## 2 Materials and LCA Methodology  
Simapro LCA software (version 9.4) was employed in this study, using its pre-configured default databases. The LCA was carried out following the LCA framework defined by the ISO 14040 standard (2006) for the life cycle inventory (LCI) phase. The literature suggests that uncontrolled methane emissions from biogas plants, primarily due to leakages, can account for approximately 2% of the total biogas produced [11]. Additionally, open-air lagoon storage of digestate is a notable source of emissions, releasing an estimated 4.465 kg of methane (CH\({}_{4}\)) and 0.115 kg of ammonia (NH\({}_{3}\)) per tonne of anaerobic digestion (AD) feedstock [39]. Furthermore, after the digestate is applied to land, an additional 0.677 kg of ammonia per tonne of AD feedstock is emitted [36]. For this study, the anaerobic digestion (AD) and biogas reforming plants were assumed to operate over a 20-year lifespan, with 8000 operational hours annually (equivalent to approximately 333 days per year under continuous operation). At the end of their operational lifespan, the infrastructure is decommissioned and dismantled.  
Component materials, including steel, concrete, and catalysts, are managed through end-of-life pathways, such as landfilling, recycling, or inceration, with associated environmental impacts (e.g., landfill emissions, energy recovery from inceration) incorporated into the LCL. These assumptions align with circular economy principles and ISO 14044 stan  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Ref.** & **Software** & **Type of Data** & \begin{tabular}{c} **Background** \\ **Database** \\ \end{tabular} & **EU.** & \
\begin{tabular}{c} **System** \\ **Boundaries** \\ \end{tabular} & **LCIA** &
\begin{tabular}{c} **Global Warming** \\ **(kg CO\({}_{2}\)-eq)/FU** \\ \end{tabular} \\ \hline
dards, ensuring comprehensive accounting of material flows across the system's lifetime. Data for this study were sourced from the Ecoinvent default database (version 3.1) [11; 26], as integrated into Simapro 9.4. Construction material data were projected by scaling from a 300 m\({}^{3}\) AD plant in the Ecoinvent database to an 800 m\({}^{3}\) capacity AD system [11]. However, the construction material requirements (concrete, iron, aluminum, steel, etc.) for the reforming plant were adapted from Ref. [34]. This section outlines the methodological framework employed in this study, detailing the goal and scope definition, system boundaries, LCI data collection, and life cycle impact assessment (LCIA) methodology. The analysis followed the ISO 14040 and ISO 14044 standards for LCA.  
According to ISO 14040-14044 standards [11], the methodological framework of LCA consists of four interconnected stages (Figure 3): (1) The goal and scope stage defines the objectives of the study, establishes the system boundaries (SBs), and identifies the functional unit (FU), which serves as a reference point for all input and output data. (2) In the life cycle inventory (LCI) stage, material and energy flows are quantified for each process within the SBs, and these flows are then estimated and distributed accordingly. (3) The life cycle impact assessment (LCIA) stage evaluates the potential environmental impacts based on the LCI results. (4) The final stage is interpretation, where the life cycle model is assessed to identify key issues using the LCI and LCIA results, check for consistency and completeness, and support decision-making and recommendations. LCA finds environmental hotspots in systems. It helps people find and choose production methods that might be more sustainable by looking at their effects on the environment [36]. The process involves evaluating various ecological factors, such as acidification potential, global warming potential, resource depletion potential, and eutrophication potential [12].