Because biogas systems may take many forms, utilizing different feedstock and finding different end uses for the biogas, it is becomes difficult to produce explanations, inferences, and conclusions about biogas systems in general, which is why concepts for specific types of biogas systems are needed. This paper introduces the concept of the Nordic biogas model, an urban waste-based biogas system where biogas is upgraded to biomethane and used as transport fuel and the digestate applied as biofertilizer on farmland. The Nordic biogas model has three functions, namely, renewable transport fuel production, waste management service, and biofertilizer production that all bring secondary and tertiary positive societal effects, such as reduced climate gas emissions and productivity benefits to industry. This has implications for environmental and sustainability assessment of the Nordic biogas model as the multi-functionality must be considered when choosing reference scenarios, system boundary, and indicators to use within assessments. Finally, the paper discusses policy recommendations for supporting the implementation of the Nordic biogas model. Such policy should respect the multi-functionality of the Nordic biogas model by creating coherent policy mixes that neither neglect nor over-compensate for the multi-functionality of the Nordic biogas model.
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