Dendritic chelating agents. 2. U(VI) binding to poly(amidoamine) and poly(propyleneimine) dendrimers in aqueous solutions

Chelating agents are widely employed in many separation processes used to recover uranyl [U(VI)] from contaminated aqueous solutions. This article describes an experimental investigation of the binding of U(VI) to poly(amidoamine) [PAMAM] and poly(propyleneimine) [PPI] dendrimers in aqueous solutions. We combine fluorescence spectroscopy with bench scale ultrafiltration experiments to measure the extent of binding and fractional binding of U(VI) in aqueous solutions of these dendrimers as a function of (i) metal-ion dendrimer loading, (ii) dendrimer generation, (iii) dendrimer core and terminal group chemistry, and (iv) solution pH and competing ligands (NO3-, PO4(3-), CO3(2-), and Cl-). The overall results of this study suggest that uranyl binding to PAMAM and PPI dendrimers in aqueous solutions involves the coordination of the UO2(2+) ions with the dendrimer amine, amide, and carboxylic groups. We find significant binding of U(VI) to PAMAM dendrimers in (i) acidic solutions containing up to 1.0 M HNO3 and H3PO4 and (ii) in basic solutions containing up to 0.5 M Na2CO3. However, no binding of U(VI) by PAMAM dendrimers is observed in aqueous solutions containing 1.0 M NaCl at pH 3.0. These results strongly suggest that PAMAM and PPI dendrimers can serve as high capacity and selective chelating ligands for U(VI) in aqueous solutions.     

Removal of polycyclic aromatic hydrocarbons from contaminated soil by aqueous DNA solution

An aqueous DNA solution was applied for the extraction of polycyclic aromatic hydrocarbons (PAHs) from a spiked soil. Solubilities of 0.56, 11.78, and 11.24 mg L(-1) for anthracene, phenanthrene, and pyrene, respectively, were achieved after 1 day equilibration in 1% DNA. Using a spiked soil that contained 72 mg kg(-1) anthracene, 102 mg kg(-1) phenanthrene, and 99 mg kg(-1) pyrene, extractions of close to 88, 78, and 94%, respectively, were attained with 5% DNA at a 1:50 soil/extractant ratio. Maximum PAH dissolution occurred after 4-6 h. Comparative tests showed the main advantage of DNA over methyl-beta- and gamma-cyclodextrins and Tween 80 for pyrene removal. An ionic strength of 0.1 M NaCl was found necessary for maximum PAH dissolution and extraction. The performance of hexane regenerated DNA also remained stable after three stages of recycling. These results show the huge potential of DNA as an aqueous washing agent for PAH-contaminated soil.     

Removal of penicillin G from contaminated milk by ultrafiltration

Penicillin G purposedly added to whole raw milk at concentrations from .05 to .20 IU/ml was removed to undetectable levels by a combination of ultrafiltrations and permeate washes. After penicillin removal, whole milk 3:1 vol/vol concentrated retentates were reconstituted to milk with antibiotic-free permeate with little change in composition and with very good to excellent flavor. Washing 3:1 vol/vol concentrated retentates from penicillin-contaminated milks with water also removed penicillin to an undetectable level but changed the composition of product, which displayed a flat flavor.     

络合混凝法去除香菇多糖中的镉污染

目的对香菇多糖提取过程中重金属的去除方法进行研究。方法在提取香菇多糖过程中使用络合以及混凝吸附的方法对香菇多糖粗提液进行处理,去除重金属镉(Cd),并对去除过程中p H值、试剂浓度以及KMn O4预氧化的作用进行了调查。结果香菇多糖提取过程中重金属镉的去除的工艺为:使用0.5 mg/L KMn O4预氧化30 min,在p H 10.0条件下使用络合剂25 mmol/L EDTA和25 mmol/L柠檬酸钠以及混凝剂50mg/L活性炭处理1 h;此工艺下香菇多糖中Cd的去除率高达96.3%。结论本研究为香菇以及其他食材、药材中重金属污染的处理问题提供了新的方法。     

