Enhancement of biogas production by addition of hemicellulolytic bacteria immobilised on activated zeolite.

Biogas from agricultural biomass and residues is a valuable source of renewable energy. However, recalcitrant plant cell structures represent a barrier in the fermentative biodegradation process in single- and two-stage reactors. Therefore, approaches concerning a more efficient de-polymerisation of cellulose and hemicellulose to monomeric sugars are required amongst others in order to optimise the fermentation efficiency and to increase methane yields. Here we show a new strategy for the enhancement of biogas production from hemicellulose-rich substrates. Hemicellulolytic populations from a common biogas fermenter consortium were successively enriched in batch-cultures using a synthetic medium containing xylan powder as single carbon source under anaerobic mesophilic conditions. Enriched hemicellulolytic bacteria were immobilised on trace metal activated zeolite to ensure a stable storage and easy application. Xylanase activity increased continuously during subsequent enrichment cycles by up to 162%. In batch-culture experiments we were able to observe an increase of methane by 53% compared to controls without additionally introduced microorganisms immobilised on zeolite. Specific enrichment of hemicellulolytic bacteria during the process was confirmed by using single strand conformation polymorphism (SSCP) analysis based on amplification of the eubacterial 16S rDNA fragments. Using sequence analysis conspicuous bands from SSCP patterns could be identified as belonging to the groups Bacteroides sp., Azospira oryzae (Dechlorosoma sp.) as well as to a wide spectrum of diverse species within the order of Clostridiales (Firmicutes).