Study of biosorption of heavy metals (Lead and Zinc) by bacterial exopolymer

Heavy metals pollution has become one of the most serious environmental problems today. In the present study, different parts of bacteria (exopolymer, live and dead biomass) were used for adsorption of Zinc and Lead. The bacteria used in these experiments were Azotobacter and Rhizobium. Azotobacter and Rhizobium exopolymers were used for adsorption of heavy metals. Metals concentration was measured using a Varian AA-10 atomic absorption spectrophotometer. Azotobacter produced greater exopolymer in exponential growth phase, however Rhizobium in stationary phase had maximum exopolymer production. The zinc and lead adsorption in Azotobacter exopolymers was 10% greater than Rhizobium exopolymers. Biosorption capacity of live biomass of Azotobacter and Rhizobium for zinc and lead were 46% and 33.1% respectively, but about lead adsorption there was no significant difference between live biomass of bacteria. In zinc adsorption there was no difference between dead biomass of Rhizobium and Azotobacter. The amount of lead in 100 ml of urine, river water and well water was measured by using exopolymer biosensor. The Azotobacter exopolymer from 100 ml of urine, river water and well water adsorbed 0.1, 0.25 and 4 mg of Pb+2. g-1 exopolymer respectively, but Rhizobium exopolymer adsorbed only 0.8 mg of lead from 100 ml of well water. The result showed that exopolymer biosensor measures the small amount of lead in the environment.