Effect of Fe(Ⅲ) on the bromate reduction by humic substances in aqueous solution

Humic substances are ubiquitous redox-active organic compounds of environment.In this study,experiments were conducted to determine the reduction capacity of humic acid in the matrix of bromate and Fe(Ⅲ) solutions and the role of Fe(Ⅲ) in this redox process.The results showed that the humic acid regenerated Fe(Ⅱ) and reduced bromate abiotically.The addition of Fe(Ⅲ) could accelerate the bromate reduction rate by forming humic acid-Fe(Ⅲ) complexes.Iron species acts as electron mediator and catalyst for the bromate reduction by humic acid,in which humic acid transfers electrons to the complexed Fe(Ⅲ) to form Fe(Ⅱ),and the regenerated Fe(Ⅱ) donate the electrons to bromate.The kinetics study on bromate reduction further indicated that bromate reduction by humic acid-Fe(Ⅲ) complexes is pH dependent.The rate decreased by 2-fold with the increase in solution pH by one unit.The reduction capacity of Aldrich humic acid was observed to be lower than that of humic acid or natural organic matter of Suwanne River,indicating that such redox process is expected to occur in the environment.     

Removal of perchlorate from aqueous solution by cross-linked Fe(Ⅲ)-chitosan complex

Cross-linked Fe（III）-chitosan composite （Fe-CB） was used as the adsorbent for removing perchlorate from the aqueous solution. The adsorption experiments were carried out by varying contact time, initial concentrations, temperatures, pH, and the presence of co-existing anions. The morphology of the adsorbent was discussed using FT-IR and SEM with X-EDS analysis. The pH ranging from 3.0-10.2 exhibited very little effect on the adsorption capability. The perchlorate uptake onto Fe-CB obeyed Langmuir isotherm model. The adsorption process was rapid and the kinetics data obeyed the pseudo second-order model well. The eluent of 2.5% （W/V） NaC1 could regenerate the exhausted adsorbent efficiently. The adsorption mechanism was also discussed.     

Radiation-induced reduction of chromium(Ⅵ) in aqueous solution by γ-irradiation in a laboratory-scale

Radiation-induced reduction of chromium(Ⅵ)(Cr(Ⅵ) by γ-irradiation was studied with an initial concentration of 42 mg/L in aqueous solutions. Several factors which might affect the reduction of Cr(Ⅵ) to Cr(Ⅲ) were examined. pH of aqueous solution affects the reduction efficiency significantly. Acidic condition of aqueous solution accelerates the process. At pH 2, a reduction of 86.2%was achieved with the absorbed dose of 15 kGy, while, with the same dose, at pH 5 and 7, the reduction of Cr (Ⅵ) were only 36.3%and 22.2%, respectively. Ethanol (0.1% in V:V) and sodium carbonate (1 mmol/L) were added into the solution respectively as relatively non-toxic hydroxyl radical scavengers. Reduction rate increased greatly in the presence of ethanol at each pH. Reduction efficiency of Cr(Ⅵ) was enhanced in neutral condition with the addition of sodium carbonate, however, no enhancement was found in acidic condition. The reduction of Cr(Ⅵ) was restrained when the solution was saturated with oxygen; however, the restraint was not significant.     

Radiation-induced reduction of chromium(Ⅵ) in aqueous solution by γ-irradiation in a laboratory-scale

Radiation-induced reduction of chromium（Ⅵ）（Cr（Ⅵ） by ,γ-irradiation was studied with an initial concentration of 42 mg/L in aqueous solutions. Several factors which might affect the reduction of Cr（Ⅵ） to Cr（Ⅲ） were examined, pH of aqueous solution affects the reduction efficiency significantly. Acidic condition of aqueous solution accelerates the process. At pH 2, a reduction of 86.2% was achieved with the absorbed dose of 15 kGy, while, with the same dose, at pH 5 and 7, the reduction ofCr （Ⅵ） were only 36.3% and 22.2%, respectively. Ethanol （0.1% in V：V） and sodium carbonate （1 mmol/L） were added into the solution respectively as relatively non-toxic hydroxyl radical scavengers. Reduction rate increased greatly in the presence of ethanol at each pH. Reduction efficiency of Cr（Ⅵ） was enhanced in neutral condition with the addition of sodium carbonate, however, no enhancement was found in acidic condition. The reduction of Cr（Ⅵ） was restrained when the solution was saturated with oxygen; however, the restraint was not significant.     

