PAPERmaking! Vol11 Nr2 2025

Barrios et al. Biotechnology for Biofuels and Bioproducts

(2025) 18:48

Page 17 of 23

account for 50% of the total GWP. External operations such as forest activities, transportation, and the procurement of chemicals and fuels represent 46% of the total GWP, while carbon emissions from electricity purchases make up 4%, as the mill is 93% self-sufficient in power. The GWP for bleached hardwood kraft pulp has been reported in the range of 572–1200 kg CO 2 -eq/ ADt, with variations primarily attributed to scope 1 emissions due to differences in fuel distribution and energy usage within the mill [54, 56]. In the simulation, natural gas consumption in the boiler was controlled by the MP steam demand. Thus, energy reductions in the dryer directly affect natural gas combustion and result in variations in fuel consumption. The reduction in GWP obtained in the enhanced dewatering scenario is attributed to decreased natural gas combustion. Steam demand and emissions in the dryer are reduced by 37%, and CO 2 emissions directly released from the boiler decreased by 27%, as shown in Fig. 7c and Table S9. The reductions resulted in a 23% decrease in total direct emissions. Furthermore, when considering total emissions across scopes 1, 2, and 3, the cell-free enzyme technology for enhanced dewatering achieved a net GWP reduction of 12.3% ± 2.5% (Fig. 7d). Techno-economic calculations The adoption of enzyme technologies in the pulp and paper industry is increasing, driven by advancements in enzyme production and continuous efforts to optimize manufacturing costs. However, information on the economic evaluation of enzyme applications in the paper industry remains limited. Cost analysis estimates for the application of the cell-free enzyme technology are presented in Table 8. The change in consumption is defined as the difference between the baseline and enhanced dewatering scenarios. By increasing the solids content after pressing, from 39 to 50%, 2.77 GJ of fossil fuel energy per ADt of product can be saved. The increase in solids content after the pressing reduces steam demand in the drying section, leading to lower natural gas consumption in the boiler. Since the boiler is controlled to supply only the required amount of steam, the reduction in steam demand directly translates to a decrease in purchased fuel, resulting in cost savings. A detailed breakdown of the energy cost savings from reduced natural gas consumption is provided in the supplementary material under section Breakdown of Energy Cost Savings. Considering an average cost of the natural gas in the U.S at 5.8 USD $/GJ [56], this translates to savings of 16.05 USD $/ADt in fuel procurement. However, the purchase of enzymes and starch is required for the treatment. Based on the analysis, the following were considered: the enzyme and starch usage

content by approximately 27% compared to the untreated fiber (0E, 0S). However, the FBW content was reduced, and the NFBW content remained unaltered. Specific details on the different forms of water in the fibers are presented in Table S4. The promising results observed here lay the foundation for scaleup testing of this technology. Economic and environmental impacts In an integrated mill, the dryer section of the paper machine is one of the most energy-intensive units. In the baseline scenario used to assess economic and environmental impacts, the dryer section accounts for approximately 31% of the total steam demand. Detailed energy flow values for the baseline and enhanced dewatering scenarios are provided in Table S5 in the supplementary material. The powerhouse generates steam and electricity for various mill operations. In the simulation, high pressure steam at 855 psi and 440 °C is produced and sent to back pressure and condensing turbines, where 93% of the mill’s electricity demand is met. The steam pressure is then reduced to medium pressure (160 psi) and low pressure (60 psi) for delivery to various processes. Steam from the natural gas boiler accounts for 29% of the total steam production. Energy savings and emissions reduction The results for the enhanced dewatering scenario (Table S5) indicate that increasing the solids content after pressing, from 39 to 50% by the cell-free enzyme treatment and cationic starch addition reduces steam demand in the dryer section of the paper machine by up to 37%, as shown in Fig. 7a. This reduction in water content directly correlates with a decrease in steam con- sumption in the dryer section of the paper machine, as less thermal energy is required to remove the remaining moisture [109, 110]. Since other unit operations, such as the digester, the chlorine dioxide (ClO 2 ) bleach plant, and air heater system, also consume medium-pressure (MP) steam, a 25% energy reduction in MP steam can be achieved. When accounting for total steam demand (MP and low-pressure (LP)), overall energy savings of 12% are possible. The total CO 2 emissions released on-site by the process are 3560 kg CO 2 -eq/ADt, with 79% clas- sified as biogenic emissions. Input and output flows are detailed in the life cycle inventory for both the baseline and enhanced dewatering scenarios in Tables S6 and S7. In the cradle-to-gate analysis, the GWP for the baseline is 963 kg CO 2 -eq/ADt, compared to 844 kg CO 2 -eq/ ADt for the enhanced dewatering scenario, as shown in Table S8. Figure 7b provides a breakdown of scope emission for the baseline scenario, showing that direct emissions

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