Evaluating the\nRole of Pyrochar and Hydrochar in Biological\nDenitrification under Carbon Source-Limiting Conditions

Due to the discrepancies in properties, the roles of\npyrochar (PC)\nand hydrochar (HC) in biological denitrification are different and\nunclear. Therefore, the effects of PC and HC prepared from banana\npeel (BP), rice straw, and pine on denitrification under carbon source-limiting\nconditions were comparatively investigated. The results showed that\nthe pyrolysis temperature of PC was inversely proportional to its\nperformance. PC prepared at 900 °C significantly inhibited the\ndenitrification due to the suppression of electron transfer, denitrifying\nenzymes, and microbial activity. Conversely, HC not only facilitated\nthe electron production, transfer, and consumption but also enhanced\nthe synergistic interactions of different microorganisms. When the\ninfluent contained 50 mg/L nitrate, the residual concentrations of\nnitrate and nitrite after 48 h were 1.06 and 0.00 mg/L, respectively,\nin the BPHC experiment, which were lower than those in the Blank experiment\n(11.08 and 4.34 mg/L). Microbial analysis revealed that Aliidiomarina, which favors nitrite accumulation,\nwas enriched in the experiments with 900 °C PC, while Marinobacter, a typical nitrate-reducing bacterium,\nattained maximum abundance in the BPHC experiment (37.44%). The findings\npresented here may contribute to further elucidating the role of HC\nand PC in denitrification, thereby promoting their practical application\nin wastewater treatment.