某典型铬盐厂污染场地Cr(VI)还原菌的筛选、鉴定及还原特性

从河南省义马市某典型铬盐厂污染场地3个典型区域获得污染土壤,以K2Cr2O7为供试物,用固体平板法筛选出8株菌,并进行Cr（VI）还原菌耐受性实验,挑选出耐受性较高的2株菌作为Cr（VI）的优势还原菌株,对这2株菌进行生长曲线的测定,用16S rRNA基因测序技术对其进行菌种鉴定,并研究了其在不同初始浓度、接种量、pH、温度条件下的还原特性,获得最佳还原条件。结果表明：YM4和YM7等2株菌对Cr（VI）具有高耐受性,其对50 mg·L-1和75 mg·L-1 Cr（VI）浓度的还原率均能达到97%以上。但Cr（VI）浓度提高到100 mg·L-1,YM4和YM7对Cr（VI）的还原率下降到了60%,说明100 mg·L-1 Cr（VI）对YM4和YM7产生了抑制作用。基因测序鉴定出YM4为芽孢杆菌,YM7为微小杆菌。在20～75 mg·L-1 范围内YM4和YM7均对Cr（VI）有较好去除效果。YM4的最佳还原条件是接种量为5%、pH为7.0～8.0、温度为35 ℃,YM7的最佳还原条件是接种量为5%、pH为7.0、温度为40 ℃。基于2株菌对Cr（VI）还原特性的研究,YM4和YM7可以用来作为微生物修复铬污染土壤的备选菌种。     

Emissions of chromium (VI) from arc welding

The presence of Cr in the +6 oxidation state (Cr[VI]) is still observed in ambient air samples in California despite steps taken to reduce emissions from plating operations. One known source of emission of Cr(VI) is welding, especially with high Cr-content materials, such as stainless steels. An experimental effort was undertaken to expand and update Cr(VI) emission factors by conducting tests on four types of arc-welding operations: gas-metal arc welding (GMAW), shielded metal arc welding (SMAW), fluxcore arc welding, and pulsed GMAW. Standard American Welding Society hood results were compared with a total enclosure method that permitted isokinetic sampling for particle size-cut measurement, as well as total collection of the aerosol. The fraction of Cr(VI) emitted per unit mass of Cr electrode consumed was determined. Consistent with AP-42 data, initial results indicate that a significant fraction of the total Cr in the aerosol is in the +6 oxidation state. The fraction of Cr(VI) and total aerosol mass produced by the different arc welding methods varies with the type of welding process used. Self-shielded electrodes that do not use a shield gas, for example, SMAW, produce greater amounts of Cr(VI) per unit mass of electrode consumed. The formation of Cr(VI) from standard electrode wires used for welding mild steel was below the method detection limit after eliminating an artifact in the analytical method used.     

Remediation of Cr(VI) from chromium slag by biocementation

Here we demonstrate a calcifying ureolytic bacterium Bacillus sp. CS8 for the bioremediation of chromate (Cr(VI)) from chromium slag based on microbially induced calcite precipitation (MICP). A consolidated structure like bricks was prepared from chromium slags using bacterial cells, and five stage Cr(VI) sequential extraction was carried out to know their distribution pattern. Cr(VI) mobility was found to significantly be decreased in the exchangeable fraction of Cr slag and subsequently, the Cr(VI) concentration was markedly increased in carbonated fraction after bioremediation. It was found that such Cr slag bricks developed high compressive strength with low permeability. Further, leaching behavior of Cr(VI) in the Cr slag was studied by column tests and remarkable decrease in Cr(VI) concentration was noticed after bioremediation. Cr slags from columns were characterized by SEM–EDS confirming MICP process in bioremediation. The incorporation of Cr(VI) into the calcite surface forms a strong complex that leads to obstruction in Cr(VI) release into the environment. As China is facing chromium slag accidents at the regular time intervals, the technology discussed in the present study promises to provide effective and economical treatment of such sites across the country, however, it can be used globally.     

