Heavy metal biosorption in binary systems: simulation in single- and two-stage UF/MF membrane reactors

In this paper, the continuous biosorption of binary metal systems onto Sphaerotilus natans cells confined in a membrane reactor was studied. The simulation of the dynamic response of the system to step perturbations was performed developing a model based on the metal mass balances and the Langmuir competitive isotherm. Simulation profiles predict the effect of the different affinity of the metals determined in previous batch tests: in particular considering binary systems and assuming a reversible adsorption phenomenon the metal with the lower affinity constant is replaced by the other (overshoot). A dimensionless formulation of the dynamic model was developed to describe the effect of operative (feed composition) and equilibrium parameters (maximal adsorbent capacity and relative metal affinity). Single- and two-stage reactor configurations were compared outlining the possibility of concentrating the metals in different stages according to their affinity for the adsorbent sites.