温度对生物活性炭降解卤乙酸的影响

卤乙酸(HAAs)是饮用水中常见的氯和氯胺消毒副产物,具有较高的亲水性与致癌性,为了保证水质与人体健康,各国均对其制定了相关规定。考察了生物活性碳(BAC)对9种HAA的去除性能,并探讨HAA生物降解效果随温度的变化情况与生物反应的去除机理,反应动力学与热力学。结果显示,BAC可有效去除水体中的一卤代与二卤代乙酸,难以去除三卤代乙酸。BAC的生物降解性能明显可分为2个部分:低温(5~15℃)基本不发生生物降解;高温(25~35℃)生物降解性能显著。在不同温度下,HAA的生物降解均符合一级反应动力学,反应速率常数为0.01~0.40 min-1;BAC降解HAA的过程不是逐级氢取代卤而是同时脱去所有卤素的反应,卤代乙酸生物反应的活化能为63.5~89.2 kJ/mol。     

High-level arsenite removal from groundwater by zero-valent iron

The objectives of this study were to conduct batch and column studies to (i) assess the effectiveness of zero-valent iron for arsenic remediation in groundwater, (ii) determine removal mechanisms of arsenic, and (iii) evaluate implications of these processes with regard to the stability of arsenic and long-term remedial performance of the permeable reactive barrier (PRB) technology. A high concentration arsenic solution (50 mg l(-1)) was prepared by using sodium arsenite (arsenic (III)) to simulate groundwater at a heavily contaminated Superfund site in the USA. Batch studies indicate that the removal of arsenic is a two-step reaction with fast initial disappearance of arsenite followed by a slow subsequent removal process. Flow-through columns were conducted at a flow rate of 17 ml h(-1) under reducing conditions for 6.6 mo. Kinetic analysis suggested that arsenic removal behaves as a zero-order reaction at high arsenic concentrations. Arsenic removal rate constants decreased with time and arsenic breakthrough was observed in the column study. Arsenic removal capacity of zero-valent iron was determined to be approximately 7.5 mg As/g Fe. Carbonate green rust was identified from the analysis of surface precipitates; arsenite uptake by green rust may be a major mechanism responsible for arsenic remediation by zero-valent iron. Analysis of HCl-extractable arsenic from iron samples indicated that approximately 28% of arsenic was in the form of arsenate suggesting that a surface oxidation process was involved in the arsenic removal with zero-valent iron.     

Bio-beads with immobilized anaerobic bacteria,zero-valent iron,and active carbon for the removal of trichloroethane from groundwater

Chlorinated hydrocarbons are the most common organic pollutants in groundwater systems worldwide. In this study, we developed bio-beads with immobilized anaerobic bacteria, zero-valent iron (ZVI), and activated carbon (AC) powder and evaluated their efficacy in removing 1,1,1-trichloroethane (TCA) from groundwater. Bio-beads were produced by polyvinyl alcohol, alginate, and AC powder. We found that the concentration of AC powder used significantly affected the mechanical properties of immobilized bio-beads and that 1.0 % (w/v) was the optimal concentration. The bio-beads effectively degraded TCA (160 mg L^?1) in the anaerobic medium and could be reused up to six times. The TCA degradation rate of bio-beads was 1.5 and 2.3 times greater, respectively, than ZVI + AC treatment or microbes + AC treatment. Measuring FeS produced by microbial reactions indicated that TCA removal occurred via FeS-catalyzed dechlorination. Analysis of clonal libraries derived from bio-beads demonstrated that the dominant species in the community were Betaproteobacteria and Gammaproteobacteria, which may contribute to the long-term stability of ZVI reactivity during TCA dechlorination. This study shows that the combined use of immobilized anaerobic bacteria, ZVI, and AC in bio-beads is effective and practical for TCA dechlorination and suggests they may be applicable towards developing a groundwater treatment system for the removal of TCA.     