Efficient biosorption of chromium(VI) ion by dry Araucaria leaves

Background

In this paper, batch removal of hexavalent chromium from aqueous solutions by Araucaria heterophylla leaves was investigated. The batch experiments were conducted to study the adsorption of metal species and effect of different pH, contact time, metal concentration, biosorbent concentration, and adsorption capacity.

Method

Freundlich and Langmuir??s isotherm model were used to describe the adsorption behavior, and the experimental results fitted Freundlich model well.

Results

The adsorption efficiency observed for all chromium concentrations, i.e., 1, 3, 5, and 10?mg/L was 100% and the equilibrium was achieved in 30?min for 1 and 3?mg/L, whereas for 5 and 10?mg/L, it was less than 60?min. FTIR spectra was taken to identify functional groups involved in the biosorption.

Conclusion

Thus, Araucaria leaves can be considered as one of the cheap and efficient biosorbent for toxic hexavalent chromium removal from natural or wastewaters.     

MgAl型层状化合物对六价铬的吸附性能

尿素-水热法制备层状双金属氢氧化物MgAl-LDH,系统考察了焙烧温度、pH值、初始Cr（VI）浓度、吸附时间和吸附温度对样品的吸附性能的影响。并对其吸附热力学、动力学和吸附机理进行研究。采用傅里叶红外光谱（FT-IR）对吸附Cr（VI）前后的MgAl-LDH进行表征。MgAl-LDH的最佳吸附条件为pH=2.5,吸附过程符合Langmuir等温模型,最大吸附容量为105.15 mg·g-1,其对Cr（VI）的吸附为放热过程,并遵守准二级动力学模型,化学吸附为主导。MgAl-LDH对Cr（VI）的吸附主要在酸性条件下进行,吸附机理主要为静电作用和离子交换：在酸性条件下,MgAl-LDH表面带正电荷,并通过静电作用吸附Cr（VI）阴离子,同时MgAl-LDH的层间CO32-和NO3-与溶液中的Cr（VI）阴离子进行离子交换。     

Molecular study of thermal immobilization of chromium(VI) with clay

Clay that contains kaolinite has been used extensively as a raw material for manufacturing of bricks and china at 900-1100 degrees C. This study used clay to stabilize the contaminant chromium(VI) [Cr(VI)] through a heating process at 500-1100 degrees C. X-ray absorption spectroscopic results indicated that the 500-900 degrees C heating process transformed hazardous Cr(VI) to nontoxic Cr(III); Cr2O3 was the species detected as most abundant. The 1100 degrees C heating process caused the formation of Cr2SiO5, which was not detected in the samples heated at 500-900 degrees C. Fourier transformed extended X-ray absorption fine structure spectra were fitted by use of WinXAS software. Phase shifts and backscatter(ing) amplitudes for specific atom pairs, based on the crystallographic data for CrO3 and Cr2O3, were theoretically calculated with the FEFF software. The processed XAS data show that the first shell coordination numbers were similar to each other as the temperature was increased from 500 to 900 degrees C and 1100 degrees C, implying that their Cr(III) crystallite size was relatively similar. The interatomic distance between the target center element and the first shell for the 500-1100 degrees C samples was 1.98 A. The Debye-Waller factor for the 1100 degrees C sample was increased compared with the 500 and 900 degrees C samples and probably indicates the formation of Cr2SiO5.     

催化荧光法测定环境水样中痕量铬(VI)

研究了在HAC－NaAC介质中,痕量铬（VI）催化过氧化氢氧化罗丹明6G的褪色反应及其动力学条件,建立了催化荧光测定痕量铬（VI）的新方法。催化反应在沸水浴中进行15min,为假零级反应。方法的检出限为2．1×10－9g／mL,线性范围为0．2～2．5μg／25mL。将该法用于环境水样中痕量铬（VI）的测定,结果良好。     

