Destruction Of H2O2 Research Articles

Using flow-through reactor to enhance ferric ions electrochemical regeneration in electro-fenton for wastewater treatment

Electrochemical regeneration of ferric ions catches more and more attention since it could decrease iron sludge to avoid the sludge problem while it could simultaneously obtain similar robust removal efficiency to refractory organic contaminants in wastewater treatment as the normal Fenton agent method. However, the electrochemical regeneration of ferric ions in aqueous solution was very slow. In this paper, the mass transfer limit of ferric ions in electro-Fenton reaction was evaluated. Koutecky-Levich equation reveals an extremely low diffusion coefficient (D0) value of ferric ions since its complex coordination of [Fe(HO)x(H2O)6-x]3-x. The D0 value was only 2.70 × 10−6 cm2·s−1. Flow-through reactor was therefore introduced in which the ferric ions was designed to penetrate through the 73.1 μm porous holes in the graphite fiber electrode. The μm-scaled confinement of ferric ions diffusion inside the holes was proved to successfully enhance the reduction current of ferric ions by more than 200 % since the diffusion distance of the ferric ions was significantly decreased in the flow-through reactor. However, besides the benefit of the flow-through reactor, the ferric ions reduction electro-Fenton (FeRR electro-Fenton) in flow-through still faces both the pH limit and H2O2 decomposition problems. Hydrogen evolution reaction (HER) could also cause the decrease of pH which exceeded the optimal pH window for Fenton and therefore destroyed the electro-Fenton reaction consequently although the electrochemical reaction of FeRR was 770 mV prior to HER reaction. The regeneration of Fe (II) process simultaneous destruction of H2O2 since H2O2 e-reduction was 120 mV prior to FeRR reaction, which resulted in only very low H2O2 concentration suitable for FeRR electro-Fenton. Even using stepwise addition of H2O2 in electro-Fenton, the decomposition of H2O2 still could not be avoided. Although the decomposition of H2O2 quite limited the application of FeRR electro-Fenton in real application, FeRR electro-Fenton still supports the enhancement removal efficiency of the refractory organic contaminants under low organic contaminants application.

Abrasion of sedimentary rocks as a source of hydrogen peroxide and nutrients to subglacial ecosystems

Abstract. Glaciers and ice sheets are renowned for their abrasive power, yet little is known of the mechanochemical reactions which are initiated by abrasion in these environments and their effect on subglacial biogeochemistry. Here, we use sedimentary rocks representative of different subglacial environments and from a previously glaciated terrain, along with subglacial sediments, to investigate the potential for subglacial erosion to generate H2O2 and to release bio-utilisable organic carbon and nutrients (N, Fe). Samples were crushed using a ball mill, water was added to rock powders within gastight vials, and samples were incubated in the dark at 4 ∘C. Headspace and water samples were taken immediately after the addition of water and then again after 5 and 25 h. Samples generated up to 1.5 µmol H2O2 g−1. The total sulfur content, a proxy for the sulfide content, did not correlate with H2O2 generation, suggesting that the pyrite content was not the sole determinant of net H2O2 production. Other factors including the presence of carbonates, Fe-driven Fenton reactions and the pH of the solution were also likely to be important in controlling both the initial rate of production and subsequent rates of destruction of H2O2. Further, we found that erosion can provide previously unaccounted sources of bio-utilisable energy substrates and nutrients, including up to 880 nmol CH4 g−1, 680 nmol H2 g−1, volatile fatty acids (up to 1.7 µmol acetate g−1) and 8.2 µmolNH4+g-1 to subglacial ecosystems. These results highlight the potentially important role that abrasion plays in providing nutrient and energy sources to subglacial microbial ecosystems underlain by sedimentary rocks.

