Use of enzyme alpha amylase to increase biogas yield from lucerne pellets and birch leaves pellets

Abstract

More and more biogas plants use pellets from various residues as a raw material. Their advantage is not only cheaper transport over longer distances, but also they absorb moisture well and do not form a floating layer in the fermentation reservoir. Hydraulic retention time of pellets, containing such raw materials as birch leaves, in the anaerobic digester is relatively long and requires large volumes of bioreactors. Variety of additives can be used to improve the anaerobic digestion process. This article shows the results of the study where the enzyme Alpha amylase is used for the digestion process improvement. Lucerne pellets and birch leaves pellets were digested in the laboratory 0.75 l bioreactors at the temperature 38 ºC using a single filling cycle. Two biorectors contained inoculums and were processed for control purposes only. Other 14 biorectors contained inoculums with added pellets and with or without enzymes additive. Average specific biogas or methane yield in anaerobic fermentation of lucerne or birch leaves pellets was 0.401 l·g-1DOM or 0.263 l·g-1DOM respectively. Average specific biogas or methane yield in anaerobic fermentation of birch leaves pellets was 0.245 l·g-1DOM or 0.214 l·g-1DOM respectively. Addition of enzymes (0.5 ml per bioreactor) in bioreactors with lucerne pellets and birch leaves pellets increases the average methane yield by 19.95 % or 22.9 % respectively.