CADMIUM REMOVAL FROM DILUTE AQUEOUS-SOLUTION BY GEL BEADS OF SUGAR-BEET PECTIN

The metal-accumulative capabilities of polysaccharide gel entrapped mi croorganisms may be of interest for the treatment of waste water conta ining low amounts elf metal ions. The cost of the gel matrix, however, seriously impedes the large-scale development of such immobilized-cel l systems. We have therefore considered the use of pectin extracted fr om sugar beet pulp as a cost-effective alternative to commercial algal alginate and citrus pectin. A simple, inexpensive alkaline hydrolysis was sufficient to reduce by 80% the acetylation degree of sugar beet pectin (SEP) so that the rheological properties of the polymer in aque ous solution became close to those of citrus pectin. For instance, the intrinsic viscosity of saponified SEP was 157 cm(3) g(-1), that of ci trus pectin 197 cm(3) g(-1). Hydrolyzed SEP was able to form gels (at concentrations of 2% w/v or higher) in the presence of divalent cation s (Ca2+). The cadmium-binding capacity (Q(a), mg Cd2+ g(-1) dry gel) o f SBP gel beads compared favourably to that of algal alginate but rema ined somewhat lower than that of citrus pectin: Q(a) SEP -4.6; Q(a) al ginate = 4.1; Q(a) citrus pectin = 7.6. The desorption of Cd2+ ions fr om SEP gel beads in 0.3 M calcium chloride was easy, reaching 81% of t he metal accumulated. The viability of microbial cells entrapped in SB P gel beads was maintained. (C) 1998 Elsevier Science B.V.