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Accurately characterizing the substrate used in anaerobic digestion is crucial for predicting the biogas plant's performance. This issue makes particularly challenging the application of modeling in codigestion plants. In this work, a novel methodology called substrate prediction module (SPM) has been developed and tested, using virtual codigestion data. The SPM aims to estimate the inlet properties of the substrate based on the reverse application of the anaerobic digestion model n1 (ADM1). The results show that, while the SPM can estimate some properties of the substrate based on certain output parameters, there are limitations in accurately determining all required variables. HIGHLIGHTS Extensive substrate characterization is challenging, especially for codigestion.; A reverse modeling approach is proposed to estimate unknown substrate properties.; The substrate prediction module processes measured AD data based on the ADM1.; Two data processing strategies are assessed: 7-day moving block and daily data.; The SPM could estimate some substrate properties but there are limitations.;

Abstract Background New regulations and market conditions in Germany affect the profitability of biomethane upgrading as a repowering option for existing biogas plants following on-site CHP utilization. These conditions present trade-off challenges between higher sustainability requirements, maintaining production capacity and new revenue opportunities. Optimization methods, such as linear programming (LP), are essential for determining the ideal substrate mixture and profitable solutions amidst multiple market conditions, plant-specific process constraints, and substrate properties. Methods We updated a substrate mixture optimization model within an assessment framework for the repowering of existing biogas plants (BGPs), which focuses on the operator’s perspective. By integrating multiple German biomethane markets for various BGPs, we assessed changes in the substrate mixture, GHG emissions, contribution margins, and constraint parameters to derive conclusions for operators and future framework design. Results Integrating market revenues and constraints can increase contribution margins by 12–55%. Additional gains can be achieved by considering multiple markets simultaneously but limited to a few BGPs. The plant-specific LP solution space and used benchmark market are decisive. The former limits the potential of high substrate-specific contribution margins, which has a significantly higher impact than the relation between plant-specific characteristics and process constraints. The advanced fuel market is currently the lead market for biomethane, incentivizing GHG-emission extensive substrates, decreasing gas production and GHG emissions but increasing levelized cost of energy (LCOE) and partially CO2 abatement costs. Conclusions The key to improve profitability and to supply an increasing biomethane demand while fulfilling new requirements is a large LP solution space. Increasing market options, substrate availability, and digestion system capacity achieve this on the operator’s side. Policy makers could reduce normative requirements such as the maize cap or double counting of advanced fuels and favor high but uniform GHG requirements. Operators can prepare robustly for the future substrate mixture by adding digester volume and pre-treatment tech, ensuring long-term and diverse substrate availability, and contracts with flexible components. Although current market conditions can improve specific GHG emissions, they do not necessarily increase manure usage when other options, such as straw, are viable. Other regulatory support systems will be required to do so.

Background: New regulations and market conditions in Germany affect the profitability of biomethane upgrading as a repowering option for existing biogas plants following on-site CHP utilization. These conditions present trade-off challenges between higher sustainability requirements, maintaining production capacity and new revenue opportunities. Optimization methods, such as linear programming (LP), are essential for determining the ideal substrate mixture and profitable solutions amidst multiple market conditions, plant-specific process constraints, and substrate properties. Methods: We updated a substrate mixture optimization model within an assessment framework for the repowering of existing biogas plants (BGPs), which focuses on the operator's perspective. By integrating multiple German biomethane markets for various BGPs, we assessed changes in the substrate mixture, GHG emissions, contribution margins, and constraint parameters to derive conclusions for operators and future framework design. Results: Integrating market revenues and constraints can increase contribution margins by 12–55%. Additional gains can be achieved by considering multiple markets simultaneously but limited to a few BGPs. The plant-specific LP solution space and used benchmark market are decisive. The former limits the potential of high substrate-specific contribution margins, which has a significantly higher impact than the relation between plant-specific characteristics and process constraints. The advanced fuel market is currently the lead market for biomethane, incentivizing GHG-emission extensive substrates, decreasing gas production and GHG emissions but increasing levelized cost of energy (LCOE) and partially CO2 abatement costs. Conclusions: The key to improve profitability and to supply an increasing biomethane demand while fulfilling new requirements is a large LP solution space. Increasing market options, substrate availability, and digestion system capacity achieve this on the operator's side. Policy makers could reduce normative requirements such as the maize cap or double counting of advanced fuels and favor high but uniform GHG requirements. Operators can prepare robustly for the future substrate mixture by adding digester volume and pre-treatment tech, ensuring long-term and diverse substrate availability, and contracts with flexible components. Although current market conditions can improve specific GHG emissions, they do not necessarily increase manure usage when other options, such as straw, are viable. Other regulatory support systems will be required to do so. [ABSTRACT FROM AUTHOR]

Annually, a huge amount of waste from plant biomass and animal manure is produced from agriculture and animal farming. Many studies provide information on the biomethane potential of agricultural and livestock wastes, but only a few studies have investigated the application of the substrates in combination. The objective of the study is to enhance the fermentation process in the digester for biogas production, obtained from animal and plant waste substrates. In four batch processes for three months, the temperatures and the residence time of the substrates in the fermenter were analyzed. Simultaneously, electricity and thermal energy were produced via cogeneration units, which were exported to the public grid and city heating network. The plant substrate is a silage mixture of corn and wheat waste. The animal substrate is a mixture of beef and pig manure. Animal and vegetable waste raw materials are collected and transported to the site, located in the region of southeastern Bulgaria. The total annual consumption of animal and plant waste is 17,971 t/year. The enhancement of the process leads to the production of 1,506,000 Nm3 CH4/a of methane, the generation of which requires 299.63 MWh/a of electricity and 649.09 MWh/a thermal energy. [ABSTRACT FROM AUTHOR]

