Enhancement of uranium bioaccumulation by a Citrobacter sp. via enzymically-mediated growth of polycrystalline NH4UO2PO4

The objective of this work was to study the effect of pH and ionic matrix on product release and on the removal of uranyl ion by a Citrobacter. sp phosphatase enzyme-catalysed reaction. An improvement in the efficiency of uranyl removal was obtained by incorporating ammonium acetate (NH₄Ac) into the solution. It was confirmed using X-ray diffraction (XRD), and other analytical techniques, that the insoluble, cell-bound product was NH₄UO₂PO₄.     

The role of sulfate as a competitive inhibitor of enzymatically‐mediated heavy metal uptake by Citrobacter sp: implications in the bioremediation of acid mine drainage water using biogenic phosphate precipitant

Heavy metals can be removed from solution via biocrystallization with enzymatically‐liberated inorganic phosphate, according to Michaelis–Menten kinetics, in free whole cells and cells immobilized within polyacrylamide gel in a flow‐through reactor. Sulfate is a competitive inhibitor of phosphate release and a predictive model was developed and shown to describe the effect of sulfate on the efficiency of phosphate release by flow‐through columns. The inhibitory effect was substantially less than anticipated in the case of metal removal by the columns. In the case of lanthanum removal metal removal efficiency was restored by increasing the substrate concentration in accordance with model predictions. In the case of uranyl ion its removal with an equivalent substrate supplement increased the activity by 20% over the initial value at a limiting flow rate. Since the initial loss in activity in the presence of 40 mmol dm⁻³ SO₄²⁻ (approximately twice the K_i value) was only approximately 20% with both metals this was considered to be a minor problem for bioprocess application. In confirmation, calculations made from a published ‘case history’ of application of the system to the bioremediation of acid mine drainage water (AMD) containing 0.22 mmol dm⁻³ of uranyl ion and 35 mmol dm⁻³ of SO showed that the benchscale model is a good representation of performance under actual load conditions. © 1999 Society of Chemical Industry     

Rate of Adsorption of Uranium from Seawater with a Calix[6]arene Adsorbent

Abstract

The rate of complex formation between calix[6]arene-p-hexasulfonate and uranyl ion is studied over a wide range of carbonate ion concentrations. The presence of carbonate ion decreases the complexation rate. The distribution of various uranyl species is calculated from a set of mass balances of participating ions with their stability constants. UO₂(CO₃)₃ ^4? has the highest concentration, followed by UO₂(OH)₃ ^? and UO₂(CO₃)₂ ^2?. Other uranyl species are negligible. The complexation rate is proportional to the 0.27–1.0 power of the total concentration of uranyl species other than UO₂(CO₃)₃ ^4?. This implies that the rate-determining step of the complexation is the reaction between calix[6]arene-p-hexasulfonate and UO₂(OH)₃ ^? or UO₂(CO₃)₂ ^2?.     

Development of novel adsorbent materials for recovery and enrichment of uranium from aqueous media

A new polymeric adsorbent bearing both hydrophilic groups providing swelling in water and amidoxime groups for chelating with uranyl ions (UO₂²⁺), has been developed and its adsorptive ability for recovering uranium from aqueous media has been investigated. The polymers obtained by irradiating the solution of polyethylene glycol (PEG) in acrylonitrile (AN) are defined as interpenetrating polymer networks (IPNs) and the adsorbent has been obtained by applying the amidoximation reaction to the IPNs with a conversion ratio of ∼ 60%. Kinetics of the conversion reaction of the cyano (CN) group to the amidoxime (HONCNH₂) group has been studied by reacting with hydroxylamine (NH₂OH) solution at a molar ratio of NH₂OH/CN = 1.25 in aqueous media at three different temperatures, 30, 40, and 50°C, for 3–4 days. The degree of amidoximation ratio was determined by UO₂²⁺ ion adsorption and FTIR spectrometry and the UO₂²⁺ ion adsorption values were found by both UV and gamma spectrometry and also by gravimetry. It was found that the polymeric adsorbent has a very high adsorption ability for uranium and quite a good stability in aqueous media. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2475–2480, 1997     

Ion Induced Surface Alterations Due to Electronic Charge Exchange and Chemical Reactions

