Separation of oligoglucuronans of low degrees of polymerization by using a high shear rotating disk filtration module

This paper investigates the purification of oligosaccharides of small degrees of polymerization (DP) obtained by enzymatic degradation of a bacterial polysaccharide produced during fermentation by a Sinorhizobium meliloti mutant strain. We have used a dynamic filtration module consisting in a disk equipped with radial vanes rotating at high speed near a fixed organic membrane. Two processes were tested. The first one consisted in two ultrafiltrations (UF) at 20 and 10 kDa followed by a nanofiltration (NF) at 1 kDa to extract glucuronans of 6 < DP < 55 in the 1 kDa retentate and in the second process we added an initial UF at 50 kDa and a final NF at 0.7 kDa to collect oligomers of 4 <= DP <= 6 in the last retentate. Due to high shear rates produced at the membrane by the disk, permeate fluxes were very large at all ultrafiltration steps, ranging from 370 L h(-1) m(-2) with the 20 kDa membrane, 350 with the 50 kDa one (600 kPa) and 280 with the 10 kDa (1500 kPa). They also decayed relatively little with increasing concentration, to, respectively, 360 and 230 L h(-1) 1 M-2 for 50 and 20 kDa at a volume reduction factor of 4. In NF, these permeate fluxes were, respectively, 80 L h- 1 M-2 at I kDa (' 2000 kPa) and 70 L h(-1) m(-2) at 0.7 kDa. The addition of an initial UF at 50 kDa reduced the membrane fouling by large solutes in the next ultrafiltrations and raised the oligomers mass collected in the I kDa retentate from 3.89 to 6.83 g from the same initial total glucuronans mass of 40 g. These results confirm the high potential of dynamic filtration for fractionation of complex biotechnological solutions due to high shear rates generated at the membrane which, not only increase permeate fluxes by reducing concentration polarization but raise the membrane rejection by reducing diffusive transport through NF membranes. (c) 2007 Elsevier B.V. All rights reserved.