Solid-state anaerobic digestion (SS-AD) is a promising technology for treating organic waste and producing renewable energy. This study explores the feasibility of using 3D printing to rapidly design cost-effective laboratory-scale digesters for optimization experiments. Batch reactors were designed using fused deposition modeling (FDM) with polylactic acid (PLA) and stereolithography (SLA) with High Temp V2 resin. PLA had a negligible impact on methane yields, while raw SLA resin positively influenced methanogenic potential, likely due to residual isopropanol used in post-processing, causing a 19% increase in CH4 yield. The performance of the 3D-printed reactors was compared to that of a conventionally machined PMMA reactor using cattle manure as a substrate, showing comparable methane yields and process stability. Three-dimensional printing technologies have demonstrated remarkable efficiency in designing laboratory-scale digesters, with a 70% cost reduction for SLA technology and an 80% reduction in design time compared to conventional reactors designed by plastics processing, while maintaining comparable biogas production. FDM technologies with PLA have shown that they are not suitable for these uses. This study demonstrates the potential of additive manufacturing to accelerate SS-AD research and development. However, care must be taken in material selection and post-processing to avoid introducing experimental bias.

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.

In the anaerobic digestion world, the dry matter (DM) and organic matter (OM) contents of the samples are major data for the design, handling, and maintenance of the processing of biogas plants. Volatile compounds, such as volatile fatty acids and ammonia, are likely to volatilize during drying at 105 °C and, thus, distort DM values; they have been described at length in the literature. On the other hand, the partial decomposition of bicarbonate, present in the digestion media, has been little described in the scientific literature. In this work, it appears that, in accordance with the stoichiometry of the partial decomposition of bicarbonate into CO2 and H2O, about 37% is volatilized as early as 70 °C and a fortiori at 105 °C, whether in aqueous solutions of pure bicarbonate or in different real digester media. With freeze-drying, no degradation of bicarbonate was observed, confirming the thermo-dependence of this reaction. This decomposition leads to an underestimation of DM measurements and some erroneous DM mass balances. It also led to an indirect overestimation of the OM, when expressed as a percentage of the DM.

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.

The determination of a volatile fatty acid content (FOS) and total alkalinity (TAC) can be carried out using Nordmann’s FOS/TAC titration method developed in the 1970s. This two-point titration (pH = 5 and 4.4) can be simply implemented and is widely employed by both the academic and industrial worlds. However, the present study proves that Nordmann’s method is only valid in limited ranges, since the titration of one FOS and TAC has an impact on the determination of the other, especially in extreme conditions. The present work develops a numerical tool with Scilab simulating the acid–base equilibria of titration. The program is efficient in predicting the experimental equivalent volumes obtained from Nordmann’s method with different combinations of sodium acetate and sodium bicarbonate contents. The mean absolute percentage errors (MAPE) between the simulation and experiment are below 7%. Two new formulas are developed, considering both equivalent volumes at pH = 5 and 4.4 to calibrate FOS and TAC values. The proposed formulas show their good performance in predicting various combinations of FOS and TAC contents in an anaerobic digestate at TAC ranging from 0 to 20,000 mg CaCO3·L−1 and FOS ranging from 0 to 31,000 mg HAc·L−1.

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.

Biochemical methane potential (BMP) is essential to determine the production of methane for various substrates; literature shows important discrepancies for the same substrates. In this paper, a harmonized BMP protocol was developed and tested with two phases of BMP tests carried out by eleven French laboratories. Surprisingly, for the three same solid tested substrates (straw; raw mix and dried-shredded mix of potatoes, maize, beef meat and straw; and mayonnaise), the standard deviations of the repeatability and reproducibility inter-laboratory were not enhanced by the harmonized protocol (average of about 25% depending on the substrate), as compared to a previous step where all laboratories used their own protocols. Moreover, statistical analyses of all the results, after removal of the outliers (about 15% of all observations), did not highlight significant effect of the operational effect on BMP (stirring, automatic or manual gas quantification, use of trace metal, uses a bicarbonate buffer, inoculum to substrate ratio) at least for the tested ranges. On the other hand, the average intra-laboratory repeatability was low, about 7%, whatever the protocol, the substrate and the laboratory. It also appears that drying the SA substrate, which contained proteins, carbohydrates, lipids and fibers, does not impact its BMP.

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.

Composting or anaerobic digestion of the grass mowed along roadsides is developing in France, but little information on grass contaminants (heavy metals and organic compounds) is available. During the CARMEN project, roadside grass was sampled in different locations in western France, during different mowing periods (spring and autumn) to evaluate the traffic load and seasonal influences. The project also involved other operations not detailed here: pilot anaerobic digestion tests and a cost-benefit study of mowing and exporting the grass to an anaerobic digester.

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).

In this paper, a state-of-art about solid anaerobic digestion (AD), focused on recent progress and trends of research is proposed. Solid anaerobic digestion should be the most appropriate process for degradation of by-products with high total solid (TS) content, especially lignocellulosic materials like agricultural waste (straw, manure), household waste and food waste. Solid AD is already widely used in waste water treatment plant for treating plant for sewage sludge but could be more developed for lignocellulosic materials with high TS content. Many research works were carried out in Europe on solid AD, focused on current hurdles (BMP, codigestion, inhibition, microbial population, rheology, water transfers, inoculum, etc.) in order to optimize the solid AD process. In conclusion, hurdles of solid AD process should and must be solved in order to propose better productivity and profitability of such system operating with high TS content (>15%), favouring reliable industrial processes.

Valorization of the grass which is mowed on roadsides is developing in France, and little information on contaminants (heavy metals and organic compounds) is available. During the CARMEN project, roadside grass was sampled on different locations in Western France, during different mowing periods (spring and autumn) in order to evaluate the trafic load and the seasonal influences. In addition, small scale AD tests were performed in order to evaluate the methane potential of grass and manure mixtures and contaminant transfer between the inputs: grass and manure and the ourputs : liquid phase and the digestate, in controlled conditions.

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.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Application of a geophysical tool to monitor liquid repartition during agricultural wastes degradation for biogas production Laura Andre, Edvina Lamy, Pascale Lutz, Morgane Pernier, André Pauss, Thierry Ribeiro

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.