## 2 Materials and Methods
### Environmental Impact Assessment  
In order to quantify the environmental impact of the LCI adopted in the study, the life cycle impact assessment (LCIA) has been adopted. The impact assessment process is made of three main phases: (i) characterization, (ii) normalization, and (iii) weighting. The first step concerns the classification of the emissions into impact categories and their characterization in common units, allowing a direct comparison. In this study, the impact assessment has been performed following the methodology proposed by the Joint Research Center, Institute for Environment and Sustainability (JRC-IES), in accordance with the International Reference Life Cycle Data system (ILCD). In the ILCD guidance document [46], a detailed description of models, methods, and methodological choices is provided. The JCR-IES recommendations are based on existing models evaluated in the general framework of the three conventional areas of human health, natural environment, and natural resources ([37]), and suggest the following impact categories: Acidification; Climate change (100 year horizon); Freshwater (ecotoxicity and eutrophication); Human toxicity (carcinogenics and non-carcinogenics); Ionizing radiation (ecosystems and human health); Land use; Marine eutrophication; Ozone depletion; Particulate matter/Respiratory inorganics; Photochemical ozone formation; Mineral, fossils and renewables resource depletion; Water resource depletion; and Terrestrial eutrophication.  
This work has given relevance to nine impact categories in particular, from the ILCD 2011 Midpoint+ methodology, based on their characteristics:  
* global warming: 100-year time horizon global warming potentials [47] are used for the assessment of climate change category. It is measured in terms of CO\({}_{2}\) equivalent indicator and referred to greenhouse gas emissions throughout the study;
* land use: impact category reflects the damage to ecosystems due to the effects of occupation and transformation of land;
* minerals, fossils, and renewable resource depletion: impact category considers variation on their availability;
* water resource depletion: category addressing the use of water in relation to the scarcity of this fundamental and primary resource;
* acidification: category addressing the impacts generated by the emission of airborne acidifying chemicals. It refers literally to processes that increase the acidity of water and soil systems by hydrogen ion concentration. It is caused by atmospheric deposition of acidifying substances generated largely from emissions of nitrogen oxides(NO\({}_{x}\)), sulphur dioxide (SO\({}_{2}\)), and ammonia (NH\({}_{3}\)), the latter contributing to acidification after its nitrification in the soil;
* human toxicity: category based on models that account for particular chemical compounds in the environment, human exposure, and differences in toxicological response;
* ecotoxicity and eutrophication of freshwater: two categories addressing the impacts not only from the macro-nutrients, nitrogen and phosphorus, in bio-available forms on aquatic and terrestrial ecosystems, but also, similarly to human toxicity, from chemical compounds in the environment, species exposure, and differences in toxicological response;
* terrestrial eutrophication: category addressing the excess atmospheric nitrogen deposition causing damages on ecosystems and biodiversity.  
In addition, the energy consumption of the investigated processes has been analyzed and considered based on the Cumulative Energy Demand (CED) methodology. The method is suited to determine and compare the energy intensity of different processes [48; 49].