Radiation-induced reduction of chromium(VI) in aqueous solution by γ-irradiation in a laboratory-scale

Introduction Chrom ium com pounds are extensively used in electroplating, leather-tanning and other industries. In C hina, chrom ium is incorporated into the environ- m ent, m ainly into soils and stream s of w ater, as a result of unregulated application…     

Partitioning of water soluble organic carbon in three sediment size fractions： Effect of the humic substances

Water soluble organic carbon (WSOC) in sediments plays an important role in transference and transformation of aquatic pollutants. This article investigated the inherent mechanisms of how sediemnt grain size affect the partitioning coeffcient (k) of WSOC. Influences of NaOH extracted humic substances were particularly focused on. Sediments were sampled from two cross-sections of the middle Yellow River and sieved into three size fractions (< 63 μm, 63-100 μm, and 100--300 μm). The total concentration of WSOC in sediments (CWSOC) and k were estimated using multiple water-sediment ratio experiments. Results show that CWSOC ranges from 0.012 to 0.022 mg/g, while k ranges from 0.8 to 3.9 L/kg. Correlations between the spectrum characteristics of NaOH extracted humic substances and k were analyzed. Strong positive correlations are determined between k and the aromaticity indicators of NaOH extracted humic substances in different sediment size fractions. Comparing with finer fractions (< 63 μm), k is higher in larger size fractions (63--100 and 100--300 μm) related to higher aromaticity degree of NaOH extracted humic substances mostly. While negative relationship between k and the area ratio of fourier transform infrared spectroscopy (FT-IR) at 3400 and 1430 cm-1 implied that the lowest k was related to the highest concentration of the acidic humic groups in particles < 63 μm. WSOC in finer fractions (< 63 μm) is likely to enter into pore water, which may further accelerate the transportation of aquatic contaminants from sediment to water.     

Photodegradation of 17α-ethynylestradiol in dissolved humic substances solution: Kinetics, mechanism and estrogenicity variation

17α-Ethynylestradiol(EE2) in natural waters may cause adverse effects on organisms due to its high estrogenic potency. Laboratory studies were performed to study the effects of a local humic acid(LHA), fulvic acid(LFA) and Aldrich humic acid(AHA) on the photochemical behavior and estrogenic potency of EE2. Here photolytic experiments demonstrated that pure aqueous EE2 could undergo direct and self-sensitized photodegradation at a global rate of 0.0068 hr~(-1).Photodegradation rate of EE2 in 5.0 mg/L dissolved humic substances(DHS) was determined to be 0.0274, 0.0296 and 0.0254 hr~(-1) for LHA, LFA and AHA, respectively. Reactive oxygen species(ROS) and triplet dissolved humic substances(~3DHS*) scavenging experiments indicated that the promotion effect of DHS on EE2 photodegradation was mainly aroused by the reactions of HOU(35%–50%),~1O_2(10%) andDHS*(22%–34%). However, the photodegradation of EE2 could also be inhibited when DHS exceeded the threshold of 10 mg/L. Three hydroxylation products of EE2 were identified using GC–MS and their formation pathways were also proposed. In vitro estrogenicity tests showed that EE2 was transformed into chemicals without estrogenic potency. These findings could extend our knowledge on the photochemical behaviors of steroid estrogens in sunlit natural waters.     

