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Cradle-to-Grave Life-Cycle Assessment of Wooden Pallet Production in the United States 15 to be 80% and 74% for natural gas and wood boilers, respectively (FPL 2004, Puettmann and Milota 2017). The environmental burdens of generating the coproducts were accounted for by calculating the GWP credit. Electricity consumed for grinding the pallet parts used as fuel at the end-of-life was accounted for in this module. Electricity consumption for the grinder was assumed to be 13.3 kWh/ OD t (Spinelli and others 2012). Transportation of wood fuel to users was taken into consideration and was assumed to be 50 km. In addition, the potential environmental benefits of recycled steel used in Module [A3] was calculated using data generated by the World Steel Association (2011). 2.8 Secondary Data Sources Secondary data sources for raw material inputs, ancillary materials and packaging, transportation of materials and resources, fuels and energy for manufacturing, water sources, and waste streams used in this LCA study are shown in Table 13. Secondary data on fuels and electrical grid inputs were taken from the U.S. LCI Database and European datasets modified specifically to be representative of U.S. operations (DATASMART) (LTS 2017). 3 Life-Cycle Impact Assessment 3.1 Cradle-to-Grave Life-Cycle Assessment LCIA results are presented in this section along with the information on end-of-life indicators used in the analysis (Table 14). The end-of-life stage began when the pallet left the use phase and describes the treatment options of wood pallets. These indicators showing waste and resource recovery were reported per UL Environment PCR clause 6.2 based on survey data. The pallet end-of-life treatment corresponded to the mass of 2.13 pallets (35.30 OD kg), and the various output flows showed the wood went where the highest output was wood material used for recycling. Inventory and impact results for cradle-to-grave production of wooden pallets are presented in Table 15. Impact assessment results were presented for the weighted-average impact assessment for the four pallet types analyzed in this study. It was assumed that 78% of the pallets were stringer pallets and 22% were block pallets in line with the 2016 production data (Gerber 2018, Gerber and others 2020). In addition, it was assumed that 50% of the pallets produced were HD for both the stringer and block pallets. Table 15 shows the summary results for the inventory analysis and impact assessment from cradle-to-grave along with Module [D]. For GW impact, the total was 10.4 kg CO 2 e per FU for which raw material supply and manufacturing were the major contributors. Most of the GHGs were derived from the sawing and (kiln) drying processes at the raw material supply module (Bergman and Bowe 2008, 2011, 2012; Milota and Puettmann 2017; Hubbard and others 2020). A negative sign refers to environmental benefits, and Module [D] offset these GHG emissions when the environmental benefits were accounted for. Renewable biomass energy comprised about 40% of total primary energy consumption. Table 16 presents the potential environmental benefits of beneficially used coproducts and end-of-life material. All core mandatory impact indicators were negative overall but the greatest opportunities for credit (i.e., negative environmental impacts) changed depending on the indicator and the material and energy recovery scenario assessed. 3.2 Additional Environmental Information This section provides additional indicators related to life cycle of a wooden pallet including the environmental impacts from the use phase and biogenic carbon accounting results. The use phase for wooden pallets is subject to high variability and uncertainty. Therefore, scenario analyses were performed to calculate the resulting impact conforming to the PCR (Table 17). The emission factor for wooden pallet transportation was assumed at 0.0946 kg CO 2 eq/t.km (UL Environment 2019a). A biogenic carbon balance was performed for the cradle- to-grave system boundary showing the biogenic carbon removal and emissions of wooden pallet life-cycle stages (Table 18). Biogenic carbon associated with the product recycled is reported in Module [C]. About 79.36 kg CO 2 e were removed in Module [A1] in the pallets used to deliver 100,000 lb (45.4 metric tons) of pallet loads of product, whereas 76.63 kg CO 2 e were emitted in Modules [A3] and [C]. 4 Interpretation In this section, the contribution analysis, completeness, sensitivity analysis, and consistency of the LCI results, conclusions, limitations, and recommendations are provided. 4.1 Life-Cycle Phase Contribution Analysis The contribution analysis provided information on which life-cycle stage had a greater contribution to the selected environmental indicators. The product stage was composed of raw material supply Module [A1], raw material transport Module [A2], and pallet manufacturing Module [A3]. The use and repair stage was composed of Module [B1] and repair–reuse Module [B2]. The end-of-life was composed of Module [C]. Module [D], which was beyond the system boundary, reported additional benefits. Table 19 presents the results of the contribution analysis for five modules analyzed. The contribution analysis showed that the raw material supply Module [A1] and manufacturing Module [A3] were the major contributors to the impact categories investigated. Lower environmental impact can be achieved through improved performance of raw material processing Module [A1] and transportation Module [A2]. At the raw material supply Module [A1], kiln-drying is a major

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