Biosorption of chromium (VI) from aqueous solutions and ANN modelling

The use of sustainable, green and biodegradable natural wastes for Cr(VI) detoxification from the contaminated wastewater is considered as a challenging issue. The present research is aimed to assess the effectiveness of seven different natural biomaterials, such as jackfruit leaf, mango leaf, onion peel, garlic peel, bamboo leaf, acid treated rubber leaf and coconut shell powder, for Cr(VI) eradication from aqueous solution by biosorption process. Characterizations were conducted using SEM, BET and FTIR spectroscopy. The effects of operating parameters, viz., pH, initial Cr(VI) ion concentration, adsorbent dosages, contact time and temperature on metal removal efficiency, were studied. The biosorption mechanism was described by the pseudo-second-order model and Langmuir isotherm model. The biosorption process was exothermic, spontaneous and chemical (except garlic peel) in nature. The sequence of adsorption capacity was mango leaf > jackfruit leaf > acid treated rubber leaf > onion peel > bamboo leaf > garlic peel > coconut shell with maximum Langmuir adsorption capacity of 35.7 mg g^?1 for mango leaf. The treated effluent can be reused. Desorption study suggested effective reuse of the adsorbents up to three cycles, and safe disposal method of the used adsorbents suggested biodegradability and sustainability of the process by reapplication of the spent adsorbent and ultimately leading towards zero wastages. The performances of the adsorbents were verified with wastewater from electroplating industry. The scale-up study reported for industrial applications. ANN modelling using multilayer perception with gradient descent (GD) and Levenberg-Marquart (LM) algorithm had been successfully used for prediction of Cr(VI) removal efficiency. The study explores the undiscovered potential of the natural waste materials for sustainable existence of small and medium sector industries, especially in the third world countries by protecting the environment by eco-innovation.     

Accumulation of chromium (VI) from aqueous solutions using water lilies (Nymphaea spontanea)

This study describes an investigation using tropical water lilies (Nymphaea spontanea) to remove hexavalent chromium from aqueous solutions and electroplating waste. The results show that water lilies are capable of accumulating substantial amount of Cr(VI), up to 2.119 mg g(-1) from a 10 mg l(-1) solution. The roots of the plant accumulated the highest amount of Cr(VI) followed by leaves and petioles, indicating that roots play an important role in the bioremediation process. The maturity of the plant exerts a great effect on the removal and accumulation of Cr(VI). Plants of 9 weeks old accumulated the most Cr(VI) followed by those of 6 and 3 weeks old. The results also show that removal of Cr(VI) by water lilies is more efficient when the metal is present singly than in the presence of Cu(II) or in waste solution. This may be largely associated with more pronounced phytotoxicity effect on the biochemical changes in the plants and saturation of binding sites. Significant toxicity effect on the plant was evident as shown in the reduction of chlorophyll, protein and sugar contents in plants exposed to Cr(VI) in this investigation.     

苯胺-2,4-二氨基酚共聚物对水中Cr(Ⅵ)吸附性能的研究

利用化学氧化法合成了苯胺-2,4-二氨基酚的共聚物,并通过静态吸附实验研究了该材料对水中Cr(Ⅵ)的吸附性能.研究表明,该共聚物对废水中Cr(Ⅵ)的去除效果显著,该吸附过程为自发吸热反应,符合Langmuir单层吸附模型;其动力学行为符合准二级动力学方程.溶液pH值对吸附性能影响较大,pH 3～6范围内吸附效果较好.吸...     

Manganese uptake and accumulation by the hyperaccumulator plant Phytolacca acinosa Roxb. (Phytolaccaceae)

