Improvement of anaerobic fermentation of mechanically pretreated lignocellulosic biomass

The aim of the study is to improve anaerobic fermentation (AF) of lignocellulose biomass by mechanical pre-treatment of willow biomass and by addition of used cooking rapeseed oil, trace element selenium and by application a low-voltage electric field during the AF process in batch mode at temperature 38 °C. Experimental setup includes 2 bioreactors of 0.75 L volume filled with 0.5 l inoculums (control) and 22 bioreactors filled with 0.50 L inoculums, 12 g milled or pelletised willow biomass, with added rapeseed oil (1 mL or 2 mL) or selenium (15 μg) in different groups of bioreactors. One group of bioreactors was equipped with electrodes for application of low-voltage (1.00 V) electric field. AF process was provided for a 28-day period until gases emission ceases. Methane yield from unpelletized willow biomass was 0.13 L·gDOM and was 0.4 L·gDOM with 2 mL rapeseed oil added. Methane yield from willow pellets was in the range from 0.22 L·gDOM without additives to 0.361 L·gDOM for the combination of willow pellets with 2 mL rapeseed oil and selenium 15 μg under influence of 1.0 V low voltage electric field. Addition of the trace element 15 μg selenium in pelletised willow substrate plus 1 mL oil gave specific methane yield 0.29 L·gDOM or higher by 48%, compared to pelletized willow biomass plus 1 mL oil without selenium. Methane formation was higher from biomass with average particle size 3 mm compared to biomass with average particle size 9 mm. Using the electric field in the substrate provides an additional amount of methane with energy, which is 32% more than the energy consumed.