Synthesis of nanoscale zero-valent iron/ordered mesoporous carbon for adsorption and synergistic reduction of nitrobenzene

Nanoscale zero-valent iron (NZVI) supported on ordered mesoporous carbon (OMC) was synthesized through liquid phase reduction route. The NZVI/OMC composite was characterized by X-ray diffraction, N(2) adsorption/desorption and transmission electron microscopy. Results reveal that the composite possesses ordered mesostructure with NZVI distributing homogeneously on the surface of OMC support. The removal effects of nitrobenzene (NB) in water with OMC, NZVI/OMC and non-supported NZVI were evaluated. Results indicate that NZVI/OMC shows enhanced removal efficiency, which is attributed to its adsorption and synergistic reduction for NB. The transformation process of NB was further investigated by HPLC. Nitrosobenzene and phenylhydroxylamine were detected as intermediate products and aniline was the final reductive product.     

高铁酸钾降解苯胺废水的机制研究

研究了高铁酸钾投加量、初始pH及苯胺初始浓度对苯胺降解效果的影响.结果表明.苯胺废水的COD去除事随高铁酸钾投加量和苯胺初始浓度的增大而升高,而初始pH对COD去除率影响不明显.对高铁酸钾降解苯胺废水后的产物进行了气相色谱/质谱(GCIMS)分析.在此基础上详细探讨了高铁酸钾降解苯胺的机制.     

Chlorinated herbicide (triallate) dehalogenation by iron powder

The reductive degradation of a chlorinated herbicide by iron powder was investigated at lab scale. The studied substrate was triallate (S-2,3,3-trichloroallyl di-isopropyl thiocarbamate) which contains a trichloroethylene moiety potentially reducible by zero-valent iron. Degradation reactions were carried out in batch, at 25 degrees C, in the absence of oxygen, by contacting electrolytic iron powder (size range: 20-50 microm) with a triallate aqueous solution (2.5 mgl(-1)). Herbicide decay, corresponding evolutions of TOC, TOX and chloride ion release were regularly monitored throughout the reactions. Furthermore, the main degradation by-products were identified by HPLC/MS. The results showed that, after 5 days, herbicide degradation extent was about 97% and that the reaction proceeded through the formation of a dechlorinated alkyne by-product (S-2-propinyl di-isopropyl thiocarbamate) resulting from the complete dechlorination of triallate. The subsequent reduction of such an alkyne intermediate gave S-allyl di-isopropyl thiocarbamate as main end by-product. The identified by-products suggested that dechlorination took place mainly via reductive beta-elimination. However, as traces of dichloroallyl di-isopropyl thiocarbamate were also detected, a role, although minor, was assigned even to hydrogenolysis in the overall dechlorination process.     

Reduction of nitrobenzene in groundwater by iron nanoparticles immobilized in PEG/nylon membrane

The highly reactive iron nanoparticles (NPs) immobilized in nylon membrane were synthesized and characterized, and the reduction of nitrobenzene (NB) in groundwater by the NPs was investigated. Environmental scanning electron microscopy (ESEM) images showed that the NPs distributed homogeneously on the membrane surface without agglomeration. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the NPs immobilized in membrane were mainly composed of Fe-oxides rather than zero-valent iron. Thermogravimetric (TG) analysis suggested that the weight percentage of the immobilized NPs and the oxygen introduced to the reacted sample after 80min reaction were about 18.5% and 13%, respectively. Moreover, Fourier transform infrared (FTIR) analysis further demonstrated the changes on the membrane surface after thermal grafting, NPs immobilizing and reacting for 80min. Using the reactive NPs immobilized in nylon membrane, NB in groundwater was rapidly and quantitatively decreased by 68.9% just in the first 20min, the Fe(2+) associated with the iron NPs immobilized in PEG/nylon66 membrane was mainly responsible for this reduction. The reaction appeared to follow pseudo-first-order kinetics and the rate constants increased upon decreasing the pH value. The samples we prepared exhibited good corrosion resistance for humic acid (HA) but had a short-term performance for NB degradation. More so, the groundwater chemistry had a negative influence on the reactivity of membrane immobilized NPs.     

