Separation Science and Technology
A multistage process was used for biosorption of heavy metals from liquid effluents using grape stalks as the biosorbent. The biosorption was carried out with a free biomass suspension in a two-stage, counter-current, stirred batch system. The biomass was separated from the treated effluent using flocculation, sedimentation, and filtering. The filter cake was used, as a small packed column loaded with heavy metals where the elution was performed. The efficiency of the overall system was studied using three synthetic effluents. The first two effluents labeled in this work as F1 and F2 had 10 and 50 ppm of copper, respectively. The third effluent had a complex metal mixture containing 10 ppm of copper, 50 ppm of zinc, 5 ppm of nickel, 100 ppm of calcium, and 100 ppm of sodium. The biosorption system was able to remove 99% of the copper from the F1 effluent (0.08 ppm of copper in the final effluent), using a biomass concentration of 2 g/L. For the F2 effluent, a biomass concentration of 4 g/L was required to obtain a final copper concentration 0.18 ppm. Copper was also removed from the F3 effluent with an efficiency of 98% (final metal concentration of 0.15 ppm). However, it required a biomass concentration of 6 g/L in the two biosorption stages and the other target metals under study, Zn and Ni, had modest removals of 46% and 35%, respectively. The results from the elution experiments demonstrate that the key variables to obtain high metal concentration in the eluate are the metal concentration bounded to the biomass, the superficial velocity of the eluant, and the filter cake depth. Using the F2 effluent to load the biomass up to 12.5 mg/g of copper and performing the elution with a superficial velocity of 0.9 cm/min in a filter cake with depth of 10 cm, a copper concentration in the eluate of 1.8 g/L was achieved, which correspond to a concentration factor of 38-fold.
Year of publication: 2003