Impact of feeding and stirring regimes on the internal stratification of microbial communities in the fermenter of anaerobic digestion plants

[Display omitted] •First investigation of microbial stratification in full-scale anaerobic digestion plants.•No indications for significant zoning of microbial communities found.•Stirring and feeding regimes were sufficient to homogenize the microorganisms. In anaerobic digestion plants (ADs), homogenization of the feed, fermenter content and microbial communities is crucial for efficient and robust biogas production. However, mixing also requires a significant amount of energy. For an 850 m3 agricultural AD equipped with eight sampling ports, we investigated whether different feeding and stirring regimes enable a sufficient homogenization of the microbial community using metaproteomics and terminal restriction fragment length polymorphism (TRFLP) analysis. Systematic comparison of samples taken at the top and the bottom as well as at the rim and the center of the AD using scatter plots and students t-test revealed only a small number of differences in metaproteins, taxonomies and biological processes. Obviously, the applied stirring and feeding conditions were sufficient to largely homogenize the content of the AD.