Abstract
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 Salix 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 Salix 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 Salix feedstock for anaerobic digestion. The biomethane production performance of the sequential digestion of minimally pretreated Salix mirrors that of hydrothermally pretreated hardwoods and may provide an option where such pretreatments are not feasible.
Highlights
Anaerobic digestion (AD) is an energy-production and waste-management method whereby organic matter is metabolized by complex microbial communities into biogas, consisting mainly of CH4 and CO2 gases
The results demonstrated that the sequential co-digestion of non-pretreated Salix biomass can provide methane yields similar to that of pretreated biomass, at the expense of an increased hydraulic retention time (HRT)
Lignocellulosic energy crops considered for use as feedstock for biogas production in co-digestion systems are often herbaceous, owing to the lower recalcitrance of these species compared with woody crops
Summary
Anaerobic digestion (AD) is an energy-production and waste-management method whereby organic matter is metabolized by complex microbial communities into biogas, consisting mainly of CH4 and CO2 gases. AD was the fastest growing bioenergy-producing sector in Europe between 2005 and 2015, and its continued growth may help the EU attain its goals of increased bioenergy use and reduced greenhouse gas (GHG) emissions [1]. The largest potentials for increasing biogas production are estimated to come from agricultural residues and energy crops, in both the EU [2] and Sweden [3]. Animal manure makes up a large part of the potential for biogas production from agricultural residues, with the realistic potential in the EU estimated at 16 billion m3 [4]. In addition to producing renewable energy, AD reduces GHG emissions from manure storage, making its use as feedstock especially attractive as a means of meeting climate targets. Volumetric biogas production from manure alone is relatively low owing to the high moisture content and relatively low biomethanation
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