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* 1 , 2 , 2 , 1 , 2
1  Lithuanian energy institute
2  Vytautas Magnus University, Lithuania
Academic Editor: Antoni Sánchez


Grass biomass (GB) is an excellent feedstock as biogas production material for anaerobic co-digestion (AD) because of its organic solids content of more than 20%. However, a high concentration of fibres and material ability to layering makes this substrate problematic to digest in bioreactors. Lignocellulosic grass biomass has a huge potential to be used as feedstock for the sustainable production of fuels and chemicals through fermentation. Today, plant substrates, also entitled lignocellulosic biomass, are seen as one of the most promising materials to replace fossil resources in the production of fuels and chemicals with reduced GHG emissions. However, the recalcitrance of these materials is one of the major hurdles in their efficient utilization. In this sense, microbial research has been mainly focused on the production of cheaper enzymes and in more efficient utilization of biomass derived sugars. The influence of selected inoculum for anaerobic fermentation of lignocellulosic grass biomass in every specific case varies. In cellulolytic rumen bacteria, highly active cellulolytic and hemicellulolytic enzymes are combined in extracellular multienzyme complexes, cellulosomes.

In this study, the degradation of lignocellulose in biogas processes has been focused on the innoculant microorganisms involved, with a view to gaining a deeper understanding and improving lignocellulose degradation. The aim of this study was to determine the effect of dairy rumen anaerobic bacteria inoculum on grass biomass biogas production and how anaerobic bacteria inoculated into dairy rumen will influence the quality of biogas generated from grass biomass.

It was examined in this study how dairy rumen fluid inoculum influences the anaerobic treatment of organic fractions of GB. To evaluate the influence of dairy rumen fluid inoculum BMP experiment was performed in four sets of two 500 mL glass bottles (bioreactors) with a working volume of 800 mL at 37 ± 0,2 oC. There was a constant amount of GB added to all experiments - 16 g. Reactor set “A” was loaded with 800 grams rumen fluid (proportion 100%/0%), Reactor set “B” was loaded with 400 g rumen fluid and 400 g digestate from bioreactor (proportion 50%/50%), Reactor set “C” was loaded with 800 g digestate directly from the same bioreactor as mentioned in Reactor “B” (proportion 0%/100 %). To evaluate inoculum BMP Reactor “D” was started without any GB addition and it served as a negative control for residual methanogenic activity. All experimental sets were set as triplicate samples.

The outcome parameters of the BMP experiment showed that the maximum volumetric biogas yield (12,17 ± 0,62 l/l) was obtained from the substances used in experiment “B” with rumen fluid and the digestate composition. According to the results, the second largest volumetric biogas yield was achieved in experiment “C”, where grass biomass and digestate were used as inputs. With rumen fluid and grass biomass, experiment “A” yielded the least biogas at only 1,14 l/l. The least volumetric yield of biogas came from digestate (0,35 ± 0,08 l/l) as it did not contain additional green biomass. The highest concentration of methane was gained from experiment B (63,2 ± 1,5 %). Biogas gained from digestate (experiment “C”) had a slightly lower concentration of methane, at 54,6 ± 1,1%).

Keywords: biogas, grass, biomass, biomethane, rumen, inoculum