Reductive degradation of carbaryl in water by zero-valent iron

Reduction of carbaryl solution by zero-valent iron powder (ZVIP) was studied in a rotator batch system (70 rpm) in order to evaluate the utility of this reaction in remediation of carbamate contaminated water. Degradation with different amount of ZVIP: 0.01, 0.02, 0.03, 0.04 g/ml at pH 6.6 and at ambient temperature was investigated. The results show that the process exhibits a degradation rate appearing to be directly proportional to the surface contact area of ZVIP (325-mesh) with the carbaryl molecules. Three analytical techniques were used to monitor carbaryl degradation: (1) A UV-Vis diode array spectrophotometer was used to record all spectra. (2) A high performance liquid chromatography was used to separate by-products and examine the evolution of breakdown products. (3) A home-built spectrophosphorimeter that uses the solid surface room temperature phosphorescence (SSRTP) was employed to observe selectively the decline of the carbaryl concentration at different amount of ZVIP on Whatman no. 1 filter paper. Results show that the reducing degradation of carbaryl with ZVIP as the source of electrons is effective with a half-life close to several minutes.     

Enhanced degradation of ortho-nitrochlorobenzene by the combined system of zero-valent iron reduction and persulfate oxidation in soils

ortho-Nitrochlorobenzene (o-NCB) in soil poses significant health risks to human because of its persistence and high toxicity. The removal of o-NCB by both zero-valent iron (ZVI) and chemical oxidation (persulfate) was investigated by batch experiments. The o-NCB removal rate increases significantly from 15.1 to 97.3 % with an increase of iron dosage from 0.1 to 1.0 mmol g^?1. The o-NCB removal rate increases with the decrease of the initial solution pH, and a removal efficiency of 90.3 % is obtained at an initial pH value of 6.8 in this combined system. It is found that temperature and soil moisture could also increase the o-NCB removal rate. The o-NCB degradation rate increases from 83.9 to 96.2 % and from 41.5 to 82.4 % with an increase of temperature (15 to 35 °C) and soil moisture (0.25 to 1.50 mL g^?1), respectively. Compared to the persulfate oxidation system and ZVI system, the persulfate–iron system shows high o-NCB removal capacity. o-NCB removal rates of 41.5 and 62.4 % are obtained in both the persulfate oxidation system and the ZVI system, while the removal rate of o-NCB is 90.3 % in the persulfate–iron system.     

Rapid removal of flutriafol in water by zero-valent iron powder

A study of the effect of zero-valent iron (ZVI) powder is carried out for the first time on the degradation of flutriafol ((RS)-2,4'-difluoro-alpha-(1H-1,2,4-triazol-1-ylmethyl)-benzhydryl alcohol, C(16)H(13)F(2)N(3)O), a bifluorinated soil and water persistent triazole pesticide using a laboratory scale device consisting of a 20 ml pyrex serum vials fixed to a Vortex agitator. Different amounts of ZVI powder (10-50 g l(-1)) at pH 6.6 and room temperature were investigated. Experiments showed an observed degradation rate k(obs) directly proportional to the surface of contact of flutriafol with ZVI. Flutriafol degradation reactions demonstrated first order kinetic with a half-live of about 10.8+/-0.5 min and 3.6+/-0.2 min when experiments were conducted at [ZVI]=10 g l(-1) into oxygenated and anoxic solutions, respectively. Three analytical techniques were employed to monitor flutriafol degradation and to understand solution and by-products behaviors: (1) A UV-Vis spectrophotometer; (2) a high performance liquid chromatography (HPLC) coupled with a photo diode array (PDA) and fluorescence detectors; (3) a similar HPLC coupled with a PDA and a mass spectrometer detectors equipped with an atmospheric pressure photoionization source. Results showed a complete disappearance of flutriafol after 20 min of contact with ZVI, the loss of fluorescence properties of the final by-products, the defluorination of the triazole pesticide via hydroxylation reaction and finally the hydrogenation of the triazole ring.     

几种印染助剂对壳聚糖稳定纳米铁去除酸性品红的影响

以氯化铁为铁源,硼氢化钠为还原剂,壳聚糖为稳定剂,采用液相还原法制备壳聚糖稳定纳米铁（CS-nZⅥ）;研究了印染废水中常见助剂NaNO₃、Na₂SO₄、NaH₂PO₄、K₂Cr₂O₇、EDTA二钠盐存在下,超声波辅助CS-nZⅥ对酸性品红（AF）降解的影响。结果表明,反应15 min,0.01 g CS-nZⅥ对25 mL、100 mg/L AF的去除率高达99.9%;各种助剂的存在使得纳米铁表面不同程度失活,阻碍反应的进行,使得AF的去除率下降。NaNO₃、K₂Cr₂O₇、EDTA二钠盐与纳米铁发生反应,与AF存在明显的竞争作用。重复利用实验表明,CS-nZⅥ重复利用7次仍具有一定的反应活性。此外,CS-nZⅥ对加标（50 mg/L）实际废水中AF的去除率达到99%以上,表明CS-nZⅥ是一种潜在的环境修复材料。     

