In an original research article published in the journal Biochar, authors Hua Shang, Chao Jia, Song Wu, Ning Chen, Yujun Wang, and Xiangdong Zhu investigated the mechanisms through which graphitized biochar accelerates the natural decontamination of antibiotic-polluted paddy fields. Paddy soils frequently accumulate organic residues, such as veterinary antibiotics, through manure amendments and contaminated irrigation water, often surpassing natural attenuation limits. While conventional biochars rely primarily on surface oxygen-containing functional groups that act as chemical batteries to store and release electrons, these functional groups disrupt conjugated electron networks and impede rapid electron conduction. By converting raw bamboo biochar into a highly graphitized material using flash Joule heating, the research team restructured the carbon lattice to enhance electrical conductivity, creating a direct conduit for electron transfer between soil microorganisms and oxidized iron minerals.

The authors observed that this structural graphitization altered the electrochemical behavior of the material, shifting it from an electron-storing battery into a high-performance electrical conductor. The electrical conductivity of the graphitized biochar reached 5.51 siemens per centimeter, representing a 2.64-fold enhancement over conventional biochar, while its total electron exchange capacity decreased as non-conductive surface oxygen groups were removed. When applied to paddy soil experiencing five alternating cycles of twelve-hour oxygen-free and twelve-hour oxygenated conditions, the conductive framework bridged electron flow between native iron-reducing bacterial communities and oxidized iron species. Consequently, active divalent iron generation increased by 18.9 percent after 108 hours of reaction compared to untreated soil controls, with surface-bound and ion-exchangeable iron species expanding to 8.63 and 7.18 grams per kilogram, respectively.

Microbial community analyses demonstrated that graphitized biochar selectively enriched vital iron-reducing bacterial populations across multiple taxonomic groups. High-throughput sequencing revealed significant expansions in the relative abundances of Proteobacteria and Firmicutes, specifically increasing dominant iron-reducing genera such as Bacillus, Anaeromyxobacter, Citrifermentans, and Flavisolibacter. The elevated electrical conductivity relieved cellular metabolic bottlenecks by providing a rapid respiratory pathway for iron reducers, thereby locking microbes and minerals into a self-reinforcing, mutually beneficial electron transfer network that depressed reduction-oxidation potential. Control experiments with gamma-sterilized soils confirmed that this accelerated iron transformation was entirely microbial and depended strictly on living bacterial consortia.

The generated divalent iron reacted with dissolved oxygen during aeration phases, amplifying the formation of reactive oxygen species and driving rapid pollutant breakdown. Graphitized biochar boosted hydroxyl radical accumulation by 54.9 percent relative to untreated soils, reaching 1.34 micromoles per gram of soil, while conventional biochar produced only a 17.1 percent increase. Chemical quenching experiments verified that superoxide radicals and hydrogen peroxide served as intermediate reaction products leading to hydroxyl radical generation. This surge in oxidative capacity resulted in a 57.2 percent acceleration in degradation rates, achieving 100 percent removal of the model antibiotic sulfamethoxazole within 120 hours, compared to 79.8 percent removal with conventional biochar and 46.3 percent in untreated soil. Across diverse agricultural soils, hydroxyl radical production climbed by 14.5 percent in red soil, 21.4 percent in cinnamon soil, and 57.1 percent in black soil, demonstrating that native microbial community composition dictates the ultimate remediation efficacy.

Source: Shang, H., Jia, C., Wu, S., Chen, N., Wang, Y., & Zhu, X. (2026). Geoconductor function of graphitized biochar redirects microbial Fe(III) reduction and stimulates hydroxyl radical production in paddy soil. Biochar, 8, Article 92.