Michel Baudu

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.

Aqueous heavy metals removal on amine-functionalized Si-MCM-41 and Si-MCM-48.

Ordered mesoporous silica with hexagonal and cubic structure, type MCM-41 and MCM-48 respectively, were synthesized under basic media using pure silica, cetyltrimethylammonium bromide and tetramethylammonium hydroxide, for MCM-41 and tetraethylorthosilica, cetyltrimethylammonium and NaOH for MCM-48. The expanded materials were prepared by post-synthesis method with N-N dimethyldodecylamine (DMDDA) and dodecylamine (DDA). Small angle X-ray diffraction, nitrogen adsorption-desorption measurements, FT-IR and thermogravimetry were used to characterize the samples. The expanded materials were tested for adsorption of Cd(2+), Co(2+), Cu(2+) and Pb(2+) in aqueous solution. Aminated materials were found to be fast adsorbents for metallic ions cation with affinity for Cu(2+), Pb(2+), than for Cd(2+) and Co(2+) from single solution. In mixed metallic ions cation solutions, competition by the adsorption sites is likely to occur, the adsorption preference is for Cu(2+)and Pb(2+). The kinetic of the reaction is very rapid and follow pseudo-second order and clearly indicated that Langmuir model describe better the for metal ions adsorption on aminated mesoporous material than Freundlich model.

Cell surface characterisation of Microcystis aeruginosa and Chlorella vulgaris

According to previous studies, Microcystis aeruginosa, a picocyanobacteria, is more sensitive to copper than the other phytoplanktonic species such as Chlorella vulgaris a chlorophycea. An experimental study was carried out to determine the cell wall characteristics of both species. The cell surface of M. aeruginosa presented a lower hydrophobic character and a more negative surface charge over a larger pH range than for C. vulgaris, according to hydrophobicity and zeta potentials measurements. By combining infrared spectroscopy data and potentiometric titrations, the total concentration of functional groups determined for M. aeruginosa (1.60x10(-3)mol/g), as well as the number of carboxyl groups, was higher than for the C. vulgaris ones (0.22x10(-3)mol/g). The differences in surface properties, as shown by chemical, physicochemical and spectroscopic measurements would justify the differences in sensitivities to copper ions up-take between the two specimens.

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.

Short term copper toxicity on Microcystis aeruginosa and Chlorella vulgaris using flow cytometry

Copper sulphate is a common algaecide applied to ponds in order to keep phytoplanktonic blooms under control, especially those prone to cyanobacterial development. The copper toxicity was evaluated for two phytoplanktonic species with the same size and shape: one cyanobacteria Microcystis aeruginosa and one chlorophyceae Chlorella vulgaris. Under controlled conditions in order to keep free copper concentration constant, three bioassays were carried out: growth inhibition tests and two sets of flow cytometric analysis (autofluorescence and esterase activity inhibition). The results showed: (1) that regardless of the cell type, as copper concentrations increased, cell division rate and autofluorescence decreased, (2) a difference in sensitivity according to the length of exposure to copper: 24 or 48 h, and (3) that M. aeruginosa showed a greater sensitivity than C. vulgaris in the 24h copper exposure assay according to esterase activity data.

Cooperative coadsorption of 4-nitrophenol and basic yellow 28 dye onto an iron organo-inorgano pillared montmorillonite clay.

Sorption properties of an iron surfactant-modified pillared montmorillonite (Fe-SMPM) toward two organic pollutants, basic yellow 28 dye (BY28) and 4-nitrophenol (4-NP), were studied at different pH values in both single component and binary pollutant systems. The pseudo-first-order model fits well with the kinetic data obtained in single component studies and sorption capacities of both BY28 and 4-NP increased with the pH value. A sorption synergetic mechanism was observed in binary systems; 4-nitrophenol adsorption was enhanced by the presence of BY28 in the mixture and increased with dye concentrations. Isotherms were described using the Freundlich model in single component systems and the Sheindorf-Rebhun-Sheintuch (SRS) model, an extended Freundlich model, in binary mixtures systems. Hydrophobic interactions between the surfactant-modified pillared clay and the pollutants were suggested to explain the sorption mechanisms.

