Abstract

This paper represents the heavy metal adsorptive potential of exopolysaccharides (EPS) produced by two cyanobacteria Anabaena variabilis and Nostoc muscorum. The results indicated that 30 mg dry wt. of cyanobacterial EPS was optimal for biosorption of tested heavy metals. The adsorption capacity of tested EPS decreased as initial metal concentration increased. The EPS of the two organisms adsorbed the metal ions with nearly similar efficiency. The maximum removal for Cu2+ (86 and 88%), Cd2+ (78 and 82%), Zn2+ (55 and 49%) and Ni2+ (48 and 44%) were observed at 200 ppm metal concentration with 30 mg dry wt. EPS of A. variables and N. muscorum, respectively. However, Co2+ recorded the maximum uptake (68 and 71%) at 400 ppm with 30 mg dry wt. of the EPS of A. variabilis and N. muscorum, respectively. The minimum metal removal was observed at 1000 ppm of Zn2+ (6 and 10%), Ni2+ (12 and 17%) and Co2+ (23 and 17 %) by 30 mg dry wt. EPS of A. variabilis and N. muscorum, respectively. The affinity of the two cyanobacterial EPS to metal binding was in the order: Cu2+ > Cd2+ > Co2+ > Zn2+ > Ni2+. The present study indicated that the cyanobacterial EPS are promising for the removal of toxic heavy metals from polluted water.

Key words: Exopolysaccharides, heavy metals, A. variabilis, N. muscorum.