Effect of some parameters on the rate of the catalysed decomposition of hydrogen peroxide by iron(III)-nitrilotriacetate in water

The decomposition rate of H₂O₂ by iron(III)-nitrilotriacetate complexes (Fe^IIINTA) has been investigated over a large range of experimental conditions: 3 < pH < 11, [Fe(III)]_T,0: 0.05-1 mM; [NTA]_T,0/[Fe(III)]_T,0 molar ratios : 1-250; [H₂O₂]₀: 1 mM-4 M) and concentrations of HO radical scavengers: 0-53 mM. Spectrophotometric analyses revealed that reactions of H₂O₂ with Fe^IIINTA (1 mM) at neutral pH immediately lead to the formation of intermediates (presumably peroxocomplexes of Fe^IIINTA) which absorb light in the region 350-600 nm where Fe^IIINTA and H₂O₂ do not absorb. Kinetic experiments showed that the decomposition rates of H₂O₂ were first-order with respect to H₂O₂ and that the apparent first-order rate constants were found to be proportional to the total concentration of Fe^IIINTA complexes, were at a maximum at pH 7.95 ± 0.10 and depend on the [NTA]_T,0/[Fe(III)]_T,0 and [H₂O₂]₀/[Fe(III)]_T,0 molar ratios. The addition of increasing concentrations of tert-butanol or sodium bicarbonate significantly decreased the decomposition rate of H₂O₂, suggesting the involvement of HO radicals in the decomposition of H₂O₂. The decomposition of H₂O₂ by Fe^IIINTA at neutral pH was accompanied by a production of dioxygen and by the oxidation of NTA. The degradation of the organic ligand during the course of the reaction led to a progressive decomplexation of Fe^IIINTA followed by a subsequent precipitation of iron(III) oxyhydroxides and by a significant decrease in the catalytic activity of Fe(III) species for the decomposition of H₂O₂.     

Effect of hydrogen peroxide on the decomposition of monochlorophenols by sonolysis in aqueous solution

The decomposition rates of several monochlorophenol by sonolysis were enhanced by the presence of hydrogen peroxide. An optimum concentration of hydrogen peroxide was observed for achieving maximum sonolysis rate of monochlorophenol. The decomposition rates of 3-chlorophenol by sonolysis were higher than those for 2- and 4-chlorophenol for most experiments conducted, suggesting that the ring structure of 3-chlorophenol provides more sites available for free radical attack. The temporal decomposition behavior of monochlorophenol in aqueous solutions is markedly influenced by the species distribution and the volatility of specific monochlorophenol.     

Hydroxyl radical involvement in the decomposition of hydrogen peroxide by ferrous and ferric-nitrilotriacetate complexes at neutral pH

The relative rates of degradation of three hydroxyl radical probe compounds (atrazine, fenuron and parachlorobenzoic acid (pCBA)) by Fe^III/H₂O₂ (pH = 2.85), Fe^IIINTA/H₂O₂ (neutral pH), Fe^II/O₂, Fe^IINTA/O₂, Fe^II/H₂O₂ and Fe^IINTA/H₂O₂ (neutral pH) have been investigated using the competitive kinetic method. Experiments were carried out in batch and in semi-batch reactors, in the dark, at 25 °C. The data showed that the three probe compounds could be degraded by all the systems studied, and in particular by Fe^IINTA/H₂O₂ and Fe^IIINTA/H₂O₂ at neutral pH. The relative rate constants of degradation of the three probe compounds obtained for all the systems tested were identical and equal to 1.45 ± 0.03 and 0.47 ± 0.02 for k_Atrazine/k_pCBA and k_Fenuron/k_pCBA, respectively. These values as well as the decrease of the rates of degradation of the probe compounds upon the addition of hydroxyl radical scavengers (tert-butanol, bicarbonate ions) suggest that the degradation of atrazine, fenuron and pCBA by Fe^IINTA/O₂, Fe^IINTA/H₂O₂ and Fe^IIINTA/H₂O₂ is initiated by hydroxyl radicals.     

