Solid residence time distribution (SRTD) analysis is important in the design, modeling, and operation of solid biomass in continuous dry anaerobic digestion (D-AD) reactors. SRTD analysis could allow the appropriately adjust of the applicable organic charge and the study of unusable volume due to solid accumulation and preferential pathways. The lack of sustainable, environmentally friendly, and cost-effective solid tracers limits the study of solid flow patterns in D-AD digesters. In this study, 3D printing enabled the fabrication of customized Poly Lactic Acid (PLA) tracers with a specific shape to perform SRTD analysis of the semi-continuous digestion of straw-cattle manure (SCM) in a horizontal reactor of 0.5 m3. The recovery of tracers at the reactor outlet allowed the determination of the average SRTD at 29.43 days. Solid convection was predominant over diffusion, indicating that the reactor behaves closer to a plug flow reactor (PFR) rather than a complete stirred tank reactor.

A simplified AM2 model was developed to characterize mussel solid-state anaerobic digestion. This model considers two different substrates for mussels' degradation: the mussel meat and the mussel juice obtained after sanitization. This model was implemented to characterize the anaerobic degradation of Mytilus edulis species. This model was verified, implemented, and validated in 60 L batch reactors in mesophilic conditions. Two different experiments were used to calibrate kinetics using reaction invariants and an interior point optimization method. A conditioning study and a sensitivity analysis were done and had shown a better sensitivity with delayed substrate injections throughout the experiment with a factor of 10. An 88.6 % accumulation of methane yield of the BMP measurement was observed, corresponding to 57.7 % volatile removal with a minimum mass balance of 96.1 %. Additionally, the model proposed in this study was able to successfully predict the two characteristic methane yield peaks observed during solid-state anaerobic digestion.

Cet article propose un état des lieux des méthodes pour la détermination des paramètres rhéologiques des biomasses grossières appliquées à la méthanisation en voie solide. La méthanisation en voie solide est un procédé biologique permettant la valorisation sous forme de biogaz des sous-produits à forte teneur en matières sèches, en particulier les sous-produits agricoles, les déchets ménagers et les déchets alimentaires. Afin d’assurer le développement de plusieurs technologies de méthanisation, des connaissances précises sur les propriétés rhéologiques des substrats et du milieu réactionnel sont indispensables pour la conception, l’opération et la simulation de procédés. Malgré l’importance des propriétés rhéologiques, très peu de données du comportement rhéologique de la biomasse grossière sont présentes dans la littérature. Cela s’explique par le fait que les rhéomètres rotatifs conventionnels ne sont pas bien adaptés à la biomasse hétérogène comportant des particules grossières et de longues fibres. Jusqu’à présent, les équipements rotatifs conçus permettent de déterminer les propriétés rhéologiques de biomasse concentrée contenant des particules d’une taille maximale de 3 cm alors que les biomasses peuvent contenir des fibres lignocellulosiques ayant jusqu’à 25 cm de longueur. Compte tenu de cette limitation instrumentale, différents appareils alternatifs issus des domaines de l’analyse du béton, des sols ou des aliments ont été récemment adaptés pour accéder à des propriétés rhéologiques des biomasses agricoles. Dans cet article, ces différents outils ont été répertoriés en précisant des informations sur les facteurs d’influence, les principes physiques théoriques, le montage expérimental et leur gamme d’application pour la biomasse. Hélas, pour certains de ces appareils, les relations trouvées sont à ce jour plutôt qualitatives que quantitatives et les raisonnements mathématiques permettant d’intégrer complètement les phénomènes physiques observés avec les facteurs influençant la rhéologie de la biomasse doivent encore être investigués afin de mettre en place des méthodes normalisées spécifiques à une biomasse grossière.

Knowledge of rheological evolution of biomass during dry anaerobic digestion (D-AD) is important in the engineering design, modeling, and operation of D-AD reactors. In this work, two methods of rheological analysis, the slump test and the shear-box, were used to measure the evolution of the yield stress, cohesion and friction angle of the straw-cattle manure (SCM) during the D-AD. Firstly, four 60 L batch leach-bed reactors (LBR) were started in parallel and stopped at different stages of the D-AD process on days 0, 10, 21 and 31. Secondly, a 500 L and 2 m length plug flow reactor (PFR) was operated with 40 days of solid retention time and samples were recovered at different positions. The solid degradation during D-AD process was monitored by analysis of the degradation of volatile solids, the fiber content and the Flash BMP. Similar degradation patterns of SCM and rheological evolution were observed in both reactors type. VS content decreased of 10.7% and 10.2% in 30 days in PFR and LBR respectively. VS degradation in both cases was well explained by hemicellulose and cellulose consuming in D-AD process. Considering the rheological analysis, the results showed that D-AD induced a reduction of the yield stress of 28.1 and 24.2% in 30 days in PFR and LBR respectively. Moreover, a similar evolution of cohesion and friction angle value for samples from both reactors was observed. This study demonstrates the close relationship between the state of degradation of the solid biomass and its rheological properties.