Bimetallic iron-aluminum particles for dechlorination of carbon tetrachloride

Bimetallic iron-aluminum (Fe/Al) particles were synthesized and tested for their reactivity toward carbon tetrachloride using batch reactors and a flow-through column at near neutral pH. Preparation of bimetallic Fe/Al particles was conducted under acidic conditions under which iron was readily deposited onto the aluminum surface. The SEM image showed clusters of iron on the aluminum surface at the measured Fe:Al molar ratio of about 2:3. Results showed that the presence of zero-valent aluminum successfully prevented the formation of a passive layer at the iron surface and maintained the reactivity of iron. The dechlorination of carbon tetrachloride by bimetallic Fe/Al particles produced chloroform (9%), dichloromethane (17%) and methane (38%). Kinetic analysis suggests that bimetallic Fe/Al particles increased the reactivity toward carbon tetrachloride degradation by a factor of 10 compared to zero-valent iron and possessed a comparable reactivity with nano-sized Fe. The effectiveness of bimetallic Fe/Al particles was further confirmed by the continuous flow column study from which an ageing of bimetallic particles was also observed.     

强化土著微生物处理硝基苯和苯胺污染地下水

以硝基苯、苯胺为主要污染物的污染地下水为研究对象,加入激活剂(乳糖、Na2HPO4、乳糖+Na2HPO4、乙醇、牛肉膏、蛋白胨)激活土著微生物,并考察其对土著微生物生长及硝基苯、苯胺降解效果的影响。加入激活剂3d后测各个水样的脱氢酶活性,对培养9d后的水样进行气相色谱/质谱(GC/MS)分析。结果表明,加入乳糖的水样中,其微生物相对增长率达157.2%,硝基苯、苯胺的相对去除率分别为14.90%和0.79%;加入Na2HPO4和乙醇的水样中,其微生物增长和硝基苯、苯胺降解情况均没有明显变化;加入乳糖+Na2HPO4的水样中,微生物相对增长率达180.3%,硝基苯、苯胺的相对去除率分别为24.20%和1.21%;加入牛肉膏的水样中,微生物的相对增长率为830.7%,硝基苯、苯胺的相对去除率分别为99.99%和99.67%;加入蛋白胨的水样中,其微生物相对增长率为686.0%,硝基苯、苯胺的相对去除率分别为99.33%和58.94%。GC/MS分析结果表明,加入激活剂后对氯苯胺、1-甲基-4-硝基苯等其他有机物的降解率均有提高。由此可见,通过激活土著微生物修复有机物污染地下水是可行的。     

Isotopic fractionation during reductive dechlorination of trichloroethene by zero-valent iron: influence of surface treatment

During reductive dechlorination of trichloroethene (TCE) by zero-valent iron, stable carbon isotopic values of residual TCE fractionate significantly and can be described by a Rayleigh model. This study investigated the effect of observed reaction rate, surface oxidation and iron type on isotopic fractionation of TCE during reductive dechlorination. Variation of observed reaction rate did not produce significant differences in isotopic fractionation in degradation experiments. However, a small influence on isotopic fractionation was observed for experiments using acid-cleaned electrolytic iron versus experiments using autoclaved electrolytic iron, acid-cleaned Peerless cast iron or autoclaved Peerless cast iron. A consistent isotopic enrichment factor of epsilon = -16.7/1000 was determined for all experiments using cast iron, and for the experiments with autoclaved electrolytic iron. Column experiments using 100% cast iron and a 28% cast iron/72% aquifer matrix mixture also resulted in an enrichment factor of -16.9/1000. The consistency in enrichment factors between batch and column systems suggests that isotopic trends observed in batch systems may be extrapolated to flowing systems such as field sites. The fact that significant isotopic fractionation was observed in all experiments implies that isotopic analysis can provide a direct qualitative indication of whether or not reductive dechlorination of TCE by Fe0 is occurring. This evidence may be useful in answering questions which arise at field sites, such as determining whether TCE observed down-gradient of an iron wall remediation scheme is the result of incomplete degradation within the wall, or of the dissolved TCE plume by passing the wall.     

