摘要:

AbstractThe continuing release of caesium isotopes into the environment has highlighted the necessity for efficient removal of Cs from industrial waste effluents prior to discharge. Existing technologies, e.g. zeolite ion‐exchange for Cs removal, can be expensive and microbial metal adsorption/accumulation may represent a cheap alternative. The distinct chemical properties of Cs+, which dictate a high degree of metabolism‐dependent uptake via monovalent cation transport systems, indicate that different approaches are required for biological Cs removal to those which are generally adopted for other metals/radionuclides. The low toxicity of Cs+eliminates one potential problem in the use of live cells for Cs removal. High levels of Cs+accumulation have been reported in a number of microorganisms, but uptake levels vary markedly in different organisms and are strongly influenced by a number of physico‐chemical and mechanical parameters, e.g. the use of batch or continuous‐flow systems, biomass immobilization (which tends to increase Cs+adsorption at the expense of metabolism‐dependent accumulation), pH and particularly the prevalence of other monovalent cations such as K+and Na+. Inherent differences in Cs+uptake capacities of different microorganisms appear to be largely attributable to differences in the affinity of monovalent cation transport systems for Cs+. The application of rigorous screening procedures involving the use of autoradiography has great potential for isolation of microorganisms with particularly high affinities for Cs+. Alternatively, manipulation of the physiological status of microorganisms can dramatically alter the transport of Cs+and other monovalent cations. Hyper‐ and hypo‐osmotic shock, respectively, have so far proved to be the most successful treatments for stimulating Cs removal and recovery. Other manipulations, at both the cellular and molecular level, which are known to influence K+fluxes but have yet to be characterized for Cs+, are

ISSN:0268-2575    

DOI:10.1002/jctb.280620102

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe adsorption of the three metal ions, copper, cadmium and zinc in single component and multi‐component mixtures in aqueous solutions by lignite is reported. A comparison is made between the single component saturation uptake and the multi‐component uptakes. The isotherms indicate a competitive uptake with copper being preferentially absorbed by the lignite in multi‐component solutions. The isotherms are plotted to obtain the Langmuir constants, the Freundlich constants and the Redlich–Peterson constants. Lignite is shown to possess an affinity for the metal ions which make its use as an adsorbent a possible alternative to the use of more expensive activated

ISSN:0268-2575    

DOI:10.1002/jctb.280620103

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe synthetically useful chiral synthons, (R)‐ and (S)‐2‐cyclohepten‐1‐ol, can be prepared by an enantioselective transesterification of racemictrans‐2‐(phenylseleno) cycloheptanol using lipases, followed by selenoxide elimination a

ISSN:0268-2575    

DOI:10.1002/jctb.280620104

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractAdsorption isotherms for sodium and trivalent chromium uptake from aqueous solutions onto Amberlite resin were prepared at 18°C. Adsorption of each cation followed the Langmuir model. The rate of uptake of each cation was found to be film diffusion controlled with sodium showing the most rapid uptake. In aqueous solutions containing both chromium and sodium as the only cationic species, it was found that with increasing initial concentration of sodium, the trivalent chromium uptake on the resin decreased substantially. To overcome this difficulty a four step redox–adsorption system has been developed for the removal of Cr3+from tannery effluents. The first step comprises the oxidation of trivalent chromium to the hexavalent form using selected common oxidising agents. The liquid effluent is then passed through an Amberlite cation‐exchange resin in step 2 where the sodium in the waste stream is completely removed. The anionic hexavalent form of chromium (Cr2O 72−) passes unaltered through the resin along with the waste stream. In the third stage the dichromate is reduced back to the trivalent cationic form which is subsequently removed from the waste stream by a second Amberlite ion‐exchange bed in stage 4. Each step in this process is assessed in batch and flow mode using simulated and real tannery

ISSN:0268-2575    

DOI:10.1002/jctb.280620105

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractYeast, immobilised in alginate beads of known standard size and mechanical strength, has been utilised in a novel design of fluidised bed bioreactor which avoids problems of particle flotation and gas logging. Circulating substrate simultaneously entered the top and bottom of the bed. The bioreactor operated reliably for periods of up to 20 days. Increasing alginate concentration in the range 1–5% (w/w) had little effect on the performance of the immobilised yeast in converting ethanol to glucose but reduced the tendency of beads to split. Increasing bead diameter in the range 1–5 mm increased the tendency to split and reduced overall conversion of glucose. A model was developed to describe the consumption of glucose within beads based on Michaelis–Menten kinetics and the diffusion of glucose into beads. Application of the model to experimental results showed maximum reaction velocity to be independent of bead diameter and alginate concentration. The model confirmed that the observed reduction in ethanol yield compared with free yeast cells was caused by the lower substrate concentration towards the centre of the bead as opposed to any change in the metabolic rate of the immobilised

