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Abstract:To better understand the nanoparticle (NP) transport in the environment, the agglomeration and sedimentation of Al 2 O 3 , SiO 2 , and TiO 2 NPs were evaluated after being treated with bovine serum albumin (BSA) and a commercial humic acid (HA). The morphology of NP agglomerates was examined through a transmission electron microscope (TEM), and the agglomeration kinetics was evaluated using established time-resolved dynamic light scattering techniques. BSA treatments decreased the hydrodynamic diameters (d H ) of the three NPs in both NaCl and CaCl 2 electrolytes due to their steric repulsive forces caused by the BSA globular architecture. The treatments using HA induced the smallest d H of NPs in NaCl electrolyte, but the largest d H of NPs was found in CaCl 2 electrolyte, because the HA bound to each other via calcium complexation and thereby enhanced the NP agglomeration. The zeta potentials of NPs were not the dominant factor to affect agglomeration. The NP sedimentation kinetics were studied through measuring the suspension optical absorbance. It was shown that the BSA treatments retarded the sedimentation in most situations; however, HA treatments accelerated the sedimentation greatly in CaCl 2 electrolyte, which was consistent with the measured changes in the d H values. The smallest d H of HA-treated NPs in NaCl electrolyte did not result in the lowest sedimentation rate, which indicated that the agglomeration size was not the only factor to affect the NP sedimentation.