SEMICONTINUOUS PRODUCTION OF LACTIC-ACID IN A BIOREACTOR COUPLED WITHNANOFILTRATION MEMBRANES

The advantages of nanofiltration membranes coupled with a CSTR were de monstrated for the semicontinuous production of lactic acid from whey permeate. Lactic acid was removed from the growth medium while lactose was kept in the bioreactor with the bacterial cells; moreover, Mg2+ i ons were also recycled in the bioreactor at 96% and the nanofiltrate c olor was greatly reduced The highest volumetric productivity achieved with this device was 7.1 g l(-1) h(-1) and the lactate concentration w as 55 g l(-1). The specific productivity was 3.54 h(-1). More than 99% of the membrane fouling after 44 h of fermentation was reversible. Th e initial permeate flux was restored easily by a water rinse. The perf ormance of this type of membrane bioreactor was discussed. (C) 1996 by Elsevier Science Inc.