Reductive degradation of nitrobenzene in aqueous solution by zero-valent iron

The reductive degradation of nitrobenzene (NB) by zero-valent iron was investigated. Experimental results showed that the degradation of NB was influenced by pH and NB concentration. The optimum pH value was found to be 3.0 for the reductive degradation of NB in the tested pH ranges of 3.0-12.0. The formation rate of aniline, a major reductive product of NB, followed zero-order kinetics at various pH levels. Furthermore, GC/MS analysis showed that aniline, azobenzene and azoxybenzene were the reductive products of NB by zero-valent iron. With the analysis of the products with GC/MS and FTIR, possible reductive pathways of NB by zero-valent iron were suggested.     

Synergistic degradation of deca-BDE by an enrichment culture and zero-valent iron

Debromination of decabromodiphenyl ether (deca-BDE) by microbe and by zero-valent iron (ZVI) has been reported previously. However, no study has indicated the presence of microorganisms and their effect on ZVI-mediated reduction of deca-BDE. Synergistic degradation of deca-BDE by an enrichment culture and ZVI was studied. It was found that synergistic effects enhanced the debromination of deca-BDE as well as promoting the reduction of lower brominated products. ZVI stimulated microbial debromination by serving as an electron donor. Correlation analysis also confirmed that ZVI was capable of enhancing microbial population in the debromination of deca-BDE. Conversely, the enrichment culture produced acid which maintained pH stability and stimulated the oxidation of ZVI. The enrichment culture supplied its energy requirements by the oxidation of ZVI and concomitant reduction of deca-BDE, but incapable of growth and reduction of BDE-209 without ZVI and vice versa. Compared to the initial culture, the microbial community of the enrichment culture became dominated by several bacterial genera based on the results of 16S rRNA-gene pyrosequencing.     

不同阳离子对Fe~0还原硝酸盐的影响

由于水中硝酸盐污染的普遍性、难去除性和对人体健康的潜在危害性而引起人们的广泛关注。通过批实验,考察了不同阳离子(Fe2+、Fe3+和Cu2+)对Fe0还原硝酸盐的影响。结果表明,由于加入阳离子可直接或间接地增加溶液中的Fe2+而都能促进硝酸盐的还原,作用顺序为Fe3+Fe2+Cu2+;Fe2+对硝酸盐的还原具有重要作用,并随着反应的进行,转化为铁氧化物附着在铁表面而降低铁的活性;硝酸盐还原的主要产物为氨氮,亚硝酸盐只在反应初期有少量积累,尤其是加Cu2+的体系中,但随后都很快降低;在所有体系中,检测到的三氮(NO3--N、NO2--N和NH4+-N)之和只占理论总氮的51.5%~82.6%;动力学分析表明,硝酸盐的还原在不加阳离子的体系中更符合一级反应,而加了阳离子的处理更符合Lo-gistic模型。本研究结果阐明了Fe2+对Fe0还原硝酸盐的重要性。     

酸碱改性生物质炭-纳米零价铁增强六价铬去除的机理

通过氢氟酸和氢氧化钠改性水稻秸秆生物质炭(BC),得到改性材料BC-HF和BC-NaOH,在此基础上负载纳米零价铁(Nanoscale zero-valent iron,nZVI)制得生物质炭负载纳米零价铁(nZVI@BC)、氢氟酸改性生物质炭负载纳米零价铁(nZVI@BC-HF)和氢氧化钠改性生物质炭负载纳米零价铁(nZVI@BC-NaOH)。通过比表面积分析、元素分析、红外光谱分析、X射线衍射分析以及动力学等方法,研究了不同材料对Cr(Ⅵ)的去除性能与机理。结果表明：酸碱改性后的生物质炭比表面积、孔体积显著增加,促进了Cr(Ⅵ)的去除,BC-HF和BC-NaOH对Cr(Ⅵ)的去除量分别为30.87、19.59 mg·g⁻¹,为BC的2.68、1.70倍;负载nZVI后,进一步增强了Cr(Ⅵ)的去除效果,其中,nZVI@BC-HF和nZVI@BC-NaOH对Cr(Ⅵ)的去除效果显著,去除量分别为76.36、65.62 mg·g⁻¹。酸碱改性生物质炭使nZVI得到了有效分散,其表面的Si-O-Si官能团与nZVI耦合成Si-O-Fe键,增强了nZVI对Cr(Ⅵ)的还原;同时,酸碱改性生物质炭负载nZVI促进了铁铬化合物的结晶,有利于反应的持续进行。本研究表明,酸碱改性生物质炭-纳米零价铁复合材料对于地下水中Cr(Ⅵ)的去除具有较大的应用潜力。     

