Co-Digestion of <i>Salix</i> and Manure for Biogas: Importance of Clone Choice, Coppicing Frequency and Reactor Setup

• Main Authors: Jonas A. Ohlsson, Ann-Christin Rönnberg-Wästljung, Nils-Erik Nordh, Anna Schnürer
• Format: Article
• Language: English
• Published: MDPI AG 2020-07-01
• Series: Energies
• Subjects: anaerobic digestion; co-digestion; energy crops; manure; <i>Salix</i>
• Online Access: https://www.mdpi.com/1996-1073/13/15/3804

Animal manure represents a major source of renewable energy that can be converted into biogas using anaerobic digestion. In order to most efficiently utilize this resource, it can be co-digested with energy dense, high biomethanation potential feedstocks such as energy crops. However, such feedstocks typically require pretreatments which are not feasible for small-scale facilities. We investigated the use of single-stage and the sequential co-digestion of comminuted but otherwise non-pretreated <i>Salix</i> with animal manure, and further investigated the effects of coppicing frequency and clone choice on biomethanation potential and the area requirements for a typical Swedish farm-scale anaerobic digester using <i>Salix</i> and manure as feedstock. In comparison with conventional single-stage digestion, sequential digestion increased the volumetric and specific methane production by 57% to 577 NmL L⁻¹ d⁻¹ and 192 NmL (g volatile solids (VS))⁻¹, respectively. Biomethanation potential was the highest for the two-year-old shoots, although gains in biomass productivity suggest that every-third-year coppicing may be a better strategy for supplying <i>Salix</i> feedstock for anaerobic digestion. The biomethane production performance of the sequential digestion of minimally pretreated <i>Salix</i> mirrors that of hydrothermally pretreated hardwoods and may provide an option where such pretreatments are not feasible.