On July 07, 2022, the Association for the Promotion of Scientific-Technical Cooperation in the Raw Materials Sector (WTZ e.V.) held its first workshop of the series "Biogas holistically thought". Biogas / biomethane production has the potential to provide environmentally friendly and storable energy in a circular economy. The series of events is to consider how a circular economy implementation can look like from a scientific-technical perspective. The event was moderated by Prof. Dr. Hartmut Krause, board member of WTZ e.V.

In the first session "Biomasses and Residues in Biogas Production", the perspectives in biogas production by using alternative raw materials were presented in a keynote speech by Jaqueline Daniel-Gromke (Working Group Leader System Optimization Biogas, DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH) and in the subsequent discussion. It was explained that current incentives for biogas production resulted from the EU Renewable Energy Directives (RED I and II). However, for biogas production, the framework conditions would have to be supported more strongly. By means of the "REPowerEU" plan of the European Commission, an accelerated expansion of power generation capacities should also be achieved with regard to biomethane.

Ms. Daniel-Gromke presented that a major advantage of biogas is that any substrates can be used in production, as long as the wood content is not too high. Other substrates besides manure and corn with a lot of potential for biogas production are straw, manure, intercrops such as green rye or residues such as chaff, beet leaves and wild plant mixtures.

During the discussion that followed the presentation, it became clear that there was an enormous need for research into all fermentation residues. It is necessary to research what can be filtered out of the fermentation residues and used further to expand material cycles. In addition, there is currently a shortage of mineral fertilizers, so that a market value is developing for liquid manure and other substances. In addition, biodiversity had to be considered, as there was also competition for land. Also, the aspect of the regionality of the residual materials was pointed out: Since residual materials have only a low energy content, they are not worth transporting over long distances. Similarly, the transport of slurry over long distances is not worthwhile due to high transport costs.

The second session of the event dealt with the question of how material cycles can be formed along biogas production. During the session, Rene Schieritz (Project Engineer Research and Development, Veolia Klärschlammverwertung Deutschland GmbH) gave a keynote speech on the topic of "Digestate For Soil Production" with a focus on the use of digestate as an additive in the production of compost soils in horticulture. He stated that pressed fermentation residues from wet fermentation are basically more suitable. He explained that digestate from dry fermentation tends to contain higher salt loads and that a higher proportion of animal feedstock generally leads to high phosphate contents. With regard to the quality criteria of the substrate compost, these depend on the amount of compost used.

In summary, it was stated that the use of digestate composts as substrate composts is possible, but that a substrate compost with 100% digestate as starting material is almost impossible. The higher the proportion of digestate in compost mixtures, the higher the chloride and salt contents would generally be. Dry digestate from wet fermentation is the most promising. A high proportion of animal components in the digestate could limit its use. Even if substrate compost requirements were not met, use as an ingredient in potting soil, for example, would not be ruled out and would be rather helpful.

The next event in the series is expected to take place in September 2022.