Evidence for simultaneous abiotic-biotic oxidations in a microbial-Fenton's system

The conditions that support the simultaneous activity of hydroxyl radicals (OH.) and heterotrophic aerobic bacterial metabolism were investigated using two probe compounds: (1) tetrachloroethene (PCE) for the detection of OH. generated by an iron-nitrilotriacetic acid (Fe-NTA) catalyzed Fenton-like reaction and (2) oxalate (OA) for the detection of heterotrophic metabolism of Xanthobacter flavus. In the absence of the bacterium in the quasi-steady-state Fenton's system, only PCE oxidation was observed; conversely, only OA assimilation was found in non-Fenton's systems containing X. flavus. In combined Fenton's-microbial systems, loss of both probes was observed. PCE oxidation increased and heterotrophic assimilation of OA declined as a function of an increase in the quasi-steady-state H2O2 concentration. Central composite rotatable experimental designs were used to determine the conditions that provide maximum simultaneous abiotic-biotic oxidations, which were achieved with a biomass level of 10(9) CFU/mL, 4.5 mM H2O2, and 2.5 mM Fe-NTA. These results demonstrate that heterotrophic bacterial metabolism can occur in the presence of hydroxyl radicals. Such simultaneous abiotic-biotic oxidations may exist when H2O2 is injected into the subsurface as a microbial oxygen source or as a source of chemical oxidants. In addition, hybrid abiotic-biotic systems could be used for the treatment of waters containing biorefractory organic contaminants present in recycle water, cooling water, or industrial waste streams.     

Iron-catalyzed oxidation of arsenic(III) by oxygen and by hydrogen peroxide: pH-dependent formation of oxidants in the Fenton reaction

The oxidation kinetics of As(III) with natural and technical oxidants is still notwell understood, despite its importance in understanding the behavior of arsenic in the environment and in arsenic removal procedures. We have studied the oxidation of 6.6 microM As(II) by dissolved oxygen and hydrogen peroxide in the presence of Fe(II,III) at pH 3.5-7.5, on a time scale of hours. As(III) was not measurably oxidized by O2, 20-100 microM H2O2, dissolved Fe(III), or iron(III) (hydr)-oxides as single oxidants, respectively. In contrast, As(III) was partially or completely oxidized in parallel to the oxidation of 20-90 microM Fe(II) by oxygen and by 20 microM H2O2 in aerated solutions. Addition of 2-propanol as an *OH-radical scavenger quenched the As(III) oxidation at low pH but had little effect at neutral pH. High bicarbonate concentrations (100 mM) lead to increased oxidation of As-(III). On the basis of these results, a reaction scheme is proposed in which H2O2 and Fe(II) form *OH radicals at low pH but a different oxidant, possibly an Fe(IV) species, at higher pH. With bicarbonate present, carbonate radicals might also be produced. The oxidant formed at neutral pH oxidizes As(III) and Fe(II) but does not react competitively with 2-propanol. Kinetic modeling of all data simultaneously explains the results quantitatively and provides estimates for reaction rate constants. The observation that As(III) is oxidized in parallel to the oxidation of Fe(II) by O2 and by H2O2 and that the As(III) oxidation is not inhibited by *OH-radical scavengers at neutral pH is significant for the understanding of arsenic redox reactions in the environment and in arsenic removal processes as well as for the understanding of Fenton reactions in general.     

Shelf life of beef from local Spanish cattle breeds stored under modified atmosphere

Beef steaks from six Spanish cattle breeds (Asturiana de los Valles, Morucha, Parda Alpina, Pirenaica, Rubia Gallega and Retinta) were packaged under modified atmosphere (60% O(2), 30% CO(2) and 10% N(2)). Water loss, pH, thiobarbituric acid values (TBA), aerobic plate counts, lactic acid bacteria and Enterobacteriaceae counts, CIE L*a*b* colour values and the sensory properties of odour and colour were recorded before packaging (day 0) and after 5, 10 and 15 days of storage. A significant interaction (P<0.05) between breed and storage time was found for all variables, except water loss. Values of pH were between 5.3 and 5.6; maximum water loss (2.64%) was reached after 10 days of storage; aerobic plate counts, lactic acid bacteria and Enterobacteriacea counts were lower than 10(7) CFU/g, and L* increased with storage time while a* decreased (P<0.05). The maximum shelf life of beef assessed by sensory evaluation (regarding colour and odour degradation) was between days 5 and 10 in meat from Retinta breed and between days 10 and 15 in meat from the other breeds, shelf life was probably limited by lipid oxidation.     

