A mimetic drug delivery system using graphene oxide as a component carrier in denitrification: Enhancing long-term stable carbon release and electron transfer capacity of carbon source materials

To address the issue of unstable carbon release and insufficient carbon utilization from agricultural wastes (AWs) applied for nitrogen removal, this study adopted a drug carrier-inspired design that uses graphene oxide (GO) as an organic component carrier. This solid carbon source material (CCFG), with corncob loaded on GO and zero valent iron (ZVI), achieved a maximum total nitrogen removal rate of 89.55% ± 0.88% and nitrate removal rate of 93.13% ± 0.65% while the maximum COD of CCFG (48.13 ± 2.95 mg/L) was half that of the materials without GO (120.54 ± 0.56 mg/L). GO effectively enhanced the stable release property of AWs while ensuring the efficient nitrogen removal. Characterization confirmed that GO possessed abundant functional groups (e.g., O−H and C=O) and CCFG exhibited an increase of hydrogen bond content between lignocellulose and GO, thereby enhancing the stable release of organics. The microbial community structure analysis demonstrated that the core functional groups were identified as lignocellulolytic bacteria (e.g., Simplicispira), denitrifying bacteria (e.g., Thauera), and electroactive bacteria (e.g., Pseudomonas). Electrochemical testing and functional gene prediction indicated that GO combining with ZVI significantly promotes nitrate reduction through accelerating electron transfer, enhancing carbon metabolism, and up-regulating key genes encoding denitrifying enzymes (e.g., Nar). By employing GO as a component carrier, this study provides a strategy for achieving stable electron supply and enhancing electron utilization efficiency in solid carbon sources.