Verfahrenstechnische Aspekte der zweistufigen Druckfermentation von Biomasse

Durch Biogaserzeugung in einer zweistufigen Druckfermentation soll die Erzeugung, Aufbereitung und Einspeisung von Biogas in ein Erdgasnetz effizienter werden. Die Methanerzeugung unter erhöhtem Druck hat Vorteile für die anschließende Gasaufbereitung und -einspeisung. Erhöhter Druck bewirkt u.a. eine verstärkte Absorption der Gase in der Flüssigkeit, insbesondere des CO2. Der resultierende erhöhte Methangehalt im Biogas wird in der Arbeit quantifiziert

Integration of a water scrubbing technique and two-stage pressurized anaerobic digestion in one process

Two-stage pressurized anaerobic digestion is a promising technology. This technology integrates in one process biogas production with upgrading and pressure boosting for grid injection. To investigate whether the efficiency of this novel system could be further increased, a water scrubbing system was integrated into the methanogensis step. Therefore, six leach-bed reactors were used for hydrolysis/acidification and a 30-L pressurized anaerobic filter operated at 9 bar was adopted for acetogenesis/methanogenesis. The fermentation liquid of the pressurized anaerobic filter was circulated periodically via a flash tank, operating at atmospheric pressure. Due to the pressure drop, part of dissolved carbon dioxide was released from the liquid phase into the flash tank. The depressurized fermentation liquid was then recycled to the pressurized reactor. Three different flow rates (0 L·day$^{-1}$, 20 L·day$^{-1}$ and 40 L·day$^{-1}$) were tested with three repetitions. As the daily recycled flashed liquid flow was increased from 0 to 40 L, six times as much as the daily feeding, the methane content in the biogas increased from 75 molar percent (mol%) to 87 mol%. The pH value of the substrate in the methane reactor rose simultaneously from 6.5 to 6.7. The experimental data were verified by calculation

Effects of Organic Loading Rate on the Performance of a Pressurized Anaerobic Filter in Two-Phase Anaerobic Digestion

The effect of organic loading rate (OLR) on a pressurized anaerobic filter was studied in a laboratory two-phase anaerobic digestion system. The anaerobic filter was operated successively at two working pressures (9 bar and 1.5 bar). The OLR(COD) for each pressure was increased from 5 to 17.5 kg·m−3·day−1. The best performance of the reactor at 9 bar was observed at OLR(COD) of 12.5 kg·m−3·day−1 and hydraulic retention time (HRT) of 1.8 day, with specific biogas productivity (SBP) of 5.3 L·L−1·day−1 and COD degradation grade of 90.6%. At higher OLRs and shorter HRTs, the process became unstable. In contrast, there was no indication of digester failure during the experiments at 1.5 bar. The SBP peaked at OLR(COD) of 17.5 kg·m−3·day−1 with 8.2 L·L−1·day−1, where COD degradation grade was 90.4%. The biogas collected from the reactor at 9 bar and 1.5 bar contained approximately 74.5% CH4 and 66.2% CH4, respectively, regardless of OLR variation. At OLR(COD) of 5–12.5 kg·m−3·day−1, the reactor at 9 bar had the same specific methane yield as at 1.5 bar, which was in the range of 0.31–0.32 LN·g−1COD. Raising the working pressure in the reactor resulted in an increase of methane content of the produced biogas. However, the low pH value (approximately 6.5) inside the reactor, induced by high CO2 partial pressure seemed to limit the reactor performance at high OLRs and short HRT

Integration of a Water Scrubbing Technique and Two-Stage Pressurized Anaerobic Digestion in One Process

Two-stage pressurized anaerobic digestion is a promising technology. This technology integrates in one process biogas production with upgrading and pressure boosting for grid injection. To investigate whether the efficiency of this novel system could be further increased, a water scrubbing system was integrated into the methanogensis step. Therefore, six leach-bed reactors were used for hydrolysis/acidification and a 30-L pressurized anaerobic filter operated at 9 bar was adopted for acetogenesis/methanogenesis. The fermentation liquid of the pressurized anaerobic filter was circulated periodically via a flash tank, operating at atmospheric pressure. Due to the pressure drop, part of dissolved carbon dioxide was released from the liquid phase into the flash tank. The depressurized fermentation liquid was then recycled to the pressurized reactor. Three different flow rates (0 L·day−1, 20 L·day−1 and 40 L·day−1) were tested with three repetitions. As the daily recycled flashed liquid flow was increased from 0 to 40 L, six times as much as the daily feeding, the methane content in the biogas increased from 75 molar percent (mol%) to 87 mol%. The pH value of the substrate in the methane reactor rose simultaneously from 6.5 to 6.7. The experimental data were verified by calculation