Gilles Guibaud

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.

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.

Sorption of Cd(II) and Pb(II) by exopolymeric substances (EPS) extracted from activated sludges and pure bacterial strains: modeling of the metal/ligand ratio effect and role of the mineral fraction.

The present study deals with the sorption of Cd(II) and Pb(II) by exopolymeric substances (EPS) extracted from activated sludges or pure bacterial strains. The percentage of sorbed metal increases with the concentration of the EPS-water solution. Pb(II) always presents a higher affinity than Cd(II) for EPS. For the EPS extracted from pure bacterial strains, only one global binding constant from a simple equilibrium sorption model, may be used to assess the effect of microbial products such as EPS on Cd(II) and Pb(II) speciation or mobility in the environment. However, for EPS extracted from activated sludges, the wide variation of the global binding constants determined for Cd(II) and Pb(II) do not permit such a simple approach. The differences in sorption to metals between the two types of EPS (bacterial, activated sludges) could be explained by the differences in EPS composition: organic macromolecules, as well as the nature of the mineral fraction.

Characterization of the mineral fraction associated to extracellular polymeric substances (EPS) in anaerobic granular sludges

The extracellular polymeric substances (EPS) extracted from four anaerobic granular sludges contain an important mineral fraction (20-77% of the EPS dry weight). The composition of the mineral fraction of EPS depends strongly of the extraction method applied and to a lesser extend of the origin of the anaerobic sludge. Centrifugation, sonication, and heating extraction procedures yield a similar mineral composition. However, extraction using a cationic exchange resin (CER) leads to an increase of the Na(+) content in the EPS extract because the CER promotes an exchange of divalent and trivalent inorganic elements in the EPS extracts toward Na(+). Chemical extraction protocols were also shown to contaminate the EPS extracts by impurities or carry over of the extractant itself (e.g., ethanol). A part of the mineral fraction is bound to the EPS organic matter and structures the EPS matrix in the granules. Scanning electron microscopic analysis (SEM-EDX) showed that, in addition, solid particles such as CaCO(3) and Ca(5)OH(PO(4))(3) containing various metallic elements (i.e., Al, Fe, Cu, Mn...) are present in the EPS as well. This inorganic fraction, too often neglected in EPS studies, can influence the physicochemical properties of EPS.

Influence of solubilizing agents (cyclodextrin or surfactant) on phenanthrene degradation by electro-Fenton process - Study of soil washing recycling possibilities and environmental impact

One of the aims in soil washing treatment is to reuse the extracting agent and to remove the pollutant in the meantime. Thus, electro-Fenton (EF) degradation of synthetic soil washing solutions heavily loaded with phenanthrene was suggested for the first time. Two solubilising agents hydroxypropyl-beta-cyclodextrin (HPCD) and Tween 80(®) (TW 80) were chosen as cyclodextrin (CD) and surfactant representatives, respectively. In order to reuse HPCD and to degrade the pollutant simultaneously, the following optimal parameters were determined: [Fe(2+)] = 0.05 mM (catalyst), I = 2000 mA, and natural solution pH (around 6), without any adjustment. Only 50% of TW 80 (still higher than the critical micelle concentration (CMC)) can be reused against 90% in the case of HPCD while phenanthrene is completely degraded in the meantime, after only 180 min of treatment. This can be explained by the ternary complex formation (Fe(2+)-HPCD-organic pollutant) (equilibrium constant K = 56 mM(-1)) that allows OH to directly degrade the contaminant. This confirms that Fe(2+) plays an important role as a catalyst since it can promote formation of hydroxyl radicals near the pollutant and minimize HPCD degradation. After 2 h of treatment, HPCD/phenanthrene solution got better biodegradability (BOD5/COD = 0.1) and lower toxicity (80% inhibition of luminescence of Vibrio fischeri bacteria) than TW 80/phenanthrene (BOD5/COD = 0.08; 99% inhibition of V. fischeri bacteria). According to these data, HPCD employed in this integrated (soil washing + EF degradation) approach gave promising results in order to be reused whereas the pollutant is degraded in the meanwhile.

Effects of extraction procedures on metal binding properties of extracellular polymeric substances (EPS) from anaerobic granular sludges.

The effects of the extraction procedure of extracellular polymeric substances (EPS) on their proton/metal binding properties were studied. Nine extraction procedures (one control, four physical and four chemical procedures) were applied to four types of anaerobic granular sludges. The binding capacities between the EPS and lead or cadmium were investigated at pH 7 by a polarographic method. The composition of the EPS extracts varied according to the extraction technique and the origin of the sludge. This induced differences in the pK(a)s and the binding sites density of the EPS extracts. The carry-over of the extractant in the samples strongly affects the properties of the EPS from chemical extraction protocols. Lead and cadmium seem to be bound differently with the EPS, a higher binding capacity was observed for Pb(2+) than for Cd(2+).

