Characteristics of a Methanogenic Biofilm on Sand Particles in a Fluidized Bed Reactor

−− The typical microbiological groups reported in literature under the experienced environmental conditions are present in the biofilm structure investigated on sand particles. This is concluded based on microorganism morphology analyzed by scanning electron microscopy. Methanosarcina sp. (acetate consumers) and filamentous microorganisms with morphology similar to Methanospirillum sp. (H2-utilizing archaea) are distinguished among methanogens. Based on acetate levels and microorganism’s threshold concentration, a predominance of Methanosarcina mazei rather than Methanosarcina barkeri is concluded. Among acetogens, bacillus morphologically similar to the syntrophic acetogenic Syntrophobacter wolinii are observed together with Desulfovibrio sp. (hydrogen-utilizing, sulfatereducing). With respect to acidogens, short and long rod-shaped bacteria, diplococcus in chains (probably Streptococcus-like bacteria) and filamentous bacilli are morphologically distinguished but cannot be characterized from this study. A methanogenic biofilm fluidized bed reactor inoculated with the biofilm population investigated showed process efficiencies up to 98% of chemical oxygen demand reduction for treating an acetate-based substrate. Keywords−− methanogenic biofilm composition; SEM; reactor performance.