Aggregation, settling characteristics and destabilization mechanisms of nano-particles under different conditions.

An abundance of nano-particles have been exposed to water environment. Owing to the particle size effects, nano-particles are inclined to absorb harmful substances and increase their levels of toxicity. In this study, the existence state, aggregation and settlement characteristics of nano-particles in the natural water are studied. Influenced by the structural layer repulsion, nano-particles have higher stability in natural water. When coagulants were added, nano-particles could effectively aggregate with slow flocculation speed and relatively small flocs size without hydraulic shearing due to the significant effect of Brownian motion. It is worth noting that the aggregated flocs formed by Brownian motion showed high strength and strong ability to resist hydraulic disturbance, and thus the flocs were harder to break. This is because the combination among nano-particles under hydraulic shearing is the result of a single-point chain-to-chain aggregation mode, while that under the Brownian motion is the result of multi-points face-to-face aggregation mode. Therefore, in the process of re-flocculation, flocs formed by the Brownian motion were more compact. This study provides a new view in nano-particles treatment for both the in-situ treatment process of natural water body and the regular water treatment plants.