Studies on the biosorption of Pb(II) ions from aqueous solution using extracellular polymeric substances (EPS) of...

The extracellular polymeric substances (EPS) namely protein, polysaccharide, biosurfactant and deoxyribonucleic acid (DNA) in its purified forms isolated from Pseudomonas aeruginsa were independently investigated for their Pb(II) biosorption capacities and mechanisms. Two parameters namely concentration of EPS component and concentration of Pb(II) ions were optimized for maximum Pb(II) biosorption. The maximum amounts of Pb(II) uptake corresponded to 4.8 mg per mg of protein, 0.48 mg per mg of polysaccharide, 0.041 mg per mg of biosurfactant, 0.42 mg per mg of ssDNA (single-stranded DNA) and 0.30 mg per mg of dsDNA (double-stranded DNA). The biosorption isotherms of Pb(II) adhered to the Langmuir model, for the individual EPS components. The standard Gibbs free energy (ΔG°) values calculated using Langmuir constants showed that the biosorption of Pb(II) by the individual EPS component was spontaneous and attested to a chemisorption process. The FTIR studies revealed the functional groups responsible for Pb(II) binding and the EDAX studies confirmed the presence of lead on EPS after biosorption. The protein constituent showed the highest Pb(II) biosorption capacity among other components. The differences in the protein profile of P. aeruginosa in the presence and absence of Pb(II) ions using Sodium dodecyl sulphate- polyacrylamide gel electrophoresis (SDS-PAGE) could be attributed to the possible resistance mechanisms of P. aeruginosa cells.