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International audience; Fast development of centralized agricultural biogas plants leads to high amounts of digestate production. The treatment and disposal of liquid fractions after on-site digestate solid-liquid separation remains problematic due to their high organic, nutrient and aromatic contents. This work aims to study the variability of the remaining compounds in the digestate liquid fractions in relation to substrate origin, process parameters and solid-liquid separation techniques. Twenty-nine digestates from full-scale codigestion biogas plants and one waste activated sludge (WAS) digestate were collected and characterized. This study highlighted the combined effect of the solid-liquid separation process and the anaerobic digestion feedstock on the characteristics of liquid fractions of digestates. Two major clusters were found: (1) liquid fractions from high efficiency separation process equipment (e.g., centrifuge and others with addition of coagulant, flocculent or polymer) and (2) liquid fractions from low efficiency separation processes (e.g., screw press, vibrating screen and rotary drum), in this latter case, the concentration of chemical oxygen demand (COD) was associated with the proportion of cow manure and energy crops at biogas plant input. Finally, SUVA254, an indicator for aromatic molecule content and the stabilization of organic matter, was associated with the hydraulic retention time (HRT).

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.

International audience

International audience; Dry anaerobic digester operated in batch mode with liquid recirculation by sprinkling of the leachate on the static solid phase is a process well-suited for treating dry farm waste. At start-up, the recycling of liquid fraction (leachate) and/or solid fraction (digestate) from a previous batch into the new one is a key factor for a better industrial management when looking for a balance between energy production, substrate biodegradability and the initial investment. In this work, six types of manure of four different origins (sheep, goat, horse and cow) were compared. The results showed that, independently of their origin, all types of manure were rather easily digested in a dry anaerobic batch system. Indeed, after 60 days of digestion, at a S0/X0 ratio of 10 and with a leachate recirculation rate of 40 L/kgTS/day, the average volatile solid degradation was 50% and methane production ranged between 152 and 190 NmL CH4/g VS or between 32 and 59 NmL CH4/g of raw mass. After 60 days, the BMP average expression was 78 %. The influence on the degradation kinetics of the recycling at the start-up of a new batch of leachate or digestate was also investigated. The performances of three systems were compared. The first one was filled-up with only cow manure and tap water; in the second one, some digestate from a previous batch was added and; in the third one, some leachate was added. Results showed that leachate recycling is the best choice in terms of volumetric methane production, whereas digestate recycling improved the degradation kinetics and VS degradation. The batch without inoculation showed that an additional inoculation is not absolutely necessary for manure. Indeed, the simple use of water did not lead to a start-up failure but induced slightly lower global performances.

International audience

International audience; Due to the intermittent nature of solar and wind energies, on-demand biogas is a production way that could find its place in the future energy mix. It has been proven possible to modulate the biogas production without long-term consequences in literature. Experiments of punctual overloads have been conducted on three laboratory-scale reactors, with five different substrates. Each baseload production has been insured by three different substrates mixes, each with different kinetics. The effects of base organic loading rates (OLR), substrates kinetics and baseload substrates were assessed. Flexibility on reactors was defined as the margin between the maximal production and the baseload production. The maximal daily production was in the same order of magnitude on the three reactors with fast-degradable substrates (around 1 to 1.2 L CH4/L of reactor). Flexibility is optimized with a low baseload activity (coming from low OLR or slow-degrading substrates) and fast-degradable substrates used in overloads.