The recirculation flow inside the leach-bed during solid-state anaerobic co-digestion of layered cattle manure and roadside grass was characterized using three different methods on lab scale reactors. Tracing experiments and method of moments were used to characterize percolation flow properties with different leach-bed compositions and a new criterion was proposed to quantitatively evaluate the ratio between preferential pathways and dead volumes for each experiment. The impact of recirculation flow on leach-bed complexity for different moments of SS-AD and substrate layering was characterized using steady-state reactor modeling and the impact of recirculation flow on microporosity and macroporosity evolutions all along SS-AD was determined using modeling of hydrodispersive parameters. It appeared that layering and time could significantly impact percolation flow and leach-bed complexity, until 36 % of residence time variation and 110 % of leach-bed complexity. Moreover, layering could impose a different percolation flow for each layer and cause a preferential pathways disruption.

A coupling distributed solid-state anaerobic digestion model was developed and performed considering a simplified AM2 model and a saturated Mobile-Immobile water Model (MIM). This model allows considering both microporosity and macroporosity evolutions as well as the impact on biological kinetics. This model was adapted, implemented and validated on cattle manure in mesophilic conditions and carried out in a solid-state leach-bed reactor. Three 60 L sacrificial leach-bed reactors were used to determine hydrodynamics and kinetic parameters in a calibration-validation approach. A sensitivity analysis was conducted and has shown a high value of hydrolysis kinetics on outputs variables (until 92% for accumulated methane yield and 72% for volatile fatty acids accumulation) which confirmed the necessity to identify accurately the hydrolysis parameter before calibration step. Finally, the solutes present inside each mobile and immobile region evolved in a different way confirming the model relevance.

Optimization of solid-state anaerobic digestion on cattle manure and damp grass were performed simultaneously and combined to a bootstrapping tool to significantly decrease the number of experiments for a methane yield optimization. 15 batch reactors at lab scale were launched two times respecting a mix surface response methodology. A numerical method called Bootstrapping was used to verify results significance. Results have shown a significant influence with a p-value between 10-8 and 10-11: the optimal parameter values depend on the substrate composition with a maximal p-value of 5.60.10-2. The methane yield reached 156.19 NL & sdot; kgVS-1 for a mixture of cattle manure and damp grass, and 142.92 NL & sdot; kgVS-1 for cattle manure only. The bootstrapping were validated with a standard error lower than 3% in comparison with ANOVA method, which confirms that the mix surface response methodology combined to bootstrapping is an innovative and efficient way to optimize solid-state anaerobic digestion process.

The effects of the solid bed immersion in the anaerobic digestion of straw-cattle manure (SCM) were studied using two batch reactors of 2 m of solid height and 440 L of total volume. The reactors were operated in parallel with total (R1_100%) and partial solid height immersion (R2_74%) and no liquid recirculation. Recovered methane yield was 31.1% higher in R1 than in R2, 33.7 and 23 Nm3 CH4 t−1SCM respectively. The volatile solids (VS) and fiber degradation was studied in layers distributed each 0.5 m of the initial solid bed height profile; VS removal was measured at 16% at 2 m height in contrast to 39.9% at the reactor bottom. VS removal was related with hemicellulose and cellulose biodegradation, maximal hemicellulose and cellulose degradation in the studied layers were 68.2 and 49.5% respectively. Physical and rheological changes of the solid phase were measured between the SCM and the digestate. Macropores volume was reduced from 30.4% to values between 0.82 and 5.57%, this decrease was related to the water content and the fiber degradation state in each layer. Similarly, yield stress values obtained with the slump test depends on total solids content and fiber degradation state, yield stress values ranged from 1.41 and 2.23 kPa for raw and digested SCM. Moreover, values of cohesion and the friction angle were between 1.5 and 2.8 kPa and 15.6 and 47.7° respectively. Physical and rheological properties of digested SCM depends on the solid degradation state and the water availability through the material’s height profile.

The lack of rheological characterization of coarse biomass limits the design, operation and optimization of continuous Dry Anaerobic Digestion (D-AD) processes. In this work, three alternative rheological devices for the determination of rheological behavior of coarse biomass were scale-up and calibrated; the slump test, the consistometer and the shear-box. The applicability and limitations of each device were evaluated using artificial mixtures of straw-cattle manure prepared using raw and shredded Wheat Straw (WS). The slump test and consistometer results suggest that the yield stress increases exponentially from 43 to 882 Pa with the WS content increase, reducing the flowability. Cohesion and friction angle measures using the shear-box were between 1.39 and 3.17 kPa and 11.0 and 28.89° respectively. This work represents an advance in the setting-up of standardized methods to the rheological determination of coarse biomass.

