3.1 Base scenario:
Table 3 outlines the environmental costs and impacts related to the production of one metric tonnes of molten steel, using data from the base scenario. The environmental costs are quantified at the midpoint level, as per the Environmental Prices approach, amounting to 462.72 euros per FU. The environmental impacts are delineated at both the midpoint and endpoint levels. Employing the ReCiPe method, eighteen categories at the midpoint level and three categories at the endpoint level were documented, featuring both characterized and normalized values.
The rate of global warming is quantified at 1593.5 kg CO2 eq / FU, signifying the rise in Earth's temperature due to the greenhouse effect, which is a consequence of greenhouse gas emissions (Joos et al. 2013). The potential for ozone depletion, measured in CFC11 equivalents, stands at 0.00048 / FU. Over an endless time horizon, it describes a time-integrated drop in the concentration of stratospheric ozone (NOAA CSL 2010). Ionizing radiation, expressed as 3 kBq Co-60 eq / FU, represents the cumulative dose from radionuclide emissions (M. A. J. Huijbregts et al. 2020). The formation of fine particulate matter is recorded at 1.82 kg PM2.5 eq / FU. This figure denotes the increase in PM2.5 concentration due to emissions of precursors like NH3, NOx, SO2, and primary PM2.5 (van Zelm et al. 2016).
Ozone formation, which impacts human health and ecosystems, is measured at 3.3 kg NOx eq / FU and 3.4 kg NOx eq / FU, respectively. These values reflect the concentration changes in ozone due to emissions of NOx or non-methane volatile organic compounds (NMVOC) (van Zelm et al. 2016). Terrestrial acidification, a significant shift from the ideal acidity for most plant species, is gauged at 3.6 kg SO2 eq / FU (M. Huijbregts et al. 2016). Eutrophication, resulting from nutrient discharge into soils or water bodies, is quantified at 0.02036 kg P eq / FU for freshwater and 0.00644 kg N eq / FU for marine environments (M. Huijbregts et al. 2016).
The impact of chemical emissions on freshwater, marine, and terrestrial ecotoxicity is characterized using 1,4-dichlorobenzene-equivalents, with toxicity values of 1050.4, 1.4, and 2.4 per FU, respectively (M. A. J. Huijbregts et al. 2020). Human toxicity potential, indicating the harm from environmental chemical releases, is noted at 5 kg 1,4-DCB / FU for carcinogens and 59.3 kg 1,4-DCB / FU for non-carcinogens (Joos et al. 2013). Land use, in terms of annual crop equivalents, is 2.8 m²a crop eq / FU. This metric assesses species loss due to various land use types (M. A. J. Huijbregts et al. 2020). Mineral resource scarcity is 75.3 kg Cu eq / FU, reflecting the future ore production increase due to current mineral extraction (Vieira et al. 2017).
Fossil resource scarcity, calculated as 606.5 kg oil eq / FU, compares the energy value of fossil resources to crude oil (Frischknecht et al. 2007). Water consumption is using water by assimilation into other processes, such as evaporation, product creation, transportation to other watersheds, or marine disposal. The water consumption per cubic meter of recycled water serves as the unit for the water consumption midpoint (Joos et al. 2013). The amount of water used is 9.7 m3 / FU.
At the endpoint level, the effects on human health, ecosystems, and resources are 0.00268 Disability Adjusted Life Years (DALY), 5.84E-06 species.yr, and 227.9 USD2013, respectively. Human health endpoint is measured in DALY, a measure of the years lost to illness or premature death (M. Huijbregts et al. 2016). The endpoint of ecosystems is the estimated number of species that, as a result of the activities that have been evaluated, should vanish in a given region during a given time (M. Huijbregts et al. 2016). The term resources endpoint describes how present resource use is driving up extraction costs and reducing the availability of resources in the future (M. Huijbregts et al. 2016). Previous studies have corroborated these findings for the baseline scenario (Ramezani Moziraji et al. 2023, Chen et al. 2018, Vieira et al. 2017).
The aggregate normalized midpoints and endpoints' environmental effect value for producing one tonne of molten steel are quantified at 8.1 pt and 0.12902 pt, respectively.
Table 3
environmental costs and impacts of base scenario.
