Removal of lead (II) and chromium (VI) from simulated wastewater using extracellular polymeric substances from Penicillium expansum

Abstract

Extracellular polymeric substances (EPS) are products of microbial metabolism that exist as a complex of polymers found outside the cells and interior of cell aggregates. Microorganisms use EPS to protect themselves from toxic environment and this property enables the application of EPS in the treatment of wastewater. Removal of lead (II) and chromium (VI) from simulated wastewater by EPS from Penicillium expansum was studied. Maximum uptake of lead (II) was 773.05 mg/g of EPS, while the maximum uptake of chromium (VI) was found to be 618.75 mg/g of EPS in the simulated wastewater under the same removal conditions of 180 rpm, 90 mg/L EPS, 100 min contact time, 5.0 pH, 40 °C temperature, 120 mg/L initial concentration of lead (II) and 100 mg/L initial concentration of chromium (VI). Thermodynamic analyses gave respective enthalpy values of − 1.093 kJ/mol and − 1.030 kJ/mol for lead (II) and chromium (VI), with corresponding entropy values of 2.673 kJ/mol/K and 1.896 kJ/mol/K, these values indicated that the metal uptake by EPS was exothermic and the process can occur spontaneously. Pseudo-second order was the predominant model in the kinetic studies, having the highest R² values of 0.997 for lead (II) and 0.992 for chromium (VI) compared to the other studied kinetic models. Out of the 5 adsorption isotherms considered in this study, the removal process by EPS for both lead (II) and chromium (VI) fitted into the 3 models which can be ranked based on the R² values as Redlich-Peterson, Temkin and Langmuir isotherms. The findings indicate the ability of EPS produced by P. expansum to remove lead (II) and chromium (VI) simultaneously from simulated wastewater which could be due to identical binding sites for both metals with possible involvement of chemical bonds in the stabilization of complexes formed between EPS and Pb²⁺ or EPS and Cr⁶.