## 3 Methodology and Data  
In the last decades, life cycle assessment (LCA) methodology is commonly used in the literature for evaluating the environmental performance of the entire life cycle of the products, processes, or production systems. The LCA algorithm is described in the series of ISO 14040-14043 standards and consists of the following four main stages:  
(1) Goal and scope definition. At this stage, a researcher has to determine the research objective, define the functional unit, and set the system's boundaries. When determining the system's boundaries, most researchers use the \"cradle-to-grave\" or \"cradle-to-gate\" approaches. In a \"cradle-to-gate\" approach, life cycle stages such as extraction of raw materials, transportation, processing of materials, and manufacturing of the product are taken into account. When using the \"cradle-to-grave\" approach, steps such as the usage and final disposal of the product are additionally taken into account. (2) Life cycle inventory (LCI). At this stage, a complete map of the studied life cycle is constructed as a sequence of production and transportation processes. The inputs of each production/transportation process (such as raw materials, water, and energy consumption), intermediate processes, and outputs (such as main product, by-product, wastes, and emissions to the air, water, and soil) are determined. As a rule, a specific production process that occurs at a particular enterprise, including its supply chain, is investigated. If some stage of the life cycle exists so far only as a laboratory (experimental) process and has various scenarios, then averaged data from various sources can be used for calculations. If the \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Method**} & \multicolumn{2}{c}{**Fibrous Recyclate**} & \multicolumn{2}{c}{**Retained Tensile Strength of Recycled**} \\  & **Yield Rate, \%** & **Fibre Compared to Virgin Fibre, \%** & **Energy Demand, MJ/kg** \\ \hline Landfill & 0 & 0 & 0.26 \\ \hline \multirow{2}{*}{Mechanical} & \multirow{2}{*}{55–58\%} & GF—78\% & \multirow{2}{*}{0.27} \\  & & CF \textless{} 50\% & \\ \hline \multirow{2}{*}{Pyolysis} & \multirow{2}{*}{67–70\%} & GF—52\% & \multirow{2}{*}{21.2} \\  & & CF—78\% & \\ \hline \multirow{2}{*}{Fluidised-bed process} & GF—42-44\% & GF—50\% & GF—22.2 \\  & CF—86–90\% & CF—75\% & CF—9.0 \\ \hline \multirow{2}{*}{Chemical} & \multirow{2}{*}{100\%} & GF—58\% & \multirow{2}{*}{19.2} \\  & & CF—95\% & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of end-of-life (EoL) treatment methods for wind turbine blades. Source: based on data of [49]. processes are not yet profoundly understood, their inventories are incomplete. In such cases, the results of inventory analysis often complement sensitivity analysis. (3) Life cycle impact assessment (LCIA). At this stage, the identified potential environmental impacts of the production system are translated into such categories as global warming, acidification, ecotoxicity (human, marine, or terrestrial), ozone depletion, abiotic depletion, and eutrophication. Indicators for measuring these environmental impact categories are determined by one of the following mature methods of LCIA: CML 2001, Cumulative Energy Demand (CED), eco-indicator 99, EDIP, ILCD, ReCiPe, IPCC, or IMPACT 2002+. Some methods (for example, CML 2001) allow the translation of all the adverse environmental effects of the product life cycle into physical units, such as kg CO\({}_{2}\)-eq, kg NOx-eq, kg PO\({}_{4}\)-eq, and kg 1.4-DCB-eq. Others (for example, ReCiPe endpoint) allow the aggregation of all the negative effects in all categories into a single dimensionless quantity). The choice of methodology mainly depends on the preferences of the researcher and the objectives of the study. (4) Interpretation. At this stage, a researcher summarizes the LCI and LCIA results, identifies critical points of the life cycle with the most considerable adverse effects, and makes recommendations for possible improvements.