Microbial invasions in sludge anaerobic digesters.

Among processes that control microbial community assembly, microbial invasion has received little attention until recently, especially in the field of anaerobic digestion. However, knowledge of the principles regulating the taxonomic and functional stability of microbial communities is key to truly develop better predictive models and effective management strategies for the anaerobic digestion process. To date, available studies focus on microbial invasions in digesters feed with activated sludge from municipal wastewater treatment plants. Herein, this review summarizes the importance of invasions for anaerobic digestion management, the ecological theories about microbial invasions, the traits of activated sludge microorganisms entering the digesters, and the resident communities of anaerobic reactors that are relevant for invasions and the current knowledge about the success and impacts of invasions, and discusses the research needs on this topic. The initial data indicate that the impact of invasions is low and only a small percentage of the mostly aerobic microorganisms present in the activated sludge feed are able to become stablished in the anaerobic digesters. However, there are still numerous unknowns about microbial invasions in anaerobic digestion including the influence of anaerobic feedstocks or process perturbances that new approaches on microbial ecology could unveil. KEY POINTS: • Microbial invasions are key processes to develop better strategies for digesters management. • Knowledge on pathogen invasions can improve anaerobic digestion microbial safety. • To date, the number of successful invasions on anaerobic digesters from activated sludge organisms is low. • Feed organisms detected in digesters are mostly inactive residual populations. • Need to expand the range of invaders and operational scenarios studied.

The time response of anaerobic digestion microbiome during an organic loading rate shock.

Knowledge of connections between operational conditions, process stability, and microbial community dynamics is essential to enhance anaerobic digestion (AD) process efficiency and management. In this study, the detailed temporal effects of a sudden glycerol-based organic overloading on the AD microbial community and process imbalance were investigated in two replicate anaerobic digesters by a time-intensive sampling scheme. The microbial community time response to the overloading event was shorter than the shifts of reactor performance parameters. An increase in bacterial community dynamics and in the abundances of several microbial taxa, mainly within the Firmicutes, Tenericutes, and Chloroflexi phyla and Methanoculleus genera, could be detected prior to any shift on the reactor operational parameters. Reactor acidification already started within the first 24 h of the shock and headed the AD process to total inhibition in 72 h alongside with the largest shifts on microbiome, mostly the increase of Anaerosinus sp. and hydrogenotrophic methanogenic Archaea. In sum, this work proved that AD microbial community reacts very quickly to an organic overloading and some shifts occur prior to alterations on the performance parameters. The latter is very interesting as it can be used to improve AD process management protocols.