Biomedical subjects

G Guibaud

Publications and source records attributed to G Guibaud.

9 recordsLinked to original sources

PubMed2005

Effect of inoculum and sludge concentration on viscosity evolution of anaerobic granular sludges.

The rheological behaviour of granular sludges (diameter 20-315 microm) originating from different anaerobic reactors was carried out using rotation tests. The sieved granular sludges suspensions display a non-Newtonian rheological behaviour and the limit viscosity was therefore used as a rheological parameter. The values obtained, which depend on the shear rate used, were strongly influenced by the total suspended solids (TSS) content of granular sludge and an exponential relation was found between the TSS and the rheological parameter limit viscosity. The increase of viscosity as a function of TSS content of the granular sludge as well as the increase of granule size underlines the importance of the interaction between granules in the evolution of this rheological parameter. Significant differences in granular sludge limit viscosity were found for granular sludge of different origins. All measurements performed with 10 g.l(-1) TSS granular sludge indicate the ability of the chosen rheological parameter to describe different granular sludge quality.

Bacteria, Anaerobic↗

PubMed2004

[Rheological measurement used as a tool to assess sludges settleability].

The activated sludge process is the most widely used biological wastewater treatment method. The measurement of some physico-chemical parameters in aeration tanks do not still allow to avoid clarification operation failure. This study focus on the ability to apply rheological measurements on activated sludge at standard concentrations in order to assess sludge settleability. Measurements in shear flow show a pseudonewtonian region which corresponds to the maximum dispersion of the suspensions that can be detected with the rotational system used. The Bingham's viscosity and shear stress are used to characterise activated sludge. Different shear sensitivities of flocs seem to result from various operational conditions of activated sludge process. Significant relationships with different parameters of settleability point out the ability of Bingham's shear stress to express the compressibility of the activated sludge. According to the protocol of measurement of the study, Bingham's shear stress may influence the nature of the sludge on its settleability.

Bioreactors↗

PubMed2004

Application of the IAS theory combining to a three compartments description of natural organic matter to the adsorption of atrazine or diuron on activated carbon.

The study of natural organic matter (NOM) adsorption on an activated carbon showed that equilibrium cannot be described according to a simple model such as a Freundlich isotherm and confirms the need for a closer description of the organic matter to simulate the competitive adsorption with micropollutants. A representation of the organic matter in three fractions is chosen: non-adsorbable, weak and strong adsorbable. The Ideal Adsorbed Solution Theory (IAST) can, under restrictive conditions, be used to effectively predict the competition between the pesticides and the organic matter. Therefore, it was noted that the model simulated with good precision the competition between atrazine or diuron and natural organic matter in aqueous solution for two activated carbons (A and B). The same parameters for the modeling of organic matter adsorption (Freudlich constants for two absorbable fractions) are used with the two pesticides. However, IAST does not allow correct modeling of pesticide adsorption onto two other (C and D) activated carbons in solution in natural water to be described. IAS theory does not reveal competition between diuron and NOM and pore blockage mechanism by the NOM is proposed as the major effect for the adsorption capacity reduction. However, the difference observed between the two pesticides could be due to in addition to the pore blockage effect, a particular phenomenon with the diuron, especially with D activated carbon. We can suppose specific interactions between the diuron and the adsorbed organic matter and a competition between adsorption sites of NOM and activated carbon surface.

Adsorption↗

PubMed2004

Rheology measurement for on-line monitoring of filaments proliferation in activated sludge tanks.

Rheological behaviour of filamentous sludges originated from activated sludge reactors was studied. Filamentous bulking was detected via a hysteresis loop developed from rheograms resulting from increasing-decreasing shear rates. The rheological parameter reduced hysteresis area (rHa), corresponding to the loop area developed by rheograms was used to quantify filamentous bulking. Application to the evolution of several bulkings was carried out and it was shown that filaments proliferation and disappearance were correlated with, respectively, the increasing and decreasing of the value of the parameter rHa. In parallel with rheological measurement, parameters used for the study of sludge quality, such as sludge volume index (SVI) and settling initial flow (F0), were determined for comparison during the evolution of several bulkings. It was shown that rHa was more sensitive to the appearance of filamentous bulking than SVI and F0, therefore it was concluded that detection of filamentous bulking can be shown from rHa.

Biofilms↗

PubMed2003

Relation between extracellular polymers' composition and its ability to complex Cd, Cu and Pb.