A general discussion of the phenomena that can occur during ion—surface encounters is presented and specific examples of charge exchange processes on LiF surfaces and chemical reactions of N⁺₂ on metals are shown. During rare gas ion bombardment of LiF, ejection of F⁺ ions and excited Li atoms and the energy distributions of secondary F⁺ ions can be correlated with Auger primary ion—surface charge exchange transitions determined by the potential energy of the primary ion vacancy and electron promotions resulting from close atomic encounters. Nitridation of Al, Cu, Mo, and Ni to produce very thin nitride surface films is induced by 0–50 eV mass selected N⁺₂ beams. The efficiency of nitridation, monitored by the KL₂L₂ nitrogen Auger electron signal, exhibits a large kinetic energy E_k dependence below ca. 30 eV. The threshold impact energy for nitridation varies for the different metals; it is nominally zero for Al and Ni, ∼ 4 eV for Mo, probably > 0 for Cu, and does not occur at any energy below 200 eV for Ag. That the metal electronic structure is a critical parameter is evidenced by the facts that different ion doses are required to produce similar nitride signal levels on various metals and that plots of nitride intensity versus E_k exhibit structure or at least different shapes in the low E_k region. A simple quantum mechanical model is used to simulate the nitridation reaction by delineation into four elementary steps: (1) neutralization of incoming N⁺₂, (2) decomposition of N₂ into 2N, (3) deexcitation and thermalization of N, and (4) chemical reaction proper.     

Biosorptive uranium uptake by a Pseudomonas strain: characterization and equilibrium studies

The biosorptive uranium(VI) uptake capacity of live and lyophilized Pseudomonas cells was characterized in terms of equilibrium metal loading, effect of solution pH and possible interference by selected co‐ions. Uranium binding by the test biomass was rapid, achieving >90% sorption efficiency within 10 min of contact and the equilibrium was attained after 1 h. pH‐dependent uranium sorption was observed for both biomass types with the maximum being at pH 5.0. Metal uptake by live cells was not affected by culture age and the presence of an energy source or metabolic inhibitor. Sorption isotherm studies at a solution pH of either 3.5 or 5.0 indicated efficient and exceptionally high uranium loading by the test biomass, particularly at the higher pH level. At equilibrium, the lyophilized Pseudomonas exhibited a metal loading of 541 ± 34.21 mg g^?1 compared with a lower value by the live organisms (410 ± 25.93 mg g^?1). Experimental sorption data showing conformity to both Freundlich and Langmuir isotherm models indicate monolayered uranium binding by the test biomass. In bimetallic combinations a significant interference in uranium loading was offered by cations such as thorium(IV), iron(II and III), aluminium(III) and copper(II), while the anions tested, except carbonate, were ineffective. Uranium sorption studies in the presence of a range of Fe³⁺ and SO₄^2? concentrations indicate a strong inhibition (80%) by the former at an equimolar ratio while more than 70% adsorption efficiency was retained even at a high sulfate level (30 000 mg dm^?3). Overall data indicate the suitability of the Pseudomonas sp biomass in developing a biosorbent for uranium removal from aqueous waste streams. © 2001 Society of Chemical Industry     

Simultaneous removal of sulfate and selenate from wastewater by process integration of an ion exchange column and upflow anaerobic sludge blanket bioreactor

The application of an integrated process configuration comprising of an ion exchange (IX) column and an upflow anaerobic sludge blanket (UASB) bioreactor for the simultaneous removal of SO₄^2- and total Se from synthetic mine wastewater was evaluated. Use of an IX column as a pre-treatment (not as post-treatment) to the UASB bioreactor gave the best overall removal performance. The combined treatment reduced the total Se and SO₄^2- concentration from 8.0 and 1441 mg/L to 0.2 and 28.0 mg/L, respectively. This study demonstrated for the first time that an IX process as a pre-treatment to a biological process can significantly improve the oxyanion removal efficiency and the overall treatment of Se-laden wastewaters.     