Behavior of the herbicide dimepiperate with homoionic clays in aqueous solution

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Effect of ionic strength on adsorption of As（Ⅲ） and As（Ⅴ） on variable charge soils

The study was to investigate the adsorption behavior of arsenite (As(Ⅲ)) and arsenate (As(Ⅴ)) on two variable charge soils, i.e., Haplic Acrisol and Rhodic Ferralsol at different ionic strengths and pH with batch methods. Results indicated that the amount of As(Ⅲ) adsorbed by these two soils increased with increasing solution pH, whereas it decreased with increasing ionic strength under the acidic condition. This suggested that As(Ⅲ) was mainly adsorbed on soil positive charge sites through electrostatic attraction under the acidic condition. Moreover, intersects of As(Ⅴ) adsorption-pH curves at different ionic strengths (a characteristic pH) are obtained for both soils. It was noted that above this pH, the adsorption of As(Ⅴ) was increased with increasing ionic strength, whereas below it the reverse trend was true. Precisely the intersect pH was 3.6 for Haplic Acrisol and 4.5 for Rhodic Ferralsol, which was near the values of PZSE (soil point of zero salt effect) of these soils. The effects of ionic strength and pH on arsenate adsorption by these soils were interpreted by the adsorption model. The results of zeta potential suggested that the potential in adsorption plane becomes less negative with increasing ionic strength above soil PZSE and decreases with increasing ionic strength below soil PZSE. These results further supported the hypothesis of the adsorption model that the potential in the adsorption plane changes with ionic strength with an opposite trend to surface charge of the soils. Therefore, the change of the potential in the adsorption plane was mainly responsible for the change of arsenate adsorption induced by ionic strength on variable charge soils.     

Study on the action and mechanism of humic acids in Kaschin-Beck disease

Humic acids, especially FA in fractions, contain more oxygen functional groups. In this experiment, on the basis of confirming the action of humic acids on KBD, what was studied is the biological effects of one of main oxygen functional groups, hydroxy group (-OH). The results indicate that inducing pathologic process of KBD, obviously decrease the GSH-Px activity and induce peroxidation membrane injury of tissue. The SOD activity increase in the tissues caused by oxygen functional groups showed that enhancing of free radical reaction should not be neglected.     

Shewanella oneidensis MR-1异化还原Fe(III)介导的As(III)氧化转化

在实验室模拟条件下,研究了Shewanella oneidensis MR-1作用下Fe(III)还原和As(III)氧化动力学及其影响因素.结果表明,Fe(III)被还原为Fe(II)的同时伴随着As(III)氧化为As(V);S. oneidensis MR-1 在含低浓度As(III)培养基上生长良好,在高浓度培养基上生长被抑制;As(III)通过制约菌体的生长与活性来抑制Fe(III)异化还原.同样,适量浓度的Fe(III)含量对As(III)氧化转化有很强的促进作用,但是过高浓度的Fe(III)浓度使得溶液中产生过多的Fe(II),从而对As(III)氧化转化有一定程度的抑制作用.此外,弱碱环境更有利于As(III)氧化转化.     

不同Fe(III)对活性污泥异化铁还原及除磷影响研究

以SBBR反应器活性污泥作为铁还原菌菌种来源,采用兼性厌氧/严格厌氧恒温培养试验,投加不同Fe(III)考察各条件下的异化铁还原能力,同时比较对磷的去除效果.结果表明:2种条件下Fe(III)还原能力具有较好的一致性,依次为:Fe(OH)3>氧化铁皮>青矿>红矿,其中严格厌氧条件下较好.同时,除磷效果与其呈正相关,富集培养至7d, Fe(OH)3及氧化铁皮体系出水磷浓度均达到2mg/L以下,之后继续降低,最终达到0.5mg/L以下.结合异化铁还原除磷机理,可以证明,不同Fe(III)表面吸附作用对TP的去除贡献较小,其主要作用为铁还原菌驱动下的化学沉淀去除.     