Annually, a huge amount of waste from plant biomass and animal manure is produced from agriculture and animal farming. Many studies provide information on the biomethane potential of agricultural and livestock wastes, but only a few studies have investigated the application of the substrates in combination. The objective of the study is to enhance the fermentation process in the digester for biogas production, obtained from animal and plant waste substrates. In four batch processes for three months, the temperatures and the residence time of the substrates in the fermenter were analyzed. Simultaneously, electricity and thermal energy were produced via cogeneration units, which were exported to the public grid and city heating network. The plant substrate is a silage mixture of corn and wheat waste. The animal substrate is a mixture of beef and pig manure. Animal and vegetable waste raw materials are collected and transported to the site, located in the region of southeastern Bulgaria. The total annual consumption of animal and plant waste is 17,971 t/year. The enhancement of the process leads to the production of 1,506,000 Nm3 CH4/a of methane, the generation of which requires 299.63 MWh/a of electricity and 649.09 MWh/a thermal energy.

The economic management of lignocellulosic biomass from semi-natural grasslands is now a challenge across Europe. The abandonment of mowing these grasslands leads to the gradual degradation of these ecosystems. This study investigates how chemical and biological factors affect the suitability of biomass from abandoned grasslands for biogas production. We sampled 30 mown and 30 abandoned grassland sites in the Sudetes Mountains (Poland and Czechia). The cover contribution of short herbs was found to be significantly higher in mown grasslands (p < 0.001), while that of tall herbs was more prevalent in abandoned grasslands (p < 0.01). The specific biogas yield (SBY, NL kg−1 volatile solids) is negatively affected by an increased percentage of herbs in the biomass of mown and abandoned grasslands. This is due to the inhibitory effect of herbs on biodegradation, the increase in lignin content and the decrease in cellulose. This study highlights the importance of individual plant species in assessing grassland biomass for area biogas yield (ABY, m3 ha−1) and provides new insights into a field that has not yet been extensively investigated. In mown grasslands, ABY was most positively correlated with grass species (Arrhenatherum elatius , Trisetum flavescens and Festuca pratensis). In abandoned grasslands, the ABY was most correlated with herbaceous species (Galium aparine , Urtica dioica and Chaerophyllum aromaticum) and grasses (A. elatius and Elymus repens). Mown grasslands had significantly higher species richness (p < 0.001) compared to abandoned grasslands, but the number of species sampled did not correlate with SBY and ABY. This study contributes to the development of a sustainable bio-economy by highlighting the need for efficient use of grassland biomass. This approach helps protect semi-natural ecosystems and facilitates sustainable management of renewable resources. • Certain grassland plant species significantly impact area biogas yield. • Species richness has no negative effect on specific and area biogas yield. • Grassland management maintains an appropriate ratio of herbs to grasses. • Biogas production from hay can help restore abandoned grassland. [ABSTRACT FROM AUTHOR]

[Display omitted] • Analyzed 75 biogas plant accidents (occurrences) globally from 1990 to 2023. • Identified occurrences' common causes and results and suggested preventive measures. • Correlation screened factors related to occurrences, their likelihood, and severity. • Causes are component fail > maintenance > NaTech > equipment > operation > No PPE. • Explosions are the most common accident type, forming 69.3% of all occurrences. Biogas plants numbers are increasing worldwide, but their safety record is rarely investigated. This paper analyzes 75 occurrences of various types of accidents in biogas plants worldwide between 1990 and 2023. The study comprehensively reviewed accident reports and research literature with input from plant operators and safety experts. We aim to identify the common causes and consequences of accidents (occurrences) and suggest preventive measures to improve safety. The occurrences' primary causes were component failure > maintenance error > natural and technological disasters (NaTech) > equipment failure > operational error > no personal protective equipment (PPE). The most common occurrences were gas explosions 69.3%, toxic gas releases (biohazard) 21.3%, asphyxia (biohazard) 4%, malfunctioning (electric and mechanical hazard) 2.7%, and fires 2.7%. The accident consequences ranged from minor injuries (76) to fatalities (51) and extensive property damage. Lack of PPE and gas pipelines (mechanical and biohazards) correlated positively and significantly (R2 = 0.70), while operational errors and asphyxia (biohazard) scenarios correlated positively and moderately (R2 = 0.55). The plant design, operating procedures, and maintenance practices strongly influence the occurrences' likelihood and severity. This study provides valuable insights for stakeholders, researchers, and policymakers interested in promoting biogas' safe and sustainable development. Future studies should investigate the relationship between plant size and accident frequency and assess the effectiveness of safety management and risk assessment methodologies in mitigating such occurrences. [ABSTRACT FROM AUTHOR]

Accurately characterizing the substrate used in anaerobic digestion is crucial for predicting the biogas plant's performance. This issue makes particularly challenging the application of modeling in codigestion plants. In this work, a novel methodology called substrate prediction module (SPM) has been developed and tested, using virtual codigestion data. The SPM aims to estimate the inlet properties of the substrate based on the reverse application of the anaerobic digestion model n1 (ADM1). The results show that, while the SPM can estimate some properties of the substrate based on certain output parameters, there are limitations in accurately determining all required variables., Competing Interests: The authors declare there is no conflict., (© 2024 The Authors This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY-NC-ND 4.0), which permits copying and redistribution for non-commercial purposes with no derivatives, provided the original work is properly cited (http://creativecommons.org/licenses/by-nc-nd/4.0/).)