Cadmium removal from contaminated soil by tunable biopolymers

An elastin-like polypeptide (ELP) composed of a polyhistidine tail (ELPH12) was exploited as a tunable, metal-binding biopolymer with high affinity toward cadmium. By taking advantage of the property of ELPH12 to undergo a reversible thermal precipitation, easy recovery of the sequestered cadmium from contaminated water was demonstrated as the result of a simple temperature change. In this study, batch soil washing experiments were performed to evaluate the feasibility of using ELPH12 as an environmentally benign strategy for removing cadmium from contaminated soil. The stability constant (log KL) for the cadmium-ELPH12 complex was determined to be 6.8, a value similar to that reported for the biosurfactant rhamnolipid. Two washings with 1.25 mg/mL of ELPH12 were able to remove more than 55% of the bound cadmium as compared to only 8% removal with ELP containing no histidine tail or 21% removal using the same concentration of EDTA. Unlike rhamnolipid from Pseudomonas aeruginosa ATCC 9027, which adsorbs extensively to soil, less than 10% of ELPH12 was adsorbed under all soil washing conditions. As a result, a significantly lower concentration of ELPH12 (0.036 mM as compared to 5-10 mM of biosurfactants) was required to achieve similar extraction efficiencies. However, cadmium recovery by simple precipitation was incomplete due to the displacement of bound cadmium by zinc ions present in soil. Owing to its benign nature, ease of production, and selective tailoring of the metal binding domain toward any target metals of interest, ELP biopolymers may find utility as an effective extractant for heavy metal removal from contaminated soil or ore processing.     

Arsenic and chromium partitioning in a podzolic soil contaminated by chromated copper arsenate

This research combined the use of selective extractions and X-ray spectroscopyto examine the fate of As and Cr in a podzolic soil contaminated by chromated copper arsenate (CCA). Iron was enriched in the upper 30 cm due to a previous one-time treatment of the soil with Fe(II). High oxalate-soluble Al concentrations in the Bs horizon of the soil and micro-XRD data indicated the presence of short-range ordered aluminosilicates (i.e., proto-imogolite allophane, PIA). In the surface layers, Cr, as Cr(III), was partitioned between a mixed Fe(III)/ Cr(III) solid phase that formed upon the Fe(II) application (25-50%) and a recalcitrant phase (50-75%) likely consisting of organic material such as residual CCA-treated wood. Deeper in the profile Cr appeared to be largely in the form of extractable (hydr)oxides. Throughout the soil, As was present as As(V). In the surface layers a considerable fraction of As was also associated with a recalcitrant phase, probably CCA-treated woody debris, and the remainder was associated with (hydr)oxide-like solid phases. In the Bs horizon, however, XAS and XRF findings strongly pointed to the presence of PIA acting as an effective adsorbent for As. This research shows for the first time the relevance of PIA for the adsorption of As in natural soils.     

Removal of lead contaminated dusts from hard surfaces

Government guidelines have widely recommended trisodium phosphate (TSP) or "lead-specific" cleaning detergents for removal of lead-contaminated dust (LCD) from hard surfaces, such as floors and window areas. The purpose of this study was to determine if low-phosphate, non-lead-specific cleaners could be used to efficiently remove LCD from 3 types of surfaces (vinyl flooring, wood, and wallpaper). Laboratory methods were developed and validated for simulating the doping, embedding, and sponge cleaning of the 3 surface types with 4 categories of cleaners: lead-specific detergents, nonionic cleaners, anionic cleaners, and trisodium phosphate (TSP). Vinyl flooring and wood were worn using artificial means. Materials were ashed, followed by ultrasound extraction, and anodic stripping voltammetry (ASV). One-way analysis of variance approach was used to evaluate the surface and detergent effects. Surface type was found to be a significant factor in removal of lead (p < 0.001). Vinyl flooring cleaned better than wallpaper by over 14% and wood cleaned better than wallpaper by 13%. There was no difference between the cleaning action of vinyl flooring and wood. No evidence was found to support the use of TSP or lead-specific detergents over all-purpose cleaning detergents for removal of lead-contaminated dusts. No-phosphate, non-lead-specific detergents are effective in sponge cleaning of lead-contaminated hard surfaces and childhood lead prevention programs should consider recommending all-purpose household detergents for removal of lead-contaminated dust after appropriate vacuuming.     

