Microbiological study of two-stage anaerobic digestion during start-up

The changes in the microbial population of a two-stage anaerobic digestion system in terms of number and composition were studied during the start-up phase. The numbers of methanogens and non-methanogens slightly decreased in the upflow filter, whereas in the pre-acidification stage the number of acidogens was reasonably constant. Variations in the morphology of the methanogens occurred along the filter, for example the numbers of Methanosarcina and filamentous bacteria species decreased considerably in the drain, possibly becoming attached to the biofilm along the reactor, whereas in the pre-acidification stage only a few Methanosarcina species were identified. Slight variations within the bacterial populations occurred in terms of composition and numbers in the filter. The number of viable methanogens varied in the filter effluent depending on the OLR changes but this did not adversely affect the COD removal efficiency of the upflow filter. Among the autofluorescent methanogenic population, Methanococcus, Methanobacterium, Methanobrevibacteria, and Methanosarcina species were tentatively identified in the filter.