Use of Extracellular Polymeric Substances as Natural Redox Mediators to Enhance Denitrification Performance by Accelerating Electron Transfer and Carbon Source Metabolism

The extracellular polymeric substances (EPS) extracted from waste activated sludge was used as endogenous redox mediator to enhance denitrification performance in this study. The results showed that the nitrate reduction rate increased 1.45 times with EPS addition (75 mg C/L). The addition of EPS decreased the charge transfer resistance and improved electron transport system activity. The activities of nitrate reductase and nitrite reductase were improved by 29.1% and 25.2%. Compared with the control group (36.42 kJ/mol), the activation energy of the system with EPS addition (25.82 kJ/mol) was reduced by 29.1%. Besides, EPS could be used as electron carriers to accelerate electron transport of denitrification, and it mainly played a similar role to that of quinone loop in electron transfer chain. More importantly, EPS addition enhanced carbon source metabolism to increase available NADH yield (1.21-fold of the control group) for denitrification, and thus denitrification performance of activated sludge was promoted.