Investigation of the kinetics of catalytic decomposition of hydrogen peroxide depending on the solution phase state

We have investigated the kinetic curves of hydrogen peroxide decomposition of copper chloride and potassium bichromate. It has been shown that depending of the pH value and the phase state of the solution the decomposition rate may vary tens of times. We have conducted a theoretical analysis and modeling of obtained regularities.     

Evaluation of the treatment performance of a multistage ozone/hydrogen peroxide process by decomposition by-products

The performance of a multistage ozone/hydrogen peroxide (O3/H2O2) process was evaluated with respect to total organic carbon (TOC) removal of waste waters. An aqueous humic acid solution (5.2 mgC l(-1) as TOC) and a sand filtered secondary sewerage effluent (5.6mgC l(-1) as TOC) were used as model waste waters. Appropriate range of hydrogen peroxide (H2O2) dose at each stage depended upon the components of the tested solutions that changed as the process proceeded. Higher hydrogen peroxide dose was required at later stages in which low reactivity compounds with hydroxyl radical (HO*), low molecular fatty acids, were predominant. And, oxalic acid concentration related to H2O2 demand at later stages. This was assumed that the slow decomposition of oxalic acid was rate-determining step for TOC removal after its accumulation. Also, it is important to maintain dissolved ozone at low concentration for efficient TOC removal because rapid ozone consumption is required for the rapid formation of hydroxyl radical (HO*).     

Photocatalytic destruction of anionic SAS with oxygen and hydrogen peroxide in the TiO2 suspension

The articles gives a comparison of the rates and the degree of destruction of anionic SAS-alkyl benzene sodium sulfonate (ABS) in heterogeneous (O₂/TiO₂/UV, H₂O₂/TiO₂/UV) and homogeneous (O₂/UV, H₂O₂/UV) oxidizing systems on several TiO₂ samples at UV irradiation by a SVD-120 high-pressure mercury-quartz lamp. The paper has demonstrated a possibility of achieving a high degree of photocatalytic destruction of ABS by hydrogen peroxide (100, 90, and 80% respectively by the ABS concentration of ABS, COD, and TOC over two hours).     

Detoxification of phenolic solutions with horseradish peroxidase and hydrogen peroxide

Phenolic solutions were treated with hydrogen peroxide and horseradish peroxidase (HRP) resulting in more than 95% removal of phenols within 3 h. Toxic compounds were formed during the treatment of aqueous solutions of phenol, 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol and 2-methylphenol. However, the toxicities of HRP-treated solutions decreased within 21 h after the completion of the enzymatic reaction, except in the case of 2-methylphenol. The process of detoxification was significantly accelerated upon the addition of hydrogen peroxide to the dephenolized solutions. Solutions that were treated in the presence of chitosan exhibited lower toxicities than solutions treated in its absence if they were allowed to incubate for an extended period of time. Treatment in the presence of polyethylene glycol resulted in significantly higher toxicities. The toxicity of treated solutions was dependent on the addition mode of HRP and hydrogen peroxide. Treated solutions were also completely detoxified following illumination with UV light.     

微量Fe3+对过氧化氢热分解爆炸的影响

采用加速量热仪(ARC)对含微量Fe3+的30%H2O2进行热危险性分析,并与30%H2O2的热分解过程进行对比。结果表明:微量Fe3+的存在对H2O2的分解有一定的催化作用,能降低其低温分解活化能,使其在较低温度下发生缓慢的分解反应,从而导致H2O2浓度逐渐降低,并使随后的绝热自分解反应变慢、完全分解时间变长、分解过程中产生的压升速率和温升速率变低。但是,在相同绝热分解温度下,含微量Fe3+的H2O2分解压力高于纯H2O2的分解压力。     

Zero-valent iron reduction of nitrate in the presence of ultraviolet light,organic matter and hydrogen peroxide

