Enhancing methane yield of chicken litter in anaerobic digestion using magnetite nanoparticles

Methane production of chicken litter in anaerobic digestion (AD) was evaluated with different concentrations of magnetite (Fe₃O₄) nanoparticles (NPs). The Fe₃O₄ NPs were synthesized by co-precipitation, where the effect of different concentrations and dissolution temperatures of the passivant and precursors, as well as the sonication time, on NPs size was determined. The best NPs were selected based on the smallest hydrodynamic diameter (79.37 nm) with the highest absolute value of zeta potential (−18.06 mV). These NPs were analyzed in a transmission electron microscope (average size of 4.2 nm) and by X-ray diffraction (to corroborate their structure). These 4.2 nm NPs were used to evaluate their effect on AD of chicken litter under mesophilic conditions. The treatments for AD were the control (only chicken litter) and the addition of different concentrations of Fe₃O₄ NPs (20, 40 and 60 mg L⁻¹). The treatment with 20 mg L⁻¹ of NPs had the highest methane production rate (2.55 mL CH₄∙g_vsf⁻¹∙d⁻¹) and the highest cumulative methane yield (137.23 mL CH₄∙g_vsf⁻¹), the last one with an increase of 73.9% compared to the control, while the concentration of volatile fatty acids was similar in all treatments. In general, NPs had a biostimulating effect on methanogenic activity.