Rapid growth in human civilization results in an increasing demand for livestock products to accomplish societal needs, which subsequently generates animal byproducts (20 to 45% of the live animal total mass) originating in slaughterhouses. Conventional processing of slaughterhouse waste (SHW) is an energy and cost-intensive process, which limits its application for the ever-increasing accumulation of wastes. Anaerobic digestion (AD) is considered a reliable energy harvesting process to harbor waste-to-energy following augmentation with SHW due to their high organic contents and theoretical conversion efficiency, compared to sewage sludge (40–50%) alone. Our investigation revealed the relativity of improved digester performance with its microbial diversity during the AD of SHW. The methane yield was significantly improved (124-155%) through the utilization of lipid (95-98%) in SHW-augmented digesters, compared to controls with sewage sludge alone. An abundance of Firmicutes (41-54%) throughout the exponential phase followed by Bacteroidetes (11–21%) and Synergistetes (15–16%) accelerated the utilization of SHW due to their preeminent role in lipid degradation and fermentative acidogenesis and acetogenesis. Among methanogens, the dominance of Methanosaeta (86%) at the beginning of digestion was gradually overpowered by another acetoclast, Methanosarcina (68–87%) in SHW-augmented digesters. Positive interactions among the acetogenic and acetate-oxidizing species of Clostridium (11%) and Syntrophomonas (5%) with Methanosarcina during the exponential phase improved the methanogenic activity (292 mL g−1 VSinitial d−1) and final VS utilization (90%) through acetoclastic methanogenesis. Nevertheless, a concomitant increase in the population of syntrophic acetate oxidizer Clostridium with Methanosarcina suggested the activity of dual methanation processes (acetoclastic and hydrogenotrophic). These syntrophic interactions among the core microbiota induced the major metabolic activities, including butanoate, glycine, serine and threonine, methane, propanoate, and pyruvate metabolism, and quorum sensing. Thus, the association of acetoclastic methanogens and their syntrophic partners in the SHW-augmented digesters led the methanogenesis toward the acetoclastic pathway as the major route, followed by the hydrogenotrophic pathway, to facilitate maximum methanation of lipidic SHW.

Core microbiota behind the enhanced methanation in anaerobic digestion of slaughterhouse waste

ACS Spring 2022

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