Effect of grafting generations of poly(amidoamine) dendrimer from the sisal fiber surface on the mechanical properties of composites

In order to improve the mechanical properties of sisal fiber-reinforced polypropylene composites, the sisal fibers were grafted with poly(amidoamine) dendrimer and the effects of grafting generations on the mechanical properties of composites were studied. The results reveal that the tensile, flexural, and impact strength of the composites are improved considerably with the poly(amidoamine) dendrimer grafting treatment. For the 2.0 generation treatment with the poly(amidoamine) dendrimer, the tensile, flexural, and impact strength of the composites at 30 wt% fiber loading increase by 29%, 13%, and 54%, respectively. However, the thermal and mechanical properties of the sisal fibers decrease after prolonged grafting treatment.     

Removal of arsenic from contaminated soils by microbial reduction of arsenate and quinone

We investigated bioremediation of As-contaminated soils by reductive dissolution of As using a dissimilatory As(V)-reducing bacterium (DARB), Bacillus selenatarsenatis SF-1. We also examined the effect of anthraquinone-2,6-disulfonate (AQDS), an extracellular electron-shuttling quinone, on the As extraction. When B. selenatarsenatis was incubated with As(V)-laden Al precipitates, no acceleration of As dissolution was observed in the presence of AQDS, even though the microbial reduction of AQDS occurred actively. In contrast, AQDS addition significantly enhanced the reductive dissolution of As and Fe in analogous experiments with As(V)-laden Fe(III) precipitates, whereas As dissolution did not occur in the absence of the As(V) reducer. These results indicate the dissolution of As was accelerated by indirect reduction of solid-phase Fe(III) following microbial AQDS reduction, although As(V) reduction is vital for As extraction. B. selenatarsenatis was able to extract As from two types of industrially contaminated soils through reduction of solid-phase As(V) and Fe(III). The copresence of AQDS with B. selenatarsenatis improved the removal efficiency of As from the contaminated soils, concomitantly releasing Fe(II), suggesting that simultaneous use of DARB and electron-shuttling compounds can be an effective strategy for remediation of As-contaminated soils.     

Impact of transgenic tobacco on trinitrotoluene (TNT) contaminated soil community

Environmental contamination with recalcitrant toxic chemicals presents a serious and widespread problem to the functional capacity of soil. Soil bacteria play an essential role in ecosystem processes, such as nutrient cycling and decomposition; thus a decrease in their biomass and community diversity, resulting from exposure to toxic chemicals, negatively affects the functioning of soil. Plants provide the primary energy source to soil microorganisms and affect the size and composition of microbial communities, which in turn have an effect on vegetation dynamics. We have found that transgenic tobacco plants overexpressing a bacterial nitroreductase gene detoxify soil contaminated with the high explosive 2,4,6-trinitrotoluene (TNT), with a significantly increased microbial community biomass and metabolic activity in the rhizosphere of transgenic plants compared with wild type plants. This is the first report to demonstrate that transgenic plants engineered for the phytoremediation of organic pollutants can increase the functional and genetic diversity of the rhizosphere bacterial community in acutely polluted soil compared to wild type plants.     

Use of copper shavings to remove mercury from contaminated groundwater or wastewater by amalgamation

The efficacy of copper shavings (Cu(0)) for the removal of Hg2+ from aqueous solution by amalgamation is demonstrated. Two kinds of copper shavings were investigated: (a) chemically processed shavings (Fluka) and (b) recycled shavings from scrap metal. Batch sorption experiments yielded very high retardation coefficients of 28 850-82 830 for the concentration range studied (1-10 000 microg/L Hg2+ dissolved in distilled water or in a 0.01 M CaCl2 matrix solution). Sorption data were well-described bythe Freundlich isotherm equation. Kinetic batch sorption experiments showed that 96-98% of Hg2+ was removed within 2 h. Column experiments were performed with a mercury solution containing 1000 microg/L Hg in a 0.01 M CaCl2 matrix with a flow rate of 0.5 m/d. No mercury breakthrough (c/c(0) = 0.5) could be detected after more than 2300 percolated pore volumes, and the high retardation coefficients determined in the batch studies could be confirmed. Copper was released from the shavings due to the amalgamation process and to copper corrosion by oxygen, resulting in concentrations of mobilized copper of 0.2-0.6 mg/L. Due to their high efficiency in removing Hg2+ from aqueous solution, the use of copper shavings for the removal of mercury from contaminated water is suggested, employing a sequential system of mercury amalgamation followed by the removal of mobilized copper by an ion exchanger such as zeolites. Possible applications could be in environmental technologies such as wastewater treatment or permeable reactive barriers for in situ groundwater remediation.     

