Heavy metal sorption by released polysaccharides and whole cultures of two exopolysaccharide-producing cyanobacteria.

The metal removal capacity of cultures of two capsulated, exopolysaccharide-producing cyanobacteria, Cyanospira capsulata and Nostoc PCC7936, were tested using copper (II) as the model metal. C. capsulata cultures removed the greatest amount of copper, with a maximum per unit of biomass (q(max)) of 115.0+/-5.1 mg copper g(-1) of protein, compared with 85.0+/-3.2 removed with Nostoc PCC7936 cultures. Water solutions of pure polysaccharides (RPSs) released into the culture medium by C. capsulata and Nostoc PCC7936 achieved q(max) values of 20.2+/-0.8 mg g(-1) copper per polysaccharide dry weight with C. capsulata RPS and 11.0+/-1.5 mg g(-1) with Nostoc PCC7936 RPS. Cultures of the two cyanobacteria also removed Zn (II) and Ni (II), in both single-metal systems and in multimetal systems with Cu; in the various single-metal systems more copper was removed than Zn or Ni, while in the multimetal systems a smaller amount of each individual metal was removed but the overall amount of all metal ions sorbed or the amount of copper sorbed in the copper-only system was almost the same with C. capsulata, and slightly higher with Nostoc PCC7936.