Response of lab-scale methanogenic reactors inoculated from different sources to organic loading rate shocks

► We tested acidic bog methanogenic inoculum for pH stability in anaerobic digesters. ► This community, dominated by the Fen Cluster, survived an initial loading rate shock. ► Subsequent intermittent organic loading rate shocks interrupted methane production. ► Methanogenesis and acetate consumption were recovered by base addition. ► Methanogen communities converged to Methanosarcina and Methanobacteriaceae.