This paper describes the use of metallic iron (Fe(0)) powder for nitrate removal in a well-mixed batch reactor. Important variables explored include Fe(0) dosage (1-3g/L), UV light intensity (64-128 W), and the presence of propanol (20 mg/L as DOC) and H(2)O(2) (100-200 mg/L). Accumulation of ferrous ions released from the Fe(0) surface can be expressed by an S-curve, which involves lag growth phase, exponential phase, rate-declining phase, and saturation phase. The removal of nitrate increases with increasing Fe(0) dosage; however, the removal makes no difference as the Fe(0) dosage is greater than 2 g/L. UV irradiation retards the dissolution of ferrous ion and the removal of nitrate. The species of propanol, which has a functional group of -OH, plays a role of organic inhibitor for Fe(0) corrosion. The presence of H(2)O(2) appears to inactivate all reactions as the Fe(0) of 10 microm was used; the final H(2)O(2) remains intact throughout the entire reaction period, and there were no removal of nitrate and no dissolution of ferrous ion. Surprisingly, with the use of a larger Fe(0) particle size of 150 microm, the H(2)O(2) was seen to decompose rapidly through Fenton reaction. Nevertheless, the rate of ferrous accumulation or nitrate removal is slow.     

Structural and sorption properties of activated carbon modified with iron oxides

The structural and sorption characteristics of activated carbon modified with iron oxides were investigated and static exchange capacity of its surface functional groups of basic and acidic nature was determined. The modification of carbon with iron oxides was found to result in insignificant (7–13%) reduction of micropore and mesopore volume and in basification increase of the sorbent surface. The modified activated carbon is highly efficient in removing phenolic compounds from water.     

The use of hydrous iron (III) oxides for the removal of hydrogen sulphide in aqueous systems

The potential for iron (hydr)oxides to remove dissolved hydrogen sulphide from seawater has been examined under flow-through conditions. Ferrihydrite (a hydrous iron (III) oxide) was stabilised by precipitation onto zeolite pellets, and rates of sulphide removal were determined under laboratory conditions at pH 8.5. Sulphide removal kinetics were dependent on the initial sulphide concentration, substrate mass and flow rate. The experimental data suggest that these parameters can be optimised to result in the rapid and effective removal of hydrogen sulphide. The results from laboratory experiments compared favourably with sulphide removal kinetics determined in a series of experiments performed online in a recirculating mariculture production system. However, the presence in solution of ligands such as phosphate may also significantly affect reaction rates; a 50% reduction in sulphide removal rate for substrate removed from an online system was partly attributed to phosphate adsorption. The formation of a more crystalline, less reactive iron (hydr)oxide in recharged substrate was the likely result of FeS oxidation, which may also have contributed to the observed reduction in sulphide removal rates. Ferrihydrite-coated zeolite would appear to provide an efficient, low-cost method for sulphide removal, which is particularly suited to relatively small-scale aqueous flow-through systems. The reaction of iron (hydr)oxides with dissolved sulphide is also accompanied by a distinct colour change due to the formation of black FeS(s) which, under appropriate conditions, may be used as a rapid indicator of sulphidic conditions.     

过氧化氢预氧化复合高岭土去除水中颤藻的研究

研究了H2O2预氧化复合高岭土混凝工艺对水中颤藻的去除效果。结果表明,H2O2具有显著氧化抑制藻活性的功能,高岭土则具有良好的助凝作用,经H2O2预氧化复合高岭土混凝后形成的絮体大而密实,沉降速度更快。试验得出最佳复配条件为:原水pH值为7,预氧化时间为20 min,H2O2、高岭土和PAC的投加量分别为3,34和3.5 mg/L。在该最佳试验条件下,浊度和叶绿素a去除率分别达到95.6%和97.8%,残留铝含量为0.13 mg/L。     

Catalytic oxidation and decomposition of CH2Cl2 on supported CrO3 at low temperature

CrO₃ supported on porous carbonaceous adsorbent and γ‐alumina was used between 200 and 400 °C to oxidise CH₂Cl₂. The following parameters were studied in a fixed bed integral reactor: type of support, temperature, spatial rates and amounts of CH₂ Cl₂ in air. The kinetic study of the reaction revealed an order one with respect to CH₂ Cl₂ and a Mars‐Van Krevelen mechanism appeared quite satisfactory for explaining the experimental results. Conversions of CH₂Cl₂ as high as 99% were achieved at 340°C on CrO₃/γ‐Al₂O₃ at concentration up to 15000 ppm CH₂Cl₂ in air.     

