Characteristics of Cadmium(II) Adsorbed by the Extracellular Polymeric Substance Extracted from Waste-Activated Sludge After Short-Time Aerobic Digestion

The extracellular polymeric substance (EPS) extracted from waste-activated sludge after short-time aerobic digestion was investigated to be used as a novel biosorbent for Cd2+ removal from water. The sorption kinetics was well fit for the pseudo-second-order model, and the maximum sorption capacity of the EPS (430.3 mg Cd2+/g EPS) was markedly higher than those of the reported biosorbents. Both Langmuir model and Freundlich model commendably described the sorption isotherm. The Gibbs free energy analysis of the adsorption showed that the sorption process was feasible and spontaneous. According to the results of multiple analytical techniques, the adsorption process took place via both physical and chemical sorption, but the electrostatic interaction between sorption sites with the functional groups and Cd2+ was the major mechanism.