Removal of estrogenic pollutants from contaminated water using molecularly imprinted polymers

A synthetic molecularly imprinted polymer (MIP) sorbent for estrogenic compounds was prepared using a noncovalent imprinting technique. MIP microspheres sized from 1 to 2 microm were synthesized in acetonitrile by using alpha-estradiol as the template, acrylamide as the functional monomer, and trimethylpropanol trimethacrylate as the cross-linker. When compared with the nonimprinted polymer (NIP), the MIP showed outstanding affinity toward alpha-estradiol in aqueous solution with a binding site capacity (B(max)) of 380 nmol mg(-1) MIP, imprinting effect of 35, and a dissociation constant (Kd) of 38 microM. The MIP exhibited significant binding affinity toward other related estrogenic compounds such as beta-estradiol, diethylstilbestrol, estriol, and estrone, suggesting that this material may be appropriate for treating a complex mixture of estrogenic pollutants. The feasibility of removing estrogenic compounds from environmental water by the MIP was demonstrated using lake water spiked with alpha-estradiol. In addition, the MIP reusability without any deterioration in performance was demonstrated for at least five repeated cycles.     

Removal of arsenic(III) from groundwater by nanoscale zero-valent iron

Nanoscale zero-valent iron (NZVI) was synthesized and tested for the removal of As(III), which is a highly toxic, mobile, and predominant arsenic species in anoxic groundwater. We used SEM-EDX, AFM, and XRD to characterize particle size, surface morphology, and corrosion layers formed on pristine NZVI and As(III)-treated NZVI. AFM results showed that particle size ranged from 1 to 120 nm. XRD and SEM results revealed that NZVI gradually converted to magnetite/maghemite corrosion products mixed with lepidocrocite over 60 d. Arsenic(III) adsorption kinetics were rapid and occurred on a scale of minutes following a pseudo-first-order rate expression with observed reaction rate constants (K(obs)) of 0.07-1.3 min(-1) (at varied NZVI concentration). These values are about 1000x higher than K(obs) literature values for As(III) adsorption on micron size ZVI. Batch experiments were performed to determine the feasibility of NZVI as an adsorbent for As(III) treatment in groundwater as affected by initial As(III) concentration and pH (pH 3-12). The maximum As(III) adsorption capacity in batch experiments calculated by Freundlich adsorption isotherm was 3.5 mg of As(III)/g of NZVI. Laser light scattering (electrophoretic mobility measurement) confirmed NZVI-As(III) inner-sphere surface complexation. The effects of competing anions showed HCO3-, H4SiO4(0), and H2P04(2-) are potential interferences in the As(III) adsorption reaction. Our results suggest that NZVI is a suitable candidate for both in-situ and ex-situ groundwater treatment due to its high reactivity.     

Removal of Pb(II) from aqueous solutions by carbons prepared from Sal wood (Shorea robusta)

In the present work, physically and chemically activated carbons are prepared using Sal wood (Shorea robusta) sawdust by thermal process and using sulfuric acid as the activation agent to remove Pb(II) from aqueous solutions. Adsorption equilibrium studies have been done at a pH of 4 and a room temperature of 30 °C. It was found that the adsorption isotherms are favorable and chemically activated carbons are better than physically activated carbon in terms of adsorption capacity. Various two-parameter adsorption isotherm models, viz. Freundlich, Langmuir, Temkin and Dubinin-Radushkevich, were used to fit the equilibrium data and it was found that the Freundlich adsorption model provided best-fit. The first-order irreversible unimolecular reaction model and the pseudo-second-order kinetic models were used to fit the kinetic data and it was found that both the models provided good fit. Kinetic and film diffusion studies show that the adsorption of lead(II) on the activated carbons tested in this work are both intra-particle and film diffusion controlled.     