Impact category | Environmental impact | Environmental costs (2021 euros /FU) |
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Midpoint | Chraracterized (unit / FU) | Normalized (pt / FU) | |
Global warming | 1593.521 (kg CO2 eq) | 0.19951 | 207.15771 |
Stratospheric ozone depletion | 0.00048 (kg CFC11 eq) | 0.00806 | 0.01404 |
Ionizing radiation | 2.98549 (kBq Co-60 eq) | 0.00621 | 0.01260 |
Ozone formation, Human health | 3.30223 (kg NOx eq) | 0.16049 | 7.16584 |
Fine particulate matter formation | 1.81916 (kg PM2.5 eq) | 0.07113 | 180.46066 |
Ozone formation, Terrestrial ecosystems | 3.38131 (kg NOx eq) | 0.19037 | 1.40663 |
Terrestrial acidification | 3.6293 (kg SO2 eq) | 0.08855 | 19.12639 |
Freshwater eutrophication | 0.02036 (kg P eq) | 0.03136 | 0.07615 |
Marine eutrophication | 0.00644 (kg N eq) | 0.00140 | 0.09181 |
Terrestrial ecotoxicity | 1050.442 (kg 1,4-DCB) | 1.01368 | 0.67228 |
Freshwater ecotoxicity | 1.38159 (kg 1,4-DCB) | 1.12600 | 0.02888 |
Marine ecotoxicity | 2.42557 (kg 1,4-DCB) | 2.35038 | 0.00776 |
Human carcinogenic toxicity | 5.02259 (kg 1,4-DCB) | 1.81315 | 20.04012 |
Human non-carcinogenic toxicity | 59.30704 (kg 1,4-DCB) | 0.39795 | 4.21080 |
Land use | 2.84795 (m2a crop eq) | 0.00046 | 0.28195 |
Mineral resource scarcity | 75.25761 (kg Cu eq) | 0.00063 | 1.05361 |
Fossil resource scarcity | 606.4838 (kg oil eq) | 0.61861 | 16.98155 |
Water consumption | 9.65094 (m3) | 0.03619 | 3.92793 |
Total | - | 8.11412 | 462.71669 |
Endpoint | | | |
Human health | 0.00268 (DALY) | 0.11273 | - |
Ecosystem | 5.84E-06 (species.yr) | 0.00815 | - |
resources | 227.88015 (USD2013) | 0.00814 | - |
Total | - | 0.12902 | - |
Figure 5a illustrates the relative importance of each midpoint category, with marine ecotoxicity, human carcinogenic toxicity, terrestrial ecotoxicity, and freshwater ecotoxicity collectively contributing to 78% of the total environmental impact. Figure 5b accentuates the significance at the endpoint level, revealing that the effects on human health possess the highest value at 88%. Subsequently, ecosystems and resources are impacted equally, each bearing 6% of the total environmental effects.
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Figure 5. Contribution of each a) midpoint and b) endpoint to environmental impacts. |
In the analysis of steel production, three principal stages were identified: sponge iron (DRI) consumption, electricity consumption, and the assortment of other inputs and outputs associated with steel production. Figure 6a and b delineate the proportional contribution of electricity usage, sponge iron consumption, and other inputs and outputs to liquid steel production within each midpoint and endpoint category, respectively. It was observed that most midpoint categories experienced significant adverse effects attributable to the consumption of sponge iron. Consequently, sponge iron consumption exerts an influence exceeding 50% at the endpoint level across all categories.
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Figure 6. Contribution of sponge iron, electricity, and other inputs and outputs to a) midpoints and b) endpoints. |
Figure 7a illustrates the distribution of environmental costs attributed to the consumption of electrical power, sponge iron, and other inputs and outputs in liquid steel production. Sponge iron is a significant contributor, accounting for 57% of the environmental costs. Subsequently, electricity consumption holds secondary importance, with the balance of the proportion not ascribed to any particular consumption or process encompassing all other inputs and outputs. Figure 7b details the percentage contribution of each midpoint category to the environmental costs. Notably, global warming and fine particulate matter formation represent 45% and 39% of the environmental costs, respectively.
