Kinetics and gene diversity of denitrifying biocathode in biological electrochemical systems

Cathodic denitrification using a bioelectrochemical system removes nitrogen at a low C/N ratio, and also harvests energy as electricity. Denitrifying biocathodes were cultured using three electrode systems with nitrate (NO3-) and/or nitrite (NO2-) as electron acceptors. Results showed that denitrification of NOx- in biocathodes exhibit typical enzymatic reaction kinetics and denitrification rate follows the Monod equation, with r(max) = 1.33 kg N m(-3) d(-1), K-s = 5.52 g L-1 for NO3- and r(max) = 1.76 kg N m(-3) d(-1), K-s = 8.09 g L-1 for NO2-, respectively. Optimal cathodic efficiency was obtained at an initial substrate concentration of 0.5 g L-1. A high-throughput sequencing analysis of 16S rRNA gene showed high biodiversity in a denitrifying biocathode and nitrite contributed more to the formation of cathodic microbial community structure. Denitrification functional gene analysis revealed Pseudomonas are effective denitrifiers in a biocathode.