Achieving Simultaneous Nitrification and Denitrification by a Membrane Aerated Biofilm Reactor at Moderate Lumen Pressure

Abstract

Lumen pressure is of crucial importance to achieve simultaneous nitrification and denitrification (SND) in the membrane aerated biofilm reactor (MABR); so, in this study, a laboratory-scale MABR was operated under different lumen pressures (7 kPa, 10 kPa, 13 kPa, and 16 kPa) successively to verify its impact on nitrogen removal. The results showed that NH4+-N oxidation was deficient under 7 kPa due to inadequate oxygen supply, while denitrification was depressed under 16 kPa. Total nitrogen removal efficiency was similar under 10 kPa and 13 kPa (around 78.9%), much higher than that under 7 kPa and 16 kPa (approximately 50%). The biomass density (22.35 g/m2) and biofilm thickness (500.3 µm) were the highest under 13 kPa, and EPS was increasingly secreted along with the increase in lumen pressure. The relative abundance of Nitrospirae was highest under 16 kPa (3.53%), indicating a higher lumen pressure could promote nitrifiers. The denitrifying-related microbes, such as β-proteobacteria, α-proteobacteria and ε-proteobacteria, showed an increasing and then decreasing pattern along with lumen pressure increase, and were enriched at 10 kPa. The results could draw the conclusion that SND could be achieved at moderate lumen pressure, i.e., 10 kPa and 13 kPa in this study.