Accurately quantifying the reductive capacity of microbial extracellular polymeric substance by mediated electrochemical oxidation method.

The reductive capacity of microbial extracellular polymeric substances (EPS) plays important roles in environmental processes involved in heavy metal detoxification and organic contaminant degradation. However, the crucial parameter to evaluate the reductive capacity of EPS, electron donating capacity (EDC) lacks a quantitative approach. In this study, a novel mediated electrochemical oxidation (MEO) method was developed to investigate the EDCs of microbial EPS extracted from Shewanella oneidensis MR-1 (S. oneidensis MR-1), Escherichia coli (E. coli) and activated sludge. The results indicate that the MEO approach rapidly and accurately quantifies the EDCs of microbial EPS. S. oneidensis MR-1 EPS possessed the highest EDC value ascribed to their specific redox proteins components. EDCs of S. oneidensis MR-1 EPS were dependent on measurement conditions and increased with growing solution pH and applied potential. EDCs of S. oneidensis MR-1 EPS were depleted gradually during the redox reaction with irreversible oxidation of EPS. The reductive property of microbial EPS was accurately evaluated by quantifying the EDCs of EPS using the MEO approach, as well as their potential in environmental remediation.