Can POCIS be used in Water Framework Directive (2000/60/EC) monitoring networks? A study focusing on pesticides in a French agricultural watershed.

In this study, the main current limitations in the application of the Polar Organic Chemical Integrative Sampler (POCIS) in regulatory monitoring programmes were evaluated. POCIS were exposed from March to December by successive periods of 14 days in the River Trec (Lot et Garonne, France) and analysed for 34 pesticides. The study of the uncertainty related to the POCIS data was performed and we concluded that it might be up to 138%, which is higher than European Union requirements but this issue was adequately counterbalanced by the gain of temporal representativeness. Comparison with data from the official monitoring programme from the French Water Agency showed that the POCIS is already suitable for both operational and investigative monitoring. The sampled fraction issue, and then compliance with Environmental Quality Standards, was also addressed. It was confirmed that POCIS samples only the dissolved fraction of dimethenamid and showed that for compounds like atrazine, desethylatrazine and metolachlor, the POCIS concentration is equivalent to the whole water concentration. For dimethenamid, which exhibited a tendency to adsorb on suspended matter, a method was suggested to assess the raw water concentration from the POCIS measure. Finally, an innovative procedure for using passive sampler data for compliance checks in the framework of surveillance monitoring is proposed.

Fluorescence detection to determine proteins and humic-like substances fingerprints of exopolymeric substances (EPS) from biological sludges performed by size exclusion chromatography (SEC).

Fingerprints of extracellular polymeric substances (EPS) from activated and anaerobic granular sludges were obtained by size exclusion chromatography coupled to UV (210 and 280 nm) and fluorescence (221/350 nm (protein-like molecules) and 345/443 nm (humic-like substances)) detection. The total area below the peaks obtained with fluorescence detection is linked to the protein or humic-like substances EPS content. The EPS protein fingerprints, usually recorded with UV-280 nm, change dramatically, mainly in the relative size of peaks when they were measured by a florescence detection method. It means that the apparent molecular weight (aMW) distribution of EPS chomatophores and fluorophores is different. Protein-like and humic-like substances were found to be specific fingerprints of the EPS, affected by the type and origin of the bacterial aggregate and improve EPS sample differentiation. The protein-like fraction of EPS displays a wide range of aMW (>600 kDa-<10 kDa) whereas the humic-like substances fraction is composed of molecules of low aMW (6-<1.2 kDa).

Evaluation of size exclusion chromatography (SEC) for the characterization of extracellular polymeric substances (EPS) in anaerobic granular sludges

The extracellular polymeric substances (EPS) extracted from three granular and one flocculant anaerobic sludges were characterised by size exclusion chromatography (SEC) using two serially linked chromatographic columns in order to obtain more detailed chromatograms. A Superdex peptide 10/300 GL (0.1-7 kDa) and Superdex 20010/300 GL (10-600 kDa) from Amersham Biosciences were used in series with a mobile phase at pH 7 with an ionic strength of 0.223 M (phosphate buffer 50 mM and NaCl 150 mM). A part of the EPS molecules displays hydrophobic and/or ionic interactions with the column packing. Interactions could be modified by changing the mobile phase ionic strength or polarity (addition of acetonitrile). The detection wavelength (210 or 280 nm) affects strongly the EPS chromatogram. For a sludge originating from the same type of biofilms (i.e., anaerobic granules), the differences in EPS fingerprints are mainly due to differences in the absorbance of the chromatographic peaks, linked to EPS molecules content and composition. The EPS fingerprint changes significantly when the EPS originate from another type of anaerobic sludges. In addition, EPS fingerprints were affected by the extraction method used (centrifugation only; heat and centrifugation or cationic exchange resin and centrifugation). This phenomenon was observed mainly for the largest and smallest molecules and molecules which display interactions with column packing.

Role of extracellular polymeric substances (EPS) production in bioaggregation: application to wastewater treatment

This paper reviews the formation, structure, and stability of bioaggregates with an emphasis on the composition and distribution of extracellular polymeric substances (EPS) and their role in bioaggregation. Bioaggregation is ubiquitous in natural environment and is of great importance in biological wastewater treatment processes. It greatly influences the flocculability, settleability, and dewaterability for flocs and sludge retention and shear resistance for biofilms. The physico-chemical and microbial structures of bioaggregates are dependent on operational conditions as well as microbial diversity and spatial distribution. The formation of bioaggregates is mediated by the physico-chemical interactions as well as the microbial interactions such as EPS production and quorum sensing. EPS are composed of a mixture of macromolecules including proteins, polysaccharides, humic-like substances, and nucleic acids, which entrap the microbial cells in a three-dimensional matrix. The composition and physico-chemical characteristics of EPS have significant influence on the maintenance of the bioaggregate structure and the process performance of the wastewater treatment. However, the mechanisms of bioaggregation are still unclear and the conclusions on the role of EPS were mostly drawn from the established correlations and hypotheses. This paper expects to provide up-to-date knowledge on bioaggregation and insights for further studies and applications.