Nitrogen removal performances and metabolic mechanisms of denitrification systems using different volatile fatty acids as external carbon sources

Understanding the microbial and metabolic mechanisms of denitrification using different VFAs as carbon sources can provide a theoretical basis for denitrification process fed by fermentation broth. In this study, denitrification using acetate, propionate, or butyrate as a sole carbon source was compared. The propionate and butyrate systems had higher maximum nitrate removal rates (122.58 and 120 mg N/(L center dot h), respectively) when facing high nitrate volumetric loading rate (nitrate VLR of 3200 mg N/(L center dot d)). The maximum nitrate removal rate in acetate system was the lowest (80.79 mg N/(L center dot h)) and nitrite accumulation occurred when nitrate VLR is lifted to 2400 mg N/(L center dot d). Microbial community analysis showed that the enrichment of denitrification bacteria (Rhodocyclaceae and Thauera) in propionate and butyrate systems were faster, which helped to enhancing the denitrification performance. The copy numbers of nirS were also higher in propionate and butyrate systems (4.92 x 1087.82 x 109 and 1.27 x 107-2.89 x 109 copies/g MLSS, respectively). In addition, metagenomic analysis revealed the denitrification and carbon metabolic pathways. Denitrification module had higher relative abundances in Propionate (0.86%) and Butyrate (0.79%). TCA-cycle module presented highest in Acetate (2.64%). As acetate is more readily available than propionate and butyrate for most microorganisms, the indigenous genera in acetate system were more abundant. Therefore, the enrichment of functional bacteria in acetate system took longer than that in propionate and butyrate systems.

Automated summary

This study compared denitrification using different VFAs as carbon sources and found that propionate and butyrate systems had higher maximum nitrate removal rates when facing high nitrate volumetric loading rates. Microbial community analysis showed that the enrichment of denitrification bacteria in propionate and butyrate systems was faster, which helped enhance the denitrification performance. The enrichment of functional bacteria in the acetate system took longer.