Effectiveness of usage of straw and oak leave pellets for biogas production

Abstract

Biogas and methane can be obtained from various biomasses, and biogas producers should focus on usage of agricultural by-products and forest residues to replace or minimise the specially cultivated energy crops, e.g. maize, usage as the feedstock in biogas plants. In order to evaluate the effectiveness of use of wheat straw and oak leaves for biogas production, the experimental trial on wheat straw and oak leave pre-treatment and following anaerobic fermentation was provided. Pre-treatment of straw and leaves for biogas production included the common mechanical treatment by shredding and milling. Part of the straw, leaves and their mixture was further granulated to determine the energy consumption of the granulation process and to explore their potential for biogas production. The investigated energy for pelletting the wheat straw, oak leaves or straw/leaves (1:3) mixture was 2.00, 0.20 or 0.22 kWh kg-1 respectively. The anaerobic fermentation (AF) of residue biomass was provided in 16 batch bioreactors with volume 0.75 L, operated during 40-day period at temperature 38 ± 1 ºC. Average specific biogas (methane) yield from wheat straw or oak leaves was 0.618 (0.246) L·g-1DOM or 0.254 (0.151) L·g-1DOM respectively. Average biogas (methane) specific yield from the straw/leaves (3:1) mixture or straw/leaves (3:1) pellets was 0.236 (0.155) L·g-1DOM or 0.322 (0.191) L·g-1DOM respectively. Usage of straw/leaves (1:3) pellets increases the specific methane yield by 22.3 % compared to specific methane yield obtained from non-pelletized straw/leaves (3:1) mixture.