pH dependence of Fenton reagent generation and As(III) oxidation and removal by corrosion of zero valent iron in aerated water

Corrosion of zerovalent iron (ZVI) in oxygen-containing water produces reactive intermediates that can oxidize various organic and inorganic compounds. We investigated the kinetics and mechanism of Fenton reagent generation and As(III) oxidation and removal by ZVI (0.1m2/g) from pH 3-11 in aerated water. Observed half-lives for the oxidation of initially 500 microg/L As(III) by 150 mg Fe(0)/L were 26-80 min at pH 3-9. At pH 11, no As(III) oxidation was observed during the first two hours. Dissolved Fe(III) reached 325, 140, and 6 microM at pH 3, 5, and 7. H2O2 concentrations peaked within 10 min at 1.2, 0.4, and < 0.1 microM at pH 3, 5, and 7, and then decreased to undetectable levels. Addition of 2,2'-bipyridine (1-3 mM), prevented Fe(II) oxidation by O2 and H2O2 and inhibited As(III)oxidation. 2-propanol (14 mM), scavenging OH-radicals, quenched the As(III) oxidation at pH 3, but had almost no effect at pH 5 and 7. Experimental data and kinetic modeling suggest that As(III) was oxidized mainly in solution by the Fenton reaction and removed by sorption on newly formed hydrous ferric oxides. OH-radials are the main oxidant for As(III) at low pH, whereas a more selective oxidant oxidizes As(III) at circumneutral pH.     

Oxidation of sulfoxides and arsenic(III) in corrosion of nanoscale zero valent iron by oxygen: evidence against ferryl ions (Fe(IV)) as active intermediates in Fenton reaction

Previous studies have shown that the corrosion of zerovalent iron (ZVI) by oxygen (O(2)) via the Fenton reaction can lead to the oxidation of various organic and inorganic compounds. However, the nature of the oxidants involved (i.e., ferryl ion (Fe(IV)) versus hydroxyl radical (HO(?))) is still a controversial issue. In this work, we reevaluated the relative importance of these oxidants and their role in As(III) oxidation during the corrosion of nanoscale ZVI (nZVI) in air-saturated water. It was shown that Fe(IV) species could react with sulfoxides (e.g., dimethyl sulfoxide, methyl phenyl sulfoxide, and methyl p-tolyl sulfoxide) through a 2-electron transfer step producing corresponding sulfones, which markedly differed from their HO(?)-involved products. When using these sulfoxides as probe compounds, the formation of oxidation products indicative of HO(?) but no generation of sulfone products supporting Fe(IV) participation were observed in the nZVI/O(2) system over a wide pH range. As(III) could be completely or partially oxidized by nZVI in air-saturated water. Addition of scavengers for solution-phase HO(?) and/or Fe(IV) quenched As(III) oxidation at acidic pH but had little effect as solution pH increased, highlighting the importance of the heterogeneous iron surface reactions for As(III) oxidation at circumneutral pH.     

Kinetic model for Fe(II) oxidation in seawater in the absence and presence of natural organic matter

A detailed kinetic model has been developed to describe the oxidation of Fe(II) in seawater in both the absence and the presence of natural organic material. Experimental data were collected using a luminol chemiluminescence-based method to measure Fe(II), assuming that both the inorganic and the organically complexed species were detected. In the absence of organic matter, the data were modeled based on the Haber-Weiss mechanism with the inclusion of a back-reaction of Fe(III) with superoxide and precipitation of Fe(OH)3. Both reactions were found to be significant using sensitivity analysis. When organic matter is present, the model was extended by organic complexation of Fe(II) and Fe(III) with the creation of a parallel oxidation pathway for Fe(II). Fe(II) oxidation at natural (nanomolar) concentrations was accurately predicted for a range of organic concentrations. The model also accounted for scavenging of superoxide by sub-nanomolar levels of dissolved copper and by organic matter when present. The presence of a relatively strong Fe(III) binding ligand was observed to significantly increase the rate of Fe(II) oxidation, while ultimately retaining most of the iron in the system in dissolved (organically complexed) form. The complexation reactions and reaction of inorganic and organically bound Fe(II) with oxygen were found to be critical reactions in the system, while Fe(III) hydrolysis became unimportant even at low organic concentrations. The superoxide radical was also observed to have a major role in the cycling of iron due to its ability to act as both an oxidant and a reductant. The model indicates that the rate constant for the reaction of Fe(II) with O2 has generally been underestimated in previous work and that the secondary oxidation of Fe(II) by H2O2 and subsequently OH* plays a relatively minor role in these systems.     

