Biofilm development in laboratory methanogenic fluidized bed reactors

Biofilm development on sand with different heterogeneous inocula was studied in laboratory‐scale methanogenic fluidized bed reactors. Both the course of biofilm formation during reactor start‐up and the bacterial composition of newly developed biofilms at steady‐state were found to be similar irrespective of the type of inoculum applied. Biofilm formation proceeded according to a fixed pattern that could be subdivided in three consecutive phases, designated as the lag phase, biofilm production phase, and steady‐state phase. Methanogenic activity and biomass content of the fluidized bed granules were found to be accurate parameters of the course of biofilm formation. More indirect parameters monitored did not give unambiguous results in all instances. The composition of the newly developed biomass as assessed on the basis of potential methanogenic activities on different substrates and of the concentration of specific methanogenic cofactors was consistent with electron microscopic observations.