Clarification of lactic acid fermentation broths

摘要

This work is focused on the clarification of. fermentation broths in order to optimise a batch downstream process for the recovery and purification of lactic acid produced by fermentation. Lactic acid was produced in a 75-1 fermentor and the clarification was achieved using a 0.15 m2 filtration unit. Beet molasses was used as carbon source for fermentation and was inoculated with freeze-dried Lactobacillus delbrueckii ssp. lactis. The protein supplement was selected according to the fermentation and filtration performance. In batch processes, a lag time may occur between production and clarification; thus we investigated the effects of two stabilisation processes. Permeate rates were identical for the filtration of fresh, frozen or sterilised broths. pH ~as found to be a key parameter in fermentation and filtration. During fermentation, it was set at the constant value of 6.2. Lower pH values led to lower filtration rates whereas higher pH values first improved and then decreased filtration rates. The optimum pH range was between 7 and 8. The effects of the classic operating filtration parameters (pore diameter, temperature, cross-flow velocity, transmembrane pressure, permeate flux) were also investigated. Critical fluxes depending on axial velocity were identified.