Mechanistic modeling of heavy metal biosorption in batch and membrane reactor systems

In this study, a microbial culture of Arthrobacter sp. was characterized and tested as heavy metal biosorbent in different experimental conditions (pH and biomass concentrations) and operative configurations (free cell in batch system and membrane reactor). Biosorption batch trials with free cells were carried out using an original procedure defined as ‘‘subsequent additions method’’ (SAM), consisting of successive additions of heavy metal concentrated solution to a cellular suspension at constant pH. Mechanistic models for copper and cadmium biosorption have been developed taking into account the acidic properties of the cell wall constituents derived from biomass characterization. These models reveal the complexity of the metal biosorption phenomenon and the need to consider different chemico-physical mechanisms operating simultaneously. A membrane reactor system is proposed as a means for confining biomass cells, thus permitting a semicontinuous operation and avoiding immobilization procedures. A mathematical model based on metal mass balance considering the effect of pH on equilibrium adsorption fitted well the experimental data at low pH values and biomass concentrations. In contrast, a mathematical model, considering partial cell disruption during the biosorption trial, was necessary to understand and analyze the system behavior at high biomass concentrations.