Removal and Recovery of Toxic Metal Contaminants from Process Effluents Using Integrated Biosorption and Electroplating

The study aimed to apply Micrococcus luteus, an activated sludge bacterial isolate, in an integrated treatment system to remove and recover copper ions from wastewater. The system consisted of fixed-bed biosorption column, regeneration setup and purification unit. To obtain a stable form of M. luteus for packing the column, the cells were immobilized in calcium-alginate/polyacrylamide beads together with rehydration treatment. These cell-immobilized (RIM) beads could maintain a constant volume throughout batch copper biosorption/desorption cycles. No significant differences were found between the RIM beads and the untreated beads, including their biosorption capacities, kinetics, equilibrium isotherms and diffusion mechanisms. The breakthrough of the RIM column was deferred by increasing bed depths (Z) and decreasing influent concentrations (Co) and inlet upward flow rates (Q). The optimal conditions were: Z = 50 cm, Co = 50 mg-Cu/L, and Q = 1 mL/min. Binary-metal biosorption studies demonstrated the metal-binding preference of the RIM column as Pb(II) > Cu(II) >> Ni(II) > Zn(II). The linearized form of the Thomas model provided better simulations of the fixed-bed biosorption profiles and good predictions of the process performances. Of 11 common desorbing materials, CaCl2 displayed a moderate copper desorption ability and a better bead reusability in the batch studies. Similar desorption efficiencies were obtained in the fixed-bed studies under different [CaCl2] and Q. The optimal desorption conditions were: [CaCl2] = 1 M and Q = 1 mL/min. By introducing both synthetic and industrial electroplating wastewater, the copper removal of the RIM column decreased at the initial of the biosorption/desorption cycle(s) and remained steady afterward. A lower efficiency was found in the treatment of the industrial wastewater. The results of X-ray energy-dispersive analysis coupled with the material balance calculation showed that the ion-exchange between calcium and copper ions was one of the major mechanisms of the biosorption and desorption in the RIM column. After a two-step purification using Na2SO4 and Na2HPO 4, the recovered copper was isolated from the desorption effluent and directly re-used in an acid-sulfate-copper-electroplating process. No significantly change in the properties of the deposited workpieces, including their overall appearance, surface smoothness, deposit distribution, coverage, copper purity on the deposits, and electrical resistance, was found in the addition of the recycled copper. In conclusion, the integrated biosorption system could be developed as a promising technology for copper removal and recovery from industrial wastewater.