Influence of bed materials on methanogenic characteristics and immobilized microbes in anaerobic digester

This paper reports and discusses the effects of bed materials on the performance of methanogenic fluidized bed reactors with acetic acid as the sole organic substrate. Four bed materials (carbon filter, rock wool, loofah sponge and polyurethane foam) were evaluated and compared for their methanogenic characteristics and immobilized microbes. The present results indicated that the characteristics of the bed materials for immobilization had a significant influence on the methane production. The loofah sponge and polyurethane foam were suggested to be suitable for the bed material in anaerobic digestion. The best methane yield was obtained from the loofah reactor among the four kinds of bed materials. The main cellular morphologies present in the biofilms of the four different materials on the colonization were observed using scanning electron microscopy. The microphotographs indicated that the biofilm was primarily composed of coccus, diplococci-shaped Methanosarcina -like cells, long rods of Methanobacterium and coccobacillus of Methanobrevibacter -like bacteria. The morphologies observed from the microscopic analysis indicated that the different bed materials could provide specific conditions for the adherence of distinct microorganism types. Furthermore, a 16S rRNA phylogenetic analysis was conducted to compare the immobilized archaeal population. The results of the 16S rRNA phylogenetic analysis indicated that the major immobilized methanogens were Methanobacterium formicicum, Methanosarcina barkeri and Methanosarcina mazei in all the bed materials. A similar clone distribution was observed with the loofah sponge and the carbon felt.