Denitrification in bioretention systems based on corncob biochar produced at low pyrolysis temperature: The efficacy and the mechanisms

In this study, the performance of corncob biochar (CCB) produced at 250 °C, a relatively low temperature for biochar production, on nitrate removal was investigated under dynamic flow conditions based on bench column and scale-up bioretention device experiments. CCB could continuously release sufficient soluble organic compounds for denitrification. In the column experiment, the highest denitrification rate of 130.3 mg·N/(L·d) was observed at HRT of 8 h, which was much higher than the raw corncob. At the HRT of 8 h, the nitrate removal efficiency could maintain 100 % with the influent NO3–-N concentration not higher than 30 mg/L. The presence of CCB at a mass content of 5 % in the scale-up bioretention device could significantly improve the nitrate removal performance and there was barely accumulation of nitrite. The universal molecular characterization of the DOM based on FT-ICR MS showed that the DOM from CCB contained less proteins and more hydrophobic aromatic compounds than from the raw corncob, which was responsible for the prolonged and steady release of TOC and thus the better performance of denitrification for CCB. These results showed the potential of corncob biochar produced at low temperatures to apply to the bioretention facilities for urban stormwater management.