Directional Enrichment of Denitrification Biofilm and Nitrogen Removal Efficiency Based on Potential Control

In order to investigate the denitrification efficiency, nitrogen conversion pathways and corresponding microbial flora functions of bioelectrodes at different potentials, a sleeve-type bio-electrochemical system (BES) device with multiple working electrodes was constructed in this study. Three different constant potentials including -0.3 V, -0.5 V and -0.7 V were applied to the working electrodes simultaneously. The results showed that the denitrification rates and current densities were 0.88 mg/(L·h) and 36. 91 mA/m² at -0.3V, 1. 02 mg/(L· h) and 241. 92 mA/m² at -0.5 V, 1. 11 mg/(L·h) and 476. 41 mA/m² at -0.7 V, respectively. The maximum denitrification rate and current density were both obtained at -0.7V indicated that more negative potential was beneficial for microorganisms to obtain electrons from electrode to support denitrification processes. The microbial community divergence happened as a result of potential regulation. The dominant microorganisms at phylum level at different potentials were all belonged to Proteobacteria, Bacteroidota, and Actinobacteriota, with Chryseobacterium (31.35%), Unclassified Comamonadaceae (34.22%), and Azoarcus (16.53%) as the dominant genera. Additionally, electrode potential regulation showed a significant impact on the expression of functional gene and the reaction mechanism. Under -0.7 V, more napAB genes were expressed indicating that the denitrification was achieved by electron transfer through cytochromes, while, under -0.3 V and -0.5 V, denitrification process was achieved through electron transfer by the expression of narGHI genes.