Hydrophobic molecular features of EPS extracted from anaerobic granular sludge treating wastewater from a paper recycling plant

Different EPS extraction methods were used to extract loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) from anaerobic granular sludge. Supelite'(TM) DAX-8 resin was applied to investigate the hydrophobic features of the extracted EPS. Besides the quantification of protein (PN), polysaccharide (PS) and humic-like substances (HS-like) in the extracted EPS, detailed qualitative information of the molecular features of the hydrophobic EPS fraction was investigated by size exclusion chromatography (SEC) and excitation and emission fluorescence matrix (EEM) techniques. The results show that the HS-like compounds are the major organic component in the extracted EPS, as well as the main molecular support of the EPS hydrophobicity. The hydrophobic HS-like compounds are mainly small molecules (apparent molecular weight (aMW) = 8 - < 1 kDa), and their hydrophobicity can be ascribed to their humic acid-like molecular structure. PN and PS contribute to the EPS hydrophobicity to a lesser extent. PN compounds are enriched in the TB-EPS. LB-EPS display a higher global hydrophobicity (%) than TB-EPS. SEC analyses demonstrate that the LB-EPS with an aMW of > 660 kDa and the TB-EPS molecules of which aMW range from 122 to 31 kDa are highly hydrophobic.