Characterisation of acidic sites of Pseudomonas biomass capable of binding protons and cadmium and removal of cadmium via biosorption

The ability of Pseudomonas aeruginosa to accumulate Cd(II) ions from wastewater industries was experimentally investigated and mathematically modelled. From the potentiometric titration and non-ideal competitive analysis (NICA) model, it was found that the biomass contains three acidic sites. The values of proton binding (pK(i) = 1.66 +/- 3.26 x 10(-3), 1.92 +/- 1.63 x 10(-4) and 2.16 +/- 3.79 x 10(-4)) and binding constant of cadmium metal ions (pK(M1) = 1.99 +/- 2.45 x 10(-3) and pK(M2) = 1.67 +/- 4.08 x 10(-3)) on the whole surface of biomass showed that protonated functional groups and biosorption of Cd(11) ions could be attributed to a monodentate binding to one acidic site, mainly the carboxylic group. From the isothermal sorption experimental data and Langmuir model, it was also found that the value of Langmuir equilibrium (pK(f)) constant is 2.04 +/- 2.1 x 10(-5) suggesting that the carboxyl group is the main active binding site. In addition, results showed that the maximum cadmium capacity (q(max)) and affinity of biomass towards cadmium metal ions (b) at pH 5.1 and 20 min were 96.5 +/- 0.06 mg/g and 3.40 x 10(-3) +/- 2.10 x 10(-3), respectively. Finally, interfering metal ions such as Pb(II), Cu(II), Cr(III), Zn(II), Fe(II), Mn(II), Ca(II) and Mg(II) inhibited Cd(II) uptake. Comparing the biosorption of Cd(II) by various Pseudomonas isolates from contaminated environment samples (soil and sewage treatment plant) showed that maximum capacities and equilibrium times were different, indicating that there was a discrepancy in the chemical composition between biomasses of different strains.