Recovery of microbial polysaccharides from fermentation broths by microfiltration on ceramic membranes

✍ Scribed by Christelle Harscoat; Michel Y Jaffrin; Patrick Paullier; Bernard Courtois; Josiane Courtois

• Publisher: Wiley (John Wiley & Sons)
• Year: 1999
• Tongue: English
• Weight: 176 KB
• Volume: 74
• Category: Article
• ISSN: 0268-2575
• DOI: 10.1002/(sici)1097-4660(199906)74:6<571::aid-jctb78>3.0.co;2-t

✦ Synopsis

This paper investigates the extraction of microbial polymers (polysaccharides) from fermentation broths of Sinorhizobium meliloti M5N1CS using cross¯ow ®ltration through ceramic membranes of various pore sizes from 0.1 to 0.8 mm. The duration of fermentation was set at 70 h in order to maximize the production of high molecular weight polysaccharides (average 2 Â 10 5 Da). The 0.1 mm membrane underwent rapid fouling and was found inadequate for this application. For the other membranes, the sieving coef®cients decreased from 95% to about 20% in 90 min, at a slower rate than the permeate ¯ux. The largest permeate and mass ¯uxes were obtained with the 0.5 mm membrane (18.5 Â 10 À6 m s À1 and 20 Â 10 À6 gm À2 s À1 ). Increasing the ¯uid velocity from 3 to 6 m s À1 increased both the permeate ¯ux and sieving coef®cients, while raising the transmembrane pressure from 50 kPa to 100 kPa increased the ¯ux slightly but decreased the sieving coef®cient. Polysaccharide extraction will be maximized by operating at high velocities and low transmembrane pressure (TMP) which may require cocurrent recirculation of the permeate. Experiments with cell-free solutions showed that the permeate ¯ux is mostly limited by the bacterial layer deposited on the membrane while the presence of cells has a positive effect on the sieving coef®cient. Irreversible fouling due to polymer adsorption on the membrane decreased with increasing pore size and velocity but increased strongly with TMP.