Clarification of lactic acid fermentation broths

This work is focused on the clarification of fermentation broths in order t o optimise a batch downstream process for the recovery and purification of lactic acid produced by fermentation. Lactic acid was produced in a 75-1 fe rmentor and the clarification was achieved using a 0.15 m(2) filtration uni t. Beet molasses was used as carbon source for fermentation and was inocula ted with freeze-dried Lactobacillus delbrueckii ssp. lactis. The protein su pplement was selected according to the fermentation and filtration performa nce. In batch processes, a lag time may occur between production and clarif ication; thus we investigated the effects of two stabilisation processes. P ermeate rates were identical for the filtration of fresh, frozen or sterili sed broths. pH was found to be a key parameter in fermentation and filtrati on. 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 improve d and then decreased filtration rates. The optimum pH range was between 7 a nd 8. The effects of the classic operating filtration parameters (pore diam eter, temperature, cross-flow velocity, transmembrane pressure, permeate fl ux) were also investigated. Critical fluxes depending on axial velocity wer e identified. (C) 2001 Elsevier Science B.V. All rights reserved.