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 ...
6The impact of formic acid and glucose addition on the co-ensiling of cattle manure with 7 straw was assessed during 4 months at laboratory scale. Feedstock deprived of additives 8 lost 67% of its methane potential for prolonged ensiling. This was mainly due to the 9 lack of water-soluble carbohydrates and to the high methanogenic activity of cattle 10 manure. The use of co-substrates enhanced biomass and energy conservation during 11 ensiling. The best storage performance was obtained for co-ensiling of cattle manure 12 with glucose (100 g/kg of feedstock). For this condition, lactate production was 13 extensive, which allowed biomass acidification, suppressed ammonia emissions and led 14 to full preservation of methane potential after 4 months. Therefore, in field-scale 15 storage, co-ensiling with a high easily fermentable sugar content co-substrate appears to 16 be the most resourceful method to optimize cattle manure preservation. Application of 17 this promising technique will have a major impact on the methane yield of agricultural 18 biogas plants where cattle manure has to be stored for long periods. 19Highlights 22 Ensiling of cattle manure with straw led to 67% methane potential losses 23 Ammonia emissions during ensiling were minimized with the use of co-substrates 24 Formic acid addition limited energy losses to 25% during ensiling 25 Full preservation of methane potential occurred for co-ensiling with 10% of glucose 26
6The effects of ensiling and open-air storage on the conservation of cattle manure were 7 investigated for 120 days at laboratory scale. Impact of co-ensiling with wheat straw 8 was assessed as well. Up to 74% of methane potential was lost during aerobic storage.
The objectives of this study were to: (1) quantify differences in biochemical methane potential (BMP) measured using three measurement methods, including two popular methods (a commercial automated system (AMPTS II) and manual manometric) and one newer method (gravimetric), and (2) assess the importance of the mixing position in the measurement sequence. Powdered microcrystalline cellulose was used as the substrate in simultaneous tests. All methods gave similar results (<8% difference in the mean BMP) and were reasonably accurate (recovery of 80–86% of the theoretical maximum BMP). Manometric BMP values were consistently lower than gravimetric by 4–5%. Precision was lower for the automated method (relative standard deviation (RSD) of about 7%) than for the manual methods (RSD about 1–3%). Mixing after biogas measurement resulted in 3% higher BMP for both manual methods than mixing before, due to the lower measured CH4 production from blanks. This effect may be linked to a fraction of CH4 that remains dissolved or even as attached bubbles, and suggests that mixing before measurement is preferable. The automated volumetric and gravimetric methods (mode 2) gave very similar mean BMP values (1% different). However, kinetic analysis showed that methane production was faster with the automated volumetric method. This could come from an error in the estimation of the CH4 production rate for the automated method, or an increase in the degradation rate due to better mixing. Both automatic volumetric and manual gravimetric measurements met current validation criteria for mean cellulose BMP, but the RSD from the automated system exceeded the limit.
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