Application of Fe-NPs for Enhancing Methane Production in an Anaerobic Biogas Plant

Iron nanoparticles (Fe-NPs) have emerged as promising additives for enhancing biogas production through anaerobic digestion (AD). This review comprehensively examines Fe-NP synthesis methods (chemical, physical, and biological), their applications in biogas systems, and their effects on microbial communities. Analysis of recent studies reveals that Fe-NPs can increase methane production by 0.166 to 7 times compared to controls, with optimal concentrations varying from 5.5 to 4330 mg/L depending on nanoparticle type and substrate. Zero-valent iron nanoparticles (nZVI) at 20 mg/L achieved 1.96-fold enhancement, while Fe3O4 nanoparticles showed consistent improvements of 0.3–2.6 times across multiple studies. Modified Fe-NPs demonstrated a superior performance: Fe-NPs coated with magnesium hydroxide (Fe-NPs-MG) increased methane yield by 1.2 times in semicontinuous systems, Fe-NPs-U showed 1.45–1.52 times improvement, and Fe-NPs-Ze achieved 0.88 times enhancement. The highest increase (7-fold) was observed with Fe3O4-NPs using a coal substrate. Fe-NPs enhance biogas production through multiple mechanisms: facilitating direct interspecies electron transfer (DIET), promoting the growth of syntrophic bacteria (e.g., Syntrophomonas) and hydrogenotrophic methanogens (e.g., Methanospirillum), reducing H2S inhibition, and improving substrate bioavailability. Despite promising laboratory results, industrial-scale application remains limited. This review identifies optimal synthesis methods, effective concentrations, and coating strategies to bridge the gap between laboratory success and commercial implementation of Fe-NPs in biogas production.