Adsorption properties of chromium (VI) on extracellular polymeric substances (EPS)

The extraction of extracellular polymeric substances (EPS) from activated sludge and the absorption properties of chromium (VI) (Cr⁶⁺) on EPS were examined in this experiment. The effects of adsorption time, pH, mass of EPS, and initial Cr⁶⁺ concentration on Cr⁶⁺ removal efficiency were investigated. The results indicated that high speed centrifugation was efficient in the extraction of EPS and caused less damage to cells, meanwhile EPS extracted by this method was efficient in the adsorption of Cr⁶⁺. The adsorption reached equilibrium when the adsorption time was 240 min. The adsorption rate and the unit adsorption capacity were 50.83% and 19.06 mg g^-1 EPS respectively. The optimal pH and mass of EPS were 6 and 400 mg L^-1 on the condition that the initial Cr⁶⁺ concentration was 100 mg L^-1. The adsorption rate declined with the rising of initial Cr⁶⁺ concentration, but the unit adsorption capacity increased. The results demonstrated that the EPS extracted from activated sludge would be applicable to removing Cr⁶⁺.