Sediment-based biochar facilitates highly efficient nitrate removal: Physicochemical properties, biological responses and potential mechanism

Biological removal of the nitrate, a highly concerning contaminant in rivers, is limited due to the low activity of denitrifying community. Biochar is extensively used in facilitating the nitrate removal because of its unique physicochemical properties which enhance the denitrifying performance in aqueous environment. However, the physicochemical properties of biochar and its potential strengthening mechanism in denitrification process remains unknown. Herein, the sediment-based biochar was prepared for strengthening denitrification for the first time. The biochar was prepared at 400-1100 degrees C, with its conductivity increasing from 0.21 to 310.11 S m(-1) while nitrogen (oxygen) content decreasing from 5.81% (20.30%) to 3.79% (16.63%). A maximum total nitrogen (TN) removal rate of 21.67 +/- 0.66 g N m(-3) d(-1) with a nitrate nitrogen (NO3--N) removal rate of 22.43 +/- 0.62 g N m(-3) d(-1) was obtained when biochar at pyrolysis temperature of 800 degrees C (SBC800) was added, which were 11.6 and 5.0-fold higher than that without biochar, indicating an ameliorative denitrification performance. The nitrogen-containing functional groups were correlated significantly with electron donating capacity (EDC, r = 0.898, p < 0.05) and electron accepting capacity (EAC, r = 0.911, p < 0.05) of biochar, further increased the abundance of denitrifying species to 75.9% by gaining high correlation with NO3--N removal (r = 0.903, p < 0.05). Overall, this study provides a low-cost and sustainable way to efficiently remove nitrogen from fluvial systems using sediment-based biochar.