Continuous production of lactic acid in a membrane bioreactor

The production of lactic acid in a cell-recycle bioreactor was studied. The performance of an internal Zeeweed™ microfiltration membrane was evaluated. The flux through the Zeeweed™ module was double that of the flux in a conventional Millipore unit with the identical filtration area. The study of the rheology of the fermentation broth showed that the system changed from Newtonian to pseudoplastic behaviour at cell densities above 130 g/L. The effects of dilution rate, initial glucose concentration and agitation rate on biomass and lactic acid concentrations, substrate utilization and permeate flux were assessed using factorial experimental design. High substrate conversion (99%) was obtained in all runs operated at the lower initial substrate concentration. The highest product concentrations (44.9–52.7 g/L) were obtained at the higher substrate concentration. Higher dilution rate and lower substrate concentration resulted in high biomass concentrations (35.6 g/L). Stable steady-state operation was achieved using continuous cell bleeding.