Effects of Enzymes Addition on Biogas Production From Anaerobic Digestion of Agricultural Biomasses

The hydrolytic effect of a commercial enzymes mixture, containing mainly cellulose-degrading and hemicellulose-degrading enzymes, was studied during the mesophilic anaerobic digestion of two different mixtures of maize (Zea mays L.) and triticale (x Triticosecale Wittm. ex A. camus). Laboratory-scale trials demonstrated that, for the crop mixtures studied, the enzymatic pretreatment had limited practical value as enhancement agent in terms of both, specific gas production and viscosity reduction. Then, a complete set of biomethane potential essays was conducted aiming to build a more robust base of knowledge regarding hydrolytic powerfulness of enzyme supplementation. Two commercial enzymatic products were applied in different supply modes to several lignocellulosic substrates which are typically employed in real biogas plants. Results confirmed that neither enzymatic pretreatment nor direct application of enzymes in the reactor contribute meaningfully during mesophilic digestion of substrates with original high degradability such as maize and triticale. Nevertheless, significant enhancements of the degradation and conversion into biogas were observed when enzymes were supplied to digestion of agricultural biomasses with complex lignocellulosic structure: both enzymes tested improved the degradation performance of sorghum (Sorghum bicolor L. Moench) silage, straw or corn cob flour leading to increases over 30% of biogas production.