Bioremoval of PVP coated silver nanoparticles using Aspergillus niger: the role of exopolysaccharides

Abstract

The present work aims to study the removal of Polyvinylpyrrolidone coated silver nanoparticles (PVP-Ag-NPs) using Aspergillus niger and depict the role of exopolysaccharides in the removal process. Our results show that the majority of PVP-Ag-NPs were attached to fungal pellets. About 74% and 88% PVP-Ag-NPs were removed when incubated with A. niger pellets and exopolysaccharide-induced A. niger pellets, respectively. Ionized Ag decreased by 553 and 1290 fold under the same conditions as compared to stock PVP-Ag-NP. PVP-Ag-PVP resulted in an increase in reactive oxygen species (ROS) in 24h. The UV-Visible spectrum shows the disappearance of Ag characteristic peak and the broadness of the spectrum suggested an increase in size. Dynamic Light Scattering results showed an increase in PVP-Ag-NPs size from 28.4 nm to 115.9 nm for A. niger pellets and 160.3 nm after removal by stress-induced A. niger pellets and further increased to 650.1 nm for in vitro EPS removal. Our findings show that EPS can be used for nanoparticle removal, by increasing the net size of nanoparticles in aqueous media, this will, in turn, facilitate its filtration through conventional filtration techniques commonly used at wastewater treatment plants.