In this work the studies of glycerol fermentation in a bioreactor connected with separation of broth by ultrafiltration process were presented. The study was carried out with broths, which were prepared using Citrobacter freundii bacteria. A tubular tight ultrafiltration ceramic membrane (8 kD) was applied and the complete rejection of bacterial and other suspended solids was achieved. The produced permeate was clear, with a turbidity at a level of 0.1 NTU. Although a tight ultrafiltration membrane was used, the ions retention was at a low level - below 10%. In a comparison with a classical method of fermentation with broth bleeding, the yield of fermentation was increased by the application of ultrafiltration for treatment of broth from the bioreactor. However, a significant (over 70%) permeate flux decrease was observed due to a fouling, which is an essential limitation in the application of the membrane separation. A periodical module rinsing with 1% NaOH solutions was used for limitation of the fouling influence on a flux decline. (C) 2015 Elsevier B.V. All rights reserved.