Anaerobic co‐digestion of perennials: Methane potential and digestate nitrogen fertilizer value |
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| Authors: | Dorette Sophie Müller‐Stöver Guotao Sun Pablo Kroff Sune Tjalfe Thomsen Henrik Hauggaard‐Nielsen |
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| Institution: | 1. University of Copenhagen, Faculty of Science, Department of Plant and Environmental Sciences, Plant and Soil Section, Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark;2. Technical University of Denmark, Department of Chemical and Biochemical Engineering, S?ltofts Plads 229, 2800 Kgs. Lyngby, Denmark;3. Suez Environnement. 38, Rue du President Wilson;4. 78230 Le Pecq, France;5. University of Copenhagen, Faculty of Science, Department of Geosciences and Natural Resource Management, Section for Forest, Nature and Biomass, Rolighedsvej 23, 1958 Frederiksberg C, Denmark;6. Roskilde University, Department of People and Technology, Universitetsvej 1, 4000 Roskilde, Denmark |
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| Abstract: | Co‐digestion of crop biomass improves the traditional manure‐based biogas yield due to an increased content of easily degradable carbon compounds. In this study, the methane potential of three perennials (grass, legumes, and grass+legume) was determined using various amounts together with animal manure. The nitrogen (N) mineralization dynamics in soil and the N‐fertilizer value of the derived digestates were subsequently tested in both a soil incubation study and a pot experiment with spring barley. Digestion of all tested perennials together with a manure‐based inoculum increased the cumulative methane yield four to five times compared to digestion of the inoculum alone, with the highest increases observed with pure grass. However, the methane potential decreased along with increasing grass biomass concentration. In the plant pot experiment, all tested digestates increased barley shoot biomass by 40–170%, to an extent statistically comparable to mineral N fertilizer. However, the application of the digestate originating from fermentation with pure grass resulted in lower plant growth and a more fluctuating soil mineral N content throughout the incubation study compared to the other digestates. Considering the high dry matter and methane yield ha?1, the possibility to substitute mineral N fertilizer inputs by leguminous biological N2 fixation capacity, and the digestate fertilizer value, the integration of grass–legume mixtures or sole legumes into anaerobic digestion systems as co‐substrate for manure seems to be promising. This could furthermore contribute to the diversification of cropping systems for bioenergy production. |
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| Keywords: | alfalfa biogas grass perennials red clover |
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