Possibilities of Growing Stillage Usage for Anaerobic Fermentation

The possibility of the fruit stillage usage was verified in this work as a suitable material for the anaerobic fermentation for the purpose of increase in the biogas production and the proportion of methane in the biogas. The stillage is a material, which is characterized by a high content of chemical oxygen demand and biological oxygen demand with a low pH and it is produced seasonally, approximately 6 months of the year. The biogas production and the proportion of methane in the biogas was monitored during the test at organic loading rate (OLR) 4.5, 3.4 and 2.3 kg VS m−3 (VS—volatile solids). The verification was realized at a temperature of 39 °C. A single-shot adding of stillage to the substrate from biogas station caused a rapid increase in the biogas production already the second day of the tests. The biogas production began to decrease immediately the next day. The maximum methane proportion (up to 66%) in the biogas was observed from the third to the sixth day of the tests. The third test with the plum stillage showed the best results from the realized tests. In this test, after the conversion to stillage volatile solids, it was produced 924 dm3 kg−1 of biogas from the reactor at OLR 4.5 kg VS m−3 and methane in the biogas was an average of 60%. The worst results of biogas production and the proportion of methane in the biogas were obtained in the second test with pear stillage at OLR 4.5. Despite these low values the significant difference was discovered in the proportion of biogas production and methane content in the biogas reactors with the stillage compared to the reactors only with the control substrate.