Production of biogas from different organic materials is a most interesting source of renewable energy.The biomethane potential (BMP) of these materials has to be determined to get insight in design parameters for anaerobic digesters. Although several norms and guidelines for BMP tests exist, inter-laboratory tests regularly show high variability of BMPs for the same substrate. A workshop was held in June 2015, in Leysin, Switzerland, with over 40 attendees from 30 laboratories around the world, to agree on common solutions to the conundrum of inconsistent BMP test results. This paper presents the consensus of the intense roundtable discussions and cross-comparison of methodologies used in respective laboratories. Compulsory elements for the validation of BMP results were defined. They include the minimal number of replicates, the request to carry out blank and positive control assays, a criterion for the test duration, details on BMP calculation, and last but not least criteria for rejection of the BMP tests. Finally, recommendations on items that strongly influence the outcome of BMP tests such as inoculum characteristics, substrate preparation, test setup, and data analysis are presented to increase the probability of obtaining validated and reproducible results.

The biochemical composition can be seen as a good indicator of both the biodegradability and the methane potential of a given waste. The work presented here is an attempt to elaborate a typology of wastes and to compare it to the anaerobic degradation characteristics. The first data indicate that there is a link between the ligno-cellulosic content of the waste and the biodegradability. When dealing with application to anaerobic digestion processes, having a tool to predict the ability of the waste to be degraded could be of the greatest interest for preventing failures, estimating biogas production, methane content, or for the management of co-digestion processes.

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7In order to meet the legislative demands of new energy policy, investment in anaerobic 8 digestion and biogas production has increased in recent years, making it a versatile and 9 fully established technology. So as to remain competitive, anaerobic digestion should be 10 optimized not only at the level of the process, but also down and upstream, in which 11 biomass storage prior to digestion is included. Ensiling is a commonly used and promising 12 techniques to store wet biomass before anaerobic digestion. This article reviews the 13 crucial parameters for ensiling agricultural wastes and crops for biogas production, as 14 source properties, storage management and duration, temperature or additives. According 15 * Corresponding author. Tel.: +33(0) 4 72 43 87 53 E-mail addresses: ruben.teixeirafranco@insa-lyon.fr (R. Teixeira Franco), pierre.buffiere@insa-lyon.fr (P. Buffière), remy.bayard@insa-lyon.fr (R. Bayard) to the reported findings in the bibliography, feedstock and its biochemical characteristics 16 will define the course of ensiling and the impact of other parameters during storage as 17 well. Good silage preservation will occur for feedstocks with low moisture content, high 18 accessible carbohydrates and low buffering capacity. High packing density and reduced 19 particle size will contribute to minimize energy losses during ensiling. Additives are 20 widely used but are not always an asset for methane potential conservation and their 21 application should be more appropriate for poorly ensilable biomass. Finally, evidences 22 suggest that under specific conditions, ensiling may increase methane potential despite 23 non-negligible organic matter losses during storage. Exposing the answers given by the 24 literature in terms of impact of different conditions in the course of ensiling and the 25 questions still unresolved, this article highlights the good management practices of 26 substrates for biogas production.27 Highlights 30  Biochemical properties of feedstock will define the course of ensiling. 31 Good preservation requires low silage moisture, high water-soluble carbohydrates 32 content and low buffering capacity. 33 High packing density and reduced particle size minimize energy losses. 34 Additives should be a potential asset for preservation of poorly ensilable biomass. 35 Ensiling may be used as methane potential booster before anaerobic digestion. 36 Abbreviations 37 AD, anaerobic digestion; BC, buffering capacity; BMP, biochemical methane 38 potential; Ho, homofermentative; He, heterofermentative; LAB, lactic acid bacteria; 39 NH3-N, ammoniacal nitrogen; TS, total solids; VS, volatile solids; WSC, water soluble 40 carbohydrates 41 3 1. Introduction 42 Taking into account political and environmental concerns, investment in bioenergy 43 production has been intensified and diversified over the past twenty years [1]. 44 Considering recent studies [2], biogas production through anaerobic digestion (AD) is 45 one of the renewable energies that is being considered and developed, from which ...