SUBSTANTIATION OF THE ELECTROLYTE COMPOSITION IN THE ELECTROCHEMICAL SYNTHESIS OF PEROXYLIC ACID

lactic acid (PLA) is a strong disinfectant with a wide spectrum of antimicrobial activity. Its widespread use is hampered by the lack of an electrochemical technology for PLA synthesis, which will make it possible to develop local electrochemical generators for the production of disinfectants. There is no information about the standard potential of the СН3СH(OH)С(=О)ОН « СН3СH(OH)С(=О)ООН system, both in reference literature and professional scientific publications. It has been shown that the electrochemical synthesis of PLA will be combined with the processes of oxygen release and the formation of hydrogen peroxide. To inhibit side processes, an additive to a solution of lactic acid 0.5 mol dm-3 H2SO4 was used. The adsorption of sulfate ions leads to the displacement of a certain proportion of water molecules outside the boundaries between the phase boundaries. An almost 2-fold increase in the anodic current density was also noted at the potentials of electrochemical synthesis of peroxide compounds. It has-been found that a lactic acid molecule is integrated into the structure of the near-electrode layer with a carboxyl group directed towards the anode surface. The inflection of the current-voltage curve, at potentials more positive than 1.70...1.75 V, indicates the course of the combined processes of the formation of peroxide compounds, proceeding with a significant inhibition of the oxygen reaction at the Pt/PtO2 anode. The release of oxygen under these conditions occurs due to the formation and destruction of H2O2. The potential difference between the forward and reverse runs of the current-voltage curve indicates a significant effect of lactic acid on the adsorption processes on the anode surface. The results obtained confirmed the relevant the choice of the Pt/PtO2 anode for the electrochemical synthesis of PLA. The characteristics of the electrolyte for the electrochemical synthesis of PLA has been defined: 2 mol dm-3 of lactic acid, 0.5 mol dm-3 of sulfuric acid.

Swift heavy ions irradiation of water ice at different temperatures: hydrogen peroxide and ozone synthesis and sputtering yield

ABSTRACT Water ices at 15 and 144 K were bombarded by swift heavy ions, 45.8 MeV 58Ni11 + and 606 MeV 64Zn26 +, to measure the induced chemical and physical effects. The column densities of water and the synthesized species, hydrogen peroxide (H2O2) and ozone (O3), were monitored via infrared spectroscopy. The formation and destruction cross-sections of precursor and products were determined and compared with literature. The H2O2 formation and destruction cross-sections reveal a linear dependence with electronic stopping power, σ ∝ Se. The sputtering yield (Y0) shows a power law with electronic energy lost, $Y_0\propto S_\mathrm{e}^2$, and an exponential increase with the sample temperature. The findings indicate that the radiolysis rate of water ice is higher at low temperatures while the desorption yield increases at higher temperatures. A large amount of water ice is located in the grain mantles of the circumstellar envelopes and the interstellar medium regions, which are exposed to galactic cosmic rays (GCRs). The synthesis of H2O2 and O3 molecules as a function of absorbed doses of GCR irradiation and their irradiation time is analysed in detail. Besides, the extrapolation of the sputtering yield rates, as a function of time and temperature, for astrophysical conditions can contribute to a better understanding of non-thermal sputtering of water ices.

Real-time мониторинг физиологических параметров для изучения раннего ответа бактерий Escherichia coli на пероксидный стресс

The response of aerobically growing Escherichia coli cultures to peroxide stress was studied using synchronous real-time monitoring of parameters pO2 (oxygen partial pressure), pH, Eh (redox potential of the culture), extracellular levels of K+ and S2-, in combination with traditional physiological, biochemical and genetic methods. A sharp increase in pO2 level in the medium caused by the destruction of H2O2 by endogenous catalases was observed in the early response to peroxide stress. The addition of 100 µM H2O2 provoked a reversible decrease in the specific growth rate, accompanied by an increase of extra- and intracellular glutathione and a short-term increase in sulfide production. Treatment with a high dose of H2O2 (10 mM) led to growth inhibition and a CFU loss, most pronounced in glutathione synthesis mutants. Simultaneously, in 8% of cells, the membrane potential decreased, a part of potassium was released into the medium, and the expression of the sulA gene, which is part of the SOS-regulon, increased. Application of an integrated approach to the study of stress revealed a close relationship between growth parameters (specific growth rate and survival), respiratory activity, sulfide production, and the ability of E. coli cells to maintain the membrane potential and K+ gradient.

