pH, ionic strength and dissolved organic matter alter aggregation of fullerene C60 nanoparticles suspensions in wastewater

The rapid increase in the production and use of fullerene C60 nanoparticles raise concerns about environmental risks and human health. Wastewater treatment plants are key barriers to their discharge into the environment. The aggregation behavior of aqueous suspensions of C60 nanoparticles (nC60) could affect their transport, bioavailability, and removal during wastewater treatment. We tested the aggregation of nC60 in wastewater at different values of pH, ionic strength, and dissolved organic matter (DOM). The nC60 remained relatively stable in filtered wastewater under environmentally relevant conditions up to 24h. But at pH 3 or at high ionic strength (\u3e100mM NaCl), the aggregate size increased greatly, reaching micrometer scale after only 1h. However, the aggregation behavior varied among wastewater samples even at values of similar zeta potential, compared with that in filtered secondary effluent and aeration tank liquor, that in filtered primary effluent was obviously inhibited. This inhibition could be attributed to the steric stabilization due to the adsorption of DOM on nC60 aggregate in addition to electrostatic stabilization. The aggregation results also suggest that membrane filtration could be improved by adjustments to pH