Study on the Influence and Mechanism of Reflux Ratio on Anaerobic Ammonia Oxidation System

doi:10.13560/j.cnki.biotech.bull.1985.2025-0719

Abstract

Abstract:

Objective To explore the effect of reflux ratio on denitrification performance of anaerobic ammonia oxidation system and reveal its mechanism of action. Method Three reflux ratios (0%, 50%, and 100%) were set to determine the denitrification performance, granular sludge characteristics, microbial community structure, and nitrogen metabolism related functional genes of the anaerobic ammonia oxidation system at different reflux ratios. Result When the reflux ratio was 100%, the average total nitrogen removal efficiency and the average NRR (nitrogen removal rate) during the stable phase of the system increased by 9.32% and 36.09 mg/(L‧d), respectively, with more stable nitrogen removal performance. The ratios of ∆NO₂^--N/∆NH₄⁺-N and ∆NO₃^--N/∆NH₄⁺-N were closer to the theoretical values of anammox. The effluent had a lower oxidation-reduction potential, which improved the oxygen environment in the system. The color of granular sludge was redder, the degree of granulation increased, and the phenomenon of upward floating significantly reduced. The contents of tightly bound polysaccharides and loosely bound polysaccharides within the granules increased by 22.59 and 24.00 mg/g VSS, respectively, forming a more stable shear-resistant structure. The increase of C-O and C=C functional groups on the surface of granular sludge accelerated the electron transfer in the system. High-throughput sequencing showed that Candidatus Brocadia maintained a high relative abundance (38.61%), while the relative abundance of Denitratisoma increased by 4.13%. Meanwhile,nitrogen metabolism-related functional genes narG, napA, narZ and nirS were upregulated Conclusion An appropriate reflux ratio can effectively improve the denitrification performance and operational stability of anaerobic ammonia oxidation systems.

Key words: reflux ratio, anammox, granule sludge, microbial community structure, functional gene, mechanism of action

CHEN Zi-long, ZHANG Chao, HAO Wan-ting, SONG Xian-wei, CHEN Xin-yi, LU Lu, LI Peng-fei, ZHU Yi-chun. Study on the Influence and Mechanism of Reflux Ratio on Anaerobic Ammonia Oxidation System[J]. Biotechnology Bulletin, 2026, 42(2): 102-112.

Figures/Tables 9

Fig. 1 Schematic diagram of UASB device

Fig. 2 Nitrogen transformation and removal under different reflux ratiosA: Changes in ammonia nitrogen; B: changes in nitrite nitrogen; C: changes in nitrate nitrogen and total nitrogen; D: changes in NLR and NRR

Fig. 3 Variations in stoichiometric ratios and oxidation-reduction potential under different reflux ratiosA: Changes in stoichiometric ratio; B: changes in redox potential

Fig. 5 Variations in EPS composition and content of granule sludge under different reflux ratiosR1, R2, R3 indicate the reflux ratio of 0%, 50%, and 100%, respectively. The same below

Fig. 6 Variations in surface functional groups of granule sludge under different reflux ratios

Table 1 Variations in alpha diversity indices under different reflux ratios

	OTUs	Shannon	Chao1	Ace	Simpson	Shannoneven
R1	852	3.328	866	887	0.163	0.493
R2	836	3.447	850	869	0.145	0.512
R3	808	3.273	828	854	0.158	0.489

Fig. 7 Variations in microbial community structure under different reflux ratiosA: Relative abundance at the phylum level; B: relative abundance at the genus level

Fig. 8 Variations in nitrogen metabolism-related functional gene

Fig. 9 Underlying mechanism of effluent reflux in anammox systems

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