Valorization of Food Waste into Iron Oxide Nanoparticles: Characterization and Application for DIET-mediated Enhancement of Methane Production in Anaerobic Digester
J. Environ. Nanotechnol., Volume 15, No 3 (September 2026) pp. 44-59
Abstract
In the present study, the potential of using algal biomass for biogas production was enhanced by iron oxide nanoparticle (Fe₃O₄)-facilitated anaerobic digestion under mesophilic conditions. The use of algal biomass as a renewable organic substrate was proposed due to its high content of biodegradable organic matter and its potential for wastewater nutrient recovery. Nevertheless, due to the resistant algal cell wall structure and slow microbial electron transfer, the efficiency of methane production during anaerobic digestion is often limited. To address this limitation, green-synthesized Fe₃O₄ nanoparticles were employed as conductive additives to enhance microbial electron transfer and improve biomethanation efficiency, representing the key novelty of this study. Fe₃O₄ nanoparticles were added at various concentrations (25, 50 and 75 mg L⁻¹) to batch anaerobic digesters to assess their effects on biogas production, methane enrichment, COD removal efficiency, solids degradation and pH stability. The experimental results demonstrated that the addition of Fe₃O₄ nanoparticles significantly improved anaerobic digestion performance. The digester supplemented with 50 mg L⁻¹ Fe₃O₄ nanoparticles exhibited the best performance, producing a cumulative biogas yield of 685 mL g⁻¹ VS, which was 34.3% higher than that of the control digester (510 mL g⁻¹ VS). The highest methane concentration (71.4 ± 1.8%) was achieved in the nanoparticle-assisted reactor, compared with 54.2 ± 1.3% in the control. Similarly, COD removal efficiency increased from 61.8 ± 2.1% in the control reactor to 82.6 ± 2.4% in the optimized nanoparticle reactor, while total solids and volatile solids reduction efficiencies reached 58.7 ± 2.0% and 69.8 ± 2.0%, respectively. The observed improvements were statistically significant (p < 0.05), confirming the positive influence of the optimized Fe₃O₄ nanoparticle dosage on anaerobic digestion performance. These findings demonstrate the practical potential of green-synthesized Fe₃O₄ nanoparticles for improving renewable methane production and resource recovery from algal biomass, thereby contributing to sustainable bioenergy generation and wastewater valorization. The enhanced performance is attributed to improved direct interspecies electron transfer (DIET), accelerated substrate degradation, and enhanced microbial enzymatic activity facilitated by the conductive Fe₃O₄ nanoparticles. However, a higher nanoparticle concentration (75 mg L⁻¹) resulted in comparatively lower performance, likely due to nanoparticle aggregation and inhibitory effects on microbial activity.
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