, thereby yielding phenol. The {sup {sm_bullet}}OH formation rates were calculated from the measured phenol formation rates. Steady-state concentrations of {sup {sm_bullet}}OH were measured by the addition of 5 {times} 10{sup {minus}7} M nitrobenzene to the samples prior to illumination. Estimated sunlight {sup {sm_bullet}}OH formation rates range from 16 {micro}M h{sup {minus}1} to 265 {micro}M h{sup {minus}1}. Estimated sunlight steady-state {sup {sm_bullet}}OH concentrations range from 6.7 {times} 10{sup {minus}15} to 4.0 {times} 10{sup {minus}12} M. Both the formation rates and steady-state concentrations for {sup {sm_bullet}}OH are thus two to three orders of magnitude higher than values reported in the literature for other sunlit surface water samples. Due to the very high rates of formation and steady-state concentrations for {sup {sm_bullet}}OH in these samples, the authors conclude that aqueous-phase reactions involving {sup {sm_bullet}}OH represent a significant pathway by which organic pollutants inmore » illuminated surface waters receiving acidic mine drainage runoff may be consumed.« less

鉄（ＩＩＩ）塩を用いる低沸点有機塩素化合物の光分解に関する研究

The study concerns the photodecomposition of volatile chlorohydrocarbons (VCs) with hydroxyl radical which derives from the photo-dissociation of Fe (III)-monohydroxy complex at acidic pH.The initial decomposition rate of chloroform (CF) with irradiation of a 500 W high-pressure mercury lamp at pH : 3.0 was smaller than those of trichloroethylene (TCE) and tetrachloroethylene (PCE). However, the conversion of organic chlorine of CF to chloride ion was larger than those of TCE and PCE. The generation rates of ferrous ion differed greatly, depending upon chlorohydrocarbons.The initial decomposition rates of PCE with irradiation of monochromatic light (313nm) were measured at pH : 3.0. The results were in good agreement with the kinetic model that assumed the steady-state concentration of hydroxyl radicals. The intermediate identified in the photodecomposition of PCE other than chloride ion was trichloroacetic acid (TCAA).

Kinetics of ferric ion promoted photodecomposition of 2-chlorophenol

The photodecomposition of 2-chlorophenol in ferric solutions at pH:3.0 was investigated using monochromatic light(313 nm). The concentrations of 2-chlorophenol were in the range of 5.0×10 −6 to 1.5×10 −4 mol·l −1. Above 5.0×10 −5 mol·l −1 of 2-chlorophenol concentration, it decreased linearly with irradiation time and the rates of photodecomposition were independent of the initial concentrations. Below 3.0×10 −5 mol·l −1 of 2-chlorophenol concentration, the initial rates of photodecomposition decreased with lowering the initial concentration of 2-chlorophenol. The results were in good agreement with the kinetic model that assumed the steady-state concentration of hydroxyl radical formed by photo-dissociation of Fe(III)-hydroxy complex. The rates of ferrous ion formation in the presence of 2-chlorophenol were larger than that in the absence of 2-chlorophenol.

Steady-state concentrations of hydroxyl radical in titanium dioxide aqueous suspensions

The method using n-butyl chloride as a probe was demonstrated to be useful to the measurement of the steady-state concentrations of hydroxyl radical in titanium dioxide aqueous suspensions. The dependence of the steady-state concentration of hydroxyl radical on the concentration of titanium dioxide was examined.