Simultaneous Fe(III) reduction and ammonia oxidation process in Anammox sludge

In recent years, there have been a number of reports on the phenomenon in which ferric iron (Fe(III)) is reduced to ferrous iron [Fe(II)] in anaerobic environments, accompanied by simultaneous oxidation of ammonia to NO₂^-, NO₃^-, or N₂. However, studies on the relevant reaction characteristics and mechanisms are rare. Recently, in research on the effect of Fe(III) on the activity of Anammox sludge, excess ammonia oxidization has also been found. Hence, in the present study, Fe(III) was used to serve as the electron acceptor instead of NO₂^-, and the feasibility and characteristics of Anammox coupled to Fe(III) reduction (termed Feammox) were investigated. After 160days of cultivation, the conversion rate of ammonia in the reactor was above 80%, accompanied by the production of a large amount of NO₃^- and a small amount of NO₂^-. The total nitrogen removal rate was up to 71.8%. Furthermore, quantities of Fe(II) were detected in the sludge fluorescence in situ hybridization (FISH) and denaturated gradient gel electrophoresis (DGGE) analyses further revealed that in the sludge, some Anammox bacteria were retained, and some microbes were enriched during the acclimatization process. We thus deduced that in Anammox sludge, Fe(III) reduction takes place together with ammonia oxidation to NO₂^- and NO₃^- along with the Anammox process.     

Fe(II)、Fe(III)对砷与不同分子量腐植酸络合性能的影响

以腐植酸（HA）代表天然有机质,采用平衡透析和超滤的方法研究铁离子（Fe （II）、Fe （III））对不同分子量HA与砷离子（As （V）、As （III））络合作用的影响,并利用红外光谱（FT-IR）表征其络合特征.结果发现,Fe （II）和Fe （III）均能增强HA络合As能力,且对As （V）络合能力的增强作用大于As （III）;pH值显著影响HA络合As能力;溶解性有机碳（DOC）浓度由5mg/L增大到200mg/L,As络合百分比随之增加,此时HA-Fe （III）络合As （III）百分比最大,为24.55%;初始As浓度由10μg/L增加1000μg/L,As络合百分比随之降低,其中HA-Fe （III）络合As （III）百分比最低,为3.11%.相同环境条件下,分子量>100kDa络合As百分比最大,其中HA-Fe （II）络合As （III）的百分比最高为26.43%;分子量小于10kDa的HA络合As百分比明显高于其他分子量的HA.Fe的增强作用主要源于Fe与羧基形成桥梁再与As络合形成三元络合物.     

Al(III)对糖浆溶液中有机还原物质还原六价铬的影响

通过批实验研究了Al(III)对糖浆溶液化学还原六价铬反应的影响,揭示了不同条件下Al(III)对六价铬还原反应动力学的影响.结果表明:Al(III)能够促进糖浆溶液还原六价铬反应进行;其作用机制是Al(III)与糖浆溶液中有机还原物质及Cr(VI)反应形成三者的络合物,降低糖浆中多酚等有机还原物质还原Cr(VI)的反应活化能,提高六价铬还原反应速率.Al(III)存在时,该六价铬还原反应符合准一级动力学反应; pH 2.0,2.5,3.0,3.5时,添加Al(III)的实验组中六价铬反应速率常数比对应的空白对照组中反应速率常数分别增加了0.0251,0.0139,0.0058, 0.0048h-1.添加Al(III)前后反应体系中六价铬还原的反应活化能(Eа)分别为66.38,62.80kJ/mol.当糖浆浓度不足时,Al(III)能够提高糖浆溶液还原六价铬的反应去除率.     

Photo-induced transformations of Hg(Ⅱ) species in the presence of Nitzschia hantzschiana,ferric ion,and humic acid

Effects of algae Nitzschia hantzschiana, Fe(Ⅲ) ions, humic acid, and pH on the photochemical reduction of Hg(Ⅱ) using the irradiation of metal halide lamps (λ 365 nm, 250 W) were investigated. The photoreduction rate of Hg(Ⅱ) was found to increase with increasing concentrations of algae, Fe(Ⅲ) ions, and humic acid. Alteration of pH value affected the photoreduction of Hg(Ⅱ) in aqueous solution with or without algae. The photoreduction rate of Hg(II) decreased with increasing initial Hg(Ⅱ) concentration in aqueous solution in the presence of algae. The photochemical kinetics of initial Hg(Ⅱ) and algae concentrations on the photoreduction of Hg(Ⅱ) were studied at pH 7.0. The study on the total Hg mass balance in terms of photochemical process revealed that more than 42% of Hg(Ⅱ) from the algal suspension was reduced to volatile metallic Hg under the conditions investigated.     

