2.1.2. Life Cycle Inventory (LCI)

This phase aims to model the system via data collection. Data collection must follow the system boundaries and FU definition. Both scenarios are based on real case studies data from the operational power units. Data was collected within the time frame of one year. For the CCT units, data was collected from the technical project reports [12,13].

#### 2.1.3. Life Cycle Impact Assessment (LCIA)

LCIA comprises classification, characterization, normalization, and weighting process, where the energy and mass flows of the previous step are transformed into environmental impacts. These environmental impacts are calculated according to the selected impact method. Each substance of the assessed systems is multiplied by the characterization factors that determine the potential contribution to the specific environmental impact. An optional step for LCIA is normalization. Normalization enables the comparison between different impact categories. Normalization uses the dataset of the reference indicators of environmental impacts for the European region or worldwide. Thus, the results are values that show the contribution to the sum of European (or world) impacts in the specific environmental category [14].

In this study, the chosen LCIA method is the ReCiPe v.1.08 method of GaBi software at the midpoint level. Based on Carvalho et al. [2], the ReCiPe method is the LCIA, which is intended and tailored for the comprehensive environmental process impact assessment. Also, the ReCiPe method is highly recommended by the EU commission [15]. The characterized midpoint environmental indicators are ozone depletion (OD), human toxicity (HT), ionizing radiation (IR), photochemical oxidant formation (POF), particulate matter formation (PMF), terrestrial acidification (TA), climate change (CC), terrestrial ecotoxicity (TET), agricultural land occupation (ALO), urban land occupation (ULO), natural land transformation (NLT), marine ecotoxicity (MET), marine eutrophication (ME), fresh water eutrophication (FE), fresh water ecotoxicity (FET), fossil depletion (FD), metal depletion (MD), and water depletion (WD) [16].

#### 2.1.4. Interpretation

In this phase, the results are further processed and discussed. The interpretation identifies the significant environmental problems and suggests the optimization of the process toward lowering the impacts. Moreover, it describes the hotspots from assessed processes and indicates significant impact categories. The identification of the significant environmental problems can be done through a Pareto analysis, using the statistical Pareto rule (80/20 rule) [17]. It determines that 20% of all impact categories contributes to 80% of the total environmental impact [2]. Data for Pareto analysis is normalized.

To summarize, the LCA method used in this study was performed by the ReCiPe method. The characterization and normalization were done according to the midpoint level of ReCiPe v 1.08. Moreover, additional Pareto analysis were done to specify key environmental impacts, and further analysis of the concrete processes was made to identify the influence on the environmental impacts.
