The development, validation and initial results of an integrated model for determining the environmental sustainability of biogas production pathways

Biogas produced through Anaerobic Digestion can be seen as a flexible and storable energy carrier. However, the environmental sustainability and efficiency of biogas production is not fully understood. Within this article the use, operation, structure, validation, and results of a model for the environmental assessment of anaerobic biogas production pathways is discussed. The (Excel) BioGas Simulator or EBS model is capable of calculating the economic cost, efficiency, carbon footprint, and sustainability of small scale anaerobic digestion biogas production pathways (from 2000 up to 50000 ton/a biomass input). The results from the model are expressed in four main indicators: the economic cost in Net Present Value (NPV), the efficiency in Process Energy Returned On Invested or (P)EROI, the carbon footprint in Global Warming potential 100 year scale (GWP100), and the environmental impact in EcoPoints. The economic indicator is given in Euros in Net Present Value over a period of 25 years, the other indicators are given per Giga Joule of energy produced (e.g. kgCO2eq/GJ). The EBS model is based on a clear methodology, structured around the modular approach, energy and material flow analysis, and life cycle analysis. The modular approach separates the biogas production pathway into individual physical processes, which makes the model more transparent, flexible in use, and programmable with different settings. The aforementioned allows the research of several aspects of the biogas production pathway. Furthermore, the indication of sustainability in four clear indicators gives an understandable reference for comparison with other scenarios. Overall, the EBS model can help give insight on the sustainability of specific biogas production pathways and help indicate options for improvement. Results from the model indicate that from an energy efficiency and sustainability point of view, the anaerobic digestion process should be utilized for treating locally available waste feedstocks with the added advantage of producing energy, which should preferentially be used internally for powering the waste treatment process.