Vertical spatial denitrification performance and microbial community composition in denitrification biofilters coupled with water electrolysis

Abstract

In this study, a denitrification biofilter coupled with water electrolysis (DNBF-WE) was developed as a novel heterotrophic–hydrogen autotrophic denitrification system, which could enhance denitrification with limited organic carbon in the secondary effluent. The volumetric denitrification rate of DNBF-WE reached 152.16 g N m⁻³ d⁻¹ (C/N = 2, I = 60 mA, and HRT = 5 h). Besides, the vertical spatial denitrification of DNBF-WE was explored, with the nitrate removal rate being 49.5%, 16.3%, and 29.3% in the top, middle, and bottom, respectively. The concentration of extracellular polymeric substances (EPSs) was consistent with the denitrification performance vertically. The high-throughput sequencing analysis results revealed that autotrophic denitrification bacteria (e.g. Thauera) gradually enriched along DNBF-WE from top to bottom. The functional gene prediction results illustrated the vertical stratification mechanisms of the denitrification. Both dissimilatory nitrate reduction and denitrification contributed to nitrate removal, and denitrification became more advantageous with an increase in the filter depth. The research on both the performance of DNBF-WE and the characteristics of microbial communities in the vertical zones of the biofilter may lay a foundation for the biofilter denitrification process in practice.