Selection of optimum formulation for biosorbing lead and cadmium from aquatic solution by using PVA-SA’s immobilizing Lentinus edodes residue

This study focused on macrofungi Lentinus edodes residue immobilized by polyvinyl alcohol (PVA)-Na-alginate (SA) for lead (Pb) and cadmium (Cd) adsorption. Based on the ability of absorbing Pb2+ and Cd2+ from aqueous solution, the mechanical strength and balling property, an orthogonal experiment was done to confirm the optimum formulation of PVA-SA’s immobilizing L. edodes. The optimum immobilization formulation for absorbing Pb2+ was 8% (m/V) PVA + 1% SA + 3% L. edodes + 2% CaCl2 in saturated H3BO3 solution with adsorption rate of 95.4%, while that for absorbing Cd2+ was 5% PVA + 1% SA + 3% L. edodes + 2% CaCl2 in saturated H3BO3 with adsorption rate of 63.7%. The Langmuir isotherm model best described free L. edodes for Pb2+ adsorption with R2 of 0.9939. Freundlich isotherm model best described free L. edodes for Cd2+ adsorption with R2 of 0.9993 and best described Pb2+ and Cd2+ adsorption by immobilized L. edodes with R2 of 0.9587 and 0.9823 respectively. The adsorption for Pb2+ and Cd2+ by L. edodes reached equilibrium within 1 h with equilibrium quantity (qe ) of 0.8440 mg Pb2+/g and 1.8120 mg Cd2+/g respectively, while that by immobilized L.edodes reached equilibrium within 3 h and 7 h separately with qe of 0.4925 mg Pb2+/g and 0.2008 mg Cd2+/g respectively. The pseudo-second-order model fit well Cd2+ and Pb2+ adsorption kinetics by free L. edodes and immobilized L. edodes. The rate constant k2 of the pseudo-second-order model was 1.2531 for Cd2+ adsorption and was 1.3241 for Pb2+ by free L. edodes, and that was 0.7805 for Pb2+ and 0.2310 for Cd2+ by immobilized L. edodes respectively. The theoretic maximum adsorption quantity (qm ) of of 6.4475 mg/g for Cd2+ by immobilized L. edodes was higher than qm of 2.8321 mg/g for Cd2+ by free L. edodes calculated from the Langmuir model and the k value of 3.0401 by immobilized L. edodes calcuated from the Freundlich model for Pb2+ adsorption was higher than the k value of 0.7704 for Cd2+ adsorption by free L. edodes indicated that after immobilization treatment, the capacity of L. edodes for Pb2+ and Cd2+ adsorption increased, and the adsorption ability for Pb2+ was stronger than Cd2+ by immobilized L. edodes.