Anaerobic digestion of organic residues can be used to produce both renewable energy (biogas) and organic fertilizer (digestate). The effect of posttreatments (liquid-solid separation followed or not by a composting step) and digestion process (wet or dry digestion) on physico-chemical and microbiological properties of 27 digestates originating from 19 French biogas plants was analysed. Results showed that post-treatments and digestion process had a significant effect on dry matter, organic matter and nutrients contents. Raw digestates from wet digestion and liquid fractions obtained after liquid-solid separation of digestates were similar to mineral fertilizers (dry matter content < 10%, nitrogen present mainly as ammonium form and potassium content of 57 g/kg of dry matter as mean value). Inversely, raw digestates from dry digestion and solid fractions of digestates were similar to organic fertilizers (dry matter content > 17% and nitrogen as organic form). Composting of solid fractions induced a decrease of the organic matter (40-52% of dry matter) and the total organic carbon contents (mean of 252 g/kg of dry matter) and an increase of dry matter content (> 40%). Statistical analyses lead to a classification of the digestates in three groups, based on their physico-chemical characteristics. A comparison with current French standards defining fertilizers for land application (NFU 44-051, NFU 44-095 and NFU 42-001) was also performed for each of the three groups of digestates. For composted solid fractions of digestate, values were in line with regulatory thresholds of NFU 44-051 and 44-095, whereas for the other digestates, dry matter content was too low and ammonium content too high. For NFU 42-001, dry matter, nitrogen and phosphorus contents were too low for most digestates. Furthermore, some digestates contained concentrations of Escherichia coli above regulatory limit concentrations of NFU 44-095 for land application. This study highlights the importance of physico-chemical and microbiological characterization of digestates to enrich current databases in order to improve the legislation for the use of digestates as organic fertilizer., Dans un contexte de valorisation des digestats en tant que matière fertilisante pour un retour au sol, les caractéristiques physico-chimiques et microbiologiques de 27 digestats provenant de 19 sites français de méthanisation ont été mises en regard du posttraitement mis en oeuvre (séparation de phase avec ou sans compostage) et du type de procédé de méthanisation appliqué (en voie sèche ou liquide). Les résultats ont montré que les posttraitements et le type de digestion ont un effet significatif sur les taux de matière sèche, la matière organique et les éléments fertilisants. Ainsi, les digestats bruts de méthanisation en voie liquide et les fractions liquides possèdent des caractéristiques proches des engrais organiques (taux de matière sèche < 10%, azote majoritairement sous forme ammoniacale et concentration en potassium en moyenne de 57 g/kg de matière sèche), alors que les digestats bruts de méthanisation par voie sèche et les fractions solides présentent des caractéristiques proches des amendements organiques (taux de matière sèche > 17% et azote majoritairement sous forme organique). La stabilisation de la matière organique des fractions solides par compostage induit une diminution des taux de matière organique (40-52% de matière sèche) et des concentrations en carbone organique total (moyenne de 252 g/kg de matière sèche) et s’accompagne d’une augmentation du taux de matière sèche (> 40%). L’analyse statistique des données a permis de définir un classement des digestats en trois familles. Cette nouvelle typologie des digestats selon les posttraitements et le type de digestion pourrait être utile au choix de la filière de valorisation en qualifiant le caractère fertilisant ou amendant. Les valeurs obtenues pour chaque famille ont été comparées à celles exigées dans les normes relatives aux amendements organiques (NFU 44-051), composts de matières d’intérêt agronomique issues du traitement des eaux (NFU 44-095) ou engrais (NFU 42-001). Les fractions solides compostées sont généralement conformes aux critères d’évaluation des normes amendements et composts, alors que pour les autres digestats, le taux de matière sèche est trop bas et la concentration en ammonium trop élevée. Pour la norme engrais, les teneurs en matière sèche, en azote, voire phosphore, apparaissent insuffisantes pour la majorité des digestats étudiés. Par ailleurs, certains digestats présentent des concentrations élevées en Escherichia coli, ne respectant donc pas les seuils réglementaires de la NFU 44-095 pour pouvoir être utilisés en agriculture. Cette étude met en avant l’importance de la caractérisation physico-chimique et microbiologique des digestats en vue d’enrichir les bases de données pour faire évoluer la législation relative aux digestats de méthanisation.

L'invention concerne un procédé de configuration d'un modèle de prédiction des caractéristiques d'un substrat destiné à être incorporé dans un méthaniseur pour être biodégradé par digestion anaérobie qui met en œuvre une corrélation entre des données spectrales dans le proche infrarouge des caractéristiques expérimentales d'échantillons de substrats. L'invention a aussi pour objet un procédé d'estimation des caractéristiques de la biodégradation d'un substrat par digestion anaérobie dans un méthaniseur.

