Chemical description of extracellular polymers: implication on activated sludge floc structure

Abstract

Activated sludge extracellular polymers (ECP) were extracted either by sonication or a combination of sonication and cation exchange resin treatment (CER). The chemical composition of the aqueous extract was investigated by chromatographic analysis of amino acids and sugars after hydrolysis. Up to 70 to 80% of the total organic carbon (TOC) of ECP was characterized. Proteins were found to be the major constituent of ECP, which was confirmed by pyrolysis/GC/MS analysis. Sugar and protein analysis led to complementary information both on the origin of extracellular material and on sludge floc structure. The monosaccharide composition in ECP and sludge allowed the proposal of different origins for extracellular polysaccharides. The predominance of proteins in ECP underlined their key role in the floc structure, and led to hypotheses on their origin. Proteins were better extracted than sugars when the CER extraction was combined with sonication. This supposed that proteins are more involved than sugars in electrostatic bonds with multivalent cations. Electrostatic bonds were found to be uniformly distributed in the floc and closely combined with hydrophobic bonds. About 25% of ECP amino acids were negatively charged and 24% exhibited hydrophobic properties, highlighting the specific role of proteins in the floc structure.

Extraction of extracellular polymeric substances (EPS) from anaerobic granular sludges: comparison of chemical and physical extraction protocols

“…It is considered as the "control method" because it is the less degradative technique and there is a common step of centrifugation in all other protocols investigated. -Sonication (Dignac et al 1998): Sludge samples were sonicated in 50-mL fractions at 37 W for 1 min using a Bandelin Sonopuls GM 70 with a M 73 probe. -Sonication and CER (Dignac et al 1998;Liu and Fang 2002): The sludge sample was sonicated as previously described (50-mL fraction, 37 W, 1 min).…”

“…-Sonication (Dignac et al 1998): Sludge samples were sonicated in 50-mL fractions at 37 W for 1 min using a Bandelin Sonopuls GM 70 with a M 73 probe. -Sonication and CER (Dignac et al 1998;Liu and Fang 2002): The sludge sample was sonicated as previously described (50-mL fraction, 37 W, 1 min). CER (Dowex 20-50 mesh, Na + form, Sigma-Aldrich) was then added (70 gCER g −1 sludge VSS), and the mixture was stirred 1 h at 600 rpm with an orbital shaker.…”

“…Centrifugation is commonly considered as a comparative method because it is the less degradative technique and there is no addition of chemical compounds (Comte et al 2006a). Ultrasonication (Dignac et al 1998), heating (Zhang et al 1999), and cation exchange resins (CER; Frølund et al 1996) are the main physical techniques used. EPS can also be chemically extracted with the addition of ethylenediaminetetraacetic acid (EDTA) (Liu and Fang 2002), alkaline (Frølund et al 1996), and aldehydic (Fang and Jia 1996) reagents.…”

Macromolecular composition and anaerobic degradation of the sludge produced in a sequencing batch reactor

“…The principal components of activated sludge flocs are bacteria and extracellular polymers substances (EPS). Determination of the chemical composition of EPS has been the objective of many research papers (Frolund et al 1996;Dignac et al 1998;Sponza, 2003), thus proteins and carbohydrates have been identified as the principal components of EPS (Comte et al 2006). Considerably less attention has been devoted to the influence of macromolecular composition of sludge on anaerobic digestion.…”

“…Dissolved oxygen concentration has been identified as an important parameter to control simultaneous nitrification, denitrification and nitrite accumulation in SBR (Pochana and Keller, 1999;Rhee et al 1997). Sludge macromolecular composition has been monitored in continuous activated sludge systems (Frolund et al 1986;Dignac et al 1998;Sponza, 2003), in order to determine the macromolecular composition of the EPS. To date the study of the relationship between SBR operating conditions and sludge macromolecular conditions have received little attention.…”