Biodegradation of monoaromatic hydrocarbons in aquifer columns amended with hydrogen peroxide and nitrate

The ability of indigenous microorganisms to degrade benzene, toluene, ethylbenzene and xylenes (BTEX) in laboratory scale flow-through aquifer columns was tested separately with hydrogen peroxide (110 mg/l) and nitrate (330 mg/l as NO₃⁻) amendments to air-saturated influent nutrient solution. The continuous removal of individual components from all columns relative to the sterile controls provided evidence for biodegradation. In the presence of hydrogen peroxide, the indigeneous microorganisms degraded benzene and toluene (> 95%), meta- plus para-xylene (80%) and ortho-xylene (70%). Nitrate addition resulted in 90% removal of toluene and 25% removal of ortho-xylene. However, benzene, ethylbenzene, meta- and para-xylene concentrations were not significantly reduced after 42 days of operation. Following this experiment, low dissolved oxygen (< 1 mg/l) conditions were initiated with the nitrate-amended column influent in order to mimic contaminated groundwater conditions distal from a nutrient injection well. Toluene continued to be effectively degraded (> 90%), and more than 25% of the benzene, 40% of the ethylbenzene, 50% of the meta- plus para-xylenes and 60% of the ortho-xylene were removed after several months of operation.     

Micellar effect on the photolysis of hydrogen peroxide

Photolysis experiments were performed to quantify the effect of three anionic surfactants on the photolysis of hydrogen peroxide (H2O2) at the ambient laboratory temperature of 22+/-1 degrees C. H2O2 photolysis in water, methanol, and surfactant monomeric solution was also conducted to compare the photochemical reactivity of H2O2 in different media. Photolysis rates were highest for water, followed by micellar solutions, and lowest for methanol. The results show that the photochemical reactivity of H2O2 is less favorable in organic solvent than in water and surfactant micelles affect H2O2 photolysis. Retarded photolysis of H2O2 in micellar solutions implies that a fraction of H2O2 dissolved in water partitions into micellar pseudophase of surfactant. H2O2 partitioned into micelles has less photochemical reactivity and thus photolysis rate was retarded in the presence of micelles. Photolysis inhibitory level by micelles was shown to be dependent on the kinds of surfactants used in this study. In addition, the inhibitory effect by surfactant monomers was negligible due to the absence of micelles.     

Selective suppression of harmful cyanobacteria in an entire lake with hydrogen peroxide

Although harmful cyanobacteria form a major threat to water quality, few methods exist for the rapid suppression of cyanobacterial blooms. Since laboratory studies indicated that cyanobacteria are more sensitive to hydrogen peroxide (H₂O₂) than eukaryotic phytoplankton, we tested the application of H₂O₂ in natural waters. First, we exposed water samples from a recreational lake dominated by the toxic cyanobacterium Planktothrix agardhii to dilute H₂O₂. This reduced the photosynthetic vitality by more than 70% within a few hours. Next, we installed experimental enclosures in the lake, which revealed that H₂O₂ selectively killed the cyanobacteria without major impacts on eukaryotic phytoplankton, zooplankton, or macrofauna. Based on these tests, we introduced 2 mg L⁻¹ (60 μM) of H₂O₂ homogeneously into the entire water volume of the lake with a special dispersal device, called the water harrow. The cyanobacterial population as well as the microcystin concentration collapsed by 99% within a few days. Eukaryotic phytoplankton (including green algae, cryptophytes, chrysophytes and diatoms), zooplankton and macrofauna remained largely unaffected. Following the treatment, cyanobacterial abundances remained low for 7 weeks. Based on these results, we propose the use of dilute H₂O₂ for the selective elimination of harmful cyanobacteria from recreational lakes and drinking water reservoirs, especially when immediate action is urgent and/or cyanobacterial control by reduction of eutrophication is currently not feasible. A key advantage of this method is that the added H₂O₂ degrades to water and oxygen within a few days, and thus leaves no long-term chemical traces in the environment.     

