Influence of extraction method on size exclusion chromatography fingerprints of EPS from wastewater sludges

Extracellular polymeric substances (EPS) were separated using two serial-linked size exclusion chromatography (SEC) columns to obtain detailed fingerprints. The chromatographic profile results were influenced by the nature of biological sludge (activated sludges, anaerobic granules, anaerobic flocculated sludges). Furthermore, our results highlight that EPS fingerprints are also highly dependent on the extraction method. If physical extractions modify only the relative absorbance of the chromatographic peaks, heating during extraction induces significant modifications of the fingerprints, probably owing to better organic matter extraction efficiency as well as an increase in hydrolysis for some compounds but not for EPS extracted from anaerobic granular sludges. This confirms that thermal treatment is a proper method to extract EPS from anaerobic granular sludges. The use of chemical extraction results in major changes on the EPS fingerprints. This work demonstrates that some chromatographic peaks are due to residues from the chemical reagent (such as EDTA, glutaraldehyde) which can modify or form complexes with some EPS macromolecules. As a result, due to its sensitivity to sludge origin and/or extraction procedure, SEC appears to be a suitable tool for an accurate qualitative EPS characterization.