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.