Environmental life cycle assessment of monosodium glutamate production in China: Based on the progress of cleaner production in recent ten years

China is the world's leading producer of the flavor-enhancer monosodium glutamate (MSG), which is mainly produced by maize starch fermentation. Four typical scenarios (Scenario 1–Scenario 4) of MSG production from 2008 to 2019 in China were established for life cycle environmental impact assessment. Values for five midpoint environmental impact categories [primary energy demand (PED), resource depletion-water use (WU), global warming potential (GWP), acidification potential (AP), and eutrophication potential (EP)] were calculated with eFootprint based on data collected in China. The environmental impacts of producing 1 t of MSG in China in terms of PED, WU, GWP, AP, and EP were 52,800 MJ, 169,000 kg, 4590 kg CO₂ eq, 42.1 kg SO₂ eq, and 6.35 kg PO₄³⁻ eq, respectively, in 2019. The life cycle of MSG from cradle to gate includes maize cultivation (high WU values), and the MSG production process (high PED, GWP, AP, and EP values). The normalization results of environmental impacts significantly decreased from S1 to S4 with the improvement in cleaner production in recent ten years. Sensitivity and uncertainty analyses identified steam for MSG production, irrigation water, and ammonia volatilization during maize growth as the three main factors affecting the environment. There were obvious differences in calculated environmental impacts depending on the maize cultivation data source; i.e., data from the Ecoinvent 3.1 database, or collected data for the maize-wheat rotation system in north China or the maize monoculture system in northeastern China. This demonstrates the importance of collecting local data rather than applying database from other world regions. Compared with the use of coal and natural gas, the use of biogas to produce steam had much lower PED, WU, and GWP. Which types of alternative energy to use and the replacement ratio should be based on the actual resource reserves in each region.