SUBSTANTIATION OF THE ELECTROLYTE COMPOSITION IN THE ELECTROCHEMICAL SYNTHESIS OF PEROXYLIC ACID

lactic acid (PLA) is a strong disinfectant with a wide spectrum of antimicrobial activity. Its widespread use is hampered by the lack of an electrochemical technology for PLA synthesis, which will make it possible to develop local electrochemical generators for the production of disinfectants. There is no information about the standard potential of the СН3СH(OH)С(=О)ОН « СН3СH(OH)С(=О)ООН system, both in reference literature and professional scientific publications. It has been shown that the electrochemical synthesis of PLA will be combined with the processes of oxygen release and the formation of hydrogen peroxide. To inhibit side processes, an additive to a solution of lactic acid 0.5 mol dm-3 H2SO4 was used. The adsorption of sulfate ions leads to the displacement of a certain proportion of water molecules outside the boundaries between the phase boundaries. An almost 2-fold increase in the anodic current density was also noted at the potentials of electrochemical synthesis of peroxide compounds. It has-been found that a lactic acid molecule is integrated into the structure of the near-electrode layer with a carboxyl group directed towards the anode surface. The inflection of the current-voltage curve, at potentials more positive than 1.70...1.75 V, indicates the course of the combined processes of the formation of peroxide compounds, proceeding with a significant inhibition of the oxygen reaction at the Pt/PtO2 anode. The release of oxygen under these conditions occurs due to the formation and destruction of H2O2. The potential difference between the forward and reverse runs of the current-voltage curve indicates a significant effect of lactic acid on the adsorption processes on the anode surface. The results obtained confirmed the relevant the choice of the Pt/PtO2 anode for the electrochemical synthesis of PLA. The characteristics of the electrolyte for the electrochemical synthesis of PLA has been defined: 2 mol dm-3 of lactic acid, 0.5 mol dm-3 of sulfuric acid.

Understanding and modeling the formation and transformation of hydrogen peroxide in water irradiated by 254nm ultraviolet (UV) and 185nm vacuum UV (VUV): Effects of pH and oxygen.

Understanding ultraviolet photolysis induced by low pressure mercury lamp that emits both 254nm ultraviolet (UV254) and 185nm vacuum UV (VUV185) is currently challenging due to the copresence of multiple direct and indirect photochemical processes involving a series of highly-reactive radicals. Herein we examined the formation and transformation of H2O2 in water, which is both a precursor and a product of radicals, under various pH and dissolved oxygen (DO) conditions. The trends show that H2O2 increased rapidly at early stage and then remained steady in DO-rich water or declined somewhat in DO-poor water, ultimately leading to higher steady-state H2O2 in DO-rich water. The maximum H2O2 contents nonetheless were similar among waters with different DO, suggesting that H2O2 in this system was mostly generated by hydroxyl radical (OH) recombination, which is an oxygen-independent H2O2 formation pathway, rather than by reduced oxygen via hydrogen atom (H) or hydrated electron (eaq-), which is an oxygen-dependent pathway. Increasing pH (from 6.3 to 10.0) or bicarbonate dosage dramatically decreased H2O2 formation too. Mathematically, the fates of H2O2 as a function of pH, DO, and time were well modeled (R2≥0.92), in which the rates of H2O2 formation and destruction were greater in DO-poor water than those in DO-rich water. In addition, we found that the steady-state concentrations of OH used for degradation of p-chlorobenzoic acid, an OH probe, correlated well with the OH levels used for H2O2 formation (R2=0.98). These results hence may help better understand the UV/VUV process via H2O2 evolutions.

HULIS Enhancement of Hydroxyl Radical Formation from Fe(II): Kinetics of Fulvic Acid-Fe(II) Complexes in the Presence of Lung Antioxidants.