Méthanisation en 3 étapes pour l’amélioration de la production de biogaz : comparaison de procédés physicochimiques et impact du digestat sur les performances du procédé. Journées Recherche et Industrie biogaz méthanisation - JRI 2017

L’ensilage de résidus agro-industriels avant digestion anaérobie: Une solution pour le stockage longue durée. Journées de la Méthanisation : Applications Agricoles et Industrielles

Codigestion : Prédiction de la production de méthane en mode continu à partir des données cinétiques des substrats acquises en mode batch. Journées de la Méthanisation : Applications Agricoles et Industrielles

Détermination des limites de production de biogaz de digesteurs pour une production flexible. Journées de la Méthanisation : Applications Agricoles et Industrielles

Optimisation du démarrage d'un digesteur anaérobie discontinu pour la valorisation de fumiers bovins. Journées de la Méthanisation : Applications Agricoles et Industrielles

International audience; In the current context of waste recovering, production of renewable energy and reduction of greenhouse gases emission, anaerobic digestion (AD) is a technology receiving increasing interest. AD is a biological process, which allows the degradation of organic waste, related to human activity, producing a biogas storable and recoverable in the form of energy. Substrates are often selected according to their biodegradability and availability. Therefore, crop residues, such as wheat straws, are interesting because of their high abundance and low cost. However the low biodegradability of such lignocellulosic materials must to be considered. Similarly, agroindustrial organic waste are interesting due to their fast degradation, but the preservation of this seasonal waste might become problematic when considering the feeding of continuous AD reactors throughout the year. Silage represents an interesting storage technology but, difficult to be applied on agroindustrial organic waste because of their high water content. The use of a co-substrate having high solid contents, such as wheat straw, could be an innovative solution by reducing the water content of the waste mixture. Indeed, silage or anaerobic fermentation might be a way to maintain the methane potential of agroindustrial organic waste while pre-treating lignocellulosic materials due to the acidification of the silage process. The aim of this study is to evaluate the potential of ensiling a mixture of fresh seasonal agroindustrial waste with wheat straw for long term storage prior to AD process. Furthermore, the effect of the initial substrate mixtures on the metabolic pathways followed was investigated. Anaerobic fermentation was performed at laboratory-scale in batch tests. A mixture of beet leaves and wheat straw was carried out to obtain a Total Solid (TS) of 35%. This mixture was introduced in 50 plastic vacuum-packed bags and stored in a dark room at ambient temperature. Three bags were analysed periodically in triplicates at 10 different storage times from 0 to 180 days. Different analyses were performed: biogas production and composition, concentrations of nitrogen, carbon, soluble sugars and metabolites, as well as a monitoring of the microbial communities by 16S rRNA sequencing (MiSeq). Finally, the methane potential was assessed in order to evaluate the effectiveness of the storage. As results, beet leaves contained initially soluble sugars (25.5g Glucose/gTS ; 45g Xylose/gTS) and microbial metabolites (30.9g Lactate/gTS ; 27 g Acetate/gTS). The presence of lactic acid indicates that the fermentation process partially occurred before the start of the experiment. During the storage step, sugars were consumed and a succession of metabolic pathways was clearly observed. Interestingly, a lactic fermentation pathway was followed by butyric fermentation, homoacetogenesis and then methanogenesis. Microbial community characterization by New Generation Sequencing is under progress. These results will provide better understanding of the fermentation process with the succession of metabolic pathways. These different pathways did not affect the methane potential during the storage. Even though no improvement of the biodegradability of wheat straw was observed, mixing wheat straw with beet leaves was successful to store fresh waste. To determine the effect of more specifics substrate characteristics (e.g. sugar content) on the metabolic pathways followed, experiments are currently in progress. Moreover, inoculation with lactic acid bacteria is also investigated to redirect the process towards lactic acid fermentation. To conclude, this study has shown that anaerobic storage is a relevant solution to long term storage of fresh biodegradable biomass prior to anaerobic digestion.

