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Item type:Publication, Access status: with files , Long-term continuous anaerobic co-digestion of residual biomass—model validation and model-based Investigation of different carbon-to-nitrogen ratios(2025-06-17); ; ; Major challenges in using lignocellulosic residues as biogas substrates arise from their high diversity and their typically low nitrogen content, which may not provide sufficient nitrogen for the microorganisms. To investigate to what extent such substrates can be used in biogas plants without extensive pre-treatment, this study presents a 300-day continuous co-digestion of lignocellulosic substrates (i.e., sugarcane reed, lemon, and grape leaves) and goat manure while continuously monitoring various process parameters. The results suggest a stable and effective biogas production at a carbon-to-nitrogen ratio (C/N ratio) of 33, with a production of 244 ± 15 mLngvs⁻¹ d ⁻¹ biogas. At a higher C/N ratio of 43, the process remained stable, but hindrance was encountered. Process failure occurred at a C/N ratio of 52, where a rapid decline in biogas production was observed, accompanied by an increase in the volatile fatty acids to total alkalinity ratio (from < 0.2 to 0.9), a drop in the pH-value (from > 7 to 5.4), and an increased CO₂-content of the provided biogas (from > 50% to 43%). The compositional analysis of the digestate suggests an insufficient N-supply and a failure of the carbonate and ammonium buffer systems inside the reactor. The experiment also served to validate a previously developed model based on the individual substrates’ degradation kinetics. With a relative root mean square error rRMSE of 8%, the model adequately predicted biogas production within defined limits. However, it could not anticipate process breakdown at high C/N ratios, highlighting a strong limitation.Publicationtype: Journal Article29 21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The Influence of Co-product Handling Methodology on Greenhouse Gas Savings of Biofuels in the European Context(2017-08-19); The handling of multi-output systems presents a crucial aspect of greenhouse gas (GHG) emission calculation as well as the certification of biofuels, and finding a robust and applicable method that accounts for distinctive characteristics of and benefits generated by all products is a challenge. In this work, GHG emission savings of 11 biofuel production concepts are assessed and the implications of methodological assumptions are discussed by applying the methodology defined by the Renewable Energy Directive (RED), allocation based on physical parameters, two hybrid approaches, as well as six variants of substitution. GHG emission savings according to RED methodology range from 35 to 57 %. Sugar beet-based ethanol shows highest savings. Results reveal that GHG savings according to the RED methodology present, in sum, a relatively good approximation of emission savings occurring due to substitution effects under given assumptions. An introduction of credits for products that are barely or not considered by the RED methodology due to allocation based on the lower heating value (LHV), i.e. fertilizers and wet feed co-products, reduces the difference between RED results and results based on substitution. If displacement mechanisms are considered by substitution, sugar beet-based ethanol, ethanol production by wet milling of wheat and sunflower biodiesel result in highest emission savings under given assumptions if oil that needs to be supplied due to occurring displacement mechanisms stems from rapeseed. The implementation of a method that supports concepts with high emission saving potential, e.g. allocation based the lower heating value of dry material, could promote emission reductions from biofuel provision.Publicationtype: Journal Article136