Efficiently intensified nitrogen transformation in electrolysis-integrated constructed wetlands: Comparative performance and mechanism.

This study developed constructed wetlands (CWs) with direct current (DC) electrolysis and iron-carbon (IC) microelectrolysis. Ammonium removal was more significantly enhanced with IC by 12.7-27.3 %, while the promotion of DC only existed with lower voltage. DC electrolysis continuously promoted nitrate conversion by 5.7-13.3 % compared to the control. Total nitrogen removal was 75.0-92.7 % and 85.4-93.4 % with DC and IC electrolysis, respectively limited by ammonium and nitrite accumulation. Bioelectrolysis enriched nitrifying bacteria such as Ellin6067, Nitrospira, and Nitrosomonas. Moreover, IC stimulated hydrogenotrophic denitrifying bacteria (Paracoccus, Pseudomonas, and Dechloromonas) and up-regulated gene narG, narH, and narI, aligned with higher nitrate reductase activity. In contrast, DC caused higher abundance involved in electroautotrophic denitrifying bacteria (Thiobacillus) and genes of assimilatory nitrate and nitrite reduction (narB and nirA). Additionally, both electrolysis stimulated electron production and energy metabolism for nitrogen cycling. This work provided comparative methods to intensify nitrogen transformation in CW systems.