Enhanced denitrification using iron modified biochar under low carbon source condition: Modulating community assembly, allocating carbon metabolism and facilitating electron transfer

Biochar can modulate microbial community structure to enhance denitrification but the activity is still restricted by the availability of electron transfer (ETS) under metabolic imbalance conditions. Here we developed iron (Ⅲ) modified biochar (FeBC) to substantially mitigate this electron limitation, enhance ETS and accelerate denitrification reaction via intracellular metabolism and community interaction. The results demonstrated that FeBC could significantly improve the denitrification performance, the nitrate removal rate was significantly increased by 30 % at C/N ratio of 3 (W/W) with little nitrite and nitrous oxide accumulation, attributing to the enhanced activities of the ETS and denitrifying reductases and complex microbial interactions via increased abundance of microorganisms involved in carbon and nitrogen transformations. Biochemical quantification and electrochemical analysis, revealed that FeBC activated the acceleration of the ETS process. Comparative metagenome analyses indicated that upregulating key enzymes in the tricarboxylic acid cycle was the potential respiratory enzyme associated with FeBC-mediated ETS. NADH/NAD⁺ circulation stimulate the startup of carbon metabolism. This energy-linked mechanism could provide ATP for denitrification. This study revealed the functional roles of FeBC in mediating ETS and regulating the bacterial community to achieve enhanced denitrification.