硝基苯类废水的全混态零价铁-芬顿组合预处理工艺优化与工程验证

针对企业硝基氯苯装置产生的高毒性、难降解的硝基苯类废水,开发出全混态零价铁-芬顿组合预处理工艺,并分别优化了零价铁还原和芬顿氧化的工艺条件。结果表明,pH为2.0、零价铁投加量为220 mg/L时,废水中硝基苯类物质的去除率可达98.5%以上。出水pH约为3.0,继续投加3000 mg/L的H₂O₂,Fe²⁺投加比按C(Fe²⁺,mg/L):C(H₂O₂,mg/L)=1:10,1 h内COD去除率可达90%以上,且B/C由0.08提高到0.45。可见该组合预处理工艺可大幅削减废水毒性、改善可生化性,且直接运行成本仅为26.28元/吨,具有良好的环境和经济效益。     

超声波-零价铁协同降解废水中活性深蓝M-2GE的研究

研究了超声波-零价铁对废水中活性深蓝M-2GE的协同降解,探讨了铁粉添加量、超声波功率、介质pH和染料的浓度等对活性深蓝M-2GE降解效率的影响。结果表明,零价铁的存在可显著提高废水中活性深蓝M-2GE的超声降解效率,其降解率随着铁粉添加量的增多而升高。介质pH对活性深蓝M-2GE的降解有显著影响,pH=3时降解率最高。另外增大超声功率有利于有机污染物的降解,有机染料的浓度越低,降解率越高。     

Enhanced biodegradation of azo dyes using an integrated elemental iron-activated sludge system: I. Evaluation of system performance.

The objective of this research is to evaluate an integrated system coupling zero-valent iron (Fe(0)) and aerobic biological oxidation for the treatment of azo dye wastewater. Zero-valent (elemental) iron can reduce the azo bond, cleaving dye molecules into products that are more amenable to aerobic biological treatment processes. Azo dye reduction products, including aniline and sulfanilic acid, were shown to be readily biodegradable at concentrations up to approximately 25 mg/L. Batch reduction and biodegradation data support the proposed integrated iron pretreatment and activated sludge process for the degradation of the azo dyes orange G and orange I. The integrated system was able to decolorize dye solutions and yield effluents with lower total organic carbon concentrations than control systems without iron pretreatment. The success of the bench-scale integrated system suggests that iron pretreatment may be a feasible approach to treat azo dye containing wastewaters.     

Fe-Cu催化还原法处理废水的稳定性分析

采用扫描电镜(SEM)和X射线衍射(XRD)技术对Fe-Cu催化还原法处理硝基苯配水反应前后铁屑和铜的表面进行分析,研究了Fe-Cu催化还原法的长期运行效果.结果表明,运行数周后铜表面性状基本保持不变,化学稳定性好,抗中毒能力强.处理效果的下降主要起因于铁屑表面的金属铁发生反应而被逐渐消耗,以及铁屑表面为沉淀物覆盖而逐渐失效.     

Enhanced reductive dechlorination of polychlorinated biphenyl-contaminated soil by in-vessel anaerobic composting with zero-valent iron

Anaerobic dechlorination is an effective degradation pathway for higher chlorinated polychlorinated biphenyls (PCBs). The enhanced reductive dechlorination of PCB-contaminated soil by anaerobic composting with zero-valent iron (ZVI) was studied, and preliminary reasons for the enhanced reductive dechlorination with ZVI were investigated. The results show that the addition of nanoscale ZVI can enhance dechlorination during in-vessel anaerobic composting. After 140 days, the average number of removed Cl per biphenyl with 10 mg g^?1 of added nanoscale ZVI was 0.63, enhancing the dechlorination by 34 % and improving the initial dechlorination speed. The ZVI enhances dechlorination by providing a suitable acid base environment, reducing volatile fatty acid inhibition and stimulating the microorganisms. The C/N ratios for treatments with the highest rate of ZVI addition were smaller than for the control, indicating that ZVI addition can promote compost maturity.     

