Gas-releasing potential of biogas digestate

The aim of the present study was to investigate the amount of CH4, CO2 and NH3 in biogas digestate by laboratory experiments. For these experiments, fresh digestate (FD), solid fractions (SFD) and liquid fractions (LFD) of digestate as well as untreated digestate from the secondary fermenter (SD) were used. Gas release was measured by Fourier transform infrared spectrometry. Based on the total solids content, the highest amount of NH3 was released from LFD followed by SD. SFD and FD released similar amounts of NH3. CH4 was released from all digestates, with the exception of SFD. Stirring of digestates at 90 °C led to CH4 concentrations of 237.6 µg·gTS−1 released from LFD, 40.8 µg·gTS−1 from SD and 71.7 µg·gTS−1 from FD after 10 min. CO2 release from digestate is high compared to release of NH3 and CH4, although degassing was not completed within the experimental period. Digestate degassing experiments conducted while stirring at high temperatures are suitable to determine digestate gas-release potential.