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International audience; Anaerobic digestion (AD) is a waste treatment technology based on organic matter degradation by microorganisms in the absence of oxygen. This process generates two valuables products, biogas and digestate. While biogas is recognized and exploited for its energy potential, digestate could be an interesting fertilizer thanks to its rich-nutrient composition. However, implementation of AD still raises concerns about energy transportation, consequences of digestate spreading and poor conversion to carbon during digestion. To overcome the issues linked to AD, to integrate anaerobic digestion with the pyrolysis of digestate is an innovate path. This study aims to analyze sustainability of a multifunctional process coupling anaerobic digestion and pyrolysis. The process is applied to the treatment of sewage sludge and quinoa residue in co-digestion. To evaluate environmental impacts, life cycle assessment (LCA) is realized from a cradle-to-gate perspective, using SimaPro software (V8.5.2) and Environmental Footprint EF 3.0 method. Results underline that the main contributor to environmental impacts is the treatment of bio-oil, a pyrolysis product, while other impacts could be counterbalance thanks to energy production

This document presents the minimal requirements for measurement and validation of biochemical methane potential (also called biomethane potential)(BMP) in batch tests, and represents the consensus of more than 40 biogas researchers. The list of requirements is based on Holliger et al.[2016], with some recent modifications of validation criteria as described in Hafner et al.[2020c] and additional details on calculation standardization.

The aim of this study was to explore the efficiency of a mechano-enzymatic deconstruction of two macroalgae species for sugars and bioethanol production, by using a new enzymatic cocktail (Haliatase) and two types of milling modes (vibro-ball: VBM and centrifugal milling: CM). By increasing the enzymatic concentration from 3.4 to 30 g/L, the total sugars released after 72 h of hydrolysis increased (from 6.7 to 13.1 g/100 g TS and from 7.95 to 10.8 g/100 g TS for the green algae U. lactuca and the red algae G. sesquipedale, respectively). Conversely, total sugars released from G. sesquipedale increased (up to 126% and 129% after VBM and CM, respectively). The best bioethanol yield (6 g(eth)/100 g TS) was reached after 72 h of fermentation of U. lactuca and no increase was obtained after centrifugal milling. The latter led to an enhancement of the ethanol yield of G. sesquipedale (from 2 to 4 g/100 g TS).

Over the past decade, increasing interest has been addressed to anaerobic fermentation. These bioprocesses have been investigated to not only produce hydrogen but also other high-value by-products, such as carboxylic acids (mainly acetate, butyrate, lactate), ethanol and other solvents. Indeed, hydrogen is characterised by a clean combustion process and is an efficient energy carrier with a considerable calorific value (122 MJ/kg), but represent only 20% of the total COD in fermentation, with more than 80% of valuable metabolites. Interestingly, anaerobic dark fermentative processes imply complex mixed microbial consortia able to operate in non-sterile conditions and to use various kinds of waste as feedstocks. Nevertheless, hydrogen yields from solid waste are directly correlated to the initial content in soluble carbohydrates (Guo et al., 2010; Monlau et al., 2012). In this context, lignocellulosic residues, rich in carbohydrates, constitute relevant feedstocks for dark fermentation but pretreatment is required to solubilise hemicelluloses and cellulose and make carbohydrates more available to microorganisms. High release of soluble carbohydrates can be obtained by thermal-acid pretreatment, enzymatic hydrolysis, combined or not with alkali upstream pretreatment. This paper will present a synthetic view of several studies combining thermo-chemical and/or enzymatic pretreatment of lignocellulosic biomass (wheat straw (WS) and sunflower stalks (SS)) with the purpose of H2 production by dark fermentation. As main findings, enzymatic hydrolysis of WS with an enzyme cocktail secreted by Trichoderma strain showed the necessity of working under sterile conditions to avoid a re-consumption of solubilized sugars by the endogenous bacteria naturally present in the substrate. A two-fold hydrogen production from 10 to 20 mL/g VS was obtained after addition of 5 mg enzymes/ g wheat straw. Interestingly, same results were obtained by adding enzymes directly into the fermenter, leading to a simpler and cheaper process (Quemeneur et al., 2012). The combination of thermal-alkali pretreatment (55°C, 4% NaOH (w/wTS) for 24 h) and enzymatic hydrolysis (cellulose 50 FPU/gTS; glucosidase 25 U/gTS and xylanase 50 U/gTS) on SS led to a 21 fold increase in hydrogen production from 2.4 to 49 mL/gVS (Monlau et al., 2013b). In comparison, thermal acid (170°C, 4% HCl for 1 hour) of SS led to a decrease of hydrogen production which was explained by the release of inhibitory by-products during pretreatments (furfural, 5-HMFand phenolic compounds). Interestingly, performing glucose fermentation with increasing amounts of acid pretreatment hydrolysate showed a metabolism shift from acetate/butyrate/hydrogen to lactate/ethanol and finally ethanol production with a yield of 2 mol ethanol/mol glucose consumed (Monlau et al., 2013a).

