Biochar enhances partial denitrification/anammox by sustaining high rates of nitrate to nitrite reduction

To examine the short-term effects of biochar on the partial-denitrification anammox (PD/A) process, the adsorption kinetics, nitrogen degradation, electron transfer properties, and microbial community succession of wastewater treatment systems with and without biochar added were monitored and characterized. The results showed that biochar increased nitrate reduction rates, which enhanced total nitrogen (TN) removal of the system by about 10%. The findings attributed improved TN removal to biochar's influence in accelerating electron transfer rather than its adsorption properties. Analysis of the nitrogen transfer pathway showed that when sufficient substrate was available, the anammox and denitrification reactions simultaneously removed nitrogen. When the nitrite supply was insufficient, the anammox reaction outcompeted the denitrification reaction for regenerated nitrite. Integrated microbial community and functional protein analyses indicated that biochar addition increased the abundance of Ca. Kuenenia and Pseudomonas. Meanwhile, biochar modulates denitrifying cellular metabolism by inducing protein changes.