Accumulation of zirconium and nickel by Citrobacter sp

Zirconium in aqueous flows was moderately biomineralized by immobilized Citrobacter N14 cells, in the form of gel‐like deposits, probably comprising a mixture of zirconium hydrogen phosphate (Zr(HPO₄)₂) and hydrated zirconia (ZrO₂). The simultaneous presence of uranyl ion (UO) did not facilitate zirconium deposition and the biomineralization of uranium itself as HUO₂PO₄ was repressed by zirconium in the presence of excess inorganic phosphate, liberated enzymatically. Nickel (Ni²⁺) was not significantly removed from aqueous flows by sorption into cell‐bound zirconium deposits, although cell‐bound hydrogen uranyl phosphate (HUP) facilitated nickel removal via intercalative ion exchange into its polycrystalline lattice. A preformed layer of HUP also promoted zirconium removal, at 100% efficiency at pH 2.6, maintained over 38 column fluid‐volumes before saturation. © 1999 Society of Chemical Industry     

Effect of hydrogen‐bonding in the development of high‐affinity metal ion complexants: Polymer‐bound phosphorylated cyclodextrin

In a series of phosphorylated polyols bound to a polystyrene support, the position of the FTIR band assigned to hydrogen bonding between the  OH and phosphoryl oxygen correlates with the affinity of that phosphoryl oxygen for metal ions. Polymer with phosphorylated β‐cyclodextrin (pCD) ligands is now reported as a further test of this correlation. The metal ion affinity is probed with the uranyl ion. pCD is the most red‐shifted of a series of five phosphorylated polyols: the strongest polyol had been phosphorylated pentaerythritol (pPE) with a band at 873 cm⁻¹; pCD has a band at 868 cm⁻¹. Consistent with the FTIR bands, pCD has a significantly higher affinity for the uranyl ion than pPE: the percents complexed from a 10⁻⁴M uranyl solution in a background of 1.0N HNO₃, HCl, and H₂SO₄ are 94.7%, 90.5%, and 93.6%, respectively, for pCD and 68.6%, 52.1%, and 40.1%, respectively, for pPE. This further supports the hypothesis that the strong complexing ability of phosphorylated polyols is due to activation of the phosphoryl oxygen through hydrogen bonding between the PO and the  OH groups within the polyol. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Bioaccumulation of lanthanum,uranium and thorium,and use of a model system to develop a method for the biologically-mediated removal of plutonium from solution

Removal of La³⁺, UO₂²⁺ and Th⁴⁺ from aqueous solution by a Citrobacter sp. was dependent on phosphatase-mediated phosphate release and the residence time in a plug-flow reactor (PFR) containing polyacrylamide gel-immobilized cells. In a stirred tank reactor (STR) lanthanum phosphate accumulated on the biomass rapidly, in preference to uranium or thorium phosphates. Thorium removal was not affected by the presence of uranium but was promoted in the presence of lanthanum. Analysis of the accumulated polycrystalline material by X-ray powder diffraction (XRD) analysis and proton induced X-ray emission (PIXE) suggested the formation of a mixed crystal of lanthanum and thorium phosphate. La³⁺, UO₂²⁺ and Th⁴⁺ are analogues of the corresponding species of Pu³⁺, PuO₂²⁺ and Pu⁴⁺. The La/U/Th model system was used to identify some potential problems in the bioremediation of wastes containing plutonium and to develop a method for the biologically-mediated removal of plutonium from solution, in a test solution of ²³⁹Pu ‘spiked’ with a ²⁴¹Pu tracer. © 1998 SCI.     

固定床生物反应器模拟溶浸采铀吸附尾液中Fe2+的氧化试验

以活性炭作载体固定嗜酸氧化亚铁硫杆菌,构建固定床生物反应器,模拟溶浸采铀矿山吸附尾液全Fe浓度和溶液pH条件,对生物反应器氧化Fe²⁺工艺参数进行了试验研究。结果表明:活性炭作载体比无载体时生物反应器氧化Fe²⁺速率增加了1.4倍,由0.5 g·L^-1·h^-1增大至1.2 g·L^-1·h^-1;生物反应器运行过程中溶液中全Fe因生成铁钒而不断消耗,需要定期清理反应器中的铁矾和补充FeSO₄以保持溶液中全Fe浓度;生物反应器最优的操作条件是:底部通气,Fe²⁺浓度为5 g·L^-1时,溶液流量为1.2~1.4 L·h^-1;Fe²⁺浓度为1 g·L^-1时,溶液流量为5.4 L·h^-1。     

