Abstract
The aim of the presented work is introducing a simple and rapid way with high profit not only to reduce expenses and efforts, but also to guarantee safety and eco-friendly biogas source. Thus, the effect of nanoferrites, as a source of metal ion, on biogas production rate was studied. Nanoferrites MFe2O4 (M = Fe, Ni, Co) were synthesized via a modified aqueous co-precipitation method under alkaline conditions using monoisopropanolamine (MIPA) as a base and capping agent. The prepared nanoparticles were investigated by transmission electron microscopy (TEM), X-ray diffractometry (XRD), and vibrating sample magnetometer (VSM). Anaerobic system was constructed from special bench-scale digesters for examination of the nanoferrite effect on biogas production rate. The TEM images showed ultra-small, spherically, slightly aggregated, and well-distributed nanoparticles in the range of 5.7, 4.9, and 3.5 nm for magnetite (Fe3O4), cobalt ferrite (CoFe2O4), and nickel ferrite (NiFe2O4) nanoparticles (NPs), respectively. XRD patterns confirmed the cubic spinel structure for the prepared nanoparticles. VSM measurements predicted the superparamagnetic behaviors for all prepared nanoparticles. The effects of Fe3O4, CoFe2O4, and NiFe2O4 NPs with same concentrations on biogas production were investigated and yielded biogas cumulative volumes of 210.8%, 220.5%, and 171.9%, respectively, with respect to control, after 50 days of incubation. CoFe2O4 nanoparticles showed the greatest enhanced effect on the cumulative biogas production, followed by Fe3O4 nanoparticles.