Keynote; Anaerobic digestion is a key process for urban solid waste management converting organic waste into biogas, mainly composed of methane and carbon dioxide, and a residue called digestate which is generally separated into solid and liquid fractions. Based on an overview of the abundant literature published on municipal solid waste and lignocellulosic biomasses, the potentialities of anaerobic digestion processes will be presented. The first part of the lecture will discuss the interest of using pretreatment techniques to improve the conversion of wastes into biogas. Some intermediary products of anaerobic digestion such as fatty acids, ethanol and hydrogen present a higher added value than methane. Different anaerobic process parameters and the selection of specific microbial consortia allow an optimal production of these products while preventing methane production in the so-called dark fermentation process. The impact of waste pretreatment on the production of hydrogen and metabolites will also be discussed. Dark fermentation effluents may be treated in anaerobic digestion to produce biohythane, consisting of a mixture of biohydrogen and methane, and leading a cleaner and more efficient combustion than that of methane alone. In addition, digestates are rich in nitrogen, phosphorous and more or less stabilized carbon and can be used as fertilizers or soil improvers. More original uses of digestates have been proposed such as the conversion of the digestate solid fraction into activated biochar, bio-oil and syngas through thermal processes, or the use of nutrients present in the liquid fraction in biological processes such as algae growth or bioethanol production.

In many European countries, biogas production through anaerobic digestion (AD) is a very fastgrowing market in the agricultural sector. AD converts biologically organic matrix into biogas anddigestate, the latter corresponding to the anaerobically not degraded fraction. Until yet, digestate ismostly used as soil improver or fertilizer at farm scale, but its increasing amount causes problemsrelative to its transport cost, greenhouse gases emissions during its storage and its used is regulate bythe European Nitrate Directive.In this study, we investigated two energetically valorization routes (i.e. biofuels, pyrolysis) tomaximize the energy recovery from the initial feedstock and reduce the digestate amount.In the first experiment, digestate that contains still a high amount of sugars especially cellulose wasinvestigated for soluble sugars production for further biofuels used (i.e. bioethanol, biohydrogen…).For this purpose, digestate was mechanically treated (i.e. centrifugal milling, 0.12 mm) and furthersubmitted to enzymatic hydrolysis. Energy requirement of mechanical pretreatment and enzymatichydrolysis yields were compared between the anaerobic digestate and the original feedstock. First,energy requirement for mechanical pretreatment was less important for digestate (1.3 kWh.kg-1) thanoriginal feedstocks (3.3 kWh.kg-1). AD has a positive effect on the physicochemical structures of theoriginal feedstocks and consequently leads to a reduction of the energy requirement. Then, theenzymatic hydrolysis yield of digestate (63%) was increased compared to raw feedstock (54%). Theseresults suggests that digestate from AD process could represent a suitable residues for sugar release inthe optic of biofuels production.In the second experiment, a new concept of coupling AD with digestate post-pyrolysis wasinvestigated. Pyrolysis of digestate at 500°C results to 8.8 wt. %, 58.4 wt. % and 32.8 wt. % of syngas,oil and pyrochar, respectively. Like methane produced from AD process, syngas and bio-oil can befurther converted into heat and electricity through a combined Heat and Power system. By couplinganaerobic digestion with pyrolysis process the electricity producted raised from 9896 KWhel day-1 to14066 KWhel day-1 corresponding to an increase of 42% compared to AD process alone. On the otherhand, pyrochar can be used as soil amendment in order to preserve the fragile soil quality, a practicewhich is in line with the principles of ecology and sustainable agriculture.

The high crude oil prices, the decline of fossil fuel reserves and the increase of greenhousegas emissions are motivating the development of biorefineries that produce energy fromrenewable resources (i.e. lignocellulosic biomass). However, the key driver for the successfulconversion of biomasses into biofuels is the selection of efficient pretreatments that permit tomaximize the sugars recovery and to minimize the consumption of water, chemicals andenergy. This study proposes the application of “dry” chemo-mechanical pretreatments thatpermit to enhance enzymatic hydrolysis and thereafter bioethanol production fromlignocellulosic biomasses.In a first experiment, wheat straw was pretreated with NH3, NaOH, NaOH-H2O2 and NH3-H2O2 at both high (5 kg L-1) and at low (0.2 kg L-1) biomass concentrations, named “dry” and“diluted” pretreatments. Then, untreated and pretreated samples were subjected to centrifugaland ball milling, followed by enzymatic hydrolysis. Compared to diluted mechano -NaOHpretreatments, dry mechano -NaOH and -NaOH-H2O2 were found to be more effective indecreasing the particle size (up to 55%), increasing the surface area (up to 88%) anddecreasing the total energy requirement (up to 50%). Enzymatic hydrolysis was enhanced bypretreatments, as suggested by higher glucose yields (332, 320, 140, 322, 141 g glucose kg-1biomass for diluted –NaOH, dry – NaOH, dry -NH3, dry -NaOH-H2O2 and dry -NH3-H2O2,respectively), compared to that of untreated wheat straw (118 g glucose kg-1). However, lowerenergy efficiency was obtained for dilute mechano -NaOH treatment, compared to drymechano -NaOH treatments.In a second experiment, sugarcane bagasse was pretreated with NaOH and H3PO4 at highbiomass concentration (5 kg L-1) and then milled by using different methods, such asvibratory milling (VBM), ball milling (BM) and centrifugal milling (CM). Results indicatethat NaOH-BM and NaOH-VBM was preferred to enhance glucose yields and bioethanolproduction (up to 76%), while CM consumed 75% and 58% lesser energy than BM and VBM,respectively. The highest energy efficiency was obtained with NaOH-CM. Therefore, thecombination of dry NaOH and CM appears the most suitable and interesting pretreatment forthe production of bioethanol from SB.