Showing papers by "João G. Crespo published in 2000"
TL;DR: A novel ion-exchange membrane bioreactor, able to prevent secondary pollution of biologically treated drinking water, was developed and specifically tested for water denitrification, and proved to be effective in producing a treated water effluent that does not require the extensive posttreatment associated with c...
Abstract: A novel ion-exchange membrane bioreactor, able to prevent secondary pollution of biologically treated drinking water, was developed and specifically tested for water denitrification. This system co...
87 citations
TL;DR: In this paper, the use of liquid membrane contactors for extraction of fermentation and pharmaceutical products using different types of carriers is discussed and the importance of using a correct description of solute partition between the feed and the extractant phase (use of a variable partition description versus constant partition) is discussed.
54 citations
TL;DR: By adjusting the ratio of co-ions between the biocompartment and the polluted water compartment, the magnitude and direction of each individual anion flux can be easily regulated, allowing for flexible process operation and control.
Abstract: The mechanism of anionic pollutant removal in an ion exchange membrane bioreactor (IEMB) was studied for drinking water denitrification. This hybrid process combines continuous ion exchange transport (Donnan dialysis) of nitrate and its simultaneous bioreduction to gaseous nitrogen. A nonporous mono-anion permselective membrane precludes direct contact between the polluted water and the denitrifying culture and prevents secondary pollution of the treated water with dissolved nutrients and metabolic products. Complete denitrification may be achieved without accumulation of NO3− and NO2− ions in the biocompartment. Focus was given to the effect of the concentration of co-ions, counterions, and ethanol on the IEMB performance. The nitrate overall mass transfer coefficient in this hybrid process was found to be 2.8 times higher compared to that in a pure Donnan dialysis process without denitrification. Furthermore, by adjusting the ratio of co-ions between the biocompartment and the polluted water compartment, the magnitude and direction of each individual anion flux can be easily regulated, allowing for flexible process operation and control. Synthetic groundwater containing 135–350 mg NO3− L−1 was treated in the IEMB system. A surface denitrification rate of 33 g NO3− per square meter of membrane per day was obtained at a nitrate loading rate of 360 g NO3− m−3d−1, resulting in a nitrate removal efficiency of 85%. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 71: 245–254, 2000/2001.
43 citations
TL;DR: In this paper, the authors used the iodine-laser temperature jump (ILTJ) technique to probe the interfacial and intermicellar dynamics of water-in-isooctane microemulsions stabilized by AOT both in the presence and in the absence of a cosurfactant such as aliphatic chained alcohol (hexanol or decanol) or poly(oxyethylene) alkyl ether (C10E4 or C10E8).
Abstract: The iodine-laser temperature jump (ILTJ) technique was used to probe the interfacial and intermicellar dynamics of water-in-isooctane microemulsions stabilized by AOT both in the presence and in the absence of a cosurfactant such as an aliphatic chained alcohol (hexanol or decanol) or poly(oxyethylene) alkyl ether (C10E4 or C10E8). These cosurfactants have been shown to induce changes in the interfacial rigidity; the former increase it, and the latter decrease it. Two relaxation times were observed, one in the microsecond range and another, previously undetected, in the millisecond range. The relaxation times obtained in the microsecond range were higher for CiEj-containing microemulsions and lower for decanol-containing ones. This is consistent with the effect of the cosurfactants on interfacial rigidity, as this relaxation is inversely proportional to the bending modulus, κ. The value of κ = 0.3 kT determined for AOT reversed micelles (Wo = 55) is in agreement with those found in the literature. The rel...
29 citations
01 Jan 2000
TL;DR: Rodriguez et al. as mentioned in this paper discussed the problems in the practice of preparative high-performance liquid chromatography with silica as the stationary phase and showed that column preparation and particle size of silica can affect the performance of the mobile phase transfer.