Rapid reductive destruction of hazardous organic compounds by nanoscale Fe0

Fe0-mediated reductive destruction of hazardous organic compounds such as chlorinated organic compounds (COCs) and nitroaromatic compounds (NACs) in the aqueous phase is one of the latest innovative technologies. In this paper, rapid reductive degradation of COCs and NACs by synthesized nanoscale Fe0 in anaerobic batch systems was presented. The nanoscale Fe0, characterized by high specific surface area and high reactivity, rapidly transformed trichloroethylene (TCE), chloroform (CF), nitrobenzene (NB), nitrotoluene (NT), dinitrobenzene (DNB) and dinitrotoluene (DNT) under ambient conditions, which results in complete disappearance of the parent compounds from the aqueous phase within a few minutes. GC analysis reported that the main products of the dechlorination of TCE and CF were ethane and methane as well as that most of the nitro groups in NACs were reductively transformed to amine groups. These results suggest that the rapid reductive destruction by nanoscale Fe0 is potentially a viable in situ or aboveground treatment of groundwater contaminated with hazardous organic compounds including COCs and NACs.     

零价铁与厌氧微生物协同还原地下水中的硝基苯

通过间歇式实验,考察了零价铁与厌氧微生物协同还原地下水中硝基苯的效果。实验结果表明,由零价铁腐蚀为厌氧微生物提供H2电子供体还原硝基苯的效果明显优于零价铁和微生物单独作用,硝基苯去除率分别提高21.8%和57.0%。弱酸性条件有利于协同反应进行,当初始pH为5.0和6.0时,4 d后硝基苯去除率比初始pH为7.0时的提高74.4%和35.2%。增加零价铁投加量可提高协同还原的效果,零价铁最佳投加量为250 mg/L。零价铁腐蚀产生的Fe2+无法作为电子供体被微生物利用,但可作为无机营养元素促进协同过程。由于零价铁产H2速率受表面覆盖物影响不明显,在地下水修复过程中可保证协同效果并延长零价铁的使用寿命。     

Dechlorination of trichloroethylene by a steel converter slag amended with Fe(II)

This study aims to assess the feasibility of using slag, byproduct from iron and steel making industries, as a new reactive material for dechlorination reactions and to investigate dechlorination chemistries of the systems containing the slag and Fe(II). Initially, screening experiments were conducted to evaluate various systems containing slags with or without Fe(II). A combination of the steel converter slag and Fe(II) showed a potential to be developed as a reactive material to treat chlorinated organics. Further kinetic studies with the steel converter slag/Fe(II) systems revealed that the dechlorination capacity of the slag/Fe(II) system is comparable to that of zero-valent iron and generally higher than the cement/Fe(II) system. The slag/Fe(II) system can substantially dechlorinate trichloroethylene (TCE) in the neutral pH region, although the dechlorination rate was greatest in the pH region between 12 and 13. TCE reductions in the slag/Fe(II) system were observed to occur through reductive beta-elimination pathways that produce primarily acetylene and no chlorinated intermediates such as vinyl chloride. These results demonstrate that the steel converter slag with Fe(II) has sound characteristics for an alternative reactive medium for subsurface remediation.     

Relevance study of bare and coated zero valent iron nanoparticles for lindane degradation from its by-product monitorization

Zero-valent iron nanoparticles (NZVI) as well as polymer–stabilized nanoparticles were synthesized and used for lindane (γ-hexachlorocyclohexane) degradation in aqueous solution. To study the effectiveness of the different coated nanoparticles, simple and rapid analytical methods have been developed to measure and to detect lindane and its by-products. For the monitorization of lindane degradation solid-phase extraction (SPE) was used, while volatile by-products formation measurement was carried out by headspace-solid phase microextraction (HS–SPME) followed by GC/MS. The SPE–GC/MS method provides low detection limits (0.2 μg L⁻¹), high recovery (above 95%) and it is a valuable tool for kinetic studies of the degradation process for each polymer used, while HS–SPME–GC/MS has proved to be an effective tool for the extraction and evaluation of volatile degradation by-products.     

Reducing degradation of azo dye by zero-valent iron in aqueous solution

The reducing degradation kinetics of five azo dyes, Acid orange II, Acid orange IV, Acid orange GG, Acid red 3B and Orange I, by zero-valent iron powder in aqueous solution were studied. It showed that the degradation is a two-step reaction, with the first step being reversible. Solution acidity and iron surface area are the factors greatly influencing the degradation rates, and with increasing of acidity and iron surface area, the degradation rates increase.     