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Figure 7. Contribution of a) sponge iron, electricity, and other inputs and outputs, and b) midpoints in environmental costs. |
3.2 Comparing different scenarios
Based on the preceding findings presented in Section 3.1, the LCA of one tonne of molten steel production in the base scenario was calculated. The study revealed that electricity consumption and the use of sponge iron had the most significant impact on environmental factors and costs. To mitigate these issues, two potential solutions were suggested: replacing conventional gas power plants with solar power plants and increasing the utilization of scrap instead of sponge iron. The consequences of these two options were tested in five different scenarios. The last scenario (VI) is mixed since it has the most remarkable shift in the scrap to sponge iron ratio and the source of electricity production.
Table 4S displays the characterized and normalized detailed results of a LCA of one tonne of molten steel manufacturing under five scenarios. Across most midpoint impact categories, adjusting the scrap-to-sponge-iron ratio proves more effective in reducing environmental impact and costs compared to altering the electricity production source. However, in specific cases (such as ionizing radiation, terrestrial ecotoxicity, and human carcinogenic toxicity), the opposite holds true.
Concerning total normalized midpoints, scenario II has the most signicant environmental impact with 8.3 pt, followed by scenarios IV, V, III, and VI with 7.7 pt, 7.2 pt, 7.1 pt, and 5 pt, respectively. Scenario VI is the most favorable across all midpoint categories, according to the characterized and normalized values. Considering the relationship between midpoint and endpoint impact categories, opting for increased scrap usage over sponge iron proves more effective in reducing impacts at the endpoint level. The ensuing figures represent the hierarchy of environmental effects predicated on normalized data at the endpoint level: Scenario IV stands at 0.11851 pt, Scenario II at 0.11059 pt, Scenario V at 0.10801 pt, Scenario III at 0.07301 pt, and Scenario VI emerges as the most favorable with 0.04037 pt. The environmental prices were successfully reduced for each scenario. In scenario VI, the environmental expenses decreased to 167.7 euros, a substantial reduction.
Scenario VI demonstrates superior carbon management, resulting in a reduction of 496.67 kg CO2 eq / FU in global warming potential. Additionally, it contributes to mitigating harm to the ozone layer, with a reduction of 0.00009 kg CFC11 eq / FU in stratospheric ozone depletion. Air quality improves due to reduced impact, as indicated by 1.37466 kg NOx eq / FU in terrestrial ecosystems and 1.39078 kg NOx eq / FU in human health ozone formation.The formation of fine particulate matter is lower, with 0.59305 kg PM2.5 equivalent, suggesting decreased emissions of fine particle-increasing pollutants. Soil chemistry, plant life, and biodiversity face less harm due to the 1.41558 kg SO2 / FU equivalent in terrestrial acidification. Freshwater and marine eutrophication are better managed, as evidenced by 0.01849 kg Peq / FU and 0.00387 kg Neq / FU, indicating more controlled nutrient runoff or emissions.
Scenario VI also shows improved management of toxic emissions or effluents, with 637.5 kg 1,4-DCB / FU in ecotoxicity across terrestrial, freshwater, and marine environments. Human carcinogenic and non-carcinogenic toxicity are addressed with lower emissions of harmful chemicals, at 6.52831 kg / FU and 28.7384 kg 1,4-DCB / FU, respectively. Resource use efficiency is highlighted by 1.51507 kg Cu eq / FU in mineral resource use and 64.13712 kg oil eq / FU in fossil resource use, pointing to more effective use or recycling. Ionizing radiation is minimized, with 1.34218 kBq Co-60 eq / FU, suggesting less use of radiative materials or better containment. Lastly, water consumption is optimized, with only 6.48111 m3 / FU used, reflecting a commitment to conserving this vital resource.
Figure 8a shows normalized data related to all scenarios in comparison with each other and the importance of each impact category at the midpoint level. According to Fig. 8a, environmental and human toxicities have the highest impact among all categories. Figure 8b presents the characterized data for all scenarios, comparing them individually at each midpoint level. In Fig. 8b, the highest scenario for each midpoint level is 100, and other scenarios are presented and compared to it. The base scenario exhibits the highest harmful impact across all categories, while the VI scenario emerges as the most favorable option in most midpoint assessments.
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Figure 8. a) Normalized value comparison of all scenarios at midpoints level, b) comparison of all scenario to the highest scenario in each midpoint level. |
Figure 9 shows the environmental prices at every midpoint level for all scenarios. According to Fig. 9, the base scenario is not the worst scenario at all midpoint levels, but scenario VI is the best scenario at all midpoints. Among all scenarios, the midpoints of global warming potential and particulate matter formation account for most environmental costs.
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Figure 9. Environmental price comparison of all scenarios at midpoints level. |
Figure 10a shows normalized data related to all scenarios in comparison with each other and the importance of each impact category at the endpoint level. Figure 10b presents the characterized data for all scenarios, comparing them individually at each endpoint level. Within each endpoint level, the paramount scenario illustrated in Fig. 10b is assigned a value of 100; the corollary scenarios are depicted in proportion to this benchmark. To Fig. 10a and b, it is discernible that the environmental impacts of the base scenario surpass those of the alternative scenarios, with Scenario VI being the most exemplary. The advancements in human health, ecosystems, and resources from the basic scenario to Scenario VI are quantified at 67.8%, 65.9%, and 91.6%, respectively.
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Figure 10. a) normalized value comparison of all scenarios at endpoints level, b) comparison of all scenario to the highest scenario in each endpoint level. |
3.3 Perspective comparison:
In Section 2.4, LCA using the ReCiPe method was categorized into three perspectives: hierarchist, individualist, and egalitarian. The assumptions behind each of these perspectives impact how the calculations proceed. In this section, a comparison of viewpoints was applied to scenario I and scenario VI. The characterized and normalized data for these circumstances from multiple perspectives are displayed in Table 5S. The results show no significant differences in key categories, including land use, water consumption, freshwater eutrophication, marine eutrophication, terrestrial ecosystems ozone formation, human health ozone formation, fossil resource scarcity, and terrestrial acidification. However, other impact categories exhibit distinct differences. For global warming, the individualist perspective indicates a more harmful impact compared to the egalitarian and hierarchist perspectives. Because many of the pollutants that contributed to global warming were eliminated over a long time horizon, but from an individual standpoint, a short time horizon (20 years) was adopted (M. Huijbregts et al. 2016).
Regarding mineral resource scarcity, the individualist perspective holds less value than the hierarchist and egalitarian perspectives. In hierarchical and egalitarian views, it is assumed that the estimation should be done based on extracting the total mineral resources available in the Earth’s crust. However, in the individualistic view, the analysis is based on the amount of extraction at the time of calculation and with the available technologies (M. Huijbregts et al. 2016). The formation of fine particulate matter is similar to the scarcity of mineral resources. The individualist perspective reported less value than the hierarchist and egalitarian perspectives. While the hierarchist and egalitarian viewpoints acknowledge that secondary aerosols contribute to particle formation, the individualist perspective contends that only primary aerosols impact fine particle formation (M. Huijbregts et al. 2016), (Avinal and Ergenekon 2022).
In the remaining midpoint impact categories, such as stratospheric ozone depletion, ionizing radiation, freshwater environmental toxicity, marine environmental toxicity, terrestrial environmental toxicity, human carcinogenic toxicity, and human and non-carcinogenic toxicity, the egalitarian perspective calculates more influence than the hierarchical and individualist perspectives. The egalitarian perspective considers a longer time horizon than the hierarchical perspective, and the hierarchical perspective, in turn, has a longer time horizon than the individualistic perspective. In addition, the egalitarian view considers more diseases caused by pollutants compared to the hierarchical and individualistic view, and the egalitarian perspective considers more protection in different cases (M. Huijbregts et al. 2016). The hierarchist viewpoint assumes that society prefers effects that are long-lasting, global, and certain. It is predicated on the belief that society will manage environmental problems with caution and is based on an expert consensus (Dong and Ng 2014). The individualist viewpoint assumes that, society favors immediate, focused, and local effects. It is predicated on an market-driven perspective and presumes that society will handle environmental effects following short-term requirements and advantages (Dong and Ng 2014). The egalitarian view assumes that society prefers effects that are broad, ambiguous, and long-term. Its foundation lies in a perspective that prioritizes fairness and equality, assuming that even in the face of uncertainty, society will manage environmental repercussions with caution (Dong and Ng 2014). The egalitarian approach reported the highest value among all endpoint groups, with the hierarchical and individualistic approaches following in second and third place, respectively.