The perennial herb Phytolacca acinosa Roxb. (Phytolaccaceae), which occurs in Southern China, has been found to be a new manganese hyperaccumulator by means of field surveys on Mn-rich soils and by glasshouse experiments. This species not only has remarkable tolerance to Mn but also has extraordinary uptake and accumulation capacity for this element. The maximum Mn concentration in the leaf dry matter was 19,300 microg/g on Xiangtan Mn tailings wastelands, with a mean of 14,480 microg/g. Under nutrient solution culture conditions, P. acinosa could grow normally with Mn supplied at a concentration of 8000 micromol/l, although with less biomass than in control samples supplied with Mn at 5 micromol/l. Manganese concentration in the shoots increased with increasing external Mn levels, but the total mass of Mn accumulated in the shoots first increased and then decreased. At an Mn concentration of 5000 micromol/l in the culture solution, the Mn accumulation in the shoot dry matter was highest (258 mg/plant). However, the Mn concentration in the leaves reached its highest value (36,380 microg/g) at an Mn supply level of 12,000 micromol/l. These results confirm that P. acinosa is an Mn hyperaccumulator which grows rapidly, has substantial biomass, wide distribution and a broad ecological amplitude. This species provides a new plant resource for exploring the mechanism of Mn hyperaccumulation, and has potential for use in the phytoremediation of Mn-contaminated soils.     

Synthesis of chromium-doped malayaite pigments from wastewater containing low chromium(VI)

A malayaite pigment was synthesized with wastewater containing low chromium (Cr)(VI) by a novel liquid-phase reaction method. The effects of the particle size of the precursor and calcination temperature on the final product are examined. The result of scanning electron microscopy shows that the obtained precursor is amorphous and the particle size is approximately 250 nm. The results of X-ray diffraction and differential scanning calorimetry show that the complete transformation temperature was approximately 1050 degrees C. Furthermore, the Commission International de l'Eclairage laboratory shows that the red color of as-prepared pigments is more saturated with a high a* value at 34.1. This process of malayaite pigment preparation via reuse of the Cr(VI)-containing wastewater is quite simple, economical, and energy-saving for the industry, and the products have a saturated red color. There is considerable foreground for the industrial application of this work.     

还原剂添加的矿物聚合物对Cr(Ⅵ)的解毒/固化

在对现有Cr(Ⅵ)污染控制方法分析的基础上,提出用还原剂添加的矿物聚合物对Cr(Ⅵ)进行解毒/固化的研究思路。以煤矸石为原料,以水玻璃和NaOH为碱性激发剂,合成矿物聚合物;以FeCl2·4H2O为还原剂,用还原剂添加的矿物聚合物对Cr(Ⅵ)进行解毒/固化实验,并采用XRD、TEM/EDS、XPS对固化体进行检测。当添加的Fe(Ⅱ)与Cr(Ⅵ)的摩尔比≥3:1时,矿物聚合物中总铬的浸出浓度小于1 mg/L,铬固化率大于99%。还原剂添加的矿物聚合物对Cr(Ⅵ)最大固化量为0.8%。在合成过程中,Fe(Ⅱ)和Cr(Ⅵ)添加的矿物聚合物发生了氧化还原反应,Fe(Ⅱ)被氧化成了Fe(Ⅲ),Cr(Ⅵ)被还原成了Cr(Ⅲ),随后Fe(Ⅲ)和Cr(Ⅲ)同时被矿物聚合物中的—OAl(-)(OH)3吸引,并固化在非晶质结构中。     

地下水化学类型对硫系还原剂去除Cr (VI)的影响

为研究铬污染地下水化学类型对硫系还原剂除铬的影响,采用批实验的方式,分别比较了3种还原剂焦亚硫酸钠（Na2S2O5）、连二亚硫酸钠（Na2S2O4）、多硫化钙（CaSx）对SO4-Na型、SO4-Ca型、Cl-Na型和HCO3-Ca型4种地下水中去除Cr（VI）的效果。结果表明,在20℃有氧条件下,4种地下水环境中还原剂的除铬能力受到了不同程度的抑制,其中HCO3-Ca型地下水中的抑制作用最大。但当Na2S2O5、Na2S2O4、CaSx投加量分别为理论投加量的30.8、21.7和2.4倍时,4种地下水中Cr（VI）的去除率均大于90%。Na2S2O5投加量与水中HCO3-含量的摩尔比大于0.5时,Cr（VI）才可能被还原去除;Na2S2O4对Cr（VI）的去除率由高到低排序是：SO4-Na型 > Cl-Na型 > SO4-Ca型 > HCO3-Ca型;CaSx的除铬效果在不同地下水化学类型中的差异最小。地下水的HCO3-含量越高,缓冲能力越强,抑制作用越明显,所需还原剂投加量越多。     

