Biomethanation of NaOH pretreated petroleum coke using coal mine derived anaerobes

PC is a carbon-rich solid by-product generated in substantial volumes during oil refining processes, presenting significant environmental and disposal challenges for the petroleum industry. This study investigates the potential of PC as a substrate for biomethane production through anaerobic digestion using a coal mine-derived microbial consortium, before and after alkaline pretreatment. The microbial consortium was developed and characterized using metagenomic analysis, while structural and physicochemical changes in PC were examined using X-Ray diffraction (XRD), DLS, Fourier transform infrared (FTIR), scanning electron microscope coupled with an energy dispersive X-Ray (SEM–EDX), inductively coupled plasma (ICP)–Carbon, sulfur oxygen, hydrogen, and nitrogen (CSOHN), and micro-FTIR (μ-FTIR) techniques. Alkaline pretreatment was carried out using sodium hydroxide (NaOH) concentrations ranging from 0.5 to 2.0 M. Metagenomic profiling revealed the dominance of Arcobacter, Mesotoga (16%), Paracoccus (9%), Clostridium, Clostridioides, Desulfovibrio, Desulfomicrobium, Pseudomonas, and Flavobacterium, which collectively facilitated hydrolysis, acidogenesis, acetogenesis, and methanogenesis under anaerobic conditions. DLS and XRD analyses demonstrated an average petcoke particle size of ∼344 µm, with a d -spacing of 3.5 Å and an average crystallite diameter of 57.9 nm. SEM–EDX, ICP, and CSOHN analyses has confirmed notable reductions in organic sulfur and heavy metals (Ni, Ba, Fe, and V) after biomethane production, indicating effective bioleaching and desulfurization. μ-FTIR analyses revealed the presence of linear aliphatic hydrocarbon chains. The highest methane concentration of 32.5% (v/v) was obtained on day 30 in the reactor containing PC pretreated with 1.5 M NaOH, indicating that alkaline pretreatment considerably enhanced the anaerobic biodegradability of the PC substrate and provided mechanistic insights into biomethane production from this recalcitrant feedstock.