Stimulating volatile fatty acid production in anaerobic digestion: Bacterial community shifts induced by nano-zero valent iron and magnetite nanoparticles

The production of volatile fatty acids (VFA) through anaerobic digestion has gained significant attention due to its potential benefits for renewable energy, biofuel production, waste valorization, bioproduct synthesis, and wastewater treatment. Nano-zero valent iron (nZVI) and magnetite nanoparticles (Fe₃O₄-NPs) have been identified as effective nanomaterials for enhancing methane production, although their application in stimulating VFA production remains underexplored. This study aimed to increase VFA production by adding nZVI, Fe 3 O 4 -NPs, and nZVI/Fe 3 O 4 -NPs while investigating the associated changes in bacterial communities. AD of glucose was performed using municipal wastewater sludge over 25 days, with the sludge amended with 400 mg L⁻¹ of nanoparticles. Total DNA samples were collected post-digestion to analyze bacterial community shifts. Results showed a significant enhancement of VFA production by both nZVI and Fe₃O₄-NPs, with the highest output in the Fe₃O₄-NPs treatment (811.7 mg COD L⁻¹), followed by nZVI (769.9 mg COD L⁻¹) and combined nZVI/Fe₃O₄-NPs (455.7 mg COD L⁻¹). This significant enhancement highlights the potential of these nanoparticles in waste-to-energy anaerobic digestion systems. Propionic acid was predominant in nZVI, whereas acetic acid was most abundant in Fe₃O₄-NPs. Microbial community analysis revealed Firmicutes as the most abundant phylum across treatments, with varying effects due to nZVI and Fe₃O₄-NPs. • Our study demonstrates that nZVI and Fe 3 O 4 -NP increase volatile fatty acid yield in anaerobic digestion with up to 54% observed at 25 days. • nZVI and Fe 3 O 4 -NP treatment increase microbial diversity and support volatile fatty acid production in AD. • Exploring Fe-NP applications in anaerobic digestion systems to boost volatile fatty acid production offers new advancements in waste valorization, which aligns with the circular economy principles