柠檬酸强化纳米零价铁活化过硫酸钠体系降解水溶液中的三氯乙烯

采用螯合剂柠檬酸(CA)强化纳米零价铁(nZVI),活化过硫酸钠(PS)体系,降解水溶液中的三氯乙烯(TCE),分别考察了PS、CA、nZVI投加量、溶液初始pH和无机阴离子对TCE降解效果的影响,确定了在TCE降解过程中起主导作用的活性氧自由基,并验证了PS/nZVI/CA体系降解实际地下水中TCE的效果。结果表明:投加适量的CA可以明显提高PS/nZVI体系对TCE的降解效果,但当CA浓度过高时,TCE降解反而受到抑制,过量或不足的PS、nZVI均会降低TCE的降解率;当溶液初始pH为3～9时,PS/nZVI/CA体系可有效降解TCE;溶液中存在的Cl–和HCO_3~-会抑制TCE的降解,其中HCO_3~-的抑制作用大于Cl–;自由基清除实验和电子顺磁共振实验表明PS/nZVI/CA体系中产生了HO·、SO_4~-·和O _2~-·活性氧自由基,其中HO·、SO_4~-·对TCE降解起主导作用;CA的加入有利于实际地下水中TCE的降解,PS/nZVI/CA体系相比PS/nZVI体系,更适应实际地下水中各种水质条件的冲击,具有实际应用前景。     

Microwave-induced nanoscale zero-valent iron degradation of perchloroethylene and pentachlorophenol

Microwave (MW) is applied to enhance perchloroethylene (PCE) or pentachlorophenol (PCP) removal using zero-valent iron (ZVI; Fe⁰) as the dielectric medium. ZVI has a much higher dielectric loss factor (39.5) than other media; it is capable of absorbing MW radiation rapidly to speed up the release of electrons, leading to rises of the ZVI particle surface temperature. If the MW power is continued, excessive electricity will accumulated inside ZVI particles, resulting in sparks. The results show that during the initial 5 sec (700 W), the linear aliphatic PCE has a faster decomposing rate than the ringed PCP (82.0% vs. 4.8%) because less energy is required for decomposing the linear-chlorine bond (90 kcal mol^?1) than ring-chlorine bonds (95 kcal mol^?1). Later, the removal rate for either PCE or PCP remains the same when the exposure time is between 5 and 60 sec. Without MW irradiation, linear PCE molecules have larger surface area to contact ZVI, and hence they have better removal efficiencies than PCP molecules. Using Fe⁰ as a microwave dielectric medium to treat PCE or PCP is a new and worthwhile treatment technology; it is environmentally friendly, and its use will eliminate the secondary pollution.

Implications Nanoscale iron particles are characterized by high surface-area-to-volume ratios, high specific surface area, and high surface reactivity. With a much higher dielectric loss factor, it is capable of absorbing MW radiation rapidly to speed up the release of electrons, leading to rise in temperature. The time needed to achieve a satisfactory treatment is also reduced, leading to significant saving of energy consumption to make this method cost-effective and also environmentally friendly for the industry to pursuit sustainable development.     

纳米零价铁颗粒除磷反应机理

从溶液化学与固相表征两方面对纳米零价铁(NZVI)去除水中磷酸根(PO43-)的机理进行初步探究。分别研究不同初始pH值、溶解氧(DO)对NZVI除磷效果的影响,结果表明,酸性环境(pH为3.0~7.0)有利于NZVI除磷,且初始pH值越低,磷去除率越高;好氧环境较厌氧环境更利于磷的去除,DO>8.0 mg/L时对磷酸根的去除率是厌氧条件(DO2等7种不同去除材料中以Ca(OH)2的共沉淀作用去除率最大(99.9%),NZVI次之(87.2%),表明NZVI除磷机理中还存在共沉淀作用。采用多种固相表征手段对NZVI除磷前后进行分析:扫描电子显微镜(SEM)显示反应后出现不规则颗粒;X射线衍射(XRD)表明Fe3(PO4)2是主要反应产物;X射线光电子能谱(XPS)分析未发现磷被还原成低价态。研究表明,NZVI可有效去除水中磷酸根,主要去除机理包括:NZVI对磷酸根的吸附作用、NZVI在水中腐蚀产生的Fe2+离子对磷酸根的化学沉淀作用及铁氢氧化物与磷酸根的共沉淀作用。     

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.     

