Heavy metal biosorption in multi component system on dried activated sludge: investigation of adsorption mechanism by surface characterization

Abstract

The dried activated sludge collected from STP- Kolkata Municipal Corporation and Tannery industry, leather complex, Kolkata were used as complex biosorbent for removal of heavy metals. The metal ion concentrations were measured using ion chromatography. The adsorption efficiency with respect to time was performed; the Zn (II) and Cd (II) showed 99% removals within 10 min while Ni (II) and Co (II) attained 98% removal at 20-24 h of contact time both in single and multi metal system. The elucidation of the mechanism of biosorption is necessary to enable the technology to be developed. Mechanism of biosorption of Ni (II), Cd (II), Co (II)and Zn (II)in multi metal removal system was studied by the characterization of the structure and surface chemistry of biomaterial using functional group modification, FT-IR, FESEM-EDX and XPS analysis. FT-IR spectra of before and after multiple metal uptake revealed that the functional groups (amino, carboxylic, hydroxyl, phosphate, sulfonyl and carbonyl) present on surface of the biomaterial were involved in the biosorption process.The wide scanning XPS spectra for dried tannery sludge after biosorption of multi metals showed peaks of Cd, Zn, Ni and Co. The deconvolution of peaks C1s spectra and N1s spectra assigned to C atoms in form of C-C, C-O, O-C-O, O-C=O and N atom in the R-NH2, R-NH3+ group. Change in the peak pattern and shift in the binding energies confirm the involvement of these functional groups.