Mixed anaerobic culture was used as inoculum that was obtained from the primary digester of Nature Energy Midtfyn biogas plant, Denmark. The inoculum was coarsely sieved to remove large solids and straw, afterwards, it was filtered through 125 µm sieve. The filtered inoculum was degassed for one week at 55 °C in an incubator. The analysis of the filtered and degassed inoculum is given in Table .