Anaerobic digestion of manure and mixture of manure with lipids: biogas reactor performance and microbial community analysis.

Anaerobic digestion of cattle manure and a mixture of cattle manure with glycerol trioleate (GTO) was studied in lab-scale, continuously stirred tank reactors (CSTR) operated at 37 degrees C. The reactor codigesting manure and lipids exhibited a significantly higher specific methane yield and a higher removal of VS than the reactor treating manure. Microbial population analysis done by cultivation--most probable number (MPN) test and specific methanogenic activity (SMA) measurement, revealed higher MPN and increased SMA of methanogenic populations of biomass from the reactor codigesting manure and lipids. Spatial microbial distribution and activity was studied in digested materials fractionated into size of particles > 200 microm, 50-200 microm and 0.45-50 microm. With manure, the main pool of methanogenic activity from propionate, butyrate and hydrogen was associated with the particles > 200 microm, while the activity of acetotrophic methanogens was uniformly distributed in all fractions. When digesting manure and lipids, an enhanced methanogenesis was detected both for particles > 200 microm and the 50-200 microm fraction. The molecular methods--temperature gradient gel electrophoresis (TGGE), cloning library and sequencing of 16S rDNA--showed presence of a restricted number of archaeal species in both reactors. The vast majority of clones was phylogenetically most closely related to Methanosarcina siciliae.