===References===
* Deublein, D. and Steinhauser, A. (2011). [https://www.susana.org/en/knowledge-hub/resources-and-publications/library/details/3038 Biogas from Waste and Renewable Resources, 2nd Ed. ] Wiley-VCH, Weinheim, DE.
* Kossmann, W., Pönitz, U., Habermehl, S., Hoerz, T., Krämer, P., Klingler, B., Kellner, C., Wittur, T., von Klopotek, F., Krieg, A. and Euler H. (1999). Biogas Digest Volume II – Application and Product Development. GTZ, Eschborn, DE.