Oxidative stress mediated by reactive oxygen species (ROS) is a hypothesized mechanism for particulate-matter related health effects. Fe(II) is a key player in ROS formation in surrogate lung fluid (SLF) containing antioxidants. Humic-like substances (HULIS) in particulate matter such as biomass burning aerosol chelate Fe(II), but the effect on ROS formation in the presence of lung antioxidants is not known. We use Suwanee River Fulvic Acid (SRFA) as a surrogate for HULIS and investigate its effect on OH formation from Fe(II). For the first time, a chemical kinetics model was developed to explain behavior of Fe(II) and SRFA in SLF. Model and experimental results are used to find best-fit rate coefficients for key reactions. Modeling results indicate SRFA enhances Fe-mediated reduction of O2 to O2- and destruction of H2O2 to OH to 5.1 ± 1.5 and (4.3 ± 1.4) × 103 M-1 s-1 respectively. Best-fit rates for Citrate-Fe(II) mediated O2 to O2- and H2O2 to OH were 3.0 ± 0.7 and (4.2 ± 1.7) × 103 M-1 s-1 respectively. The kinetics model agrees with both the experimental results and thermodynamic model calculations of chemical speciation for 0 and 5 μg/mL SRFA, but both models are less successful at predicting further enhancements to OH formation at higher SRFA Concentrations.

On the selection of the anode material for the electrochemical removal of methylparaben from different aqueous media

Parabens are widely used industrial preservatives, routinely found in wastewater along with major inorganic ions like sulfate and chloride. This work investigates the oxidation ability of three electrochemical processes in tank reactors equipped with an air-diffusion cathode to electrogenerate H2O2 on site, namely electro-oxidation (EO-H2O2), electro-Fenton (EF) and UVA photoelectro-Fenton (PEF), to degrade aqueous solutions of methylparaben (MeP) at pH 3.0. Their performance using boron-doped diamond (BDD), Pt or two kinds of dimensionally stable anodes (DSA®) has been compared from the analysis of mineralization profiles and decay kinetics in the presence of sulfate and/or chloride ions. The use of BDD ensured the overall mineralization in all three processes according to the sequence: PEF>EF>EO-H2O2, thanks to the contribution of BDD(OH), OH and UVA light. Pt and DSA® became an interesting alternative in PEF, with slower organic matter removal but similar final mineralization percentages, being much less powerful than BDD in EO-H2O2. The presence of Cl− was beneficial in the latter process, due to the formation of active chlorine as an additional oxidant that caused a much faster decay of MeP. Conversely, it became significantly detrimental in EF due to the partial destruction of H2O2 and OH in the bulk by active chlorine and Cl−, respectively. The oxidation power of PEF was so high that similar fast, complex decay kinetics was found in all media regardless of the anode, although the mineralization was decelerated owing to the accumulation of chlorinated by-products. GC-MS and HPLC analysis allowed the identification of up to seven aromatic MeP derivatives in sulfate+chloride mixtures, including three non-chlorinated compounds also found in pure sulfate medium. These molecules were gradually transformed into oxalic acid, along with four chlorinated aliphatic carboxylic acids in Cl−-containing media.

Factors Influencing Hydrogenation and Decomposition of H2O2 Over Pd–Au Catalysts Supported on Activated Carbon Cloth (ACC)

The bimetallic Pd–Au catalysts were prepared by simultaneous co-impregnation or consequent impregnation of supports by palladium and gold precursors. The catalytic reactions were performed batch-wise in a Parr stainless steel autoclave and methanol (220 ml) was used as solvent. A series of experiments were conducted to study effects of several variables and conditions on the final H2O2 destruction activity of the catalysts. The factors studied where : the surface chemistry of the support, the amount and ratio of palladium and gold, the catalyst preparation method, the heat treatment of the catalysts in H2 and air, the reaction medium, and reaction temperature. As a conclusion, H2O2 destruction activities of the catalysts were strongly affected by the surface chemistry of the support and the amount and ratio of palladium and gold. Bimetallic catalysts prepared by co-impregnation of Pd and Au were less destructive than the corresponding ones prepared by consequent impregnation. The catalysts supported on activated carbon cloth (ACC) oxidized by nitric acid were considerably less destructive than the corresponding ones on non-oxidized ACC. H2O2 destruction activity of the catalysts on oxidized ACC were highly affected by the heat treatment in H2 and air at different temperatures. Using water instead of methanol as reaction medium substantially speeded up H2O2 destruction. Furthermore, increasing the reaction temperature accelerated destruction of H2O2. Catalytic destruction of H2O2 via its decomposition was considerably low as compared to hydrogenation.

