Methanogenic community and performance of fixed- and fluidized-bed reactors with reticular polyurethane foam with different pore sizes

This paper reports the effects of the pore size of bed material and bed type on the methanogenic performance and community in fixed and fluidized bed reactors supplied with acetic acid as the sole organic substrate. Fixed-bed reactors with polyurethane foam had a greater biomass retention capacity and better reactor performance than fluidized-bed reactors. A polyurethane pore size of 20 cells/25 mm was better for both beds than a pore size of 13 cells/25 mm. These results indicated that the adjusted pore size is also important for the efficient digestion. The best performance was obtained from the fixed-bed reactor with the 20 cells/25 mm polyurethane foam. Scanning electron microphotographs indicated that the immobilized microbes were primarily composed of coccal, diplococcal-shaped Methanosarcina-like cells, short-rods of Methanosaeta-like cells and long rods of Methanobacterium. Methanosarcina-like cells prevailed in the fixed-bed reactor. The results of 16S rRNA phylogenetic analysis indicated that the major immobilized methanogens belonged to the genus Methanosarcina. The results of real-time polymerase chain reaction (PCR) analysis indicated that the cell density of immobilized methanogens in the fixed-bed reactor was higher than that in the fluidized-bed reactor. The better biogas production by the fixed-bed reactor could be explained by the increase in the quantity of methanogens immobilized on the polyurethane foam.