The connection between aeration regimes and EPS composition in nitritation biofilm

The effects of aeration regimes (intermittent and continuous aeration) on nitritation performance and biofilm EPS composition were evaluated in moving bed biofilm reactors (MBBRs), and a hypothesis that the aeration regimes affect EPS composition by affecting the microbial activity and sludge discharge content was proposed. The effluent NO2-/NH4+ ratio corresponded to that of an anammox reaction (1.07 +/- 0.20) for the MBBR with continuous aeration (MBBRcon.), while that in the MBBR with intermittent aeration (20 min on/15 min off) (MBBRint.) was relatively lower (0.75 +/- 0.19). Furthermore, the activity of ammonia-oxidizing bacteria in MBBR con . was 0.4-7.9 mg-N.L-1.h(-1) more than that in MBBRint., which was consistent with the lower proportion of dead cells in MBBRcon. compared with MBBRint. (9.4% vs. 31.8%). The higher microbial activity in MBBRcon. led to more sludge discharge than MBBRint., which was reflected in the higher biofilm detachment rate in MBBRcon. compared with MBBRint. (0.15 +/- 0.02 vs. 0.11 +/- 0.02 g ). The ratio of humic substances to polysaccharides in the EPS was high (0.96 +/- 0.08) in the detachment biomass, while the ratios in the nitritation biofilm on carriers from MBBRcon. and MBBRint. were 0.52 +/- 0.13 and 0.72 +/- 0.16, respectively. We hypothesized that biofilm matrix with high ratios of humic substances to polysaccharides are structurally unstable and prone to fall off. In addition, the higher proportion of dead cells in MBBRint. made the proportion of humic substances in EPS high. Meanwhile, less sludge discharge in MBBRint. than MBBRcon. caused more humic substances to accumulate in the biofilm. These was responsible for the higher ratio of humic substances to polysaccharides in MBBRint. compared with MBBRcon. The findings elucidate the connection between aeration regimes and biofilm EPS composition, and guide the choice of aeration regimes in the design of biofilm reactors for partial nitritation. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Continuous aeration in MBBRs leads to higher microbial activity and more sludge discharge, resulting in structurally unstable biofilm; meanwhile, intermittent aeration results in biofilms with higher proportions of humic substances due to more dead cells, and the accumulation of humic substances due to less sludge discharge.