Kinetic and mechanistic studies on direct H2O2 synthesis from H2 and O2 catalyzed by Pd in the presence of H+ and Br− in water: A comprehensive paper

The kinetic analysis of direct H2O2 synthesis from H2 and O2 in water over Pd catalysts was summarized on the basis of our recent studies, which included mass-transfer processes as well as concurrent and consecutive side reactions. The parameters examined for the synthesis were the dependencies on H2 and O2 partial pressures, the effects of H+ and Br− ions, the influence of the Pd particle size, and the effects of catalyst supports. The reaction mechanisms were discussed based on the above results, the kinetics of the H2O2 decomposition, the Br− adsorption on the Pd catalysts, and the DFT calculation using the cluster models. Structure-sensitive catalysis was indicated here: there were coordinatively more unsaturated sites (Site A) and less unsaturated ones (Site B), and H2O2 would be produced selectively on Site B, whereas the direct H2O formation and the destruction of H2O2 would take place more easily on Site A. The latter decreased with adsorption of H+ and Br− in pairs. The effect of supports was discussed from the viewpoint of their isoelectric points. The direct H2O2 synthesis under practical conditions was simulated using the above results, and several parameters were suggested to be improved.

Factors affecting catalytic destruction of H2O2 by hydrogenation and decomposition over Pd catalysts supported on activated carbon cloth (ACC)

Destruction of hydrogen peroxide by its decomposition and hydrogenation over Pd catalysts supported on activated carbon cloth has been investigated. The catalysts were prepared by the impregnation method using acidic solution of palladium dichloride (PdCl2) as a metal precursor. The reactions were performed batchwise in a Parr stainless steel autoclave. Tests were run at room temperature using either methanol or water as a reaction medium. The effects of oxidation pre-treatment of the support with different acids (nitric and acetic acid), the heat treatment of the catalysts in different atmospheres (H2 and air), and Pd content on the final properties and H2O2 destruction activity of the catalysts were investigated. The results indicated that oxygen-containing surface functional groups have an important role in determining the physicochemical properties and H2O2 destruction activity of the catalysts. In fact, the presence of these groups stabilizes H2O2 in the solution and reduces its decomposition and hydrogenation. Furthermore, the presence of the oxidized state of Pd (PdO) in the catalyst makes it less active in H2O2 decomposition when compared to the corresponding zero valences (Pd0) catalyst. Using water instead of methanol dramatically increased the H2O2 decomposition.

Photolysis of H2O–H2O2 mixtures: The destruction of H2O2

We present laboratory results on the loss of H2O2 in solid H2O+H2O2 mixtures at temperatures between 21 and 145K initiated by UV photolysis (193nm). Using infrared spectroscopy and microbalance gravimetry, we measured the decrease of the 3.5μm infrared absorption band during UV irradiation and obtained a photodestruction cross section that varies with temperature, being lowest at 70K. We use our results, along with our previously measured H2O2 production rates via ionizing radiation and ion energy fluxes from the spacecraft to compare H2O2 creation and destruction at icy satellites by ions from their planetary magnetosphere and from solar UV photons. We conclude that, in many cases, H2O2 is not observed on icy satellite surfaces because the H2O2 photodestruction rate is much higher than the production rate via energetic particles, effectively keeping the H2O2 infrared signature at or below the noise level.

Reactivity Aspects of SBA15-Based Doped Supported Catalysts: H2O2 Direct Synthesis and Disproportionation Reactions

