Impact of substrate overloading on archaeal populations in anaerobic digestion of animal waste

Aims To characterize adaptive changes in methanogenic microbial community in response to substrate overloading and identify potential linkages between process performance and microbial community composition. Methods and Results Triplicate continuous anaerobic digesters were developed as model anaerobic digestion processes, which were subsequently disrupted by substrate overloading. The clone library analysis of archaeal communities experiencing substrate overloading showed that populations related to Methanosaeta were the dominant methanogens before and after substrate overloading, suggesting the functional importance of these acetoclastic methanogens in balanced anaerobic digestion processes characterized with low organic acids concentrations. Population redundancy in Methanosaeta increased following substrate overloading with the emergence of additional populations of Methanosaeta. More importantly, the methanogenic community responded to process imbalance with greater functional diversity with increased abundance of functionally distinct hydrogenotrophic and acetoclastic methanogens, which likely enhanced the functional stability of anaerobic digestion during disruptions in the anaerobic food web under process perturbation. Crenarchaeota were identified as persistent constituents of the archaeal communities in anaerobic digestion, warranting further efforts to identifying the functions of these phylogenetically distinct populations in anaerobic digestion. Conclusions Substrate overloading in anaerobic digestion resulted in an increased functional diversity of the methanogenic community, which enhanced the capacity to overcome subsequent occurrences of process perturbations without performance disruption, providing a potential strategy to maintain process stability in anaerobic digestion. Significance and Impact of the Study Anaerobic digestion is a sustainable option for waste treatment and renewable energy production. However, process instability resulting from variations in substrate loading has been one of the obstacles to the broader adoption of anaerobic digestion technology. Insight into the linkages between process performance and microbial community gained in this study is valuable for developing strategies for the mitigation of the impact of substrate overloading on anaerobic digestion processes.