Ferrihydrite regulated nitrogen metabolic pathway at biocathode of bioelectrochemical system - Insight into biofilm formation and bacterial composition.

To further understand the nitrogen metabolism disrupted by anthropogenic activities, 2.5 g/L of ferrihydrite were added into cathodic chamber of bioelectrochemical system to expediate the nitrogen removal process. It was found that the nitrate removal constant was significantly improved and maintained at around 0.09 h-1 with ferrihydrite addition, while the control group maintained only at around 0.05 h-1. Besides, it seemed that the addition of ferrihydrite lead to less biomass accumulation but higher biofilm viability. Meanwhile, ferrihydrite selectively enriched OTUs capable of participating in both iron and nitrogen metabolism, relative abundance of OTU1631 (Thiobacillus) and OTU1467 (Comamonas granuli) was accordingly upped to 58.75 % and 5.11 %, respectively. Moreover, denitrification related genes were enhanced while genes related to nitrogen fixation, dissimilatory nitrate reduction, assimilatory nitrate reduction and nitrification were downregulated, further confirming the redirected electron transfer for the promotion of denitrification.