Le but de cette étude est de concevoir et de valider un ensemble de réacteurs et de compteurs de gaz permettant d’étudier la méthanisation en voie sèche à l’échelle laboratoire. L’intérêt de cet ensemble est de permettre la mise en oeuvre d’essais sur des substrats solides complexes, tels que des fumiers pailleux, tontes d’herbe et biodéchets, avec des quantités mises en jeu significatives, tout en préservant la structure et les caractéristiques physiques des substrats à étudier (pas de prétraitements préalables tels que broyage ou séchage). Il permet également d’agir sur les paramètres physiques clés, tel que la composition en substrats, l’immersion du massif et la recirculation de l’inoculum. Sa conception permet de réaliser deux types d’expériences : un suivi de production de méthane et une expérience de traçage au sein du massif solide. Le suivi de la production de méthane peut s’effectuer pour une composition en substrats donnée, pour laquelle l’immersion et les contraintes de recirculation sont déterminées. Cela permet des expériences d’optimisation de ces paramètres, notamment par les méthodes fournies par les plans d’expériences. Le traçage permettra quant à lui de déterminer le temps de séjour de la phase liquide au sein du massif solide. La création de cet ensemble a suivi un processus de conception classique : génération d’idées, sélection du produit, développement du produit puis tests et comparaison à la littérature. Les deux premières étapes de création ont été effectuées par une veille bibliographique, puis par conception assistée par ordinateur à l’aide de l’outil AutoCAD 2020. L’ensemble ainsi créé a ensuite été construit en deux prototypes successifs afin de perfectionner sa mise en oeuvre. Le modèle final a enfin été mis en oeuvre en conditions réelles de méthanisation en voie sèche afin de valider son fonctionnement et de comparer les résultats obtenus à la littérature.

Knowledge of the porosity distribution of biomass is crucial to understand the liquid flow through porous solid biomass treated in dry anaerobic digestion (D-AD). In this study, a novel adaptation of Water Retention Curve (WRC) analysis was validated to characterize the pore distribution of representative lignocellulosic biomasses; Cattle Manure (CM), roadside grass and corn stover. WRC analysis is composed of a drainage analysis (DA) and thermogravimetry analysis (TGA). Macro, meso and micropores values ranged from 33 to 63%, 25 to 44% and 7 to 16% for listed raw biomasses. Additionally, changes in porosity distribution of CM treated in sacrificed Leach-Bed Reactor (LBR) were quantifying; macropore volume decreased from 30.4 to 1.7% with the fiber degradation reducing considerably the permeability and increasing the solid bed compaction. The findings of this study suggest that the daily recirculated liquid volume could be progressively adapted considering the physical evolution of the solid bed.

Roadside grass cuttings and solid cattle manure are resources that are available as input for dry anaerobic co-digestion. Two series of measurements were carried out, one in June 2016 and one in October 2016. The methane potentials were determined on a laboratory scale and revealed a high degree of seasonality, 202.9 and 167.9 Nm(CH4)(3).t(VS)(-1), respectively. Moreover, these substrates were co-digested in reactors by the dry process on a pilot scale (60 L). Two strategies for filling and optimization, as layers or as a mixture, were compared. The seasonality also determined the physicochemical parameters and the hydrodynamic properties involved in percolation of the liquid phase recirculated in the dry digestion process. The production of methane depended on the filling method, the seasonality, and the nature of the input, which in some cases resulted in inhibition of 34.8-44.4 Nm(CH4)(3).t(VS)(-1).

The electrical resistivity tomography (ERT) method is a non-intrusive method widely used in landfills to detect and locate liquid content. An experimental set-up was performed on a dry batch anaerobic digestion reactor to investigate liquid repartition in process and to map spatial distribution of inoculum. Two array electrodes were used: pole-dipole and gradient arrays. A technical adaptation of ERT method was necessary. Measured resistivity data were inverted and modeled by RES2DINV software to get resistivity sections. Continuous calibration along resistivity section was necessary to understand data involving sampling and physicochemical analysis. Samples were analyzed performing both biochemical methane potential and fiber quantification. Correlations were established between the protocol of reactor preparation, resistivity values, liquid content, methane potential and fiber content representing liquid repartition, high methane potential zones and degradations zones. ERT method showed a strong relevance to monitor and to optimize the dry batch anaerobic digestion process. (C) 2015 Elsevier Ltd. All rights reserved.