Influence of complex reagents on removal of chromium(VI) by zero-valent iron

The removal of Cr(VI) by zero-valent iron (Fe(0)) and the effect of three complex reagents, ethylenediaminetetraacetic acid (EDTA), NaF and 1,10-phenanthroline, on this reaction were investigated using batch reactors at pH values of 4, 5 and 6. The results indicate that the removal of Cr(VI) by Fe(0) is slow at pH 5.0 and that three complex reagents play different roles in the reaction. EDTA and NaF significantly enhance the reaction rate. The zero-order rate constants at pH 5.0 were 5.44 microM min(-1) in the presence of 4mM EDTA and 0.99 micrM min(-1) in the presence of 8 mM NaF, respectively, whereas that of control was only 0.33 micrM min(-1), even at pH=4.0. This enhancement is attributed to the formation of complex compounds between EDTA/NaF and reaction products, such as Cr(III) and Fe(III), which eliminate the precipitates of Cr(III), Fe(III) hydroxides and Cr(x)Fe(1-)(x)(OH)(3) and thus reduce surface passivation of Fe(0). In contrast, 1,10-phenanthroline, a complex reagent for Fe(II), dramatically decreases Cr(VI) reduction by Fe(0). At pH=4.0, the zero-order rate constant in the presence of 1mM of 1,10-phenanthroline was 0.02 micrM min(-1), decreasing by 99.7% and 93.9%, respectively, compared with the results in the presence and absence of EDTA. The results suggest that a pathway of the reduction of Cr(VI) to Cr(III) by Fe(0) may involve dissolution of Fe(0) to produce Fe(II), followed by reduction of Cr(VI) by Fe(II), rather than the direct reaction between Cr(VI) and Fe(0), in which Fe(0) transfers electrons to Cr(VI).     

板栗壳对重金属Cr（Ⅵ）吸附性能的研究

从废弃的植物材料中筛选出一种Cr(Ⅵ)高效吸附剂——板栗壳。研究了pH、接触时间、板栗壳用量、温度和Cr (Ⅵ)初始浓度对Cr(Ⅵ)吸附活性的影响。结果表明, 板栗壳的最佳pH为2～3。在pH 2时,Cr(Ⅵ)的去除率达99.7%。在15～35℃的温度范围内,板栗壳对Cr(Ⅵ)的去除率随温度的升高而增加。30℃时,Cr(Ⅵ)的去除率可达99%。板栗壳用量对Cr(Ⅵ)的去除有明显影响。由0.2 g增加到0.4 g时, Cr(Ⅵ)的去除率从90.6%提高到99%。在较宽的铬初始浓度范围内,板栗壳对Cr (Ⅵ)有明显的去除作用。     

Kinetics of chromium (VI) reduction by a type strain Shewanella alga under different growth conditions.

We conducted kinetic batch experiments to determine the reduction of Chromium(VI) by a type strain of Shewanella alga (BrY-MT) ATCC 55627. Chromium(VI) was reduced to Chromium(III) by BrY-MT grown in three different substrates: BHIB (brain heart infusion broth), TSB (tryptic soy broth), and M9 (minimum broth). Four different Cr(VI) concentrations 4.836, 10.00, 37.125, and 260.00 mg l-1 were reduced at different rates by BrY-MT in both aerobic and anaerobic conditions. BrY-MT grown in BHIB reduced the maximum amount of Cr(VI) followed by TSB and M9. Carbondioxide produced from bacterial respiration varied with and without Cr(VI) under both aerobic and anaerobic conditions. The Cr(VI) reduction data under anaerobic condition was fitted by a monod model to determine the bacterial kinetic parameters. The kinetic parameters determined by fitting the anaerobic experimental data were used to run a forward simulation for experiments conducted under aerobic conditions. The monod model was modified to account for an inhibition parameter for the Cr(VI) experiment at 260 mg l-1. All the parameters varied within a narrow range, and were distinct for different substrates. Our studies show that, successful in situ bioremediation of Cr(VI) is depended on the type of substrates (electron donors) and the concentration of Cr(VI) in geologic medium.     

