Extracellular Polymeric Substances Level Determines the Sludge Dewaterability in Bioleaching Process

Bioleaching treatments can significantly improve the dewaterability of sewage sludge. However, the exact mechanisms of the improvement of sludge dewaterability by bioleaching are as yet unclear. In this study, the variation of extracellular polymeric substances (EPS) content along with bound water content in sludge during bioleaching was investigated in detail. Results showed that sludge dewaterability was improved rapidly and then deteriorated slowly. The improvement of sludge dewaterability in the first 48h of bioleaching was primarily attributable to the removal of sludge EPS, and the deterioration of sludge dewaterability in the following 144h primarily resulted from the unexpected increase of sludge EPS amount in the latter stage of the bioleaching treatment. The Spearman correlation coefficients of EPS content and bound water content, EPS content and the specific resistance to filtration (SRF), and bound water content and SRF were 0.81, 0.83, and 0.94, respectively. Furthermore, the dewaterability of original sludge or the sludge being bioleached for eight days was improved by removing EPS through centrifugation, on the contrary, re-adding EPS especially from Acidithiobacillus ferrooxidans to bioleached sludge resulted in poor sludge dewaterability. Therefore, bioleaching is an innovative approach in enhancing sludge dewaterability, and an EPS level of bioleached sludge decides sludge dewaterability. (C) 2015 American Society of Civil Engineers.