*2.1. System Boundary*

This study considered a "cradle-to-grave" system boundary, encompassing both the technical and environmental impacts in the construction and operation of SSAD plants at various scales. The system boundary, as described in Figure 1, was divided into four main parts:


**Figure 1.** System boundary.

This study did not examine the processes related to the SSAD plant construction, as the material use and key manufacturing processes are unclear. Similarly, the inputs and processes related to the disposal of the plant were also not considered and are outside the study scope. Additionally, the inputs related to the production of farm equipment (e.g., tractors, machines) were not included in the system boundaries, due to the uncertainty regarding their energy input. All simulations were created and run using the software package Microsoft Office Excel (Microsoft Office 2016, Microsoft Corporation, Redmond, WA, USA).
