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. 2021 Jul 30;18(15):8070.
doi: 10.3390/ijerph18158070.

Effect of Increasing C/N Ratio on Performance and Microbial Community Structure in a Membrane Bioreactor with a High Ammonia Load

Huaihao Xu  1 , Yuepeng Deng  1 , Xiuying Li  1 , Yuxian Liu  1   2 , Shuangqiu Huang  1 , Yunhua Yang  1 , Zhu Wang  1   3 , Chun Hu  1
Affiliations

Effect of Increasing C/N Ratio on Performance and Microbial Community Structure in a Membrane Bioreactor with a High Ammonia Load

Huaihao Xu et al. Int J Environ Res Public Health. .

Abstract

Herein, the responses of the operational performance of a membrane bioreactor (MBR) with a high ammonium-nitrogen (NH4+-N) load and microbial community structure to increasing carbon to nitrogen (C/N) ratios were studied. Variation in the influent C/N ratio did not affect the removal efficiencies of chemical oxygen demand (COD) and NH4+-N but gradually abated the ammonia oxidization activity of sludge. The concentration of the sludge in the reactor at the end of the process increased four-fold compared with that of the seed sludge, ensuring the stable removal of NH4+-N. The increasing influent COD concentration resulted in an elevated production of humic acids in soluble microbial product (SMP) and accelerated the rate of membrane fouling. High-throughput sequencing analysis showed that the C/N ratio had selective effects on the microbial community structure. In the genus level, Methyloversatilis, Subsaxibacter, and Pseudomonas were enriched during the operation. However, the relative abundance of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) involved in nitrification declined gradually and were decreased by 86.54 and 90.17%, respectively, with influent COD increasing from 0 to 2000 mg/L. The present study offers a more in-depth insight into the control strategy of the C/N ratio in the operation of an MBR with a high NH4+-N load.

Keywords: C/N ratio; membrane bioreactor; membrane fouling; microbial community; nitrification.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Effect of different C/N ratios on water quality parameters of effluent ((A): COD; (B): NH4+-N; (C): NO2−-N and NO3−-N).
Figure 2
Figure 2
(A) Ammonia oxidation rate of seed sludge under different initial COD concentrations. (B) Ammonia oxidization rate of sludge at different stages. (C) Variation of the sludge concentration in the MBR.
Figure 3
Figure 3
(A) Membrane fouling of the MBR during operation. (B) EEM spectra of SMP in the effluent of the MBR.
Figure 4
Figure 4
(A) Microbial richness and (B) diversity index of all sludge samples.
Figure 5
Figure 5
(A) Cluster analysis of microbial community structure. (B) Relative abundance of bacterial phyla. (C) Relative abundance of bacterial classes in Proteobacteria. (D) Relative abundance of bacterial classes in Bacteroidetes.
Figure 6
Figure 6
Heatmap of the relative abundance of bacterial genera in all samples.
Figure 7
Figure 7
Variation of the relative abundance of (A) AOB and (B) NOB.
See this image and copyright information in PMC

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