不同来源堆肥腐殖质还原菌异化铁还原能力评估与调控

通过富集不同来源堆肥过程中的腐殖质还原菌,并分析比较其异化铁还原能力差异,发现其电子转移能力从大到小依次为：蛋白类>纤维素类>木质素类.相关性分析表明,Leucobacter、Clostridium sensu stricto和Sporosarcina是极显著影响异化铁还原的腐殖质还原菌属.利用冗余分析探究关键腐殖质还原菌与堆肥过程微环境因子的响应关系,结果发现可溶性有机氮是影响这些关键腐殖质还原菌变化的主要微环境因素.在此基础上,基于堆肥微环境因子与关键腐殖质还原菌菌群结构之间的响应关系,提出一种促进异化铁还原相关的腐殖质还原菌生长的调控方法.本研究可以深入了解堆肥中影响腐殖质还原菌群落的关键因素,而且对于环境中污染物生物地球化学循环也具有重要的生态学意义.     

环糊精对Fe(Ⅲ)引发双酚A光降解的影响

环糊精口α-CD、β-CD和γ-CD能分别与双酚A形成1:1主-客体包结物.在250W金属卤化物灯(λ≥365 nm)光照下,研究了在Fe(Ⅲ)-OH配合物体系中,不同环糊精对双酚A光降解的影响.结果表明,β-CD能较大地促进双酚A的光降解,α-CD次之,而γ-CD对双酚A的光降解存在一定的抑制;并且CDs浓度的变化对双酚A光降解的初始速率有明显的影响.双酚A光降解的初始速率随着β-CD和α-CD浓度增大而增加,当β-CD=60μmol/L时达到最大,然后随着浓度增大而降低,而BPA的光降解初始速率随γ-CD浓度的增加总的趋势是减小的.通过计算机软件Gaussian98,采用PM3方法模拟了环糊精与双酚A的包结行为,进一步说明3种环糊精与双酚A形成主-客体包结物对光降解的影响.     

Removal of humic acid from aqueous solution by cetylpyridinium bromide modified zeolite

Natural zeolite was modified by loading cetylpyridinium bromide (CPB) to create more e cient sites for humic acid (HA) adsorption. The natural and CPB modified zeolites were characterized with X-ray di raction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy and elemental analysis. The e ects of various experimental parameters such as contact time, initial HA concentration, solution pH and coexistent Ca2+, upon HA adsorption onto CPB modified zeolites were evaluated. The results showed that natural zeolite had negligible a nity for HA in aqueous solutions, but CPB modified zeolites exhibited high adsorption e ciency for HA. A higher CPB loading on natural zeolites exhibited a larger HA adsorption capacity. Acidic pH and coexistent Ca2+ were proved to be favorable for HA adsorption onto CPB modified zeolite. The kinetic process was well described by pseudo second-order model. The experimental isotherm data fitted well to Langmuir and Sips models. The maximum monolayer adsorption capacity of CPB modified zeolite with surfactant bilayer coverage was found to be 92.0 mg/g.     

胡敏酸对不同矿物结合汞的还原作用

采用扩散吸收法探讨了胡敏酸对不同矿物结合态汞的还原作用及光照的影响.结果表明:两种胡敏酸(TJ和SH)对碳酸钙、氧化锰和赤铁矿结合态汞均具有明显的还原作用,还原动力学过程表现为先递增后渐趋平稳,可用双常数方程、Elovich方程和指数方程拟合;还原容量与吸持矿物类型有关,平均还原率大小为:CaCO3-Hg(0.67%)>Fe2O3-Hg(0.42%)>MnO2-Hg(0.19%);光照对胡敏酸还原矿物结合态汞具有强化效应,以CaCO3-Hg和Fe2O3-Hg光强化效果最明显,平均还原率较遮光时高出0.10%以上;两种胡敏酸(SH和TJ)对矿物结合态汞的还原能力存在差异(P<0.1),遮光条件下SH的还原能力均高于TJ,而光照条件下TJ对CaCO3-Hg的还原能力大于SH,对MnO2-Hg的还原则无显著差异,意味着SH的光敏性低于TJ,可能与不同胡敏酸氧化还原活性基团含量和芳香化程度(E4/E6)不同有关.