International audience; In anaerobic digestion plants, the accumulation of volatile fatty acids (VFAs) is one of the most important issues especially when treating easily degradable wastes. Leach bed reactors (LBRs) is an innovative system where a leachate is sprinkled on the top of a static solid phase and percolates through it. This process is spreading rapidly because of its undiscussed advantages in respect to wet anaerobic digestion systems such as acceptance of solid dry waste, high volatile solid load, reduced liquid phase and no need in phase separation at the end of cycle. Leachate recycling the most important process parameter in such a system since it ensures a good humidity in the digester, it provides external inoculation and most of all it allows mass transfer among different reactors. This last role makes the recirculation an important key in order to solve inhibition due to intermediates accumulation. In fact, VFAs can be moved easily from a batch where they can be inhibitory to another where they can be consumed (Chynoweth, 1992). For this reason, on industrial scale, LBRs are often coupled together making the leachate recycle from one to another, thus creating a very synergic system able to treat even really putrescible wastes. In this work six LBRs of 6 L were used to test three different recycle conditions in duplicate. The same substrate, composed (on an total solid basis) of 45% cow manure, 40% carrots (used as easily degradable substrate) and 15% cereals residues, was charged with 2,1 kg of fresh substrate at a global total solid (TS) of 17% (360g TS). External leachate was sprinkled on the top and extracted daily from the bottom. The leachate volumes were fixed at 0.5, 1 and 2 L/kgTS/day and corresponded respectively to a volume of 180 mL, 360 mL and 720 mL of leachate. In the first part of the study (about 4 weeks), the experiment focused on the VFA extraction while in the second part it focused on the VFA consumption. Results from the first phase showed that recycling is an effective way to solve VFA inhibition and to establish a proper methanogenesis since all the produced VFA are extracted from the bulk phase. The cumulated extracted VFA and produced CH4 showed that recycling more allows to increase degradation kinetics consistently. That could be an important information in order to diminish solid retention time even when VFA inhibition delays the process. Moreover recycling at 1 L/kg TS/day is showed to be the most efficient in term of total mass of VFA extracted on the total recycled volume. The second phase started when methanogenesis was established (i.e., no more extraction of VFA and constant methane composition of about 60%). A synthetic VFA solution was injected into the system. Concentrations going from 5 g/L to 20 g/L were tested while the recycled volume was kept constant at 360 mL. During a first period, only C2 was used while after that a mixture of C2 and C4 (the VFA extracted most during the first phase) was injected. The results prove that with the injection volume used the average VFA retention was of 36% by mass, and this for any VFA concentration used. Whatever the VFA composition, VFA were rapidly consumed in about 10 h, 20 h and 30 h for an initial concentration of 5g/L, 10g/L and 20g/L respectively. Results show that the initial concentration in the leachate, the VFA mass retained and the degradation kinetics are the three parameters that would allow to optimize the VFA degradation in old reactors without putting at risk their biological equilibrium. A further analysis can help to design the recycling frequency of an industrial site based on this approach thus improving the system efficiency and substrate degradation.

This paper is a discussion proposal of structural model of organic matter hydrolysis (in aerobic and anaerobic bioprocesses) based on laboratory and model results. Indeed, the hydrolysis mechanism is mechanistically not well understood. Consequently, models are sometimes not appropriate to describe experimental results. Where there are multiple fractions, a model that considers simultaneous degradation of the substrates may not have the resolution to separate the different kinetics. In this paper, we assess sequential extractions to evaluate this as an alternative to simultaneous analysis.

