Michael Köttner
Intenational Biogas and Bioenergy Center of Competence IBBK, Germany
Title: Grass and cattle manure digestion – a viable feedstock alternative
Biography
Biography: Michael Köttner
Abstract
In Europe, anaerobic digestion (AD) is dedicated to the treatment of organic wastes, eventually in combination with energetic crops. For implementing these systems, favorable promotional measures have been proposed, creating high number of active anaerobic digesters. However, in order to consolidate its role as a favorable tool for sustainable waste management, it is important to decrease the usage of energy crops and substitute it, if possible, with biomass residues. Originating from small-scale farm based anaerobic digestion plants, the landscape of AD in Germany and Europe has changed significantly over the past 20 years. Regarding Germany, this is due to the implementation of generous feed-in tariffs and unlimited priority feed-in for renewable energies. This was regulated in the renewable energy laws of 2004 and 2009. Additionally, starting in the early 2000s, a specific subsidy for energy crop farming was introduced by the EU as an agro-political tool to avoid food overproduction and yet compensate the farmers to keep working their land. Energy crops include maize, corn, whole crop cereal, sugar beets and grass. This resulted in a massive boom in the total numbers of AD plants and the average installed capacity. Especially during the 8 years from 2004 to 2012, more than 6500 new AD plants digesting energy crops were commissioned in Germany alone. Why were energy crops so attractive as a feedstock for AD installations? Well, they have a higher specific gas yield compared to slurry, the necessary agricultural technology is well established and similar to dairy farming and it offers farmers the opportunity to become independent from agricultural price cycles. Major changes in subsidy policies in the German renewable energy law in 2014 and a complete redesign in 2017 threw all cards in the air again. Since 2017, new and existing
AD plants have to compete with all other biomass plants via tender processes. As a direct consequence, expensive feedstocks such as classic energy crops instantly became much less economically viable. Thus, operators are now looking into alternative feedstocks. Increased investment costs for AD plants also factors into economic calculations. The rise took place in recent years due to an elevation in professionalism in the agricultural sector. Additionally, higher safety standards and technical requirements for AD plant equipment contributed to this development. This is where manure and grass can come in. Good quality grass silage offers an impressive specific biogas yield of around 150 m³/t compared to the 200 m³/t of the corn silage, making it a viable and abundant alternative feedstock.