Abstract: porous hydrophobic membrane. Paq, aqueous-phase pressure; Porg, organic-phase pressure. Leutert T and Von Arx E (1984) PraK parative MitteldruckFluK ssigkeitschromatographie. Journal of Chromatography 292: 333}344. Nyiredy S, Dallenbach-Toelke K, Zogg GC and Sticher O (1990) Strategies of mobile phase transfer from thinlayer to medium-pressure liquid chromatography with silica as the stationary phase. Journal of Chromatography 499: 453}462. Porsch B (1994) Some speciRc problems in the practice of preparative high-performance liquid chromatography. Journal of Chromatography A 658: 179}194. Rodriguez S, Wolfender J-L, Odontuya G, Purev O and Hostettmann K (1995) Xanthones, secoiridoids and Savonoids from Halenia corniculata. Phytochemistry 40: 1265}1272. Verzele M and Geeraert E (1980) Preparative liquid chromatography. Journal of Chromatographic Science 18, 559}570. Zogg GC, Nyiredy S and Sticher O (1989a) Operating conditions in preparative medium pressure liquid chromatography (MPLC). II. InSuence of solvent strength and Sow rate of the mobile phase, capacity and dimensions of the column. Journal of Liquid Chromatography 12, 2049}2065. Zogg GC, Nyiredy S and Sticher O (1989b) Operating conditions in preparative medium pressure liquid chromatography (MPLC). I. InSuence of column preparation and particle size of silica. Journal of Liquid Chromatography 12, 2031}2048.
14 citations
TL;DR: In this article, the kinetics of phenylalanine extraction and re-extraction with a reversed micellar system consisting of TOMAC/hexanol/n-heptane was studied under different hydrodynamic conditions using a rotating diffusion cell.
11 citations
TL;DR: A kinetic study of the hydrolysis of the diester dimethyl cis-cyclohex-4-ene-1,2-dicarboxylate to the (1S,2R)-monoester, catalysed by the enzyme Pig Liver Esterase, concluded that the pH at which the enzyme exhibits a maximum activity is pH 7.5.
Abstract: A kinetic study of the hydrolysis of the diester dimethyl cis-cyclohex-4-ene-1,2-dicarboxylate, to the (1S,2R)-monoester, catalysed by the enzyme Pig Liver Esterase (PLE) was performed. The effects of the most relevant parameters that influence the enzymatic conversion were studied, such as pH, temperature and concentration of substrate and reaction products. It was concluded that the pH at which the enzyme exhibits a maximum activity is pH 7. At 25 °C PLE presents a better long-term stability and enantioselectivity than at higher temperatures, although the reaction rate is slower. The kinetic results obtained are well described by the Michaelis–Menten equation, although a slight deviation to this model was observed for low substrate concentrations. Methanol, a co-product of the enzymatic hydrolysis, was found to act as a non-competitive inhibitor of the reaction. The Michaelis–Menten parameters were determined and a comprehensive kinetic model, which already accounts for methanol inhibition, is presented.
© 2000 Society of Chemical Industry
9 citations
TL;DR: P pig liver esterase was physically immobilised in a polysulphone ultrafiltration hollow fibre membrane reactor and used for the repetitive batch two-phase hydrolysis and separation of the meso -diester dimethyl cis -cycloxex-4-ene-1,2-dicarboxylate 1 to enantiomerically pure monomethyl ester 2.
Abstract: Pig liver esterase (PLE) was physically immobilised in a polysulphone ultrafiltration hollow fibre membrane reactor and used for the repetitive batch two-phase hydrolysis and separation, on a multigram scale, of the meso-diester dimethyl cis-cycloxex-4-ene-1,2-dicarboxylate 1 to enantiomerically pure (1S,2R)-cyclohex-4-ene-1,2-dicarboxylic acid monomethyl ester 2. After 25 days, the enzyme still retained its initial activity, which corresponds to 62% of its activity in the free form, and the enantiomeric purity of monoester 2 was still higher than 97%. Simple experimental conditions were established for the large laboratory scale preparation of substrate 1 and isolation of product 2 from the aqueous phase.
9 citations
01 Jan 2000
TL;DR: In this article, a foodstuff that has been supplemented with aromas is described and compared to the foodstuff without aromas, and it is shown that the use of aromas constitutes an increasing fraction of food additives.
Abstract: Daily, we consume and encounter foodstuff that has been supplemented with aromas. Whether to compensate for aroma loss during food processing or to adjust the flavour of food according to the consumers’ expectations, aromas constitute an increasing fraction of food additives.
4 citations
01 Jan 2000
TL;DR: Monitoring of membrane bioreactors can be accomplished by using two entirely different approaches, both of which rely on periodically withdrawing samples from several key locations in the system and determining the concentrations of substrates and their bioconversion products.
Abstract: Monitoring of membrane bioreactors can be accomplished by using two entirely different approaches. Traditional ‘off-line’ analysis can be applied by periodically withdrawing samples from several key locations in the system and determining the concentrations of substrates and their bioconversion products. Based on these, substrate mass transfer and degradation rates can be evaluated.