PubMed Health⌕ Search

Biomedical subjects

João G Crespo

Publications and source records attributed to João G Crespo.

13 recordsLinked to original sources
PubMed2005

Simultaneous removal of perchlorate and nitrate from drinking water using the ion exchange membrane bioreactor concept.

This work evaluates the feasibility of the ion exchange membrane bioreactor (IEMB) concept for the simultaneous removal of perchlorate and nitrate from drinking water, when nitrate is present in the ppm range and perchlorate in the ppb range. The IEMB concept combines Donnan dialysis and simultaneous biological degradation of both pollutants. Membrane transport studies showed that Donnan dialysis is suitable for obtaining water with concentrations of perchlorate and nitrate below the recommended levels. However, the pollutants were accumulated in a receiving stream, thus requiring additional treatment before disposal. On the other hand, the IEMB process operated with hydraulic retention times ranging from 1.4 to 8.3h in the water compartment, proved to remove effectively perchlorate and nitrate while preserving the water composition with respect to other ions, thus avoiding secondary contamination of the treated water. For a polluted water stream containing 100 ppb of ClO(4)(-) and 60 ppm of NO(3)(-), the concentrations of both ions in the treated stream were kept below the recommended levels of 4 ppb for ClO(4)(-) and 25 ppm for NO(3)(-). The IEMB system was operated under ethanol limitation, but even under these conditions, an increase of the perchlorate and nitrate concentrations in the treated water was not observed for up to 6 days.

Bioreactors↗
PubMed2005

Anomalous "unquenching" of the fluorescence decay times of beta-lactoglobulin induced by the known quencher acrylamide.

Picosecond time-resolved fluorescence, together with the addition of quenching agents, was employed to discriminate the fluorescence contributions of the two tryptophans of beta-lactoglobulin (Trp19 and Trp61) to the fluorescence decays of the protein. The fluorescence decays of beta-lactoglobulin at pH 3, 5 and 8 are best fitted using sums of three exponentials and show a dominant contribution (98%) of the components associated with the buried Trp19, which decays according to a double exponential function. The addition of acrylamide (0.05 M) causes an increase of the decay times associated with Trp19. This effect is observed at all pH values studied, but the effect is stronger at pH 3 and pH 5, than at pH 8. The unexpected increase of the decay times of Trp19 and the variation of the respective amplitudes were rationalized in terms of alterations of Trp19 mobility. The hindrance of Trp19 upon acrylamide binding was also monitored and supported by fluorescence anisotropy measurements.

Acrylamide↗
PubMed2005

Direct integration of pervaporation as a sample preparation method for a dedicated "electronic nose".

The present study investigates the possibility of monitoring the bioproduction of a complex aroma profile with an analytical electronic aroma-sensing technique, the so-called "electronic nose", combined with a pervaporative sample enrichment method necessary to overcome the ethanol interference on the sensors' response. It presents in detail the development of a direct integrated pervaporation-electronic nose unit for a simple and fast analysis, which are key criteria for this technique to be broadly implemented. The system developed was investigated using model solutions simulating the muscatel wine must fermentation. It proved to be able to evaluate different relevant aroma compounds in solutions of varying degree of complexity, and also in the presence of ethanol, which is a major interference on the sensors' response to the aromas. The transient sensors' response was investigated in detail, revealing information for sample discrimination and reducing the analysis time. The system developed allowed a simple, fast, and selective analysis, therefore permitting a high sample throughput over time, with the possibility of fully automation.

Electrons↗
PubMed2005

Non-mechanistic modelling of complex biofilm reactors and the role of process operation history.

Using the example of a membrane-supported biofilm reactor for industrial effluent treatment, different non-mechanistic approaches for the modelling of complex bioprocesses are presented and evaluated. The models were obtained employing feedforward artificial neural network analysis for the association of process operation with process performance. Three modelling approaches are discussed, i.e. autonomous static (AS) modelling, non-autonomous static (NAS) modelling, as well as a novel approach termed dynamic modelling with embedding of artificial neural network inputs. They are compared with regard to their ability to infer process performance for two different pollutant case studies, employing 1,2-dichloroethane and 3-chloro-4-methylaniline, respectively. The suitability of the different approaches was found to be strongly dependent on process configuration. Especially in configurations where lag times are apparent, the dynamic modelling approach was found to be superior, and process performance prediction was found to be strongly dependent on the history of process operation.

Algorithms↗
PubMed2005

Accessing gelling ability of vegetable proteins using rheological and fluorescence techniques.

This work aims to present a comprehensive study about the macroscopic characteristics of globular vegetable proteins, in terms of their gelling ability, by understanding their molecular behaviour, when submitted to a thermal gelling process. The gels of soy, pea and lupin proteins were characterized by rheological techniques. Gelation kinetics, mechanical spectra, as well as the texture of these gels were analyzed and compared. Additionally, capillary viscometry, steady-state fluorescence and fluorescence anisotropy were used to monitor the structural changes induced by the thermal denaturation, which constitutes the main condition for the formation of a gel structure. Based on these techniques it was possible to establish a relationship between the gelling ability of each protein isolate and their structural resistance to thermal unfolding, enabling us to explain the weakest and the strongest gelling ability observed for lupin and soy proteins isolates, respectively.