Study on the phosphate removal from aqueous solution using modified fly ash

In this work the fly ash was modified by sulfuric acid for the removal of phosphate. It was found that modification of fly ash could significantly enhance the phosphate immobilization ability of the fly ash. The specific surface area of the fly ash increased from 8.8 to 32.5 m²/g after treated with sulfuric acid. The modification of the fly ash also resulted in the mobilization of acid-soluble metal ions due to partial or complete dissolution of the metals under the acidic conditions. Both adsorption and precipitation contributed to the removal of phosphate by the modified fly ash but precipitation was a major mechanism of phosphate removal. The experimental results showed that adsorption of phosphate by the modified fly ash was rapid, the removal percentage of phosphate could reach maximum in 5 min. In the range of 5–9, pH did not significantly affect the removal of phosphate and the removal percentage of phosphate increased with the increase of adsorbent dosage. The adsorption of phosphate by the modified fly ash could be described well by Langmuir isotherm equation, the Langmuir constant Q₀ was 9.15 mg g⁻¹. The XRD patterns and the SEM images of modified fly ash after sorption revealed that CaHPO₄·2H₂O was formed in the removal of phosphate. In addition, phosphate also formed precipitate with aluminum and iron.     

Optimization of chromium removal by the chromium resistant mutant of the cyanobacterium Anacystis nidulans in a continuous flow bioreactor

BACKGROUND: Chromium removal potential of the cyanobacterium Anacystis nidulans and its chromium resistant strain Cr^rI8 has been optimized. Optimized parameters include biomass load, pH, temperature and dilution rate of the bioreactor. RESULTS: Results show that chromium resistant strain has high EC₅₀ dose for chromium compared to wild strain. Chromium removal potential of both strains is strongly influenced by various factors. Optimized conditions in batch system included pH 6.5, temperature 28 °C, biomass load 150 µg protein mL^?1 for 30 µmol L^?1 Cr⁶⁺ solution. In continuous flow bioreactor at optimum pH (6.5) and temperature (28 °C) at a fixed biomass of 10 mg protein and 30 µmol L^?1 Cr⁶⁺, metal removal efficiency varied with dilution rate. For A. nidulans continuous flow bioreactor, optimum dilution rate was 0.076 h^?1 (64.6 per cent metal removal) while for Cr^rI8 it was 0.152 h^?1 (85.8 per cent metal removal). Operative time of the Cr^rI8 bioreactor was also more (85 h) compared to A. nidulans bioreactor (45 h). CONCLUSION: Under optimized conditions resistant strain Cr^rI8 removed more Cr⁶⁺ compared to A. nidulans and thus has the potential to be exploited for Cr⁶⁺ removal from industrial effluents at large scale. Copyright © 2007 Society of Chemical Industry     

Microbial Kinetics and Enzymatic Activities in Hybrid Moving‐Bed Biofilm Reactor‐Membrane Bioreactor Systems

A membrane bioreactor (MBR), a hybrid moving‐bed biofilm reactor‐membrane bioreactor (hybrid MBBR‐MBR_a) containing carriers in the anoxic and aerobic compartments, and a hybrid MBBR‐MBR_b containing carriers only in the aerobic zone were used in parallel and compared for treating municipal wastewater. The microbial kinetics and the evolution of the enzymatic activities of α‐glucosidase and acid and alkaline phosphatase as well as the bacterial diversity and bacterial community structure were studied to explain the removal of organic matter and nutrients. The MBR and the hybrid MBBR‐MBR_b showed the highest reduction percentages of chemical oxygen demand. Moreover, the hybrid MBBR‐MBR_b exhibited the highest removal performance of total nitrogen.     