Batch-test study on the dechlorination of 1,1,1-trichloroethane in contaminated aquifer material by zero-valent iron

Chlorinated aliphatic hydrocarbons are common groundwater contaminants. One possible remediation option is in-situ reductive dechlorination by zero-valent iron, either by direct injection or as reactive barriers. Chlorinated ethenes (tetrachloroethene: PCE; trichloroethene: TCE) have received extensive attention in this context. However, another common groundwater pollutant, 1,1,1-trichlorethane (TCA), has attracted much less attention. We studied TCA reduction by three types of granular zero-valent irons in a series of batch experiments using polluted groundwater, with and without added aquifer material. Two types of iron were able to reduce TCA completely with no daughter product concentration increases (1,1-dichloroethane: DCA; chloroethane: CA). One type of iron showed slower reduction, with intermediate rise of DCA and CA concentrations. When evaluating the formation of daughter products, the tests on the groundwater alone showed different results than the groundwater plus aquifer batches: DCA did not temporarily accumulate in the batches with added aquifer material, contrary to the batches without added aquifer material. 1,1-dichloroethene (DCE, also present in the groundwater as an abiotic degradation product of TCA) was also reduced slower in the batches without added aquifer material than in the batches with aquifer material. Redox potentials gradually decreased to low values in batches with aquifer material without iron, while the batches with groundwater alone maintained a constant higher redox potential. Either adsorption processes or microbiological activity in the samples could explain these phenomena. Polymerase Chain Reaction (PCR: a targeted gene probe technique) for chlorinated aliphatic compound (CAH)-degrading bacteria confirmed the presence of Dehalococcoides sp. (chloroethene-degraders) but was negative for Desulfobacterium autotrophicum (a known co-metabolic TCA degrader). DCA reduction was rate determining: first-order half-lives of 300-350 h were observed. TCA was fully removed within hours. CA is resistant to reduction by zero-valent iron but it is known to hydrolyze easily. Since CA did not accumulate in our batches, it may have disappeared by the latter mechanism or it may not have formed as a major daughter product.     

一株木材腐朽菌及其粗酶液对七氯的降解

Phlebia acanthocystis TMIC34875是一株具有七氯降解能力的木材腐朽菌。为利用微生物技术去除环境中的七氯残留提供理论依据,研究了该菌株及其粗酶液对七氯的降解性能及其动力学特性。结果表明,菌株在七氯的初始浓度为50μmol/L时具有最大降解速率,为0.3031μmol/（L·h）;而菌体接种量为15%时,降解速率达到最高,为0.2045μmol/（L·h）。降解酶定位研究表明,七氯的降解主要是胞内酶在起作用。七氯胞内酶降解的酶促反应最适温度是35℃,在30-40℃之间有较高的催化活性;最适pH值为5.0,在pH 4.5-6.0之间有较高的催化活性,最适条件下反应1 h后七氯的降解率为65%。胞内粗酶液降解七氯的米氏常数K m为5.42μmol/L,最大反应速率V max为4.55μmol/min。胞内酶处理体系的GC/MS图谱显示,主要降解产物为1-羟基六氯、1-羟基-2,3-环氧六氯和环氧七氯,表明胞内酶对七氯的初始代谢机理同菌株相似,均是通过环氧化和置换反应来完成的。     

组合阳极联合气体扩散阴极电催化降解苯胺

采用气体扩散电极为阴极,钛基氧化物（Ti／SnO2-Sb2O5-IrO2）和金属铁构成组合阳极,构建了新型电化学氧化体系用于降解有机污染物。利用该氧化体系,在不同实验条件下考察了苯胺降解的效果与降解过程的相关规律。结果表明,阴极电位、铁阳极通电时间以及苯胺初始浓度均显著影响苯胺的降解效果。当阴极电位为-0．7V,pH3．0,铁阳极通电时间20min时,电化学处理200mg／L苯胺480min,TOC的去除效率达到80．4％,矿化电流效率（MCE）为8．6％,显示了该氧化体系具有良好的有机物降解能力。此外,苯胺降解过程中氨氮和硝态氮浓度的变化表明,苯胺分子中的氮主要转化为NH4和NO3^-。