Amino-functionalized MCM-41 and MCM-48 for the removal of chromate and arsenate

The aim of the present work was to investigate the efficiency of three amino-functionalized (hexadecylamine, dodecylamine, and dimethyldodecylamine) mesoporous silicas (MCM-41 and MCM-48) toward the adsorption of arsenate and chromate. Hexadecylamine-functionalized materials were characterized; BET surface areas, pore volumes, and sizes decreased with the functionalization, whereas XRD patterns show that the hexagonal structure of MCM-41 and the cubic structure of MCM-48 were not modified. The zeta potential decreases with pH and the highest arsenate and chromate removal was observed at the lowest pHs. Adsorption of chromium and arsenate was significantly enhanced after functionalization and amino-functionalized MCM-41 adsorb larger amounts of arsenate when compared to expanded MCM-48 materials. Chromate sorption capacities increased with the chain length and the larger capacities were obtained with hexadecylamine-functionalized mesoporous silicas. Mesoporous silicas modified by dimethyldodecylamine exhibited the higher arsenate sorption capacities.

Copper and nitrophenol pollutants removal by Na-montmorillonite/alginate microcapsules

The use of renewable bioresources allows the development of low cost adsorbents that are versatile. In the present paper, the affinity and the removal capacity of montmorillonite/alginate microcapsules for a hydrophobic organic pollutant (4-nitrophenol) and an inorganic pollutant (copper) were evaluated. The physicochemical processes through sorption and kinetic experiments under different ratios of montmorillonite vs. alginate and initial contaminant concentrations were investigated. The total weight loss and diameter decrease during the drying process were 90-96% and 64%, respectively. A significant decrease in beads diameter, related to water elimination, has been observed during the first 24h. Structural modifications that occur during the drying process were evaluated using thermal analysis. From correlation coefficients, the second-order equation depicts properly the adsorption of copper by the microbeads adsorption capacity increases to saturation with time; 3 and 6h were needed to reach equilibrium on wet and dry mixed microcapsules. The pseudo-second order model properly depicts the adsorption process of 4-NP onto Na-mont and (Na-mont/SA) mixed microcapsules but failed to reproduce the data observed for the alginate beads. Isotherms data were fitted with good correlation using the Langmuir model; alginate and montmorillonite adsorption capacities (q(m)/wet beads) agree with those obtained by various studies.

Fixed-bed column studies of pentachlorophenol removal by use of alginate-encapsulated pillared clay microbeads.

Columns were packed with two alginate/pillared clays microbeads (aluminium-pillared clay and surfactant-modified aluminium-pillared clay). Pentachlorophenol sorption performance was assessed under variable operating conditions: different bed heights, influent pentachlorophenol concentrations and flow rates. These conditions greatly influenced the breakthrough time/volume, the saturation time/volume and the uptake capacity. Higher values of experimental uptake capacities were obtained for the encapsulated surfactant-modified aluminium-pillared clay compared with the encapsulated aluminium-pillared clay, and the values were compared with those obtained with other low-cost sorbents. The experimental breakthrough curves were modelled using Bed Depth Service Time (BDST), Wolborska and Thomas models. Linear relationship was obtained for the BDST model, indicating the suitability of this model; bed capacity increased sharply with the introduction of CTAB in the inorgano-pillared clay. Wolborska model was applied only to the initial part of the curves. Thomas model was no doubt the most suitable description of the adsorption mechanisms for the entire breakthrough curves. Experimental and Thomas model-predicted equilibrium uptake capacities were in accordance.

Towards a rheological parameter for activated sludge bulking characterisation

Abstract An examination of the rheological behaviour of activated sludge presenting filamentous bulking was carried out. It was shown that rheograms from filamentous sludge exhibit a particular behaviour due to its thixotropic characteristic, contrary to non-filamentous ones. A rheological protocol of measurement of thixotropy consisting of submitting sludge to increasing–decreasing shear rates was proposed and optimised to obtain the greatest sensitivity as possible on the determination of the proliferation of filamentous bacteria in activated sludge. A relevant parameter, consisting in the determination of the reduced hysteresis area developed (rHa) from rheograms, for indicating the presence and the amount of filamentous bulking was deduced. An application to the study of several bulking developments was carried out. The thixotropic characteristic of filamentous sludge was shown to originate from an irreversible breakdown of the filamentous matrix. The total suspended solid (TSS) content was shown to have a great influence on the value rHa. The morphological characteristics of filaments were supposed to have an influence on the value rHa too. The carbohydrate content of activated sludge was shown to be linearly linked to the rheological parameter rHa/TSS during the filamentous growth phase and an increase in rHa/TSS was followed by an increase in SVI.