Influences of activated sludge surface properties on adsorption of aqueous fullerene C60 nanoparticles

Rapid increases in the amounts of fullerene C₆₀ nanoparticles (nC₆₀) being produced and used will inevitably lead to increases in the amounts released into the aquatic environment. This will have implications for human and ecosystem health. Wastewater treatment plants are key barriers to nC₆₀ being released into aquatic systems, but little information is available on how adsorption processes in wastewater treatment plants affect the fates of nC₆₀. We investigated the effects of the surface properties of activated sludge on the adsorption of nC₆₀ and related mechanisms by modeling the adsorption kinetics and equilibrium process and performing correlation analyses. The adsorption of nC₆₀ closely followed the pseudo-second-order kinetic model (R > 0.983), the Freundlich isotherm model (R > 0.990), and the linear partitioning isotherm model (R > 0.966). Different adsorption coefficients, 1.070–4.623 for the Freundlich partitioning model and 1.788–6.148 for the linear partitioning model, were found for different types of activated sludge. The adsorption coefficients significantly positively correlated with the zeta (ζ) potential (R = 0.877) and hydrophobicity (R = 0.661) and negatively correlated with particle size (R = ?0.750). The results show that nC₆₀ adsorption is strongly affected by the surface properties of activated sludge because changes in surface properties cause changes in the electrostatic and hydrophobic interactions that occur.