Création d’une base de données spatialisée relative à la valorisation énergétique par méthanisation des résidus et coproduits organiques des agro-industries. Présentation du projet VALORMAP. Journées Recherche et Industrie Biogaz méthanisation

Analyse rapide des substrats pour la planification des recettes de mélanges. Journées Recherche et Industrie Biogaz méthanisation

Création d’une base de données spatialisée relative à la valorisation énergétique par méthanisation des résidus et coproduits organiques des agro-industries. Présentation du projet VALORMAP. Journées Recherche et Industrie Biogaz méthanisation

Co-digestion de déchets solides : Caractérisation de la fraction liquide des digestats après séparation liquide/solide. Focus sur la teneur en matière organique résiduelle et sa biodégradabilité. Journées Recherche et Industrie Biogaz méthanisation

L'invention concerne un procédé de configuration d'un modèle de prédiction des caractéristiques d'un substrat destiné à être incorporé dans un méthaniseur pour être biodégradé par digestion anaérobie qui met en œuvre une corrélation entre des données spectrales dans le proche infrarouge des caractéristiques expérimentales d'échantillons de substrats. L'invention a aussi pour objet un procédé d'estimation des caractéristiques de la biodégradation d'un substrat par digestion anaérobie dans un méthaniseur.

National audience; Du fait de la croissance démographique et du changement climatique, le bassin méditerranéen est soumis à une forte pression concernant l’accès aux ressources en eau, qui pourrait atteindre un seuil critique avec l’augmentation de la demande et la diminution de la disponibilité de ces ressources. Quel que soit son usage, l’eau a une valeur incontestable. Cependant, la réutilisation des eaux traitées comme source d’eau alternative, reconnue internationalement depuis plusieurs décennies, n’est que peu développée et mise en œuvre en France. Irri-Alt’Eau (projet R&D collaboratif régional, région Occitanie) est la première « Plateforme expérimentale et pédagogique de terrain » en France, sur la réutilisation des eaux traitées pour l’irrigation par goutte-à-goutte de la vigne en quantité et qualité maîtrisées. Ce projet est mené par un partenariat « Entreprise-Recherche-Collectivité » (Veolia, Aquadoc, Cave Coopérative de Gruissan, INRA UEPR et LBE , l’Agglomération du Grand Narbonne) avec l’objectif de développer une pratique raisonnée, compétitive, scientifiquement étayée et durable, de l’irrigation de la vigne avec des eaux traitées de qualité physico-chimique et microbiologique maîtrisée.

Le procédé de digestion anaérobie à percolation (procédé discontinu), où une fraction liquide percole à travers la fraction solide, est une technologie adaptée au traitement et à la valorisation des déchets agricoles. Pour cette raison, elle possède un grand intérêt en France où des unités de méthanisation à la ferme utilisent ce système pour traiter des fumiers. Afin d’étudier les potentialités de cette technologie, six fumiers différents (équin, ovin, caprin et bovins) ont été collectés dans des fermes utilisant un élevage sur litière accumulée. Le procédé a fait preuve d’une bonne stabilité biologique et les substrats se sont montrés adaptés à ce type de traitement. Grâce à leur porosité, leur alcalinité importante et leur lente dégradation, les fumiers peuvent être traités en mono-substrat dans des procédés à percolation mono-étape sans risques d’inhibition, car les AGV accumulés sont ensuite convertis en méthane sans difficulté. Dans ce type de procédé, la digestion de substrats plus facilement biodégradables peut entraîner des instabilités liées à une accumulation d’AGV qui peut ralentir les cinétiques ou inhiber les processus biologiques. Sur cette idée, différents réacteurs alimentés avec du fumier et des taux des matières facilement biodégradables variables ont été opérés. Les conditions choisies ont donné lieu à des inhibitions de plus en plus marquées liées à une accumulation d’AGV. Grace à la recirculation appliquée, ces réacteurs ont pu recouvrés une activité méthanogène et produire du méthane. Ces expériences ont permis de mettre en évidence le rôle important joué par la recirculation des percolas dans le rétablissement des conditions optimales de méthanisation grâce au lessivage des AGV et au contrôle du pH. Des expériences sont en cours pour évaluer l’effet du mode de lixiviation dans une stratégie globale de couplage de différents réacteurs possédant des niveaux de maturité (temps de réactions) différents.