Accumulation of uranium on austenitic stainless steel surfaces

The surface contamination by uranium in the primary circuit of PWR type nuclear reactors is a fairly complex problem as (i) different chemical forms (molecular, colloidal and/or disperse) of the uranium atoms can be present in the boric acid coolant, and (ii) only limited pieces of information about the extent, kinetics and mechanism of uranium accumulation on constructional materials are available in the literature. A comprehensive program has been initiated in order to gain fundamental information about the uranium accumulation onto the main constituents of the primary cooling circuit (i.e., onto austenitic stainless steel type 08X18H10T (GOSZT 5632-61) and Zr(1%Nb) alloy). In this paper, some experimental findings on the time and pH dependences of U accumulation obtained in a pilot plant model system are presented and discussed. The surface excess, oxidation state and chemical forms of uranium species sorbed on the inner surfaces of the stainless steel tubes of steam generators have been detected by radiotracer (alpha spectrometric), ICP-OES and XPS methods. In addition, the passivity, morphology and chemical composition of the oxide-layers formed on the studied surfaces of steel specimens have been analyzed by voltammetry and SEM-EDX. The experimental data imply that the uranium sorption is significant in the pH range of 4-8 where the intense hydrolysis of uranyl cations in boric acid solution can be observed. Some specific adsorption and deposition of (mainly colloidal and disperse) uranyl hydroxide to be formed in the solution prevail over the accumulation of other U(VI) hydroxo complexes. The maximum surface excess of uranium species measured at pH 6 (Γ_sample = 1.22 μg cm⁻²U ≅ 4 × 10⁻⁹ mol cm⁻² UO₂(OH)₂) exceeds a monolayer coverage.     

Competitive removal of heavy metal ions by cellulose graft copolymers

The effect of composition of graft chains of four types cellulose graft copolymers on the competitive removal of Pb²⁺, Cu²⁺, and Cd²⁺ ions from aqueous solution was investigated. The copolymers used were (1) cellulose‐g‐polyacrylic acid (cellulose‐g‐pAA) with grafting percentages of 7, 18, and 30%; (2) cellulose‐g‐p(AA–NMBA) prepared by grafting of AA onto cellulose in the presence of crosslinking agent of N,N′‐methylene bisacrylamide (NMBA); (3) cellulose‐g‐p(AA–AASO₃H) prepared by grafting of a monomer mixture of acrylic acid (AA) and 2‐acrylamido‐2‐methyl propane sulphonic acid (AASO₃H) containing 10% (in mole) AASO₃H; and (4) cellulose‐g‐pAASO₃H obtained by grafting of AASO₃H onto cellulose. The concentrations of ions which were kept constant at 4 mmol/L in an aqueous solution of pH 4.5 were equal. Metal ion removal capacities and removal percentages of the copolymers was determined. Metal ion removal capacity of cellulose‐g‐pAA did not change with the increase in grafting percentages of the copolymer and determined to be 0.27 mmol metal ion/g_copolymer. Although the metal removal rate of cellulose‐g‐p(AA–NMBA) copolymer was lower than that of cellulose‐g‐pAA, removal capacities of both copolymers were the same which was equal to 0.24 mmol metal ion/g_copolymer. Cellulose did not remove any ion under the same conditions. In addition, cellulose‐g‐pAASO₃H removed practically no ion from the aqueous solution (0.02 mmol metal ion/g_copolymer). The presence of AASO₃H in the graft chains of cellulose‐g‐p(AA–AASO₃H) created a synergistic effect with respect to metal removal and led to a slight increase in metal ion adsorption capability in comparison to that of cellulose‐g‐pAA. All types of cellulose copolymers were found to be selective for the removal of Pb²⁺ over Cu²⁺ and Cd²⁺. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2034–2039, 2003     

Uranyl ion adsorptivity of N-vinyl 2-pyrrolidone/acrylonitrile copolymeric hydrogels containing amidoxime groups

Summary N-vinyl 2-pyrrolidone (VP) / Acrylonitrile (AN) copolymeric hydrogels were synthesized by using γ-radiation and amidoximated for the purpose of uranyl ion adsorption. Optimum amidoximation time was determined by following the uranyl ion, UO₂ ²⁺, adsorption capacity. The adsorption of amidoximated copolymers was studied from different uranyl ion solutions (1000–1850 ppm). The results of all adsorption studies showed that the interaction between UO₂ ²⁺ and amidoxime groups comply with Langmuir type isotherm. The adsorption capacity was found as 0.54 g UO₂ ²⁺ /g dry amidoximated copolymeric hydrogels. From the stoichiometric calculations, it was found that the bonding between UO₂ ²⁺ and amidoxime groups is 1 to 4. Received: 7 September 1999/Revised version: 21 February 2000/Accepted: 18 March 2000     

