Biosorption of sub-micron-sized polystyrene microplastics using bacterial biofilms

Microplastics are becoming a global concern because they pose potential ecological and toxicological risks to organisms. Thus, removing microplastics from aquatic environments is important. In this study, we evaluated the capability of bacterial biofilms as a biological source for the biosorptive removal of sub-micron-sized polystyrene (PS) microplastics. Three bacterial strains-specifically, Pseudomonas aeruginosa, Bacillus subtilis, and Acinetobacter sp.-were used to form biofilms, and each biofilm was tested in batch experiments for the removal of submicron-sized PS microplastics. The Acinetobacter sp. biofilm demonstrated excellent removal performance against 430 nm-PS microplastics than other bacterial biofilms and showed a removal capacity of 715.5 mg/g upon treatment with the PS microplastics for 20 min, thus it employed further adsorption experiments. The biosorption of 430 nm-PS microplastics onto the Acinetobacter sp. biofilm was well explained by the pseudo-second-order kinetics and Freundlich isotherm models. Fourier transform infrared analysis indicated that biosorption of 430 nm-PS microplastics onto the Acinetobacter sp. biofilm involved chemisorption. Three environmental parameters-temperature, pH, and coexisting ions-marginally affected the biosorption of 430 nm-PS microplastics onto Acinetobacter sp. biofilm. However, the biosorption capability of Acinetobacter sp. diminished when the 430 nm-PS microplastics were incubated in environmental freshwaters for 7 d.