Long-term effect of fulvic acid amendment on the anammox biofilm system at 15 °C: performance, microbial community and metagenomics analysis

The role of fulvic acid (FA) on the anammox system at 15 degrees C was investigated. After operation for 113 days, total inorganic nitrogen removal efficiency in FA amendment reactor achieved to 58.6% on average, higher than that of control group (42.1%). Anammox-related functional genes, i.e., hzo and hzs, also demonstrated higher expression level after introduction of FA. It was observed that Candidatus Kuenenia became more competitive than Candidatus Brocadia with the existence of FA at 15 degrees C. Also, co-occurrence analysis showed that FA stimulated the complexity and interactive relationship of microbial communities in the anammox system. Metagenomics analysis revealed that FA introduction stimulated relative abundances of genes in central pathway of tricarboxylic acid cycle such as ACO, IDH, OGDH, SCS, FUM, and MDH. Meanwhile, metabolomics analysis revealed that metabolites related to amino sugar metabolic pathways (glucose 1-phosphate, UDP-D-glucuronate, UDP) and redox reactions (NAD+ and NADH) improved in the FA amendment reactor.

Automated summary

The study found that introducing fulvic acid at 15 degrees Celsius can improve the total inorganic nitrogen removal efficiency and the expression level of related functional genes in the anammox system. Fulvic acid can also enhance the complexity and interactive relationship of microbial communities, as well as stimulate the relative abundance of key genes in the tricarboxylic acid cycle.