ABSTRACT
This study investigated the compositional changes in the extracellular polymeric substances (EPS) matrix of anaerobic granular sludge enriched for synthesizing cadmium selenide (CdSe) nanoparticles. The methanogenic anaerobic granular sludge was enriched in the presence of cadmium (10-50 mg L−1) and selenite (79 mg L−1) for 300 days at pH 7.3 and 30 °C in a fed- batch experiment. In vitro experiments on metal(loid)-EPS interactions showed that CdSe nanoparticles found mainly in the loosely bound-EPS. Analysis of the EPS composition revealed a large increase in protein content (3 times) and a decrease in humic-like substances content (0.5 times) in the enriched granular sludge (EGS) compared to untreated granular sludge. EPS fingerprints, obtained by size exclusion chromatography (SEC) coupled to a fluorescence detector, showed a significant increase in the intensity of protein-like substances of >100 kDa aMW (apparent molecular weight) in the EPS matrix of EGS. This was accompanied by a prominent decrease in protein-like substances of aMW <10 kDa. The fingerprint of humic-like substances showed emergence of a new peak with aMW of 13 to 300 kDa in the EPS extracted from EGS. These results clearly indicate a compositional change in the EPS matrix of EGS synthesizing CdSe nanoparticles.
