In the present study, nine complex organic substrates from three classes (protein-, lipid-, and cellulose-rich) were investigated in batch experiments and compared with a control in order to evaluate their potential for utilisation as substrates for biogas production. High methane production was observed from protein-rich substrates; problems arose from lipid-containing, lactose and cellulose fermentation. Using DGGE analysis it could be shown that different classes of substrate resulted in different microbial communities, whereupon similar substrates tended to show a similar microbial structure. By means of qPCR Methanoculleus sp., a hydrogenotrophic methanogen was found to be the most abundant organism in the batch experiments. Additionally, it could be demonstrated that methanogenic organisms withstood adverse environmental conditions for at least an incubation period of 55 days, pointing to a high stability of the archaeal community even in times of decreasing or even failing fermenter performance.
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