Biomedical subjects

N Tixier

Publications and source records attributed to N Tixier.

5 recordsLinked to original sources

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

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↗