Hybrid biosorbents from exopolymeric substances immobilized in Ca-alginate and their biosorption mechanisms in single and multi-metal systems

Abstract

ABSTRACT This study developed a hybrid biosorbent consisting of exopolymeric substances (EPS) from Bacillus cereus immobilized in the gelling agent Ca-alginate. Metal removal tests revealed that the hybrid EPS beads showed significantly higher metal removal compared to plain alginate beads. This higher removal efficacy in hybrid biosorbents was attributed to the increased number of functional groups detected via FTIR analysis. Hybrid EPS beads bind metals via the formation of strong covalent bonds (chemisorption), rather than through weak van der Waals forces (physisorption), complying with the pseudo-second order model. This was consistent in both single and multi-metal systems. For adsorption isotherm, metal removal (pH 5, 25ºC, 120 rpm) by hybrid biosorbents in single metal systems fits the Langmuir isotherm (monolayer adsorption). In multi-metal systems, however, the removal of Zn and Cd demonstrated a better fit to the Freundlich isotherm (multilayer adsorption) compared to the typical Langmuir isotherm (for Cu, Pb and Cr). The isotherm models indicated that the maximum biosorption capacity for Cu, Pb, Zn, Cd and Cr was at 34.97, 156.24, 19.19, 11.66 and 38.61 mg g−1, respectively. The hybrid EPS beads are superior for the biosorption of Cu, Pb and Cr compared to existing biosorbents.