Several 60L dry batch anaerobic digestion (AD) reactors were implemented with or without liquid reserve on cattle manure. The immersed part modulation of cattle manure increased the methane flow of about 13%. The quantitative real time PCR and the optimized DNA extraction were implemented and validated to characterize and quantify the methanogen dynamic in dry batch AD process. Final quantities of methanogens converged toward the same level in several inocula at the end of AD. Methanogen dynamic was shown by dominance of Methanosarcinaceae for acetotrophic methanogens and Methanobacteriales for the hydrogenotrophic methanogens. Overall, methanogens populations were stabilized in liquid phase, except Methanosaetaceae. Solid phase was colonized by Methanomicrobiales and Methanosarcinaceae populations giving a support to biofilm development. The methane increase could be explained by a raise of Methanosarcinaceae population in presence of a total contact between solid and liquid phases. Methanosarcinaceae was a bio-indicator of the methane production.

The chemical oxygen demand (COD) is an essential parameter in waste management, particularly when monitoring wet anaerobic digestion processes. An adapted method to determine COD was developed for solid waste (total solids >15%). This method used commercial COD tubes and did not require sample dilution. A homemade plastic weighing support was used to transfer the solid sample into COD tubes. Potassium hydrogen phthalate and glucose used as standards showed an excellent repeatability. A small underestimation of the theoretical COD value (standard values around 5% lower than theoretical values) was also observed, mainly due to the intrinsic COD of the weighing support and to measurement uncertainties. The adapted COD method was tested using various solid wastes in the range of 1–8 mgCOD, determining the COD of dried and ground cellulose, cattle manure, straw and a mixed-substrate sample. This new adapted method could be used to monitor and design dry anaerobic digestion processes.

The aim of this study was to investigate and quantify non-uniform water flow during dry AD and its implication for biogas production. Laboratory tracer experiments were performed on cattle manure over the course of AD. The evolution of the permeability, the dry bulk density, the dry porosity, the total and volatile solid contents of cattle manure at different stages of AD, revealed waste structure changes, impacting water flow and methane production. Tracer experiments and numerical modeling performed by using a physical non-equilibrium model indicated non-uniform preferential flow patterns during degradation. According to literature, the increase of inoculum recirculation frequency improved methane production rate. However, these results demonstrated that this improvement occurs only at the beginning of manure degradation. After 19 days of degradation the inoculum recirculation and the flow patterns modification had no effect on methane production rate.

This study aims at the optimisation of a microwave pretreatment for wheat straw solubilisation and anaerobic biodegradability. The maximum yield of methane production was obtained at 150°C with an improvement of 28% compared to an untreated sample. In addition, at this temperature, the time to reach 80% of the methane volume obtained from untreated straw was about 35%. The study of ramp time and holding time at targeted temperature showed that they had no improvement effect. Thus, the best conditions are the highest heating rate for a final temperature 150°C without any holding time. The reading of energy consumed by pretreatment and energy overproduced by pretreated samples showed that increasing tVS amount and heating rate led to a saving of energy consumption. Nevertheless, to obtain a positive energy balance, a microwave device should consume less than 2.65 kJ/g(tVS).

This study investigated the effects of microwave pretreatment of switchgrass in order to enhance its anaerobic digestibility. Response surface analysis was applied to screen the effects of temperature and time of microwave pretreatment on matter solubilisation. The composite design showed that only temperature had a significant effect on solubilisation level. Then the effects of the microwave pretreatment were correlated to the pretreatment temperature. The sCOD/tCOD ratio was equal to 9.4% at 90°C and increased until 13.8% at 180°C. The BMP assays of 42days showed that microwave pretreatment induced no change on the ultimate volume of methane but had an interesting effect on the reaction kinetic. Indeed, the time required to reach 80% of ultimate volume CH4 is reduced by 4.5days at 150°C using the microwave pretreatment.

The impedancemetry method can be used in Microbiology to perform the detection, quantification and even identification of some bacteria. Basic knowledge about this subject can be stated from Ur and Brown (1975), Firstenberg-Eden and Eden (1984), the reviews of Silley and Forsythe (1996), and Wawerla et al. (1999). With Escherichia coli, Bacillus subtilis and Saccharomyces cerevisiae cultures, the conductimetric responses were highly replicable, and repeatable for inocula concentrations from 1 to 10(8) CFU mL(-1). The main use of such devices could be the detection of contaminations of foodstuff. Several of these foodstuffs incubated at 37 degrees C spontaneously release quite large amounts of CO2. Our impedancemeter, however, was able to detect an Escherichia coli presence in canned French beans down to 2.35 10(-2) colony forming units (CFU) mL(-1), and a Saccharomyces cerevisae contamination of apple purée in glass jars down to 6.1 10(-3) CFU mL(-1).