Objective Acid protease has been widely used in the brewing, food, feed, pharmaceutical, and leather industries. For example, acid proteases are often used to bate wet blue during the leather-making process to improve the quality of crust leather. However, the background data for the life cycle assessment (LCA) of the protease are currently lacking, which restricts the accurate assessment of the environmental footprint of related products. Therefore, this study aims to establish a life cycle inventory (LCI) model for acid protease to fill this data gap.

Methods The LCA method was employed to quantify the environmental impacts of the production stage (System Boundary I: fermentation, separation and purification, sterilization, waste treatment, etc.) and the use stage (System Boundary II: rewetting, bating, neutralizing, etc.) of acid protease. This assessment was based on ISO 14040/14044 and GB/T 24040/24044 standards and utilized actual production data from a typical domestic enzyme preparation company. The declared units were defined as the production of 1 kg of acid protease (100 000 U/g) and the bating of 1 000 kg of shaved wet blue, respectively. The LCI model was built using the eFootprint software, linking the domestic database CLCD-China and the international database Ecoinvent 3.1. Nine environmental impact categories were selected, including global warming potential (GWP), primary energy demand (PED), water use (WU), and ecotoxicity (ET). The life cycle impact assessment (LCIA) results were calculated, and further sensitivity and uncertainty analyses of the LCIA results were conducted to form conclusions and recommendations.

Results In the production stage, the environmental impacts of producing 1 kg of acid protease were 5.68 kg CO₂ eq for GWP, 124.07 MJ for PED, 83.83 kg for WU, and 1.23 CTUe for ET. Energy consumption (electricity and steam), glucose syrup, and glycerol were the main contributors to these impacts. Electricity was primarily used for aeration and stirring during the fermentation process, while steam was applied for sterilization and temperature control. Glucose syrup served as the main carbon source, and its upstream production was associated with high energy consumption. Glycerol was used to maintain the structural stability and activity of acid protease during separation and purification, and its production process also involved high energy and emission burdens. In the use stage, the bating of 1 000 kg of shaved wet blue resulted in 179.92 kg CO₂ eq for GWP, 3 427.29 MJ for PED, 15 995.47 kg for WU, and 13.24 CTUe for ET. The acid protease had a minor environmental contribution due to its high efficiency and low dosage. Consequently, the environmental impact in this stage mainly came from process energy consumption, sodium formate, and production water. Electricity was primarily used to drive the rotation of the drum, while steam was used to maintain the process temperature. The production water was mainly consumed in multiple washing steps. Sodium formate was the chemical with the highest dosage in the process, and its upstream production was associated with high energy consumption and emissions. Uncertainty analyses indicated good data quality and reliable assessment results.

Conclusions This study established a LCA background dataset for acid protease and systematically quantified the environmental impacts of its production and use stages. The results show that GWP, PED, and WU are the main environmental impact categories. In the production stage, energy consumption, glucose syrup, and glycerol are key components of the inventory data. In the use stage, energy consumption, sodium formate, and process water are key components of the inventory data. This research provides a scientific basis for optimizing the green process of acid protease. It also offers critical data support for accurate environmental footprint assessment and sustainable decision-making in related downstream industries, such as leather manufacturing.