Activated sludges originated from wastewater treatment plants (WWTPs) play an important role in heavy metal removal from effluents. Extracellular polymers (ECP) form a major part of the activated sludge and are heavily involved in biosorption of heavy metals. The complexation of three heavy metals (Cd, Cu and Pb) with ECP extracted from six activated sludges, originated from different WWTPs, was investigated at pH 7. ECP in the study were shown to be mainly composed of proteins, humic acids, uronic acids and polysaccharides along with smaller amounts of lipids and nucleic acids. IR spectra confirmed the presence of the functional groups usually found in the ECP and the content in each fraction was determined using colorimetric methods. The determination of surface charge was carried out on each ECP sample and allowed two pK(a) values characteristic of two distinctive functional groups to be determined. At the pH used in the study, the value of these constants indicates that only one functional group is under protonated form. A polarographic method was used to determine the complexation parameters (number of binding sites and complexation constant) of ECP solutions towards metals. The following orders were established for the number of binding sites: Cu > Pb > or = Cd and for the stability of the ECP-metal complex: Cd > Pb approximately = Cu. A matrix of correlation between the composition of the polymers and the complexation parameters showed that the number of binding sites and the complexation constant were strongly linked to proteins, polysaccharides and humic substances content.

Binding Sites↗

PubMed2003

Determination of some rheological parameters for the characterization of activated sludge.

The rheological characterization of activated sludge originating from different aeration tanks and from a lab-scale plant was carried out using rotation tests. Two rheological parameters were used: limit viscosity (mu(infinity)) and reduced hysteresis area (rHa). Mu(infinity) was strongly influenced by the total suspended solids (TSS) content of sludge and an exponential relation was found between TSS and the rheological parameter mu(infinity). Significant differences in sludge viscosity were found for sludge of different origins, but all of 10 g/l TSS content, indicating ability of viscosity to show different sludge qualities. Marked changes in activated sludge microorganisms communities were shown to have an influence on rheological parameters. During aerobic digestion of sludge, variations in mu(infinity) were noticed, indicating change of sludge quality. An over-growth of filamentous bacteria species was shown to induce a particular rheological behavior which could be characterized by rHa. This parameter was proposed as an index of filamentous bacteria proliferation in activated sludge aeration tanks.

Bacterial Physiological Phenomena↗

PubMed2003

Effect of pH and ionic environment changes on interparticle interactions affecting activated sludge flocs: a rheological approach.

The rheological behaviour of activated sludge was investigated through the determination of sludge suspension equilibrium viscosity (micro(eq)) while varying the pH, sodium chloride and calcium chloride concentrations over a wide range. Micro(eq) was used to investigate the influence of environmental changes on the rheological behaviour of activated sludges, on the basis that it is representative of interparticle interactions affecting sludge flocs. Micro(eq) was shown to increase with increasing pH and to decrease with cation addition. The surface charge presented by sludge flocs was shown to be a factor that greatly affects micro(eq), as demonstrated by the linear correlation with zeta-potential (zeta-potential). A decrease in electrostatic charge was supposed to decrease repulsive effect between particles that facilitate flow and to promote a compaction of flocs that lower viscosity. Cation addition was shown to generate a viscosity decrease, in the same proportion, independent of the valency of the cation. The decrease in the particles double layer thickness coupled to the decrease in surface charge were supposed to induce a decrease in interparticle interactions which leads to lower viscosity values.

Flocculation↗

PubMed2001

Use of image analysis and rheological studies for the control of settleability of filamentous bacteria: application in SBR reactor.

To monitor the ability of flocs to settle in Sequencing Batch Reactor sludge, two methods were tested during two operation cycles. Firstly, an automated image analysis procedure has been tested to quantify the floc size and the length and number of filaments. Secondly, rheological measurements (Bingham viscosity and shear stress) have been used to characterise the dispersion of the sludge which can reflect the cohesive strength of aggregates and so the influence of filamentous bacteria on rheological properties. These results were compared with settling parameters such as Sludge Volume Index or settling velocity. Correlations between the measured parameters with image analysis and parameters such as Sludge Volume Index have been obtained. If it is more difficult to analyze rheological results, it seems however that the thixotropy and the Bingham viscosity distinguish poor settlement owing to some filamentous bulking. The first results are promising, although they require confirmation in the long term.

Bacterial Physiological Phenomena↗

PubMed1991

Rapid and sensitive discriminating determination of acetylcholinesterase activity in amniotic fluid with a choline sensor.

A simple method for the separate determination of acetylcholinesterase and butyrylcholinesterase activities in amniotic fluid is reported. This determination is performed with an enzyme electrode involving an immobilized choline oxidase membrane associated with the amperometric detection of hydrogen peroxide. Acetylcholine or butyrylcholine, in the presence of samples containing acetylcholinesterase or butyrylcholinesterase are specifically hydrolyzed, the formation of choline being detected vs time by the sensor with no need for a selective inhibitor. The dynamic linear ranges for acetylcholinesterase and butyrylcholinesterase are respectively 100 microU to 10 mU and 30 microU to 3 mU per ml sample.

Acetylcholine↗