2.6.1 Ultrafiltration and concentration of the fermentation broth
Fermentation broth from the 1 m3 crude glycerol fermentation in this study was used to evaluate the DSP. Removal of biomass and protein was performed by ultrafiltration described by Zhanget al (Zhang et al., 2021 ). The pH of the permeate from ultrafiltration was then adjusted to 9 by adding 50% NaOH water solution, and the glycerol content in the permeate was adjusted to 4% by adding 80% raw glycerol. After the adjustment of pH and glycerol content, the fermentation broth was fed to a rotary evaporator (IKA, Germany) for concentration. In the first stage, 85% of the water was evaporated under a heating temperature of 80oC and a vacuum pressure of 50 mbar. In the second stage, the heating temperature was increased to 120oC for the complete water removal.