Separation and Purification of Lactic Acid from Fermentation Broth Using Membrane-Integrated Separation Processes

Lactic acid is produced industrially from bacterial fermentation of carbohydrates (e.g., sugar, starch) followed by separation processes such as precipitation, distillation, and reactive extraction. However, these conventional separation processes are energy intensive. In this study, we report an integrated membrane separation process consisting of ultrafiltration (UF) and nanofiltration (NF) for lactic acid recovery from fermentation broth, combined with ion exchange (IEX) and vacuum-assisted evaporation. Most organic and inorganic components in lactic acid fermentation broth, including microbes, glucose, and inorganic salt ions were successfully removed by UF and NF processes. Membrane fouling in the UF process became severe due to the high concentration of microbes and organic compounds. The effects of various UF membranes on the extent of membrane fouling were also studied to enhance separation efficiency. The separation of lactic acid continued using NF membranes, considering both size exclusion and Donnan exclusion effects. Finally, IEX and vacuum evaporation (VE) processes were also used to eliminate residual salt ions and to increase lactic acid purity. The hybrid membrane-separation process produced lactic acid with high purity (>99.5%).