Industrial Crops and Products 56 (2014) 137–144 Contents lists available at ScienceDirect Industrial Crops and Products jo ur nal home p age: www.elsevier.com/locate/indcrop Anaerobic digestion of annual and multi-annual biomass crops Lorenzo Barbanti a,∗ , Giuseppe Di Girolamo a , Marco Grigatti a , Lorenzo Bertin b , Claudio Ciavatta a a Department of Agricultural Sciences, University of Bologna, Viale Fanin 44, 40127 Bologna, Italy b Department of Civil, Environmental, and Materials Engineering, University of Bologna, Via Terracini 28, 40131 Bologna, Italy a r t i c l e i n f o Article history: Received 16 November 2013 Received in revised form 23 January 2014 Accepted 2 March 2014 Keywords: Anaerobic digestion Biomass crops Methane Net energy yield Energy efficiency a b s t r a c t This paper addresses the anaerobic digestion (AD) of seven biomass crops: three multi-annual species, Arundo donax (Arundo), Panicum virgatum (Switchgrass) and Sorghum Silk; three sorghum hybrids (B 133, Sucros 506 and Trudan Headless); one Maize hybrid as reference crop for AD. Dry biomass yield (DBY) was assessed in a field plot experiment in Northern Italy, and biomass samples were subjected to chemical analysis (volatile solids (VS), raw proteins and lipids, soluble sugars, starch, structural carbohydrates and lignin). Thereafter, an AD assay was carried out in batch mode with 4 g VS l -1 at 35 ◦ C for 58 days, during which time potential methane yield (ml CH 4 g -1 VS) was determined. Gross energy yield (GE = DBY × VS × potential CH 4 yield × methane lower heating value) and cumulative energy demand (CED) led to net energy yield (NE = GE - CED) and energy efficiency (EE = GE/CED) as indicators of crop suitability for AD. Arundo, B 133 and Sucros 506 achieved ±10% DBY compared to Maize (this latter, 27.8 Mg ha -1 ). Conversely, Maize prevailed in terms of potential methane yield (316 ml CH 4 g -1 VS). Among the six alternative crops, Arundo and Switchgrass exhibited the lowest values (average, 216 ml CH 4 g -1 VS), associated with low kinetics of degradation. This is consistent with the two crops’ characteristics: low easily degradable fractions as lipids, soluble sugars and starch; high structural carbohydrates and lignin. Maize achieved a top level also in GE (286 GJ ha -1 , corresponding to ca. 8400 N m 3 CH 4 ha -1 ) and NE (248 GJ ha -1 ). B 133 and Sucros 506 were undifferentiated from Maize in NE (their average, 215 GJ ha -1 ), whereas Trudan Headless and the three multi-annual species were out- performed (average NE, 149 GJ ha -1 ). Conversely, Maize ranked worst in EE (7.4 GJ GJ -1 ) while sorghum B 133 and Arundo attained top levels (average, 12.1 GJ GJ -1 ), thanks to a good GE associated with a modest CED in B 133; to a very low CED in Arundo. It is concluded that alternative crops to maize deserve attention in view of a low need of external inputs but necessitate improvements in biodegrad- ability (harvest stage and biomass pre-treatments) to bridge the gap in the amount of net energy produced. © 2014 Published by Elsevier B.V. 1. Introduction Policy makers all over the world are showing increasing con- cern for the growth in energy consumption, while promoting the conversion from a fossil fuel-based to a bio-based economy (Richardson, 2012). The agricultural sector participates in this Abbreviations: AD, anaerobic digestion; AIL, acid insoluble lignin; CED, cumu- lative energy demand; DBY, dry biomass yield; EE, energy efficiency; FBY, fresh biomass yield; GE, gross energy yield; GHG, greenhouse gas; NE, net energy yield; SNK, Student–Newman–Keuls; TKN, total Kjeldahl nitrogen; TOC, total organic car- bon; TS, total solids; VS, volatile solids. ∗ Corresponding author. Tel.: +30 0512096643; fax: +39 0512096241. E-mail address: lorenzo.barbanti@unibo.it (L. Barbanti). effort, supplying biomass to be transformed into various forms of energy. Among them, anaerobic digestion (AD) can successfully be used for biogas and, ultimately, methane production. Biofu- els including methane represent an important strategy to reduce greenhouse gas (GHG) emissions by substituting fossil fuels, thus complying with the Kyoto Protocol and subsequent legislation such as EU Directive 2009/28/EC. Within the European Union, biogas production increased six- fold from 1990s to 2005 (Murphy et al., 2011) and reached 10.9 million tonnes of oil equivalent in 2010 (EBA, 2012). Biosolids of agro-industrial origin (e.g., crop, market and transformation residues; animal manure and slurries) are valuable feedstocks for AD in view of methane production. Beside them, dedicated biomass crops are increasingly being used, resulting in potential competi- tion for available land with food crops (Murphy et al., 2011). http://dx.doi.org/10.1016/j.indcrop.2014.03.002 0926-6690/© 2014 Published by Elsevier B.V.