Modeling of polychlorinated biphenyl removal from contaminated soil using steam

Microwave-generated steam technology shows promise as an effective remediation alternative for removal of polychlorinated biphenyls (PCBs) from contaminated soils, based on our laboratory-scale experiments. The overall process can be described by a nonisothermal, unsteady, coupled heat and multicomponent PCB mass-transport model in a multiphase, variably saturated, porous soil medium. In this paper, a multicomponent PCB mass-transport model is presented that assumes evaporation is an important removal mechanism and that is based on first-order mass transfer between the interface of PCB films and the bulk steam. The model was calibrated using the experimental data, and the calibrated model was verified by computational mass-balance checks and comparisons with laboratory-scale column experimental results. From a qualitative point of view, the calibrated model successfully simulated the transport of PCBs in variably saturated soil media. The calculated increase/decrease factors of physicochemical properties of PCBs as a function of temperature in the soil, water, and free phases were consistent with the model hypothesis of an evaporation process. The effects of mass-transfer coefficients and initial PCB concentrations in the soils on PCB removal rates were investigated using the numerical code. It was determined that the PCB removal rates were sensitive to mass-transfer coefficients and initial PCB concentrations. Although the steam:soil mass ratios required to achieve a given percentage removal were lower for lower initial PCB soil concentrations, steam: soil mass ratios required to achieve a given unit mass removal were higherfor lower initial PCB soil concentrations.     

Lactic acid bacteria-enclosing poly(epsilon-caprolactone) microcapsules as soil bioamendment

Free plant growth-promoting bacteria in soil bioamendments (SBA) are easily outnumbered by competitors and predators in agricultural soils. Microencapsulation of the bacteria is an effective technique that provides a suitable microenvironment for their survival. In this study, we attempted to prepare poly(epsilon-caprolactone) (PCL) microcapsules enclosing lactic acid bacteria (LAB), a plant growth-promoting bacteria, using the solvent-evaporation method via water-in-oil-in-water (W/O/W) emulsion. Three preparation parameters in the emulsion system were optimized based on the lactic acid production activity of the encapsulated LAB. A sodium alginate aqueous solution suspending the bacteria, a dichloromethane solution with dissolved PCL, and a poly(vinyl alcohol) aqueous solution were used as the inner aqueous phase (W(i)), the oil phase (O), and the outer aqueous phase (W(o)), respectively. Suitable volume ratio of W(i) to O, concentration of sodium alginate in W(i), and the molecular weight of PCL in O were 0.1, 1.0%, and 40 kDa, respectively. The lactic acid production activity of the microcapsules prepared under the optimized conditions was approximately nine times higher than that of commercial SBA. Application to soil demonstrated that the microcapsules are effective in the removal of the root-knot nematodes.     

Removal of Cr(VI) from aqueous solutions by modified walnut shells

Walnut shell (WNS) (Juglans regia) has been utilised as an adsorbent for the removal of Cr(VI) ions from aqueous solutions after treatment with citric acid. The modification reaction variables, such as citric acid level (5-10 g), reaction time (0-24 h), and temperature (110-130 °C) were studied in batch experiments. The rate of adsorption was studied under a variety of conditions, including initial Cr(VI) concentration (0.1-1.0 mM), amount of adsorbent (0.02-0.20 g), pH (2-9), temperature and contact time (10-240 min). Adsorption of Cr(VI) is in all cases pH-dependent showing a maximum at equilibrium pH values between 2.0 and 3.0 for citric acid modified walnut shell (CA-WNS). The applicability of the Langmuir, Freundlich and D-R adsorption isotherms has been tested for the equilibrium. Maximum adsorption capacities of CA-WNS and untreated WNS under experimental conditions were 0.596 and 0.154 mmol/g for Cr(VI) ions, respectively.     

Removal of dairy soil from heated stainless steel surfaces: use of ozonated water as a prerinse

Square (2.54 x 2.54 cm2) 304 stainless steel metal plates were cleaned, passivated, and soiled by autoclaving (121 degrees C at 15 psi for 15 min) with reconstituted nonfat dry milk (20% solids). Fifteen-minute treatments using either warm water (40 degrees C) or ozonated cold water (10 degrees C) were conducted to compare prerinse cleaning potential of soiled metal plates. The chemical oxygen demand determination was performed on extracted organic material from treated metal plates. Results indicated that the ozone treatment removed 84% of soil from metal plates versus 51% soil removal by the warm water treatment, but the effectiveness of the two treatments did not differ (P > 0.05). Cleaning effects were visualized using scanning electron microscopy at 200x and 2000x magnification. The amount of soil film present on stainless steel metal surfaces was visibly lower on ozonated treatments versus on warm water treatments.