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

Anaerobic digester failure due to a pH drop may be overcome with the use of an acidotolerant methanogenic community. To test this, lab-scale reactors were inoculated from acidic bog sediments, a municipal sludge digester, or a combination of these inocula and challenged with glucose pulses without pH control. Only the bog reactor survived the first glucose shock, and the methanogen community was dominated by members of the acidic Fen Cluster. After restarting the digester and hybrid reactors, two subsequent glucose shocks were applied. Methanogenic communities converged in all reactors and were dominated by Methanosarcina and Methanobacteriaceae. The Fen Cluster was eventually nondetectable in bog and hybrid reactors, presumably due to periods of circumneutral pH with only intermittent periods of low pH following glucose shocks. Although the resultant communities required base addition, an increase in Methanosarcina numbers after glucose pulses resulted in decreased acetate and increased reactor pH and methane production.