Biodegradation of activated sludge extracellular polymeric substances as the electron donors for denitrification

The biological denitrification requires a carbon source as the electron donor and the type and quantity of the carbon source directly affects the denitrification performance of activated sludge. Many sewage treatment plants in China currently face the challenge of low organic matter content in the influent, which leads to low denitrification efficiency in biological systems owing to insufficient carbon sources. LB-EPS and TB-EPS extracted from activated sludge were utilized as the sole electron donors for denitrification in this study, its biodegradation and the denitrification performance of activated sludge was analyzed. The results showed that the BOD5/COD of LB-EPS and TB-EPS were 0.20 ± 0.02 and 0.44 ± 0.03, respectively. LB-EPS and TB-EPS demonstrated their suitability as electron donors for denitrification, three linear phases of nitrate concentration reduction during the denitrification were observed and the maximum denitrification rate of activated sludge was 1.34 and 1.42 mg NO3--N/(g MLSS·h), respectively. LB-EPS and TB-EPS showed high biodegradation under anoxic condition, and 65.2% of LB-EPS and 52.2% of TB-EPS were utilised by denitrifying bacteria. The bioavailability of polysaccharides in EPS, especially in TB-EPS, was higher than that of proteins, and the degradation rate of polysaccharides was higher than that of proteins. Both fluorescence and infrared spectra showed the changes in the EPS structure under anoxic condition.