Adsorbent minimisation in a two-stage batch adsorber for cadmium removal

Cadmium is a toxic metal prevalent in a variety of industrial effluents that is toxic to both humans and animals. This study utilizes nanochitosan, a polymer derived from crustacean shells, as an adsorbent for cadmium removal. The uptake capacity has been determined at 2.01 mmol/g and modelled by Langmuir, Freundlich and Sips isotherms, with the Sips isotherm the most suitable model for the adsorbent. In order to minimise the amount of adsorbent used in a batch treatment process for the cadmium removal, a two-stage batch treatment has been proposed and optimised. A detailed evaluation is made of the consequences of utilizing a less suitable isotherm, and on the benefits of utilizing a two-stage system over a single stage. Both errors from incorrect isotherms and advantages of a two-stage system are most significant at low influent concentrations and high target removal efficiencies, relevant to environmental regulatory discharge limits.