Biogas Crops - Part I: Specifications and Suitability of Field Crops for Anaerobic Digestion

In Germany, the growing number of agricultural biogas plants causes an increasing demand for crops as a feedstock in both mono‑ and co‑digestion processes. Laboratory scale batch anaerobic digestion tests under mesophilic conditions according to the German Standard Procedure VDI 4630 were conducted to investigate the suitability of different plant species like barley (Hordeum vulgare), rye (Secale cereale), triticale (X Triticosecale), alfalfa (Medicago sativa), hemp (Cannabis sativa), Jerusalem artichoke (Helianthus tuberosus) and maize (Zea mays) for biogas production. Emphasis was placed on growing stage and maturity, respectively as well as on whole crop silage preparation without additives as a preservation method for biogas crops. Results presented indicate that biogas yield is clearly influenced by plant species and harvest stage. Ensiled matter shows a positive effect on biomethanation with higher biogas yields and methane contents than fresh matter investigated. Hence, storage as silages can be considered as pre‑treatment which has also potential to improve methane production from plant matter. Analyses of digested materials reveal considerable reduction of organic matter of all crops investigated