催化剂在Fe0还原污水硝态氮中的催化作用

为降低水体中的硝态氮对环境的危害,提高污水处理厂出水水质,将催化剂运用到零价铁还原硝态氮反应中,分别对含TiO2及Pd的催化剂进行了探索性实验。该实验以配置的KNO3溶液为实验水样,在比较研究添加H+、TiO2/Al2O3催化剂、Pd/Al2O3催化剂去除效果的基础上,深入研究了负载量、载体类型、pH、溶解氧、共存离子等因素对去除效果的影响。结果表明,催化剂TiO2/Al2O3对零价铁还原硝态氮的去除率有促进作用,水样pH=3.1时去除率为72%,产物主要为氨氮,应用性较差;而催化剂Pd/Al2O3在pH=3.1时去除率虽为43%,但产物以N2为主。在负载量为5%的情况下,N2转化率为76%,这对去除总氮有重要意义,并从电子转移角度探讨了该反应的反应机理,提出了活性氢（H*）为核心的机理模型。     

Simultaneous removal of NO and SO2 by high-temperature fluidized zero-valent iron processes

A new approach to simultaneously remove nitrogen monoxide (NO) and sulfur dioxide (SO2) by zero valent iron (ZVI) was investigated. Three different parameters, temperature, flux, and ZVI dosage, were tested in fluidized ZVI column studies containing 500 ppmv of NO and SO2, respectively. Under the ZVI dosage of 0.5 g at flux of 0.6 L/cm2 x min for temperature 573 K, there is neither NO nor SO2 reduction. For 623 K and 673 K, complete removal for NO and > 90% removal for SO2 were achieved. For temperatures of 723 K and 773 K, 100% removal was achieved for both NO and SO2. The amounts of NO or SO2 reduction (as milligrams of NO or SO2 per gram ZVI) increased as temperature increased, and linearities were observed with both correlation coefficients > 0.97. Compared with NO, SO2 had earlier breakthrough because of a slower diffusion rate and less reactivity but higher mass reduction because of a higher molecular weight for SO2 (64 g/mol for SO2 and 30 g/mol for NO). At same temperature, both NO and SO2 reductions (as milligrams of NO or SO2 per gram of ZVI) were constant regardless of either flux or ZVI dosage variation, but breakthrough time was affected by both flux and ZVI dosage. A parameter weight of ZVI/flux (W/F) was developed to represent these two parameters at the same time to assess the breakthrough time of NO and SO2. Higher breakthrough time was achieved for higher W/F value. Moreover, interestingly, longer breakthrough time and more NO and SO2 mass reduction were achieved for combined NO and SO2 than individual NO or SO2 treated by ZVI, and both oxidation and reduction reactions occurred instead of a reduction reaction only. Chemical reactions among ZVI/NO, ZVI/ SO2, and ZVI/NO/SO2 were also proposed and verified by X-ray diffraction analyses.     

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.     

In field arsenic removal from natural water by zero-valent iron assisted by solar radiation

An in situ arsenic removal method applicable to highly contaminated water is presented. The method is based in the use of steel wool, lemon juice and solar radiation. The method was evaluated using water from the Camarones River, Atacama Desert in northern Chile, in which the arsenic concentration ranges between 1000 and 1300 μg L⁻¹. Response surface method analysis was used to optimize the amount of zero-valent iron (steel wool) and the citrate concentration (lemon juice) to be used. The optimal conditions when using solar radiation to remove arsenic from natural water from the Camarones river are: 1.3 g L⁻¹ of steel wool and one drop (ca. 0.04 mL) of lemon juice. Under these conditions, removal percentages are higher than 99.5% and the final arsenic concentration is below 10 μg L⁻¹. This highly effective arsenic removal method is easy to use and inexpensive to implement.