MATHEMATICALLY MODELING THE REMOVAL OF HEAVY-METALS FROM A WASTE-WATER USING IMMOBILIZED BIOMASS

A technique developed by the U.S. Bureau of Mines using biomass, sphagnum peat moss, immobilized in porous polysulfone beads selectively removed Zn, Cd, and other metals from a zinc mining wastewater to concentrations well below the National Drinking Water Standards. The objective of this paper was to obtain experimental data on the biosorption of several heavy metals onto the beads containing sphagnum peat moss and to develop the appropriate mathematical models that might be used to describe the multicomponent phenomena. Nonequilibrium multicomponent mathematical models were developed and experimental data obtained for the simultaneous, competitive adsorption of six metal ions from an actual wastewater for both batch kinetic and semicontinuous packed-bed experiments. Experimental results indicated a selectivity order of Al > Cd > Zn > Ca > Mn > Mg and that metal ion breakthroughs were quite sensitive to ionic concentrations and adsorptive capacity. In addition, it was observed that, for the packed-bed experiments, the adsorptive capacity of the beads appeared to increase after the first few cycles. Mathematical models provided effective multicomponent equilibrium constants, adsorptive capacities, and reduced overall mass-transfer coefficients. The constants obtained from the packed-bed model were in reasonable agreement with those obtained from the batch kinetic model.