Waste Activated Sludge Fermentation with Nitrite: The Influence of Electron Acceptor Concentration on Denitrification

To deal with the problem of carbon source lacking and the difficulties of waste activated sludge (WAS) disposal in wastewater treatment plant (WWTP), nitrite was added into WAS fermentation system (NSF) to develop a new way to accomplish denitrification and WAS reduction simultaneously in this paper, and the effect of electron acceptor concentration (200, 400, 600, and 800 mg/L nitrite) on denitrification in NSF was studied. Experiment results showed that different NO₂^--N concentration of NSF systems presented different denitrification ability, the best denitrification performance was found in 400 mg/L, and it was investigated that the nitrite removal amount per unit of volatile suspended solid (VSS) reduction in different NSF systems was presented as this order: 400>;600>;200>;800 (mg/L), with values of 0.66, 0.60, 0.46, 0.44 mg NO₂^--N /mgVSS-reduction respectively. Furthermore, there was no volatile fatty acids (VFAs) accumulation in 400mg/L NO₂^--N concentration system, while different level of accumulation in other NO₂^--N concentration systems was found, which meant denitrifiers in 400mg/L NSF could utilize carbon sources much better than that of others. Additionally, all the systems showed a great sludge reduction capacity, with more than 40% of VSS reduction.