Photochemical oxidation of As(III) in ferrioxalate solutions

Photochemical reactions involving aqueous Fe(III) complexes are known to generate free radical species such as OH* that are capable of oxidizing numerous inorganic and organic compounds. Recent work has shown that As(III) can be oxidized to As(V) via photochemical reactions in ferric-citrate solutions; however, the mechanisms of As(III) oxidation and the potential importance of photochemical oxidation in natural waters are poorly understood. Consequently, the objectives of this study were to evaluate oxidation rates of As(III) in irradiated ferrioxalate solutions as a function of pH, identify mechanisms of photochemical As(III) oxidation, and evaluate the oxidation of As(III) in a representative natural water containing dissolved organic C (DOC). The oxidation of As(III) was studied in irradiated ferrioxalate solutions as a function of pH (3-7), As(III), Fe(III), and 2-propanol concentration. Rates of As(III) oxidation (0.5-254 microM h(-1)) were first-order in As(III) and Fe(III) concentration and increased with decreasing pH. Experiments conducted at pH 5.0 using 2-propanol as an OH* scavenger in light and dark reactions suggested that OH* is the important free radical responsible for As(III) oxidation. Significant rates of As(III) oxidation (4-6 microM h(-1)) were also observed in a natural water sample containing DOC, indicating that photochemical oxidation of As(III) may contribute to arsenic (As) cycling in natural waters.     

Iron-mediated oxidation of antimony(III) by oxygen and hydrogen peroxide compared to arsenic(III) oxidation

Antimony is used in large quantities in a variety of products, though it has been declared as a pollutant of priority interest by the Environmental Protection Agency of the United States (USEPA). Oxidation processes critically affect the mobility of antimony in the environment since Sb(V) has a greater solubility than Sb(lll). In this study, the cooxidation reactions of Sb(lIl) with Fe(ll) and both O2 and H2O2 were investigated and compared to those of As(III). With increasing pH, the oxidation rate coefficients of Sb(lll) in the presence of Fe(ll) and O2 increased and followed a similar pH trend as the Fe(ll) oxidation by O2. Half-lives of Sb(lll) were 35 and 1.4 h at pH 5.0 and pH 6.2, respectively. The co-oxidation with Fe(ll) and H2O2 is about 7000 and 20 times faster than with Fe(ll) and O2 at pH 3 and pH 7, respectively. For both systems, *OH radicals appear to be the predominant oxidant below approximately pH 4, while at more neutral pH values, other unknown intermediates become important. The oxidation of As(lll) follows a similar pH trend as the Sb(lll) oxidation; however, As(lll) oxidation was roughly 10 times slower and only partly oxidized in most of the experiments. This study shows that the Fe(ll)-mediated oxidation of Sb(Ill) can be an important oxidation pathway at neutral pH values.     

Decomposition of hydrogen peroxide and organic compounds in the presence of dissolved iron and ferrihydrite

This work examines the contribution of solution phase reactions, especially those involving a chain reaction mechanism, to the decomposition of hydrogen peroxide (H2O2) and organic compounds in the presence of dissolved iron and ferrihydrite. In solutions at pH 4, where Fe was introduced as dissolved Fe(III), both H2O2 and 14C-labeled formic acid decomposed at measurable rates that agreed reasonably well with those predicted by a kinetic model of the chain reaction mechanism, using published rate constants extrapolated to pH 4. The ratio of the formic acid and H2O2 decomposition rates, as well as the dramatic effect of tert-butyl alcohol on these rates, confirmed that a solution chain reaction mechanism involving *OH controlled the decomposition kinetics of both compounds. In the presence of ferrihydrite as the iron source, the ratio of the rate of formic acid decomposition to that of H2O2 decomposition was significantly lower than that observed in the presence of only dissolved Fe. Moreover, neither rate diminished drastically upon addition of tert-butyl alcohol, indicating that the solution phase chain reaction is not a dominant decomposition pathway of H2O2 and formic acid. Relative decomposition rates of formic acid and a second *OH probe, benzoic acid, were consistent with oxidation of these compounds by *OH. These observations can be reproduced by a kinetic model including (a) decomposition of H2O2 at the iron oxide surface, producing *OH with lower yield than the reaction sequence with dissolved Fe, and (b) low concentrations of dissolved Fe in the presence of ferrihydrite, preventing propagation of the solution phase chain reaction.     

