Impact of iron nanoparticles on biogas production and effluent chemical composition from anaerobic digestion of cattle manure

Many nanoparticles (NPs) were reported to enhance biogas production from anaerobic digestion (AD) of organic wastes. However, the influence of iron (Fe) NPs on processes stability of AD of cattle manure and effluent chemical composition has not yet been studied in depth. Therefore, three concentrations (15, 30, and 60 mg/L) of Fe NPs were added to the separate lab-scale batch bio-digester to investigate their impact on biogas production and effluent chemical composition from the AD of cattle manure compared with cattle manure only. The results indicated that the highest specific biogas production (p < 0.05) was attained with 15 mg/L Fe NPs and was 953.41 mL biogas/g VS compared with cattle manure only which produce only 589.2 mL biogas/g VS. The addition of 30 mg/L Fe NPs increased the specific methane (CH4) production (p < 0.05) by 118.8% compared with cattle manure only. Moreover, the rate of hydrogen sulfide (H2S) production was also reduced (p < 0.05) by 81%, 93%, and 110% using the 15, 30, and 60 mg/L Fe NPs, respectively, compared with cattle manure only. Further investigations confirmed that the addition of 15 mg/L Fe NPs maintained pH 6.9 and improved total and volatile solids removal efficiencies by 25.6% and 10.9%, respectively; this concentration of Fe NPs produced the highest concentration of volatile fatty acids (VFAs) and was 4050 mg/L and increases sulfide content by 12%. FTIR spectrum of effluent presented the addition of Fe NPs change the intensity and shift of peaks compared with cattle manure-only peak.