3.1. Glycerol Fermentation

In the present study, as a feed, the real glycerol post-fermentation solution was used. The glycerol fermentation was carried out using Citrobacter freundii bacteria (isolated and characterized in the Department of Biotechnology and Food Microbiology, Poznań University of Life Science, Poland). The process was carried out in a LiFlusGX bioreactor (Biotron Inc., Seoul, Korea) at temperature 304 K. A prepared broth contained per liter: glycerol (30.0 g), yeast extract (2.0 g), meat extract (1.5 g), peptone K (2.5 g), K₂HPO₄·3H₂O (3.4 g), KH₂PO₄ (1.3 g), MgSO₄·7H₂O (0.4 g), (NH₄)₂SO₄ (2.0 g), CaCl₂·2H₂O (0.1 g), and CoCl₂·6H₂O (0.004 g). After sterilization, the medium was inoculated with bacteria in a lag phase (10% v/v) and the batch fermentation was performed using a bioreactor (LiFlusGX, Biotron Inc., Seoul, Korea) at 300 K for 2 days. The pH value was maintained at 7.0 (±0.2) by automatic additions of 5 M NaOH. The conditions of the fermentation process are presented in more detail in previous works [89,90].

The composition of the obtained post-fermentation solutions is presented in Table 1 and Table 2. The fermentation processes was performed ten times. In the paper, the results of two series of experimental runs were reported (Series 1 and Series 2). After completing the fermentation process, the solution was pretreated by gravitational sedimentation for four hours. Subsequently, it were used as a feed for the treatment by the RO process (Figure 10). In the absence of sedimentation, high turbidity of the fermentation broths could lead to intense fouling phenomenon, resulting in low membrane performance, frequent membrane cleaning, and low permeate quality.

Flow diagram of process performed in the present study.