Kinetics and modeling of the Fe(III)/H2O2 system in the presence of sulfate in acidic aqueous solutions

This work examined the effect of sulfate ions on the rate of decomposition of H2O2 by Fe(III) in homogeneous aqueous solutions. Experiments were carried out at 25 degrees C, pH < or = 3 and the concentrations of sulfate ranged from 0 to 200 mM ([Fe(III)]0 = 0.2 or 1 mM, [H2O2]0 = 10 or 50 mM). The spectrophometric study shows that addition of sulfate decreased the formation of iron(III)-peroxo complexes and that H2O2 does not form complexes with iron(III)-sulfato complexes. The rates of decomposition of H2O2 markedly decreased in the presence of sulfate. The measured rates were accurately predicted by a kinetic model based on reactions previously validated in NaClO4/HClO4 solutions and on additional reactions involving sulfate ions and sulfate radicals. At a fixed pH, the pseudo-first-order rate constants were found to decrease linearly with the molar fraction of Fe(II) complexed with sulfate. The model was also able to predict the rate of oxidation of a probe compound (atrazine) by Fe(III)/H2O2. Computer simulations indicate that the decrease of the rate of oxidation of organic solutes by Fe(III)/H2O2 can be mainly attributed to the complexation of Fe(III) by sulfate ions, while sulfate radicals play a minor role on the overall reaction rates.     

Anchored oxygen-donor coordination to iron for photodegradation of organic pollutants

A photocatalyst of oxygen-donor coordination to iron, complex of 5-sulfosalicylic acid (SSA) with ferric ion, supported on resin to cycle Fe3+/Fe2+ center under visible irradiation can effectively generate *OH radicals from H2O2, leading to degradation of organic pollutants in water. The higher turnover number was achieved by this catalyst for the degradation of model compound than those reported for the general N-donor ligands catalysts. The reversible "on/ off" switching of Fe3+/Fe2+ complexation with SSA, coupled with the phenol/phenoxyl radical conversion of the o-phenoxyl moiety of SSA, produces an ideal catalytic system that separates the Fenton reaction and the followed oxidations by *OH radicals (in water phase) from the regeneration of the catalytic species, Fe (SSA)2-, which occurs on the surface of resin. This system not only inhibits the undesired destruction of the ligands by *OH radicals, improving the stability of the catalyst, but also avoids the unnecessary decomposition of H2O2 into HO2* that occurs in the homogeneous Fenton system. Therefore, the system suggests an efficient utilization of H2O2 for degradation of organic pollutants.     

Strong enhancement on fenton oxidation by addition of hydroxylamine to accelerate the ferric and ferrous iron cycles

The Fenton system generates reactive species with high oxidation potential such as hydroxyl radicals (HO(?)) or ferryl via the reaction between Fe (II) and H?O?. However, a number of drawbacks limit its widespread application including the accumulation of Fe (III) and the narrow pH range limits, etc. The aim of this study is to propose a much more efficient Fenton-HA system which is characterized by combining Fenton system with hydroxylamine (NH?OH), a common reducing agent, to relieve the aforementioned drawbacks, with benzoic acid (BA) as the probe reagent. The presence of NH?OH in Fenton's reagent accelerated the Fe (III)/Fe (II) redox cycles, leading to relatively steady Fe (II) recovery, thus, increased the pseudo first-order reaction rates and expanded the effective pH range up to 5.7. The HO(?) mechanism was confirmed to be dominating in the Fenton-HA system, and the generation of HO(?) was much faster and the amount of HO(?) formed was higher than that in the classical Fenton system. Furthermore, the major end products of NH?OH in Fenton-HA system were supposed to be NO?(-) and N?O.     

Ligand-enhanced reactive oxidant generation by nanoparticulate zero-valent iron and oxygen

The reaction of zero-valent iron or ferrous iron with oxygen produces reactive oxidants capable of oxidizing organic compounds. However, the oxidant yield in the absence of ligands is too low for practical applications. The addition of oxalate, nitrilotriacetic acid (NTA), or ethylenediaminetetraacetic acid (EDTA) to oxygen-containing solutions of nanoparticulate zero-valent iron (nZVI) significantly increases oxidant yield, with yields approaching their theoretical maxima near neutral pH. These ligands improve oxidant production by limiting iron precipitation and by accelerating the rates of key reactions, including ferrous iron oxidation by oxygen and hydrogen peroxide. Product yields indicate that the oxic nZVI system produces hydroxyl radical (OH*) over the entire pH range in the presence of oxalate and NTA. In the presence of EDTA, probe compound oxidation is attributed to OH under acidic conditions and a mixture of OH* and ferryl ion (Fe[IV]) at circumneutral pH.     

