Anaerobic co-digestion of grass and forbs – Influence of cattle manure or grass based inoculum

• Published in: Biomass & bioenergy 2018-12, Vol.119, p.90-96
• Main Authors: Cong, Wen-Feng, Moset, Veronica, Feng, Lu, Møller, Henrik Bjarne, Eriksen, Jørgen
• Format: Article
• Language: English
• Subjects: Anaerobic co-digestion; Biogas; Forbs; Inoculum source; Multi-species grassland
• ISSN: 0961-9534; 1873-2909
• DOI: 10.1016/j.biombioe.2018.09.009

Anaerobic co-digestion of agricultural by-products or wastes with complementarity characteristics is commonly used to enhance methane yield. This study firstly explores the possibility of co-digesting grass and forb species (white clover, chicory and plantain) differing in nutrient composition in enhancing methane yield. This was examined with two inocula (a cattle manure-based inoculum and a grass-based inoculum) in a batch assay. Results showed that co-digesting grass and forbs synergistically enhanced methane yield potential on average by 31 L kg−1 volatile solids (+11%) and reduced lag phase time by 0.8 day in the grass-based inoculum, but not in the cattle manure-based inoculum. Mixtures containing plantain showed more consistent synergistic effect than chicory. Synergistic effects were attributed to more balanced nutrient composition (especially C/N ratio) in grass-forb mixtures. We demonstrate that anaerobic co-digestion of grass and forbs is feasible for enhancing methane yield, which promotes the utilization of multi-species grasslands for bioenergy production. •Co-digestion of grass and forbs was examined with two inocula in a batch assay.•Co-digestion enhanced bio-methane potential in grass-based inoculum.•Co-digestion reduced the lag phase time in grass-based inoculum.•Synergistic effect was attributed to better nutrient balance in grass-forb mixtures.•No effect of co-digestion occurred in cattle manure-based inoculum.