Development of fermentation and respiration bioprocesses for efficient nitrogen removal through microbial catabolism

Abstract

Conventional activated sludge processes are primarily designed for nitrogen and phosphorus removal, with carbon transformation regarded as a concomitant process that supports downstream denitrification rather than a proactively regulated process. Inspired by the metabolic division of labor in gut ecosystems, we proposed and validated a metabolism-guided strategy for an experimental membrane bioreactor (MBR-E) with a prefermentation unit that couples upstream fermentation with downstream denitrification to restructure carbon flux toward more bioavailable electron donors for nitrogen removal. Long-term operation showed that MBR-E achieved significantly lower effluent total nitrogen (7.9 ± 2.4 mg/L) compared with the control MBR system (MBR-C, 12.3 ± 3.5 mg/L), which was attributed to its elevated specific denitrification rate. Influent organics were efficiently converted into volatile fatty acids (VFAs) via fermentation and shortening hydraulic retention time from 0.67 h to 0.5 h shifted VFA composition from propionate/butyrate dominance to acetate enrichment. Further, 16S rRNA gene sequencing demonstrated that functional denitrifiers and nitrifiers were selectively enriched in MBR-E. Co-occurrence network analysis revealed strengthened cooperative interactions and tighter functional coupling between carbon degradation and nitrogen removal in MBR-E. Overall, this study demonstrates that fermentation-driven carbon reprogramming can effectively regulate downstream respiratory pathways and reshape the microbial community structure, providing a novel approach for efficient nitrogen removal from low-carbon/nitrogen wastewater.

Keywords

Biological nitrogen removal / Fermentation / Volatile fatty acids / Microbial metabolism / Microbial community

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