Decoding the carbon and nitrogen metabolism mechanism in anammox system treating pharmaceutical wastewater with varying COD/N ratios through metagenomic analysis

In current study, the underlying mechanism of coupling dissimilatory nitrate reduction to ammonium (DNRA) pathway with anaerobic ammonium oxidation (anammox) process was explored through metagenomics sequencing analysis in an anammox granular system treating pharmaceutical wastewater under varying COD/N ratios. It was found that average NH4+-N and NO2--N concentration in effluent was stabled around 2.89 ± 2.53 and 14.23 ± 9.23 mg L-1 with nitrogen removal efficiency (NRE) increase to 85.3% when influent COD/N ratio was around 0.63. Besides, metagenomics sequencing analysis revealed that different COD/N ratios significantly influenced the abundances of functional nitrogen and carbon metabolic genes and microbial community succession. The low COD/N ratio strengthened DNRA pathway in Ca. Kuenenia_stuttgartiensis, as well as the abundance of functional gene nrf. The abundance of the genes encoding acetate degradation, for example, AMP-acs, ADP-acs and AckA increased, suggesting the acetate could stimulate the multiple carbon metabolic potentials of AnAOB. On the contrary, the genes encoding for propionate metabolism were enriched in denitrification bacteria. Our findings revealed the new insight into the mixotrophic characteristic of AnAOB which might help widen engineering application of anammox proocess in various industrial wastewater.