Journal of Agricultural Engineering

Green-synthesized iron oxide nanoparticles (IONPs), formed using Murraya koenigii leaf extract as a capping and reducing agent, were evaluated for their potential to enhance biogas and methane production during the anaerobic digestion of cattle dung. ultraviolet-visible (UV-vis) spectrophotometric analysis identified the maximum absorbance of the synthesized IONPs at 432 nm. Transmission electron microscopy (TEM) imaging revealed that the IONPs were spherical with diameters ranging from 20 to 30 nm, while the polydispersity index (PDI) was determined to be 0.396 nm, and the zeta potential was measured as -12.1 mV, indicating moderate stability. The impact of varying concentrations of IONPs on biogas production was assessed using a bio-digester, with the treatment containing 18 mg L^-1 IONPs (T5: Cattle dung + 18 mg L^-1 IONPs) demonstrating the most significant improvements. The maximum specific biogas and methane production was 98.6 L g^-1 of volatile solids (VS) and 51.5%, respectively, in treatment T5 as compared to the control value (85.2 L g^-1 VS and 41.4%). With 18 mg L^-1 IONPs (T5), there was an increase in biogas (15.7%) and methane (24.3%) content as compared to the control (T1). Additionally, T5 treatment resulted in an increase in pH and a reduction in total volatile fatty acids (TVFA), total solids (TS), volatile solids (VS), and dehydrogenase activity. The highest reduction rates for TS (38.2%) and VS (10.5%) were observed in T5 after eight weeks of digestion. These findings suggest that Murraya koenigii derived IONPs effectively stimulate microbial activity, enhancing biogas and methane production through improved substrate degradation.