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

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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.


Document Type: Research Article


Publication date: October 13, 2007

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