Adsorption of fullerene nC60 on activated sludge: Kinetics, equilibrium and influencing factors

• nC60 adsorption well followed pseudo-second-order kinetics and Freundlich model.
• The adsorption process depended strongly on pH and activated sludge concentration.
• There was no significant effect by low ionic strength on nC60 adsorption.
• nC60 adsorption on activated sludge demonstrated high removal efficiency.

The increasing production and use of fullerene C60 nanomaterials raises concerns about environmental risks and human health. However, the materials’ behavior and fate during wastewater treatment are still unclear. We investigated the adsorption of aqueous nanoscale fullerene (nC60) on activated sludge by analysis of adsorption kinetics and equilibrium. The adsorption process closely followed the pseudo-second-order kinetics model, and the adsorption isotherm was well described by the Freundlich model. The adsorption process depended strongly on the activated sludge concentration and pH, but there was no significant effect by the temperature and low ionic strength. The dissolved organic matter in wastewater could obviously inhibit the adsorption process. At mixed liquor suspended solids concentrations of 1000 and 2000 mg/L after 1 h mixing, nC60 removal by adsorption reached 47% and 74%, respectively. Thus, adsorption could play an important role in the fate of nC60 during conventional biological wastewater treatment. The analysis of factors influencing the adsorption amounts indicated that the nC60 adsorption behavior on activated sludge was affected by the combined forces of the hydrophobic attraction, electrostatic repulsion and steric interaction.