Pd and PdAu catalysts supported on SBA15 and SiO2 were prepared and investigated for H2O2 direct synthesis in a batch autoclave (10 °C and 17.5 bar) and in the absence of halides and acids. The SiO2 supported catalysts exhibited inferior performances compared to the mesoporous ordered SBA15. A good control of both the catalysts dispersion and nanoparticle stability was achieved using SBA15. Catalysts were doped with bromine, a promoter in the H2O2 direct synthesis. Productivity and selectivity decreased when bromine was incorporated in the catalysts, thus indicating a possible poisoning due to the grafting process. A synergetic effect between Pd and Au was observed both in presence and absence of bromopropylsilane grafting on the catalyst surface. Three modifiers of the SBA15 support (Al, CeO2 and Ti) were chosen to elucidate the influence of the surface properties on metal dispersion and catalytic performance. Higher productivity and selectivity were achieved incorporating Al into the SBA15 framework, whereas neither Ti nor CeO2 improved H2O2 yields. The enhanced performance observed for the Prau/Al–SBA15 catalysts was attributed to the increased number of Bronsted acid sites. A modification of this catalyst with bromine was confirmed to impair both productivity and selectivity, possibly due to the broader particle size distribution and the poor stability of the metal nanoparticles, as demonstrate by transmission electron microscopy (TEM) images. H2O2 disproportionation was also investigated. A much slower reaction rate was observed compared to the H2O2 production, suggesting that the major contributor in the process of H2O2 destruction must be connected to the hydrogenation reaction.

Experimental and modeling study of the oxidation of n-butane in a jet stirred reactor using cw-CRDS measurements.

The gas-phase oxidation of n-butane has been studied in an atmospheric jet-stirred reactor (JSR) at temperatures up to 950 K. For the first time, continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared has been used, together with gas chromatography (GC), to analyze the products formed during its oxidation. In addition to the quantification of formaldehyde and water, which is always difficult by GC, cw-CRDS allowed as well the quantification of hydrogen peroxide (H2O2). A comparison of the obtained mole fraction temperature profiles with simulations using a detailed gas-phase mechanism shows a good agreement at temperatures below 750 K, but an overestimation of the overall reactivity above this temperature. Also, a strong overestimation was found for the H2O2 mole fraction at higher temperatures. In order to improve the agreement between model and experimental results, two modifications have been implemented to the model: (a) the rate constant for the decomposition of H2O2 (+M) ↔ 2OH (+M) has been updated to the value recently proposed by Troe (Combust. Flame, 2011, 158, 594-601) and (b) a temperature dependent heterogeneous destruction of H2O2 on the hot reactor walls with assumed rate parameters has been added. The improvement (a) slows down the overall reactivity at higher temperatures, but has a negligible impact on the maximal H2O2 mole fraction. Improvement (b) has also a small impact on the overall reactivity at higher temperatures, but a large effect on the maximal H2O2 mole fraction. Both modifications lead to an improved agreement between model and experiment for the oxidation of n-butane in a JSR at temperatures above 750 K.

Structure and Mechanism of Iron Translocation by a Dps Protein from Microbacterium arborescens

Dps (DNA protection during starvation) enzymes are a major class of dodecameric proteins that bacteria use to detoxify their cytosol through the uptake of reactive iron species. In the stationary growth phase of bacteria, Dps enzymes are primarily used to protect DNA by biocrystallization. To characterize the wild type Dps protein from Microbacterium arborescens that displays additional catalytic functions (amide hydrolysis and synthesis), we determined the crystal structure to a resolution of 2.05 Å at low iron content. The structure shows a single iron at the ferroxidase center coordinated by an oxo atom, one water molecule, and three ligating residues. An iron-enriched protein structure was obtained at 2 Å and shows the stepwise uptake of two hexahydrated iron atoms moving along channels at the 3-fold axis before a restriction site inside the channels requires removal of the hydration sphere. Supporting biochemical data provide insight into the regulation of this acylamino acid hydrolase. Moreover, the peroxidase activity of the protein was determined. The influence of iron and siderophores on the expression of acylamino acid hydrolase was monitored during several stages of cell growth. Altogether our data provide an interesting view of an unusual Dps-like enzyme evolutionarily located apart from the large Dps sequence clusters.