Hydroxyl radical production via the photo-Fenton reaction in the presence of fulvic acid

The photo-Fenton reaction, the reaction of photoproduced Fe(II) with H2O2 to form the highly reactive hydroxyl radical (OH*), could be an important source of OH* in sunlit natural waters. To determine if the photo-Fenton reaction is significant in mildly acidic surface waters, we conducted experiments simulating conditions representative of natural freshwaters using solutions of standard fulvic acid and amorphous iron oxide at pH 6.0. A probe method measuring 14CO2 produced by the reaction of 14C-labeled formate with OH* was used to detect small OH* production rates without otherwise influencing the chemical reactions occurring in the experiments. Net H2O2 accumulation was simultaneously measured using an acridinium ester chemiluminescence method. Measured losses of H2O2 by reaction with Fe(II) in dark experiments produced approximately the expected quantities of OH*. The difference between H2O2 accumulation in the presence and absence of Fe(III) in fulvic acid solutions exposed to light was interpreted as the loss of H2O2 by reaction with photoproduced Fe(II), consistent with measured OH* production rates. The Fe ligand desferrioxamine mesylate eliminated both OH* production and H2O2 photoloss induced by Fe. Our results imply that when Fe is a major sink of H2O2, the photo-Fenton reaction is likely to be the most important source of OH*, leading to a significant sink of organic compounds in a wide variety of sunlit freshwaters.     

Photoassisted Fenton degradation of polystyrene

Fenton and photoassisted Fenton degradation of ordinary hydrophobic cross-linked polystyrene microspheres and sulfonated polystyrene beads (DOWEX 50WX8) have been attempted. While the Fenton process was not able to degrade these polystyrene materials, photoassisted Fenton reaction (mediated by broad-band UV irradiation from a 250 W Hg(Xe) light source) was found to be efficient in mineralizing cross-linked sulfonated polystyrene materials. The optimal loadings of the Fe(III) catalyst and the H(2)O(2) oxidant for such a photoassisted Fenton degradation were found to be 42 μmol-Fe(III) and 14.1 mmol-H(2)O(2) per gram of the sulfonated polystyrene material. The initial pH for the degradation was set at pH 2.0. This photoassisted Fenton degradation process was also able to mineralize commonly encountered polystyrene wastes. After a simple sulfonation pretreatment, a mineralization efficiency of >99% (by net polymer weight) was achieved within 250 min. The mechanism of this advanced oxidative degradation process was investigated. Sulfonate groups introduced to the surface of the treated polystyrene polymer chains were capable of rapidly binding the cationic Fe(III) catalyst, probably via a cation-exchange mechanism. Such a sorption of the photoassisted Fenton catalyst was crucial to the heterogeneous degradation process.     

Microbially catalyzed nitrate-dependent oxidation of biogenic solid-phase Fe(II) compounds

The potential for microbially catalyzed NO3(-)-dependent oxidation of solid-phase Fe(II) compounds was examined using a previously described autotrophic, denitrifying, Fe(II)-oxidizing enrichment culture. The following solid-phase Fe(II)-bearing minerals were considered: microbially reduced synthetic goethite, two different end products of microbially hydrous ferric oxide (HFO) reduction (biogenic Fe3O4 and biogenic FeCO3), chemically precipitated FeCO3, and two microbially reduced iron(III) oxide-rich subsoils. The microbially reduced goethite, subsoils, and chemically precipitated FeCO3 were subject to rapid NO3(-)-dependent Fe(II) oxidation. Significant oxidation of biogenic Fe3O4 was observed. Very little biogenic FeCO3 was oxidized. No reduction of NO3- or oxidation of Fe(II) occurred in pasteurized cultures. The molar ratio of NO3- reduced to Fe(II) oxidized in cultures containing chemically precipitated FeCO3, and one of the microbially reduced subsoils approximated the theoretical stoichiometry of 0.2:1. However, molar ratios obtained for oxidation of microbially reduced goethite, the other subsoil, and the HFO reduction end products did not agree with this theoretical value. These discrepancies may be related to heterotrophic NO3- reduction coupled to oxidation of dead Fe(III)-reducing bacterial biomass. Our findings demonstrate that microbally catalyzed NO3(-)-dependent Fe(II) oxidation has the potential to significantly accelerate the oxidation of solid-phase Fe(II) compounds by oxidized N species. This process could have an important influence on the migration of contaminant metals and radionuclides in subsurface environments.     