Accelerated reoxygenation of water bodies using hydrogen peroxide

This paper reports a laboratory study of an accelerated reoxygenation treatment of polluted water bodies, using hydrogen peroxide (H₂O₂): conditions such as the discharge of waters from domestic sewers or polluted storm-water resulting from intense rainfall that lead to a reduction in the level of dissolved oxygen (DO). We studied the water from rivers that make up the basin of the Lagoa Rodrigo de Freitas (LRF) lagoon, Rio de Janeiro, Brazil. When intense rainfall coincides with discharge from sewers, the polluted water may reach LRF. This has in the past led to episodes of critical deficit in DO in the waters of the lagoon, resulting in fish kill. To study this, we carried out experiments with water samples taken from the river feeding the lagoon. To study the accelerated reoxygenation of the river waters, we used different doses of H₂O₂. We concluded that the addition of H₂O₂ to the waters of the river during polluting events can prevent the level of DO in the lagoon going below a critical value. This treatment resulted in an immediate increase in DO that lasted hours and in the sustainability of the DO above the legal limit 5.0 mg L^?1, enough to avoid fish kill.     

Treatment of a foul condensate from Kraft pulping with horseradish peroxidase and hydrogen peroxide

Foul condensates originating from the Kraft recovery process contain phenolic compounds whose removal might render these process streams more useful for reuse in other plant operations or more amenable to biological degradation. Treatment of a foul condensate with horseradish peroxidase and H2O2 selectively targeted phenolic compounds resulting in a reduction of the total phenols concentration below 1 mg/L as well as a substantial toxicity drop as measured using the Microtox assay; however, only marginal COD removal was achieved. Comparisons of treatments between synthetic wastewaters and real wastewaters to which phenol were added revealed that the condensate contained species that protect the enzyme from inactivation by reaction products. Analytical data as well as experimental results suggest that these species are lignin derivatives.     

过氧化氢热爆炸危险性研究

为防止过氧化氢在生产、贮存和运输中爆炸事故的发生，采用绝热量热实验方法模拟过氧化氢的放热分解过程。研究结果表明过氧化氢绝热初始分解温度为34．5℃。反应热301J／g，最高温升速率为35℃／min，最大单位质量爆炸压力为1．7MPa／g，具有显著的热爆炸危险性。根据绝热分析结果，对过氧化氢储罐进行了冷却计算。     

Removal of phosphorus from solution using biogenic iron oxides

Phosphorus removal by biogenic iron oxides was investigated, providing an initial characterization of a potentially regenerable iron-rich sorbent. The biogenic iron oxides were collected from a wetland ecosystem and were dominated by the sheaths of Leptothrix ochracea. Sorption kinetics followed a pseudo-1st order model (R² = 0.998) with a rate constant of 0.154 ± 0.013 h⁻¹. The Langmuir isotherm adequately described sorption for all samples (R² = 0.923-0.981); the Freundlich model was a better fit for only one of four samples. Maximum phosphorus sorption estimated using the Langmuir parameter ranged from 46.9 ± 2.9 to 165.0 ± 21.2 mg P/g Fe and was similar to other iron-rich substrates. Maximum sorption normalized to total solids ranged from 10.8 ± 0.7 to 39.9 ± 3.2 mg P/g, which represented the highest published values for iron-rich substrates. The high sorption capacity with respect to both iron and solids warrants further evaluation of biogenic iron oxides as a substrate for phosphorus removal.