Decomposition of H2O2 at Dimensionally Stable Anode Electrodes and Its Effect on Aniline Oxidation

In the electro-Fenton process, through the chemical efficiency of H2O2 a high degradation of organic pollutants can be obtained. In this work, the decomposition of H2O2 at dimensionally stable anode (DSA) electrodes coated with IrO2, RuO2, and TiO2 prepared by thermal decomposition was investigated under two conditions: (a) no potential and (b) different potentials externally imposed. Results showed that the composition of electrodes, pH, potential had significant effects on the decomposition of H2O2. Both higher pH and higher potential could accelerate the decomposition of H2O2. In the electrolysis system with the DSA electrodes, decomposition of H2O2 involved two mechanisms: catalytic decomposition and electrochemical oxidation. Additionally, it was found that catalytic decomposition of H2O2 at the DSA electrode was inconsequential to the oxidation of aniline, and electrochemical oxidation of H2O2 was only slightly helpful to the oxidation of aniline. As the destruction of H2O2 caused by the DSA electrodes cannot be neglected in the electro-Fenton process, this work suggests that using the appropriate anodes as well as reasonable potential will lead to more H2O2 consumed by the Fenton reaction, which is beneficial for the degradation of organic compounds.

Kinetics and Simulation Including Mass-Transfer Processes of Direct H2O2 Synthesis from H2 and O2 over Pd/C Catalyst in Water Containing H+ and Br− Ions

Kinetic analysis including mass-transfer processes of the title reaction was carried out on the basis of the effects of the solution agitation rate, reaction time, and H2 and O2 partial pressures. The suggested equations were found to be in sufficient agreement with the experimental values. The reactions were then simulated to reveal the chemical engineering characteristics, as well as the process performance under practical reaction conditions. It follows that the reduction of the H2O2 destruction rate is highly desired and the mass-transfer coefficient of H2 (kLa) must be dramatically raised from 560 h−1, the value observed in the present experiments, for practical application of the technology. The effects of total pressure and other parameters are also discussed.

Influence of dissolved organic carbon on photochemically mediated cycling of hydrogen peroxide in rainwater

The influence of sunlight and dissolved organic carbon (DOC) on the photochemically mediated cycling of hydrogen peroxide (H2O2) was investigated in rainwater samples collected in Wilmington, North Carolina USA. Upon exposure to simulated sunlight 14 of 19 authentic rainwater samples exhibited significant decreases in H2O2. The concentration of hydrogen peroxide did not change significantly in organic-free synthetic rainwater spiked with H2O2 in the light or in dark controls suggesting that the loss was not due to direct photolysis or dark mediated reactions. There was a significant correlation between pseudo-first order rate constants of H2O2 decay and initial H2O2 concentrations. There was also a significant correlation between the rate constant and the abundance of DOC suggesting that rainwater organic carbon plays an important role during photolytic decay either via direct reaction or indirectly through production of peroxide reactive species or scavenging of peroxide generating radicals. Several rain samples exhibited an initial increase in H2O2 during the first 2 h of irradiation. These increases were generally small and most likely do not represent a significant input of peroxide in precipitation. The photo-induced destruction of H2O2 is important because it may partly explain the late afternoon decrease of peroxide concentrations observed in earlier field studies and the substantial under saturation (<10%) of this oxidant in rainwater compared with gas phase concentrations.

Effect of H2SO4 and HCl in the anode purging solution for the electrokinetic-Fenton remediation of soil contaminated with phenanthrene

The Electrokinetic-Fenton (EK-Fenton) process is a powerful technology to remediate organic-contaminated soil. The behavior of salts and acids introduced for the pH control has significant influence on the H2O2 stabilization and destruction of organic contaminants. In this study, the effects of the type and concentration of acids, which were introduced at the anode, were investigated for the treatment of clayey soil contaminated with phenanthrene. In experiments with H2SO4 as the anode solution, H2O2 concentration in the anode reservoir decreased due to reaction between reduced species of sulfate and H2O2, as time elapsed. By contrast, HCl as an electrolyte in the anode reservoir did not decrease the H2O2 concentration in the anode reservoir. The reaction between the reduced species of sulfate and H2O2 hindered the stabilization of H2O2 in the soil and anode reservoir. In experiments with HCl for pH control, Cl·, and Cl2 · −, which could be generated with mineral catalyzed Fenton-like reaction, did not significantly hinder H2O2 stabilization. H2O2 transportation with electro-osmotic flow and mineral catalyzed Fenton-like reaction on the soil surface resulted in the simultaneous transport and degradation of phenanthrene, which are dependent of the advancement rate of the acid front and electro-osmotic flow toward the cathode according to HCl and H2SO4 concentrations in the anode purging solution.