Polylactide/transition metal ion modified montmorillonite nanocomposite—a critical evaluation of mechanical performance and thermal stability

Polylactide (PLA) nanocomposite was prepared by melt blending of PLA and transition metal ion (TMI) adsorbed montmorillonite (MMT). PLA nanocomposite was characterized for mechanical performance, and the results revealed that the tensile modulus, flexural modulus, and impact strength were increased marginally. The nanocomposite was optimized at 5 wt% of TMI‐modified MMT (TMI‐MMT) loading. Thermogravimetric analysis displayed increase in onset of degradation temperature, and differential scanning calorimetry showed marginal increase in glass transition temperature (T_g) and melting temperature (T_m) in case of PLA nanocomposites, when compared with virgin PLA. The flammability testing of nanocomposites indicated good fire retardance characters. X‐ray diffraction patterns of TMI‐MMT and the corresponding nanocomposites indicated an intercalation of the metal ions into the clay interlayer. Fourier transform infrared spectroscopy analysis indicate formation of [Zn(EDA)₂]²⁺ and [Cu(EDA)₂]²⁺ complexes in the MMT interlayer. Dynamic mechanical analysis shows increase in glass transition temperature (T_g) and storage modulus (E′) in case of PLA nanocomposites reinforced with 5 wt% modified MMT. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Phenolic wastewater treatment in a three‐phase fluidised bed bioreactor containing low density particles

The treatment of phenolic wastewater was investigated in a gas–liquid–solid fluidised bed bioreactor containing polypropylene particles of density 910 kg m^?3. Measurements of chemical oxygen demand (COD) versus residence time (t) were performed for various ratios of settled bed volume to bioreactor volume (V_b/V_R) and air velocities (u) to determine the values of (V_b/V_R) and u for which the largest reduction in COD occurred. Optimal operation, corresponding to the largest COD removal, was attained when the bioreactor was controlled at the ratio (V_b/V_R) = 0.55 and an air velocity u = 0.036 m s^?1. Under these conditions, the value of COD was practically at steady state for times greater than 50 h. At this steady state, only about 50% COD removal was achieved in the treatment of a ‘raw’ wastewater (no mineral salts added), whereas in the operation with wastewater enriched in nutrient salts approximately 90% COD removal was attained. The following amount of mineral salts (mg dm^?3): (NH₄)₂SO₄—500; KH₂PO₄—200; MgCl₂—30; NaCl—30; CaCl₂—20; and FeCl₃—7, when added to wastewater before treatment, was sufficient for biomass growth. The application of low density particles (used as biomass support) in a bioreactor allowed the control of biomass loading in the apparatus. In the cultures conducted after change in (V_b/V_R) at a set u, the steady state mass of cells grown on the particles was achieved after approximately 6 days of operation. With change in u at a set (V_b/V_R), the new steady state biomass loading occurred after culturing for about 2 days. Phenolic wastewater was successfully treated in a bioreactor. In the operation conducted in a bioreactor optimally controlled at (V_b/V_R) = 0.55, u = 0.036 m s^?1 and t = 50 h, conversions greater than 99% were achieved for all phenolic constituents of the wastewater. Conversions of about 90% were attained for other hydrocarbons. Copyright © 2005 Society of Chemical Industry     

The kinetics of the in situ polymerization of glycidyl methacrylate in wood using dynamic mechanical measurements

The in situ polymerization of glycidyl methacrylate in wood, in the presence of uranyl nitrate, (UN), and/or 2,2′-azo-bis-isobutyronitrile, (AIBN), has been investigated in the temperature range 55°-72°C. The course of the polymerization reaction was followed by measurement of tan 5 in an automated Rheovibron viscoelastometer. The kinetics, studied by applying the Guggenheim method to the data, showed the polymerization to be first order whether catalyzed by UN or initiated by AIBN. The activation energy (E_α) for AIBN-initiated polymerization was 121 kJ/mol, and was unaffected by varying monomer concentration in acetone. On the other hand, E_α for the UN-catalyzed polymerization was found to be 59.1 and 73.5 kJ/mol respectively for the neat and 50 percent monomer concentration reaction mixture. The enhancement in E_α is attributed to the complexatton of the dioxouranium (VI) ion in the presence of solvent acetone, with consequent reduction in catalytic activity.