The difference most likely comes from the fact that approximately 90% of the energy in the USDA-FPL process is estimated to correspond to circulation of the retentate stream in the UF batch mode. In the current design, UF is run in a continuous mode, and circulation of the retentate stream is not considered for each UF stage. Input and output for mass and energy values in the CNC production systems (Figure ) are normalized to 1 kg CNC production as to obtain LCIs for the CNC61 and the CNC64 as shown in Table . Regarding the input, the differences in pulp, H2SO4 and NaOH for the two CNC products were explained above. The differences in the water-electricity nexus between the two CNC products are mainly due to the existence of the sugar layer in CNC64, 23% more water is required compared to CNC61 (no sugar layer); 34% more electricity is required for CNC64 compared to CNC61. Regarding the output, the main product is CNC, and the waste stream is a very dilute solution (0.1~0.2 wt.% sugar, ~ 1 wt.% Na2SO4), which can directly be discharged to the environment. However, water efficiency is extremely low: 96% input water is lost to the waste stream for CNC61; 95% for CNC64. Therefore, a process design for water circulation deserves investigation. * including the water for quench and UF, as well as water in acid stream and NaOH neutralization stream.