Fenton氧化和生物法结合深度处理硫化黑印染废水

采用Fenton氧化和生物氧化结合的方法,研究硫化黑印染废水的COD去除率和处理成本。探讨了Fenton氧化的条件包括氧化时间、m(H2O2)∶m(COD)、n(H2O2)∶n(Fe2+)以及Acinetobacter sp.DS-9生物氧化法二级串联处理系统的脱硫和COD去除效果。结果表明,最佳条件为:pH=3,m(H2O2)∶m(COD)=1∶2,n(H2O2)∶n(Fe2+)=10∶1,反应90 min后,按5%的接种量接入高效硫氧化菌株Acinetobacter sp.DS-9。废水脱硫效率提高了34.5%,COD去除率提高了74%。     

Growth of Listeria monocytogenes Scott A, serotype 4 and competitive spoilage organisms in raw chicken packaged under modified atmospheres and in air

The development of Listeria monocytogenes Scott A, serotype 4 and aerobic plate counts on minced raw chicken were determined independently at 4, 10 and 27 degrees C. Samples were packaged in flexible film under two modified atmospheres (one containing oxygen and one containing no oxygen) or air. The anaerobic modified atmosphere (75:25, CO2:N2) resulted in the failure of both the aerobic plate counts and L. monocytogenes to grow at all temperatures. Both the L. monocytogenes and aerobic plate counts grew in air at all temperatures. The aerobic modified atmosphere (72.5:22.5:5, CO2:N2:O2), which more closely duplicates commercial practice, inhibited the increase in aerobic plate counts by more than 4 log10 cfu/g compared to air at 4 degrees C. However, the L. monocytogenes was not affected by this atmosphere and increased in numbers by nearly 6 log10 cfu/g at 4 degrees C in 21 days. Regression analysis of the log10 growth and 95% confidence intervals showed that the differences between aerobic plate counts and L. monocytogenes in modified atmosphere were large. The ability of L. monocytogenes to grow in the aerobic modified atmosphere was not affected by level of the L. monocytogenes inoculum nor by the initial level of aerobic plate counts. These data show that modified atmosphere packaging of raw chicken (and probably other meats) can substantially inhibit the aerobic spoilage flora while allowing pathogenic L. monocytogenes to increase.     

New processes in the environmental chemistry of nitrite: nitration of phenol upon nitrite photoinduced oxidation

The role of nitrite as an environmental factor has been widely recognized. Nitrite is a relevant source of *OH in the atmosphere, both in the gas phase via photolysis of gaseous HNO2 and in atmospheric hydrometeors by photolysis of NO2-. In aqueous systems, *OH production through nitrite photolysis can be negligible due to the competition for light absorption by dissolved Fe(III), colloidal iron oxides, and nitrate. These photoexcited oxidants interact with NO2- and HNO2 to form *NO2, either directly or via formation of *OH. As a consequence, nitrite and nitrous acid may act as *NO2 rather than *OH sources. The radical *NO2 is involved in the nitration of many aromatic compounds, of which phenol is a model in this work. Kinetic measurements using 2-propanol as *OH scavenger show that the direct production of *OH by aqueous Fe(III) species decreases as pH increases. At slightly acidic and neutral pH values, oxidation of nitrite occurs by direct electron transfer to photoexcited Fe(III)aq species or colloidal iron oxides, in addition to the *OH-mediated oxidation of NO2-. The reported findings suggest a completely new role of nitrite in aquatic environments.     

Fenton高级氧化法处理化机浆废水研究

采用高级氧化法处理了某BCTMP化机浆制浆综合废水二级生化出水。研究结果表明：化机浆综合废水经厌氧-好氧处理后,再用Fenton氧化法进行深度处理,COD可降至50mg/L以下。用稀硫酸调初始pH到5.8,100ml废水投加5%的FeSO4溶液6.4ml后快速搅拌2min,加12%的H202溶液0.15ml,加Ca（OH）2溶液调节pH到6.0,整个高级氧化段COD去除率达85%,SS去除率达到90%以上。Ca（OH）2不仅调节了pH,而且还起到了絮凝的作用。与此同时,加PAM来改善污泥沉降性能,PAM的助凝作用,改变了化学污泥的沉降性。本研究结果为福建某企业化机浆废水的深度处理工程设计提供了重要的基础数据。