Investigating the Fate of Activated Sludge Extracellular Proteins in Sludge Digestion Using Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-Page)

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Courtesy of Water Environment Federation (WEF)

ABSTRACT

The purpose of this study was to examine the fate of activated sludge extracellular proteins in batch anaerobic and aerobic digestion using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). We were particularly interested in studying the fate of proteins that are bound with different sludge cations. Extracellular polymeric substances (EPS) extracted by three cation-specific extraction methods, the cation exchange resin (CER) procedure for
extracting Ca2++Mg2+, sulfide extraction for removing Fe, and base treatment (pH 10.5) for dissolving Al, were subjected to SDS-PAGE and the resultant protein profiles were compared before and after sludge digestion. The initial SDS-PAGE on undigested activated sludge showed different protein profiles by the three methods, suggesting that Ca2++Mg2+, Fe, and Al are bound with different characteristic EPS and play unique physio-biochemical roles in floc formation. The analysis of SDS-PAGE post sludge digestion revealed that CER-extracted proteins remained intact in anaerobic digestion while they were degraded in aerobic digestion. While the fate of sulfide-and base-extracted proteins in aerobic digestion was not clearly resolved, their changes in anaerobic digestion were well observed. Sulfide-extracted protein bands were reduced by anaerobic digestion, indicating that Fe-bound EPS were degraded under anaerobic condition. While parts of base-extracted proteins disappeared after anaerobic digestion, others became more
extractable along with extraction of new proteins, indicating that base-extractable EPS are dynamic in anaerobic digestion. All these results suggest that the metal content in influent sewage have a significant impact on activated sludge characteristics and sludge digestibility. The potential application of SDS-PAGE and the three extraction methods for choosing a proper sludge pretreatment and digestion method are also discussed in this study.

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