Species-dependent chromium accumulation, lipid peroxidation, and glutathione levels in germinating kiwifruit pollen under Cr(III) and Cr(VI) stress

The accumulation of chromium by germinating kiwifruit pollen appears to be significantly affected by Cr species, Cr concentration and calcium availability. Cr(III) accumulation always occurred in a linear manner while Cr(VI) uptake followed a logarithmic model. In the absence of exogenous calcium, Cr(III) accumulation was much higher than that of Cr(VI). It was observed that, as the Cr(III) concentration increased, there was a significant decrease in the endogenous calcium content of pollen, ultimately leading to complete calcium depletion after 90 min of incubation at 150 microM Cr(III). This loss of calcium could be responsible for the strong inhibition of tube emergence and growth following exposure of pollen to Cr(III). Indeed, when exogenous calcium was added to the kiwifruit pollen culture medium, significant growth recovery and reduced Cr(III) uptake occurred; the opposite was true in Cr(VI)-treatments. A significant rise in lipid peroxide production occurs in the presence of both Cr species; the effect was more pronounced following Cr(VI) exposure. Finally, glutathione pool dynamics appears to be differentially affected by chromium species and concentrations. In conclusion, results of the present study have provided important information regarding the different activity profiles of Cr(III) and Cr(VI) in relation to kiwifruit pollen performance, and have also demonstrated differences in some biochemical responses of pollen to metal stress.     

Phyto-remediation potential of Ipomoea aquatica for Cr(VI) mitigation

Phyto-remedial efficiency of Ipomoea aquatica was examined at different experimental conditions for a period of 3 months. This plant was selected due to its easy establishment, tolerance and growing easiness. In all trials, the I. aquatica was grown in coir dust to ensure an inert medium. Essential growth nutrients were supplied externally using Albert solution. Once plant growth conditions were fixed, the model system was spiked with Cr(VI) solution in the range of 7-90 ppm. Up to 28 ppm Cr(VI), I. aquatica exhibits uniform absorption characteristics showing over 75% removal of added Cr(VI). At this stage I. aquatica was not affected and it showed no toxicity symptoms. Therefore, it is suited as a potential phyto-remediant. Further I. aquatica is a vegetable particularly in Asian region; therefore caution has to be taken when selecting it for human consumption due to its high chromium accumulation capacity.     

Relationship between chromium(VI) resistance and extracellular polymeric substances (EPS) concentration by some cyanobacterial isolates

BACKGROUND, AIM, AND SCOPE: Chromium(VI) resistance and its association with extracellular polymeric substance (EPS) concentration in cyanobacteria was investigated. Increased EPS concentration was associated with Cr(VI) resistance. The most resistant isolate, Chroococcus sp. H(4), secreted the most EPS (427 mg/L). MATERIALS AND METHODS: EPS concentration of the two most resistant isolates (Chroococcus sp. H(4) and Synechocystis sp. S(63)) was investigated following exposure to 15 and 35 ppm Cr(VI). The composition of EPS produced by Chroococcus sp. H(4) following exposure to 10 ppm Cr(VI) was analyzed using high-performance liquid chromatography. Control EPS was composed of glucose (99%) and galactronic acid (1%); in the presence of 10 ppm Cr(VI), EPS composition changed to glucose (9%), xylose (75%), rhamnose (14%), and galacturonic acid (2%). RESULTS AND DISCUSSION: Results indicated that (1) exposure to elevated concentrations of Cr(VI) affected the composition of EPS produced by Chroococcus sp. H(4), and (2) there was a correlation between Cr(VI) resistance and EPS concentration in some cyanobacteria.