Simultaneous nitrification, denitrification and phosphorus removal (SNDPR) at low atmosphere pressure

Stable, efficient, and low-aeration consumption operation of the sewage treatment process under low atmosphere pressure is a major challenge in high-altitude areas. The simultaneous nitrification, denitrification, and phosphorus removal (SNDPR) process may be suitable for low-oxygen conditions and can reduce aeration energy consumption under low atmosphere pressure because of the low demand for dissolved oxygen. Here, we studied an SNDPR system at low atmosphere pressure (72 kPa) that showed stable and efficient performance. The nitrogen removal efficiency at 72 kPa was much lower than that at 100 kPa at the same aeration rate, while the residual phosphate concentration remained unchanged. To achieve the same oxygen demand, the energy consumption required at 72 kPa needed to be increased by 25% over that at 100 kPa. Lower atmosphere pressure enhanced the activities of phosphorus-accumulating organisms, nitrate-dependent denitrifying phosphorus-accumulating organisms, nitrite-dependent denitrification bacteria, and nitrate-oxidizing bacteria but suppressed the activities of ammonia-oxidizing bacteria. 16S rDNA sequencing showed that atmosphere pressure can have a large influence on the composition of microbial communities. The nitrogen removal process was the major problem that needed to be enhanced in SNDPR systems at low atmosphere pressure, especially the ammonia oxidation process.