Intensifying the organic loading rates (OLR) without inducing processes failure is a key step to making anaerobic co-digestion more economically feasible through enhanced biogas production. However, there is limited understanding of how OLR intensification impacts the anaerobic digestion microbiome and process performance. To address this knowledge gap, lab-scale anaerobic digesters co-digesting fats, oils, and greases (FOG) were exposed to different shock events (i.e. rapid increases in OLR). Two reactors were exposed to a moderate (3.3 g VS/L/d) and a large shock (9.9 g VS/L/d) with no pre-exposure to FOG. A third reactor was pre-exposed to FOG through a series of small shocks (2.6 g VS/L/d) followed by moderate and large shocks. Pre-exposure to FOG at low loading rates resulted in clear signs of beneficial microbial adaptation that enhanced process resilience. Following failure-inducing shocks, recovery times were substantially shorter for the pre-exposed reactor compared to the unexposed reactors (17 days shorter for the moderate shock and 44 days shorter for the large shock). Similarly, successive shock events during the long-term experiment increased both the concentration and the resilience of the methanogen populations, as quantified by methyl coenzyme M reductase gene concentrations. During the long-term experiment, 16S sequence analyses revealed stable alpha diversity in the microbiomes during low and moderate shocks as the community moved toward a more optimal composition for FOG co-digestion. However, following large, failure-inducing shocks, alpha diversity decreases significantly and the microbial community moves away from the optimal composition and towards the initial composition. Similar shifts towards the initial composition were also seen in the unexposed reactors after exposure to both medium and large shocks. These results indicate that pre-exposure to FOG may result in a temporal adaptation of the microbial community to anaerobic co-digestion of FOG. Specifically, the resilience of the reactors was measurably improved with pre-exposure to FOG when considering recovery times as well as the extent of failure incurred by each reactor.

Priming the pump: Benefits of FOG pre-exposure for adaptation of the anaerobic digester microbiome to organic overloads

ACS Spring 2022

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