Recently, inorganic-organic composites have become the focus of research in accelerating and stabilizing the conversion of organic wastes to biogas through anaerobic digestion process. In this study, nickel oxide-reduced graphene oxide (NiO-rGO) nanocomposite was synthesized to use as a catalyst to boost the production of biogas. Prior to synthesizing NiO-rGO nanocomposite, NiO nanoparticles (NPs) were synthesized from nickel acetate tetrahydrate precursor via hydrothermal method, and graphene oxide (GO) from lube oil wastes by modified Hummers’ method. Then, NiO-rGO nanocomposite was synthesized by reduction of GO using NaBH 4 as reducing agent and simultaneous incorporation of NiO into rGO sheet. As-synthesized NiO-rGO was characterized by XRD, FESEM, FTIR, XPS, and UV–vis spectroscopy to optimize the process for better conversion. Then it was used as an additive with a concentration of 25 mg/L in an anaerobic batch digester containing 8.5% total solid concentration at mesophilic conditions (27 ± 3ºC) for a digestion period of 60 days. It was found that addition of NiO-rGO increased biogas yield by 15.95% compared to control digester. Specific biogas and methane yield were 0.127 Lg −1 VS and 0.0741 Lg −1 VS respectively in control, whereas in the NiO-rGO catalyzed digester, specific biogas and methane yield were 0.147 Lg −1 VS and 0.089 Lg −1 VS respectively. Volatile solid (VS) reduction was found 33% in control and 44.05% in NiO-rGO catalyzed digester respectively. Highest methane content was found 66.3% in control and 71.3% catalyzed digesters.
Rabeya et al. (Thu,) studied this question.