Gas-releasing potential of biogas digestate

Abstract

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·g_TS⁻¹ released from LFD, 40.8 µg·g_TS⁻¹ from SD and 71.7 µg·g_TS⁻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.

Keywords:

• Digestate
• methane emission
• ammonia emission
• FTIR spectrometry

Acknowledgements

The authors would like to thank the technical staff of the experimental farm ‘Unterer Lindenhof’ of the University of Hohenheim for their support during the experiments.

Disclosure statement

The authors hereby declare that all contributors concur with the submission, have seen a draft copy of the manuscript and agree with its publication. This work is original and previously unpublished, and will not be published elsewhere after its publication in this journal. The authors have declared no conflict of interest and the manuscript does not contain experiments using animals or human studies.

Additional information

Funding

The study was performed within the project GOBi funded by the Federal Ministry of Education and Research (BMBF), represented by the Project Management Jülich, under grant number 03EK3525A.