Biomethane potential of agro-industrial substrates depends on the inoculum type

The biomethane potential (BMP) of a biomass substrate is the main factor for its price-setting when being purchased by owners of biogas plants for the production of renewable energy and is therefore a key parameter in setting the profit margins of the biogas plant. Standard protocols have been developed for the biologically determination of the BMP in batch assays (Angelidaki et al., 2009). In terms of inoculum, they suggested the inoculum to be ‘fresh’, homogenous, sieved, degassed for 2 to 5 days and to have a broad ‘trophic’ microbial consortium. Furthermore, they suggested to test the specific methanogenic activity being at least 0.1 g CH4-COD g-1 VSS.d, but no suggestions on the composition of the microbial community were made. An influence of the inoculum used during these batch assays has been indicated by Chamy and Ramos (2011) and Elbeshbishy et al. (2012), but no general relationship between microbial community characteristics of the inoculum and its performance during the batch assays, was established so far. The aim of this experiment was to characterize a good performing sludge by means of quantitative PCR measurements, so the first step, necessary for a standardization method of sludge used as inoculum for BMP tests