NADH accumulation during DPAO denitrification in a simultaneous nitrification, denitrification and phosphorus removal system

Abstract

Denitrifying polyphosphate-accumulating organisms (DPAOs) and denitrifying glycogen-accumulating organisms (DGAOs) are two bacterial groups that jointly complete the denitrification in a simultaneous nitrification, denitrification and phosphorus removal (SNDPR) system. By monitoring the dynamic changes of carbon, nitrogen and phosphorus in a typical cycle, this study found that DPAOs had a higher denitrification activity than DGAOs in a SNDPR system. A high concentration of nitrite was added at the end of the anaerobic operation mode, and the operation mode was changed from the anaerobic/micro-aerobic/anoxic to the anaerobic/anoxic mode. The SNDPR system showed a high level of NO accumulation, while the system without the phosphorus removal function would only produce a small amount of NO. By detecting the changes in the reduced nicotinamide adenine dinucleotide (NADH) and oxidized nicotinamide adenine dinucleotide (NAD⁺), it was found that NADH accumulation occurred in the SNDPR system during the anaerobic period, while the system without the phosphorus removal function had no significant accumulation of NADH. The accumulation of NADH could reasonably explain the higher denitrification activity of DPAOs than that of DGAOs, and could also explain the accumulation of nitric oxide (NO), the stress reaction product of nitrite. The accumulation of intracellular NADH in DPAOs during the anaerobic phase is of great significance for understanding the metabolic mechanism of DPAOs and DGAOs.