Biogas Production from Raw Digestate and its Fraction

The digestate from an agricultural biogas plant is most commonly used as a fertilizer. However, many studies are being performed to develop other ways of managing this substrate. The aim of this study was to determine the biogas and methane efficiency for digestate as well as the solid and liquid fractions from separation of digestate. The material for the research came from a real scale agricultural biogas plant. The separation of the digestate into two fractions was carried out using a mechanical press. The studies on the methane fermentation process were carried out under mesophilic conditions (37–39°C) in the Institute of Biosystems Engineering at the Poznań University of Life Sciences. It was found that the biogas and methane efficiency for the raw digestate and liquid fraction obtained from its separation is very low. For raw digestate it was 2.9 m³ of biogas from 1 Mg fresh matter (FM), including 1.58 m³ methane. For liquid fraction after separation, the biogas efficiency amounted to 1.52 m³ from 1 Mg, including 0.78 m³ of methane. In turn, for the solid fraction, the biogas efficiency was 102.93 m³∙Mg^-1, including 54.99 m³∙Mg^-1 of methane. The research results indicate that the possibility of using the digestate solid fraction for energy production (e.g. secondary methane fermentation) or the production of solid biofuels.