Anisotropy↗
PubMed2005

Biodegradation of thiomersal containing effluents by a mercury resistant Pseudomonas putida strain.

Thiomersal, a toxic organomercurial with a strong bactericidal effect, is the most widely used preservative in vaccine production. As a result, vaccine production wastewaters are frequently polluted with thiomersal concentrations above the European limit for mercury effluent discharges for which there is, presently, no remediation technology available. This work proposes a biotechnological process for the remediation of vaccine production wastewaters based on the biological degradation of thiomersal to metallic mercury, under aerobic conditions, by a mercury resistant bacterial strain. The kinetics of thiomersal degradation by a pure culture of Pseudomonas putida spi3 was firstly investigated in batch reactors using a thiomersal amended mineral medium. Subsequently, a continuous stirred tank reactor fed with the same medium was operated at a dilution rate of 0.05 h(-1), and the bioreactor performance and robustness was evaluated when exposed to thiomersal shock loads. In a second stage, the bioreactor was fed directly with a real vaccine wastewater contaminated with thiomersal and the culture ability to grow in the wastewater and remediate it was evaluated for dilution rates ranging from 0.022 to 0.1 h(-1).

Biodegradation, Environmental↗
PubMed2004

Membrane bioreactors for the removal of anionic micropollutants from drinking water.

Biological treatment processes allow for the effective elimination of anionic micropollutants from drinking water. However, special technologies have to be implemented to eliminate the target pollutants without changing water quality, either by adding new pollutants or removing essential water components. Some innovative technologies that combine the use of membranes with the biological degradation of ionic micropollutants in order to minimize the secondary contamination of treated water include pressure-driven membrane bioreactors, gas-transfer membrane bioreactors and ion exchange membrane bioreactors.

Anions↗
PubMed2002

Studies on the selective transport of organic compounds by using ionic liquids as novel supported liquid membranes.

The possibility of using room-temperature ionic liquids (RTILs) in bulk (nonsupported) and supported liquid membranes for the selective transport of organic molecules is demonstrated. A systematic selective transport study, in which 1,4-dioxane, propan-1-ol, butan-1-ol, cyclohexanol, cyclohexanone, morpholine, and methylmorpholine serve as a model seven-component mixture of representative organic compounds, and in which four RTILs based on the 1-n-alkyl-3-methylimidazolium cation (n-butyl, n-octyl, and n-decyl) are used together with the anions PF(6)(-) or BF(4)(-), immobilized in five different supporting membranes, confirms that the combination of the selected RTILs with the supporting membranes is crucial to achieve good selectivity for a specific solute. The use of the RTIL 1-n-butyl-3-methylimidazolium hexafluorophosphate, immobilized in a polyvinylidene fluoride membrane, allows an extremely highly selective transport of secondary amines over tertiary amines (up to a 55:1 ratio). The selective transport of a given solute through the RTIL/membrane system results from the high partitioning of the solute to the liquid membrane phase which, in the case of amines, is rationalized mainly by the formation of a preferential substrate/H[bond]C(2) hydrogen bonding to the imidazolium cation.

Journal Article↗
PubMed2002

Monitoring the aroma production during wine-must fermentation with an electronic nose.

This work discusses the feasibility of using the electronic nose for the on-line and real-time monitoring of the production of a complex aroma profile during a bioconversion process. As a case study, the formation of the muscatel aroma during the wine-must fermentation was selected. During wine-must fermentation, aroma compounds responsible for the organoleptic character are produced in the ppm range, while simultaneously one of the main metabolic products, ethanol, is produced in much higher quantities (up to 10% wt). Because the sensors of the electronic nose array are cross-selective to different volatile compounds, it was investigated in detail how far the electronic nose was able to evaluate the aroma profile along the fermentation. This article discusses and evaluates subsequently the integration of a membrane separation process-organophilic pervaporation-for selectively enriching aroma compounds relative to ethanol, to improve sample discrimination.

Bioreactors↗
PubMedDate not supplied

Ion exchange membrane bioreactor for selective removal of nitrate from drinking water: control of ion fluxes and process performance.

An ion exchange membrane bioreactor (IEMB), consisting of a monoanion permselective membrane dialyzer coupled to a stirred anoxic vessel with an enriched mixed denitrifying culture, has been studied for nitrate removal from drinking water. The influence of nitrate and chloride concentrations on the selectivity of nitrate transport in the IEMB process was investigated. With appropriate dosing of chloride ions to the IEMB biocompartment, it was possible to regulate the net bicarbonate flux in the system, thus maintaining the bicarbonate concentration in the treated water at the desired level. The latter was not possible to achieve in Donnan dialysis, operated as a single process in which, besides the lower nitrate removal efficiency found, bicarbonate was co-extracted together with nitrate from the polluted water stream. Residual carbon source (ethanol) and nitrite were not detected in the treated water produced in the IEMB system. With a concentration of nitrate in the polluted water three times higher than the maximum contaminant level of 50 mg L(-1) allowed, the IEMB process was successfully operated for a period of 1 month before exceeding this limit.

Biofilms↗