Influence of substrate feed patterns on biofilm development in anaerobic fluidized bed reactors (AFBR)

A study of the influence of carbon source composition on microbial biofilm development under mesophilic conditions was carried out on two pilot lab scale anaerobic fluidized bed reactors (AFBR) fed with synthetic wastewater. The first AFBR was fed with acetic acid as sole carbon source while the second AFBR was fed with wastewater containing a mixture of acetic acid, propionic acid and ethanol. Biolite was used as support on both reactors. Biomass adhesion affects bioparticle size and density and this contributes to bed segregation. Biomass concentration and biofilm density are greater at the bottom of the bed than in the upper levels. The result is that mass transfer resistance is increased in that zone. Microscopic studies revealed important differences on the biofilm structure, microbial colonization and bacterial morphotypes development depend on the type of feed used in each reactor. In all experiments the study show a predominant presence of filamentous methanogenic forms, closely resembling Methanosaeta (Methanotrix), that form the structural key element of the biofilm. When propionic acid and ethanol are included in the reactor feed, other microcolonies of trophic populations appear, probably acetogens, which are located on the outer layer and in the bacterial framework of the biofilm.