ISSN:0268-2575    

DOI:10.1002/jctb.280620106

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

Abstract4‐Amino‐3‐thio‐1,24‐triazolidine (L1) and 4‐amino‐5‐thio‐1,3,4‐thiadiazole (LII) as well as their metal complexes of the general formulae MLI·2H2O and MLIICl (M; Pb(II), Cd(II) and Zn(II)) were prepared. With Sn(II), we obtained Sn(LI)2·2H2O and SnLIICl, respectively. The structures of the compounds were identified through elemental analysis, and IR and UV spectra measurements, in addition to thermal analysis in case of the metal complexes. The antifouling properties of the compounds were tested by their incorporation into paint formulations which were applied to PVC substrates and tested in water from Alexandria western harbour. When the compounds were added at 17·5% by volume, the coated panels were fouled after 3 months of immersion. The addition of 6·7% by volume of tributyltin oxide to 15·8% of the prepared compounds in one formulation elevated the paint efficiency and prevented fouling for 11 months. Paint containing solely tributyltin oxide at the same concentration wa

ISSN:0268-2575    

DOI:10.1002/jctb.280620107

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA flow apparatus was constructed to carry out studies of supercritical fluid extraction in the temperature range 298·15–353·15 K and pressures up to 40 MPa. To test the apparatus, studies on the solubility of naphthalene in CO2at 308·15, 313·15 and 318·15 K and pressures up to 35 MPa were carried out. These experimental data were correlated through the Peng–Robinson equation of state. Samples of the microalgaeBotryococcus brauniiandChlorella vulgariswhich produce diolefines C25–C31and carotenoids, respectively, were submitted to supercritical CO2. The extraction yields for these compounds were studied and compared with those obtained using organic solvents. Supercritical CO2was also used to produce extracts from rosemary leaves (Rosmarinus officinalisL.), which were compared with those obtained by hexane

ISSN:0268-2575    

DOI:10.1002/jctb.280620108

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe extraction equilibria of various di‐ and tripeptides with di‐2‐ethylhexylphosphoric acid (D2EHPA) were studied at low pH values. The complex extracted to organic phase consisted of one molecule of peptide and two molecules of D2EHPA dimer. The extraction constants of the peptides correlated well with the distribution coefficients of peptides between 1‐octanol and water, which is a measure of hydrophobicity. The permeation rates of peptides through an emulsion liquid membrane were examined by using D2EHPA as a carrier, Span 80 as an emulsifier and kerosene as a diluent. The rates varied considerably with peptide type, depending upon the hydroph

ISSN:0268-2575    

DOI:10.1002/jctb.280620109

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe adsorption of chromium (III) onto activated carbon was investigated as a possible alternative method for its removal from aqueous solutions. The adsorption data were obtained in a batch adsorber and fitted the Langmuir adsorption isotherm well. The effect of pH on the adsorption isotherm was investigated at pH values of 2, 4, 5 and 6. It was found that at pH values below 2 the Cr(III) was not adsorbed and at pH values above 6.4 the Cr(III) was precipitated as Cr(OH)3. Maximum adsorption occurred at pH 5. The pH plays a very important role in the adsorption of Cr(III) since Cr(III) can form different complexes in aqueous solutions. The adsorption capacity was increased by about 20% as the temperature was raised from 25 to 40°C. It was concluded that Cr(III) is adsorbed to an appreciable extent on activated carbon and that the adsorption is highly dependent upon pH

ISSN:0268-2575    

DOI:10.1002/jctb.280620110

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractFlow injection systems with immobilized enzymes for the parallel determination of chemically similar substances such as xylose/glucose andL‐leucine/L‐isoleucine/L‐valine are described. The determination of xylose and glucose was performed either by differential measurement or by an ‘enzyme‐array’. Because of the different linear ranges of the calibration curves for xylose and glucose quantification was only possible when there was an excess of xylose (xylose 0·1–2·5 mmol dm−3, glucose 0·001–0·1 mmol dm−3). The parallel quantification of the branched‐chain amino acids could be realized by an array arrangement using an FIA‐system with several immobilized enzymes of slightly different selectivity. The total amount of branched‐chain amino acids can

ISSN:0268-2575    

DOI:10.1002/jctb.280620111

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY