minerals

Article Environmental Evaluation of Gypsum Plasterboard

Karin Weimann 1,*, Christian Adam 1, Matthias Buchert 2 and Juergen Sutter 2

1 Division Thermochemical Residues Treatment and (FB 4.4), Bundesanstalt für Materialforschung und -Prüfung (BAM), Unter den Eichen 87, D-12205 Berlin, Germany; [email protected] 2 Division Resources & Transport, Oeko-Institute, Rheinstrasse 95, 64295 Darmstadt, Germany; [email protected] (M.B.); [email protected] (J.S.) * Correspondence: [email protected]

Abstract: Gypsum is widely used in the construction sector, and its worldwide consumption has been increasing for several decades. Depending on the lifetime of the used gypsum products, an increase of gypsum in construction and demolition follows. Especially against the background of a circular economy, the recycling of waste gypsum is of growing importance. However, the use of recycled gypsum only makes sense if it is environmentally friendly. Therefore, an evaluation of the environmental impacts of industrial-scale processing for the recycling of post-consumer gypsum waste was conducted. The evaluation was performed with an established life cycle assessment software. Original data provided by the industry and complementary data from a database for life cycle assessments were used for the calculations. Two scenarios for recycled gypsum with different transportation distances were calculated. These results were compared with the results of the environmental evaluation of gypsum derived from coal-fired power plants (FGD gypsum) and natural gypsum. The results showed that the utilization of recycled gypsum can be environmentally advantageous compared to the use of natural gypsum or FGD gypsum, especially in the impact   categories of land transformation and resource consumption (abiotic depletion potential). For most environmental impact categories, the specific transportation distances have a strong influence. Citation: Weimann, K.; Adam, C.; Buchert, M.; Sutter, J. Environmental Keywords: gypsum plasterboards; gypsum waste; recycled gypsum; environmental evaluation; LCA Evaluation of Gypsum Plasterboard Recycling. Minerals 2021, 11, 101. https://doi.org/10.3390/min11020101

Academic Editor: Carlos 1. Introduction Hoffmann Sampaio The use of secondary building materials can meet the requirements of sustainability Received: 23 December 2020 in several ways: the extended time availability of primary raw materials and, thereby, the Accepted: 15 January 2021 protection of natural resources, as well as the conservation of landfill sites. Depending on Published: 21 January 2021 the respective circumstances, other environmental impacts like the emission of greenhouse gases could also be reduced [1]. Due to the large quantities of required raw materials Publisher’s Note: MDPI stays neutral and, also, the high volumes of construction and demolition waste (CDW), the of with regard to jurisdictional claims in waste from the building sector is of high importance for the reduction of waste masses published maps and institutional affil- in general and, also, for a circular economy [2,3]. Accordingly, many studies have been iations. conducted to perform life cycle assessments (LCA) for several aspects of the building material cycles [2,4]. There are already established procedures to recycle and reuse mineral waste materials in civil construction. Due to the large amounts and the material properties of concrete and Copyright: © 2021 by the authors. concrete waste, several studies have been performed to use crushed concrete as environ- Licensee MDPI, Basel, Switzerland. mentally friendly recycled concrete aggregates (RCA) [5]. These recycling procedures are This article is an open access article already applied in practice [1]. Furthermore, various approaches have been made to find distributed under the terms and new procedures and applications for the reuse of different CDW components. Colman et al. conditions of the Creative Commons investigated the use of the sand fraction from the CDW pieces as an additive in mortar Attribution (CC BY) license (https:// production [6]. Due to material properties like elevated water absorption or contamina- creativecommons.org/licenses/by/ tions, this sand fraction can usually not be used as an RCA. The authors found the material 4.0/).

Minerals 2021, 11, 101. https://doi.org/10.3390/min11020101 https://www.mdpi.com/journal/minerals Minerals 2021, 11, x FOR PEER REVIEW 2 of 13

Minerals 2021, 11, 101 2 of 13 mortar production [6]. Due to material properties like elevated water absorption or con- taminations, this sand fraction can usually not be used as an RCA. The authors found the material suitable for mortars and determined that even the gypsum residues in this frac- suitable for mortars and determined that even the gypsum residues in this fraction did not tion did not affect the mechanical properties of the new mortars. affect the mechanical properties of the new mortars. In a study from Azevedo et al., solid waste from the red ceramic industry was used In a study from Azevedo et al., solid waste from the red ceramic industry was used for geopolymer synthesis [7]. It was found that this waste has a great potential to be used for geopolymer synthesis [7]. It was found that this waste has a great potential to be used as the raw material for obtaining ceramic roof tiles by means of geopolymeric reactions. as the raw material for obtaining ceramic roof tiles by means of geopolymeric reactions. Amaral et al. worked on a methodology for the partial replacement of natural sand in Amaral et al. worked on a methodology for the partial replacement of natural sand in mortars by ornamental stone-processing waste [8]. They used a mathematical model for mortars by ornamental stone-processing waste [8]. They used a mathematical model for the calculation of an optimal particle size contribution. The results indicated a possibility the calculation of an optimal particle size contribution. The results indicated a possibility to produce eco-friendlyto produce mortars eco-friendly from that mortars waste. from Marvila that waste. et al. developed Marvila et al.a mixture developed of a mixture of gypsum plastergypsum and rock plaster waste and for rock the wasterepairs for of the historical repairs ofbuildings historical [9]. buildings This investiga- [9]. This investigation tion showed promisingshowed promising results in renderings results in renderings to repair the to repairstudied the buildings, studied buildings,namely when namely when 25% 25% of the sandof was the sandreplaced was by replaced rock waste. by rock waste. In recent years,In gypsum recent years, as a building gypsum mate as a buildingrial has attracted material attention. has attracted It has attention. been It has been widely used inwidely constructions used in in constructions the last decades, in the and last its decades, consumption and its has consumption increased hasin increased in many countries.many Figure countries. 1 shows Figure the develo1 showspment the of development the gypsum of consumption the gypsum in consumption Germany in Germany and the U.S. sinceand 1900. the U.S. These since numbers 1900. These include numbers gypsum include that arises gypsum as side that product arises as from side product from coal-fired powercoal-fired plants (FGD power gypsum). plants (FGDBetween gypsum). 2000 and Between 2019, the 2000 quantity and 2019,of FGD the gyp- quantity of FGD sum was aboutgypsum seven million was about tons each seven year million in Germany tons each [10]. year In in2019, Germany the contained [10]. In quan- 2019, the contained tity of FGD gypsumquantity in the of U.S. FGD was gypsum 22.9 mill inion the tons U.S. [11]. was The 22.9 estimated million tonsglobal [11 production]. The estimated global of gypsum in 2019production was 140 of million gypsum tons in 2019[12]. Accordingly, was 140 million a rise tons of [gypsum12]. Accordingly, waste (GW) a rise of gypsum in CDW is expectedwaste in (GW) the upcoming in CDW is years, expected andin the the importance upcoming of years, gypsum and recycling the importance is a of gypsum growing issue recycling[13,14]. Currently, is a growing the issue gypsum [13,14 demand]. Currently, is covered the gypsum (at least demand 60%) isby covered FGD (at least 60%) gypsum in Germany.by FGD The gypsum natural in gypsum Germany. deposits The natural fulfil gypsumthe remaining deposits gypsum fulfil thedemand remaining gypsum [10]. Due to thedemand national [10 clim]. Dueate protection to the national goals climateand the protection related shutdown goals and of thecoal-fired related shutdown of power plants, thecoal-fired FGD gypsum power plants,supply thewill FGD decr gypsumease significantly supply will in the decrease future. significantly Addition- in the future. ally, the availableAdditionally, extraction the areas available will not extraction be approved areas willdue not to nature be approved conservation due to nature rea- conservation sons. Therefore,reasons. the recycling Therefore, of gypsum the recycling waste is a of contribution gypsum waste to solving is a contribution future gypsum to solving future demand problems.gypsum demand problems.

(a) (b)

Figure 1.Figure Gypsum 1. Gypsum consumption consumption in Germany in Germany (a) and the (a) USA and the (b) USAin Mt/a (b) [15–17]. in Mt/a [15–17].

Gypsum is suitableGypsum for closed-loop is suitable forrecyclin closed-loopg due to recyclingits chemical due composition. to its chemical It con- composition. It sists mainly of consistscalcium mainlysulfate in of the calcium form of sulfate three incrystalline the form phases of three with crystalline varying hydra- phases with varying . tion levels: calciumhydration dihydrate, levels: CaSO calcium4 2H dihydrate,2O (calcium CaSO sulfate4·2H dihydrate,2O (calcium typically sulfate called dihydrate, typically · gypsum), CaSOcalled4 (anhydrite), gypsum), and CaSO calcium4 (anhydrite), sulfate hemihydrate, and calcium CaSO sulfate4 0.5H hemihydrate,2O (bassanite). CaSO 4 0.5H2O While gypsum(bassanite). and anhydrite While are gypsum naturally and oc anhydritecurring minerals, are naturally calcium occurring sulfate minerals, hemihy- calcium sulfate drate can be producedhemihydrate by dehydration can be produced in the thermal by dehydration treatment in of the gypsum thermal at a treatment tempera- of gypsum at ◦ ◦ ture range betweena temperature 125 °C and range 180 °C between (Equation 125 (1)).C andThis 180 reaction,C (Equation called calcination, (1)). This is reaction, called

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calcination, is reversible and, in contact with water calcium sulfate hemihydrate, is again transformed into calcium sulfate dihydrate in an exothermal reaction (Equation (2)) [14,18].

125◦C – 180◦C CaSO4·2H2O > CaSO4·0.5H2O + 1.5H2O (1)

Hydration CaSO4·0.5H2O + 1.5H2O > CaSO4·2H2O + Energy (2)

Hemihydrate and anhydrite can be found in various crystalline structures or modi- fications. These modifications have differing material characteristics that allow various technical applications, according to their particular material properties [19,20]. Most of the gypsum products are used in the construction industry. While gypsum can be applied in cement production to adjust the setting time, its main application area is usage for interior fittings in buildings. Besides its utilization in plaster, decorative elements, or screeds, a large proportion of gypsum is installed in the form of drywalls, wallboards, and, especially, gypsum plasterboards [14,21]. In many countries, gypsum plasterboards are of particular importance, because they make up the highest amount of used gypsum in buildings [3,22]. Approximately 734,000 tons of gypsum plasterboard waste was generated in the year 2015 in Northern Europe alone [23]. The reversibility of the hydration and dehydration of calcium sulfate dihydrate (see Equations (1) and (2)) is comparably easy to proceed. This is essential for the recycling of gypsum waste. In general, the recycling of GW can be divided into two main stages: the collecting and preparation of GW and the calcination. An important factor for the usability of recycled gypsum is also the quality, especially the purity of the GW [24,25]. The separation of the GW from the rest of the CDW is also appropriate for another reason: sulfates are unwanted in other secondary building materials (particularly in recycled concrete aggregates) and should be minimized in these waste materials for quality reasons as well [26,27]. Therefore, the demolition, the selective dismantling, has to be carried out carefully [28]. In this context, the recycling of gypsum plasterboard waste (GPW) is advantageous, because plasterboards are comparatively easy to dismantle and to collect separately so that impurities can be minimized or almost completely avoided [14,21,28]. Gypsum plaster- boards consist of gypsum embedded between cardboards. In the recycling process, these two materials have to be separated. Accordingly, a number of studies have been conducted to investigate the recycling of GW and GPW in the last several years. Many investigations focused on the calcination process. Different temperatures and holding times and, also, the material properties of the recycled gypsum were investigated. Ahmed et al. produced a recycled gypsum plas- ter from GW at a temperature range of 130–160 ◦C[29]. A paper from Brazil described the building material properties of recycled gypsum plaster waste after calcination at ~150 ◦C[30]. Camarini et al. tested recycled gypsum after calcination at temperatures between 120 ◦C and 200 ◦C[13]. The building material properties of the recycled gypsum in these investigations were of good quality. Camarini et al. also determined the energy consumption and found the process environmentally advantageous. The properties of recycled gypsum from gypsum plasterboards after up to five recycling cycles were inves- tigated by Erbs et al. [3,22]. The tests showed that the reversibility of gypsum hydration enabled the generation of recycled gypsum in three cycles without losses in the building material properties. The environmental impacts of gypsum recycling have also been investigated. Pantini et al. investigated strategies for the recycling of GW in a specific region in Italy [31]. The authors evaluated the environmental impacts of gypsum recycling in four scenarios on a theoretical basis. The study found out that the transporting distances have a significant influence on environmental impacts in the investigated system. A study about the recycling of gypsum plasterboards in Sweden also concluded the importance of the sorting accuracy and an optimization of the transporting distances for the support of gypsum recycling [32]. Minerals 2021, 11, x FOR PEER REVIEW 4 of 13

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recycling [32]. Pedreno-Rojas et al. compared the environmental impacts of the natural gypsum production and the production of recycled gypsum from pre-consumer gypsum wastePedreno-Rojas in Spain. et The al. LCA compared evaluated the environmental the processing impacts for natural of the and natural recycled gypsum gypsum, produc- in- tion and the production of recycled gypsum from pre-consumer gypsum waste in Spain. cluding calcination, but without transport. The results showed significantly lower envi- The LCA evaluated the processing for natural and recycled gypsum, including calcination, ronmental impacts from the production of recycled gypsum [33]. Another LCA in Spain, but without transport. The results showed significantly lower environmental impacts from conducted by Suarez et al., also compared recycled and natural gypsum. In this investi- the production of recycled gypsum [33]. Another LCA in Spain, conducted by Suarez et al., gation, the results for recycled gypsum were also lower in all impact categories. However, also compared recycled and natural gypsum. In this investigation, the results for recycled the low transport distances (seven km) influenced these results [34]. gypsum were also lower in all impact categories. However, the low transport distances This paper focusses on recycling GPW and the environmental impacts resulting from (seven km) influenced these results [34]. the related handling and processing in Germany. The recycling process was evaluated on This paper focusses on recycling GPW and the environmental impacts resulting from the industrial scale, and the assessment included real transportation distances as well [21]. the related handling and processing in Germany. The recycling process was evaluated on This evaluation filled the gap between gypsum recycling on a lab scale and the validation the industrial scale, and the assessment included real transportation distances as well [21]. ofThis the evaluation transportation filled theand gapgypsum between recycling gypsum un recyclingder real conditions. on a lab scale Furthermore, and the validation the re- sultsof the were transportation derived from and the gypsum recycling recycling of post-consumer under real conditions. GPW and with Furthermore, regards to the recycled results gypsumwere derived that meets from the the comparably recycling of high-qualit post-consumery standards GPW andfor gypsum with regards that are to required recycled fromgypsum the thatGerman meets gypsum the comparably industry [24,25,35]. high-quality standards for gypsum that are required from the German gypsum industry [24,25,35]. 2. Materials and Methods 2. MaterialsThis environmental and Methods evaluation was performed to calculate the ecological effects of the productionThis environmental of recycled evaluation gypsum wasfrom performed post-consumer to calculate gypsum the ecologicalplasterboard effects waste of theon anproduction industrial of scale. recycled The gypsumevaluation from included post-consumer a comparison gypsum with plasterboard data from the waste extraction on an ofindustrial natural gypsum scale. The and evaluation the use of included FGD gypsum. a comparison To clarify with the datainfluence from of the transportation extraction of fornatural the evaluation gypsum and of thethe useproduction of FGD gypsum.of recycled To gypsum, clarify the two influence calculations of transportation with different for transportationthe evaluation ofdistances the production were conducted. of recycled A gypsum,ccordingly, two calculationsfour model withscenarios different were trans- de- signed.portation distances were conducted. Accordingly, four model scenarios were designed. The environmental evaluationevaluation was was based based on on the the international international standard standard for for life life cycle cycle as- assessmentssessments ISO ISO 14040/44 14040/44 [36 [36,37].,37]. The The calculation calculation of of material material flows flows and and energy energy consumption consump- tionwas carriedwas carried out with out Umberto with Umberto (Umberto (Umberto NXT universal, NXT universal, IFU Institut IFU fuer Institut Umwelttechnik, fuer Um- welttechnik,Hamburg, Germany), Hamburg, a Germany), software for a lifesoftware cycle assessmentsfor life cycle [assessments38]. [38].

2.1. Investigated Investigated Recycling Process The processing of the gypsum plaster waste was carried out in the stationary gypsum recycling plant of a medium-sized medium-sized company. TheThe objective of the processing is the removal of impurities, as well as the the separation separation of of gypsum gypsum from from cardboard and paper. A simplified simplified flowchartflowchart of the recycling process is shown in Figure2 2..

Figure 2. SimplifiedSimplified flowchart flowchart for gypsum recycling in a stationary gypsum recycling plant.plant.

After presorting with an excavator and/or manually, the gypsum waste is fed into the system. In the first sorting step, ferrous metals are removed by a magnetic separator,

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Minerals 2021, 11, 101 5 of 13 After presorting with an excavator and/or manually, the gypsum waste is fed into the system. In the first sorting step, ferrous metals are removed by a magnetic separator, followed by various comminution stages. DuringDuring the comminution, predominantly shear forces are used to separate the gypsum from thethe cardboard andand paper.paper. DueDue toto thethe limitlimit forfor TOC (total organic carbon) in recycled gypsum,gypsum, thethe removalremoval ofof paper fibersfibers isis of particular importance. Furthermore, Furthermore, different different grain grain size sizess can can be begenerated generated and and separated separated in the in sub- the subsequentsequent classification classification stage. stage. It is ofof fundamentalfundamental importanceimportance for thethe environmentalenvironmental evaluation of a processingprocessing toto take all or residues into account. The proportions ofof the waste fractionsfractions inin gypsumgypsum recycling dependdepend onon the the acceptance acceptance criteria criteria of of the the operating operating company company and, and, accordingly, accordingly, the qualitythe quality of the of inputthe input material. material. Therefore, Therefore, large large differences differences in the in amount the amount of waste of waste materials ma- afterterials processing after processing are possible. are possible. In the In the present present case, case, the the input input material material (predominantly(predominantly used gypsum plasterboards from construction sites)sites) usuallyusually originatedoriginated fromfrom thethe selectiveselective dismantling ofof buildings.buildings. Accordingly, Accordingly, only only a few a few unsuitable unsuitable materials materials had tohad be removed.to be re- Dependingmoved. Depending on the specificon the specific input material,input material, about about 2% to 2% 3% to of 3% the of materialthe material occurred occurred as wasteas waste after after presorting presorting and and magnetic magnetic separation. separation. The removedThe removed paper paper and cardboard and cardboard waste amountedwaste amounted between between 10% and 10% 17% and of17% the of input the in material.put material. Correspondingly, Correspondingly, the the output output of recycledof recycled gypsum gypsum ranged ranged from from 80% 80% to 88%.to 88%.

2.2. Settings for the Environmental Evaluation The scopescope ofof thisthis researchresearch was was to to investigate investigate the the environmental environmental impacts impacts of theof the produc- pro- tionduction of RC-gypsum of RC-gypsum in comparison in comparison with with natural natural gypsum gypsum and and FGD FGD gypsum. gypsum. Therefore, Therefore, the functionalthe functional unit unit was was 1-t gypsum.1-t gypsum. The system boundaries were fixed with regards to the comparability of the examined The system boundaries were fixed with regards to the comparability of the examined gypsum types. For recycled gypsum from gypsum plasterboard waste, they included the gypsum types. For recycled gypsum from gypsum plasterboard waste, they included the following steps (see also Figure3): following steps (see also Figure 3): • the transportation of GPW (from construction sites or collection points) to the recy- • the transportation of GPW (from construction sites or collection points) to the recy- cling plant, cling plant, • the recycling process, • the recycling process, • transportation to the gypsum plant, • transportation to the gypsum plant, • drying process, and • drying process, and • transportation to the costumer. • transportation to the costumer.

FigureFigure 3.3. SystemSystem boundariesboundaries forfor thethe evaluationevaluation ofof RC-gypsum.RC-gypsum. Sf*:*Sf: Substitute fuel.

Recycled gypsum usually has a moisture contentcontent ofof 3–5%.3–5%. For the use ofof recycledrecycled gypsum as a secondary raw material in gypsum production, the material has to be dried. The energy consumption during this drying process is included in the environmental evaluation. The drying of the material before calcination is also necessary for natural

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gypsum and FGD gypsum and part of the respective calculations. The different moisture contents of the investigated gypsum types (natural gypsum 1%, recycled gypsum 3–5%, and FGD gypsum 8–10%) affect the energy consumption of the processing and, accordingly, influence the results of the environmental evaluation [21]. The drying is performed after transportation to the gypsum producers and before calcination. Besides the drying step, the production phase, including calcination, and the utiliza- tion phase are not part of this environmental evaluation in all four scenarios. The system boundaries for the calculations of the environmental impacts from the pro- duction of natural gypsum were similarly determined. They included the following steps: • recovery of natural gypsum from the deposits, • transportation to the gypsum plant, • the drying process, • transportation to the costumer, • transportation to a landfill after the use phase, and • landfilling. The system boundaries for the production of FGD gypsum were similarly determined. They included the following steps: • transportation to the gypsum plant, • the drying process, • transportation to the costumer, • transportation to a landfill after the use phase, and • landfilling. In contrast to RC-gypsum, the system boundaries of natural and FGD gypsum include the steps of transportation to a landfill after the use phase and landfilling. These steps are not necessary for RC-gypsum, because in this scenario, a recirculation of the material is included.

2.3. Life Cycle Inventory The data collection for the inventory analyses was conducted in cooperation with recycling companies and equipment manufacturers. Accordingly, the used data were taken from industrial-scale productions. Further data were primarily taken from the life cycle inventory (LCI) database ecoinvent v 3.1 [39]. The geographical frame of the evaluation is Germany. Therefore, relevant datasets for Germany (such as the German electricity mix) were used. Further data for the calculations (e.g., for auxiliary materials in the production) were also taken, as far as possible, related to production in Germany. The transportation distances were assessed on the basis of the known average values for the different existing routes and our own estimations. Natural gypsum: • transportation to the gypsum plant: 20 km • transportation from the gypsum manufacturer to the costumer/construction site: 200 km • transportation to a landfill after the use phase: 30 km FGD gypsum • transportation of the GPW (from construction sites or collection points) to the recy- cling plant

2.4. Applied Impact Categories With regards to already existing studies and further recommendations, the seven impact categories shown in Table1 were chosen [3,40,41] Minerals 2021, 11, x FOR PEER REVIEW 7 of 13

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Table 1. Impact categories and related units.

Table 1. Impact categoriesImpact and related Category units. Unit Global warming potential (GWP) kg CO2 equivalents Impact Category Unit Acidification potential (AP) kg SO2 equivalents Global warmingEutrophication potential potential (GWP) kg CO kg2 equivalents PO4 equivalents photochemicalAcidification ozone potential creation (AP) potential (POCP) kg SO kg 2ethyleneequivalents equivalents Eutrophication potential kg PO equivalents abiotic depletion potential (ADPelem.) 4 kg Sb equivalents photochemical ozone creation potential (POCP) kg ethylene equivalents land use transformation points abiotic depletion potential (ADPelem.) kg Sb equivalents land use transformationLand use, total points points Land use, total points Consistent with international practice, the impact category global warming potential was evaluated using the CO2 equivalents (100 years) with regards to the Intergovernmen- Consistent with international practice, the impact category global warming potential tal Panel of Climate Change (IPCC) [42]. The impact categories’ acidification potential was evaluated using the CO equivalents (100 years) with regards to the Intergovernmental (AP), eutrophication potential2 (EP), photochemical ozone creation potential (POCP, sum- Panel of Climate Change (IPCC) [42]. The impact categories’ acidification potential (AP), mer smog), and abiotic depletion potential (ADPelem.) were calculated with the characteri- eutrophication potential (EP), photochemical ozone creation potential (POCP, summer zation factors given in the impact assessment model CML 2015 method [43]. smog), and abiotic depletion potential (ADP ) were calculated with the characterization Land usage and the threat to nature andelem. the biodiversity were perceived using the factors given in the impact assessment model CML 2015 method [43]. ecosystem damage potential (EDP) with the categories land transformation and total land Land usage and the threat to nature and the biodiversity were perceived using the use [44,45]. ecosystem damage potential (EDP) with the categories land transformation and total land use [44,45]. 3. Results 3. ResultsThe results of the calculations are subdivided into the seven investigated impact cat- egories.The The results specific of the figures calculations map the areresults subdivided of each scenario into the divided seven investigated into the values impact for eachcategories. specific The step: specific processing, figures maptransportation the results,of and each landfilling. scenario divided The step into processing the values in- for cludeseach specific the drying step: of processing, the gypsum transportation, but, also, the and extraction landfilling. for Thenatural step gypsum processing and includes the as- sociatedthe drying upstream of the gypsum impacts but, from also, the the applied extraction materials for natural and gypsumenergy. Transportation and the associated in- cludesupstream the impactsassociated from upstream the applied impacts materials as well. andRegarding energy. the Transportation step landfilling, includes the use the of machinesassociated and upstream the upstream impacts impacts as well. of Regardingdiesel and, the e.g., step lubricating landfilling, oil influence the use of the machines results asand well. the upstream impacts of diesel and, e.g., lubricating oil influence the results as well.

3.1.3.1. Global Global Warming Warming Potential Potential (GWP) (GWP) InIn the the impact impact category category for for climate climate chan change,ge, FGD FGD gypsum gypsum shows shows the the highest highest environ- environ- mentalmental impacts, impacts, resulting resulting from from transportation, landfilling, landfilling, and drying. The outcomes for recycledrecycled gypsum gypsum in in comparison comparison to to natural gypsum are dependent on the transportation distances.distances. The The emissions emissions are are related related to to the the di dieselesel consumption during transportation and landfilling.landfilling. The The results results for for the the four four scenarios scenarios are are shown shown in Figure 44..

FigureFigure 4. 4. ResultsResults for for the the global global warming warming potential. potential. *eq.: eq.*: equivalents equivalents

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3.2. Acidification Potential (AP) 3.2.3.2. Acidification Acidification Potential Potential (AP) (AP) Figure 5 presents the results of the impact category acidification for the investigated FigureFigure 55 presents presents the the results results of of the the impact impact category category acidification acidification for for the the investigated investigated scenarios. The electricity for the processing of recycled gypsum has a significant input to scenarios.scenarios. The The electricity electricity for for the the processing processing of of recycled recycled gypsum gypsum has has a asignificant significant input input to to the acidification potential, due to the lignite-based generation of electricity in Germany. thethe acidification acidification potential, potential, due due to to the the lignite-b lignite-basedased generation generation of of electricity electricity in in Germany. Germany. The AP of FGD gypsum is between the two RC-gypsum scenarios and is particularly in- TheThe AP AP of of FGD FGD gypsum gypsum is between is between the the two two RC-gypsum RC-gypsum scenarios scenarios and andis particularly is particularly in- fluenced by the diesel used in the landfilling procedure and the transportation. fluencedinfluenced by the by thediesel diesel used used in the in theland landfillingfilling procedure procedure and and the the transportation. transportation.

Figure 5. Results for the acidification potential. FigureFigure 5. 5. ResultsResults for for the the acidification acidification potential. potential. 3.3.3.3. Eutrophication Eutrophication Potential Potential (EP) (EP) 3.3. Eutrophication Potential (EP) InIn Figure Figure 6,6, the the results results for for the the calculations calculations of of the the eutrophication eutrophication potential potential are are shown. shown. In Figure 6, the results for the calculations of the eutrophication potential are shown. ThisThis impact impact category category is is dominated dominated by by the the use use of of electricity electricity for for the the processing processing and, and, also, also, by by This impact category is dominated by the use of electricity for the processing and, also, by thethe high high proportion proportion of lignite-based resourcesresources inin the the German German electricity electricity mix. mix. Compared Compared to the high proportion of lignite-based resources in the German electricity mix. Compared tonatural natural gypsum gypsum and and FGD FGD gypsum, gypsum, both both scenarios scenarios for recycledfor recycled gypsum gypsum show show a significantly a signifi- to natural gypsum and FGD gypsum, both scenarios for recycled gypsum show a signifi- cantlyhigher higher eutrophication eutrophication potential. potential. cantly higher eutrophication potential.

Figure 6. Results for the eutrophication potential. FigureFigure 6. 6. ResultsResults for for the the eutrophication eutrophication potential. potential. 3.4.3.4. Photochemical Photochemical Ozone Ozone Creation Creation Potential Potential (POCP) (POCP) 3.4. Photochemical Ozone Creation Potential (POCP) TheThe impact impact category category photochemical photochemical ozone ozone creation creation potential potential is is also also dominated dominated by by the the The impact category photochemical ozone creation potential is also dominated by the emissionsemissions caused caused by transportation andand landfilling.landfilling. UnlikeUnlike in in the the category category global global warming warm- emissions caused by transportation and landfilling. Unlike in the category global warm- ingpotential, potential, the the scenarios scenarios for for RC-gypsum RC-gypsum outperform outperform the thescenarios scenarios forfor natural and FGD FGD ing potential, the scenarios for RC-gypsum outperform the scenarios for natural and FGD gypsumgypsum (see (see Figure Figure 7).7). Although Although the emission emissionss linked to the energy consumption during gypsum (see Figure 7). Although the emissions linked to the energy consumption during

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the processing of RC-gypsum are higher than those resulting from the processing of nat- uralthethe andprocessing processing FGD gypsum, of RC-gypsumRC-gypsum the overall areare higher POCPhigher thanfor than RC-gypsum those those resulting resulting shows from from a thebetter the processing processing performance. of naturalof nat- uraland and FGD FGD gypsum, gypsum, the overallthe overall POCP POCP for RC-gypsum for RC-gypsum shows shows a better a better performance. performance.

Figure 7. Results for the photochemical ozone creation potential. FigureFigure 7. 7. ResultsResults for for the the photochemical photochemical ozone ozone creation creation potential. potential. 3.5. Abiotic Depletion Potential (ADPelem.) 3.5. Abiotic Depletion Potential (ADPelem.) 3.5. ThisAbiotic impact Depletion category Potential represents (ADPelem. the) use of abiotic elements and is dominated by the consumptionThis impact of natural category gypsum represents and the the relat useed of depletion abiotic elements potential and (see is dominatedFigure 8). Other by the consumptionThis impact of naturalcategory gypsum represents and the the use related of abiotic depletion elements potential and (seeis dominated Figure8). by Other the resources,consumption like ofmetals, natural are gypsum negligible. and Therefore, the related the depletion ADPelem potential of transports (see Figureand landfilling 8). Other areresources, comparatively like metals, low and are negligible.are summarized Therefore, for use the in ADP Figureelem 8.of transports and landfilling resources,are comparatively like metals, low are and negligible. are summarized Therefore, for usethe inADP Figureelem of8. transports and landfilling are comparatively low and are summarized for use in Figure 8.

FigureFigure 8. 8.ResultsResults for for the the eutrophication eutrophication potential. potential. Figure 8. Results for the eutrophication potential. 3.6.3.6. Ecological Ecological Damage Damage Potential Potential (EDP): (EDP): Land Land Use Use Transformation Transformation 3.6. TheEcologicalThe impact impact Damage category category Potential land land (EDP):transformation transformation Land Use isTransformation ismainly mainly influenced influenced by by the the use use of of near- near- natural forests during the quarrying of natural gypsum, whose extraction sites in Germany naturalThe forests impact during category the quarryingland transformation of natural isgypsum, mainly whoseinfluenced extraction by the sites use inof Ger-near- are often located in the areas of old beech forests (see Figure9). Renaturation measures can- manynatural are forests often duringlocated the in quarryingthe areas ofof oldnatu beechral gypsum, forests whose(see Figure extraction 9). Renaturation sites in Ger- not compensate for the ecological damage completely. The values calculated for landfilling measuresmany are cannot often compensatelocated in the for theareas ecological of old beechdamage forests completely. (see Figure The values 9). Renaturation calculated are derived from converting other areas into landfill sites. formeasures landfilling cannot are compensatederived from for converting the ecological other damage areas into completely. landfill sites. The values calculated for landfilling are derived from converting other areas into landfill sites.

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Figure 9. Results for land use transformation (ecosystem damage potential (EDP)). FigureFigure 9. 9. ResultsResults for for land land use use transformation transformation (ecosystem (ecosystem damage damage potential potential (EDP)). (EDP)). 3.7. Ecological Damage Potential (EDP): Land Use, Total 3.7.3.7. Ecological Ecological Damage Damage Potential Potential (EDP): (EDP): Land Land Use, Use, Total Total In contrast to the impact category “land transformation”, which contains changes in InIn contrast contrast to to the the impact impact category category “land “land transformation”, transformation”, which which contains contains changes changes in in the quality of land after usage, the category “land use, total” stands for the complete land thethe quality quality of of land land after after usage, usage, the the category category “l “landand use, use, total” total” stands stands for for the the complete complete land land use (Figure 10). The values for recycled gypsum caused by processing are comparatively useuse (Figure (Figure 10).10). The The values values for for recycled recycled gypsum gypsum caused caused by by processing processing are are comparatively comparatively higher. This is mainly due to the use of lignite-based electricity and the related usage of higher.higher. This This is is mainly mainly due due to to the the use use of of lign lignite-basedite-based electricity electricity and and the the related related usage usage of lignite mining sites. As a result of the land usage for landfilling and the land use caused lignitelignite mining mining sites. sites. As As a a result result of of the the land land usage usage for for landfilling landfilling and and the the land land use use caused caused by upstream chains from the production of landfill sealings, the total land use of natural byby upstream upstream chains chains from from the the production production of of la landfillndfill sealings, sealings, the the total total land land use use of of natural gypsum is higher than for both recycled gypsum scenarios. The total land use for the pro- gypsumgypsum is is higher higher than than for for both both recycled recycled gypsum gypsum scenarios. scenarios. The Thetotal total land land use for use the for pro- the duction of FGD gypsum is in the same range as for the RC 200 scenario. ductionproduction of FGD of FGD gypsum gypsum is in is the in thesame same range range as for as the for theRC RC200 200scenario. scenario.

FigureFigure 10. 10. ResultsResults for for land land use, use, total total (EDP). (EDP). Figure 10. Results for land use, total (EDP). 4.4. Discussion Discussion 4. Discussion TheThe evaluation evaluation of of the the environmental environmental impacts impacts of ofthe the recycling recycling of gypsum of gypsum waste waste on an on The evaluation of the environmental impacts of the recycling of gypsum waste on an industrialan industrial scale scale shows—in shows—in comparison comparison to the to results the results for natural for natural and FGD and FGDgypsum—a gypsum—a pre- industrial scale shows—in comparison to the results for natural and FGD gypsum—a pre- dominantlypredominantly positive positive but di butfferentiated differentiated picture. picture. dominantly positive but differentiated picture. TheThe calculations calculations for for RC 100 gypsumgypsum displayeddisplayed the the best best results results in in the the following following five five (of The calculations for RC 100 gypsum displayed the best results in the following five (ofseven) seven) impact impact categories: categories: GWP, GWP, AP, AP, POCP, POCP, land land use use transformation, transformation, and and land land use use (total). (to- (of seven) impact categories: GWP, AP, POCP, land use transformation, and land use (to- tal).RC RC 200 200 gypsum gypsum showed showed better better results results than than natural natural and and FGD FGD gypsum gypsum in in the the categories categories of tal). RC 200 gypsum showed better results than natural and FGD gypsum in the categories ofPOCP POCP and and land land use use transformation transformation and and overperformed overperformed natural natural gypsum gypsum in the in categoriesthe catego- of ofAP POCP and land and useland (total). use transformation Furthermore, the and results overperformed for RC 200 natural gypsum gypsum in the impact in the category catego- ries of AP and land use (total). Furthermore, the results for RC 200 gypsum in the impact riesof GWP of AP were and betterland use than (total). for FGD Furthermore, gypsum. the Regarding results for the RC eutrophication 200 gypsum potential,in the impact the impacts of RC 100 gypsum and RC 200 gypsum were larger than those of natural and

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FGD gypsum. This can be explained by the German electricity mix, which included a comparatively higher proportion of lignite-based electricity. The extraction of natural gypsum is the most influential parameter in the impact category ADPelem.. Therefore, the resulting value for natural gypsum is several times higher than the values for RC-gypsum and FGD gypsum, which are approximately at the same level. The results show that transport distances and landfilling have a significant influence on the calculation results of the impact categories of GWP, AP, POCP, and land use total. This can mainly be explained by the environmental effects of diesel consumption. Another factor is the avoiding of landfilling as a result of gypsum recycling in the corresponding scenarios. Furthermore, it is important that the input flows of FGD gypsum and gypsum waste into the respective system boundaries are unencumbered, due to their origins as by-products. The use of secondary raw materials and the related waste reductions have a calculable positive effect on the results of environmental evaluations. Previous studies have stated that the environmental impacts generated by GPW recycling are clearly lower than the comparative values in all inventory categories. Several authors from Spain, the country with the largest gypsum production in the European Union, came to this result [13,33,34]. Compared to these studies, it must be stated that the results of our calculations seem to be not so straightforward. Besides the use of different calculation methodologies, this can be explained by several facts. On one hand, these studies calculated their tests with considerably shorter transportation distances, which affected the results, especially by avoiding emissions due to diesel consumption. On the other hand, in our study, post-consumer GPW was recycled, which means, that—compared to the recycling of pre-consumer gypsum—this material contains more impurities, and greater efforts during processing are necessary. Furthermore, in Germany, the quality standards for recycled gypsum that must be met are comparatively higher. This study showed that the recycling of post-consumer gypsum is feasible and can be environmentally advantageous. However, the importance of a good presorting accuracy on the construction sites should be emphasized. Therefore, good communication between the demolition contractor and gypsum recycling company is required to keep the amount of occurring waste materials low. The development of new sources for gypsum is a further important element for future gypsum production. Therefore, the authors are going to investigate the usability of synthetic gypsums from industrial wastes (e.g., phosphogypsum or gypsum from food production) and, also, from gypsum fiberboards. An environmental evaluation of the different investigated recycled gypsum types will also be an important part of that work. Since the electricity mix in Germany will change due to the planned shutdown of coal- fired power plants, it can be expected that the environmental impacts related to electricity consumption will decrease. In the upcoming years, the share of renewable energy in the German energy mix should lead to a better performance of recycled gypsum in the impact categories EP, AP, and, also, GWP.

5. Conclusions Working towards greater resource efficiency in the construction sector is essential for addressing global issues such as slowing climate change and moving towards a circular economy. Therefore, the recycling of building materials is of particular importance. Based on the findings of this evaluation, it can be stated that the recycling of post-consumer GPW from the construction industry is feasible. Furthermore, although the meeting of high- quality standards is essential, the procedure, including comparatively long transporting distances, can be environmentally advantageous compared to the investigated natural and FGD gypsum scenarios. Especially in Germany, where a replacement of FGD gypsum in the upcoming years will be required, recycled gypsum is of increasing importance. The results presented in this study showed that GPW recycling on an industrial scale can be eco-friendly. Additionally, the need for a substitute for FGD gypsum is expected to lead to further GW recycling Minerals 2021, 11, 101 12 of 13

facilities and, accordingly, to a development of transport logistics and a related reduction of transport distances. Furthermore, the expected changes in the German electricity mix will make the recycling of GW even more environmentally friendly.

Author Contributions: Conceptualization, K.W. and C.A.; methodology, K.W., M.B., and C.A.; data curation, J.S. and M.B.; writing—original draft preparation, K.W.; writing—review and editing, K.W., C.A., and M.B.; project administration, M.B.; and funding acquisition, M.B. and K.W. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by Federal Environmental Agency (UBA), grant number FKZ 3715343200. Data Availability Statement: The data presented in this study are available on request from the corresponding author. The data are not publicly available due to a confidentiality agreement with a company that provided some of the original data. Acknowledgments: The authors wish to thank Nadja Schuetz and Holger Alwast. Conflicts of Interest: The authors declare no conflict of interest.

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