Microbial acclimatization to lipidic-waste facilitates the efficacy of acidogenic fermentation

Lipidic-waste such as fat, oil, and grease (FOG) are promising substrates for achieving higher bioenergy yields. An inadequate presence of an effective microbiome in the anaerobic digesters is the bottleneck for the proper utilization of FOG. Gradual introduction of FOG (0.2%, 1.2%, and 2.4% as volatile solids) in acidogenic fermentation showed a significant improvement in hydrogen yield (72%), compared to the control, after 2.4% FOG loading. Volatile solid (VS) reduction reached up to 65% in high FOG reactors with complete removal of major unsaturated fatty acids. Removal of saturated fatty acids increased to 90%. Improvement in hydrogen productivity (46 mL d⁻¹) occurred during step-wise loading of 2.4% FOG to the acclimatized microbiome. The metabolic shift toward carboxylic chain elongation produced C4 and C6 fatty acids at concentrations of 1.61 mM and 0.90 mM, respectively in the acidogenic reactors. High-throughput sequencing of 16S rRNA amplicons revealed that the acclimatization process enriched the phylum Firmicutes (90%), followed by Bacteroidetes (12%) and Cloacimonetes (11%). The abundance of these phyla and their respective genera confirmed their preeminent role in hydrolysis, hydrogenogenic acidogenesis, and carboxylic chain elongation to produce hydrogen and C4–C7 fatty acids. Thus, we suggest that the improvement of hydrogen production using a microbiome acclimatized to FOG, and simultaneous production of high value organics (C4–C7 fatty acids), could facilitate the greater efficacy of the acidogenic fermentation.