Equilibrium model for cadmium adsorption by green algae in a batch reactor

Abstract

This paper reports the results of a study on the equilibrium behavior of cadmium adsorption by a tropical, indigenous single-cell algal species, identified as Oocystis sp., in a static reactor. An exponential equation, in the form of Ce / Co = α exp (βM/Co), was found to be statistically significant in expressing the relationship between the ratio of equilibrium cadmium (Cd) concentration in solution (Ce) to the initial cadmium concentration (Co) and the ratio of algal biomass (M) to initial cadmium concentration (Co) for both living and dead algal biomass. Based on the above equation and the mass balance of cadmium in the system, another two equations were developed and verified by a series of batch experiments. One equation, in the form of ×/m = [1 - α exp(βM/Co)]/(M/Co), describes the relationship between the cadmium content per unit algal biomass (×/m) and the ratio M/Co. The other equation takes the form of x/m = β (1 - Ce/Co)/In(Ce/αCo) and describes the relationship between the ratio of equilibrium cadmium concentration to initial cadmium concentration and cadmium content per unit algal biomass. The above models for Cd adsorption were found to be applicable over a pH range of 4.5-10.5 even though it was found that pH affects the Cd adsorption potential significantly.