(619c) Removal of Oxide Nanoparticles In a Model Waste Water Treatment Plant

The rapid growth of nanotechnology has resulted in various implementations of nanomaterials in advantageous products or as process enhancers in manufacturing. As a result of the increasing production it is important to obtain a better insight in possible risks related to these ultra small particles in the environment. Of particular interest is the clearing efficiency of nanomaterials within sewage plants that could avoid the propagation of nanoparticulate contamination into the aquatic environment.

However, little is known so far about the clearing efficiency of nanomaterials in sewage treatment. Reijnders (Reijnders, 2006) supposes that the standard waste water treatment seems to be poorly suited to the capture of nanomaterials, whereas others (Wiesner et al., 2006) did not support scenarios where containment of nanoparticles in current water treatment infrastructure may become problematic. Due to the present lack of experimental data, the disposal of nanomaterials is not regulated. This appears problematic as it is not clear what happens when inorganic nanomaterials are dispersed in the environment or brought into public sewage treatment plants.

Efficient removal is particularly important in view of increasing long term persistence and evidence for considerable ecotoxicity of specific nanoparticles. The present work investigates the use of a model waste water treatment plant for removal of oxide nanoparticles. (Limbach et al., 2008) While a majority of the nanoparticles could be captured through adhesion to clearing sludge, a significant fraction of the engineered nanoparticles escaped the waste water plant's clearing system and was found in the exit stream of the model plant. Our study demonstrates a significant influence of surface charge and the addition of dispersion stabilizing surfactants as routinely used in the preparation of nanoparticle derived products. A detailed investigation on the agglomeration of oxide nanoparticles in waste water streams revealed an astonishingly high stabilization of the particles against clearance (adsorption on the bacteria from the sludge) presumably through peptide adsorption (Figure 1).

Since cerium oxide is only one representative of the currently rapidly growing material class of nanoparticles, we have additionally compared stability measurements with titania, silica, iron oxide, zinc oxide and calcium phosphate nanoparticles to the here investigated cerium oxide.

This unexpected finding suggests a need to investigate nanoparticle clearance in more detail and demonstrates the complex interactions between dissolved species and the nanoparticles within the continuously changing environment of the clearing sludge

Figure 1. Scanning Transmission electrograph of ceria nanoparticles exposed to clearing sludge. In the Z-contrast images, the high density cerium oxide nanoparticles are bright.

Limbach, L.K., Bereiter,R., Müller, R., Krebs, R., Gälli, R., Stark, W.J., Removal of oxide nano-particles in a model waste-water treatment plant: Influence of agglomeration and surfactants on clearing efficiency (2008) Envrion. Sci. Technol, accepted.

Reijnders, L., Cleaner nanotechnology and hazard reduction of manufactured nanoparticles, (2006), J. Clean Prod. 14 (2), 124-133.

Wiesner, M. R., Lowry, G. V., Alvarez, P., Dionysiou, D., Biswas, P., Assessing the risks of manufactured nanomaterials (2006), Environ. Sci. Technol., 40 (14), 4336-4345.

Limbach, L.K, Li, Y., Grass, R.N., Brunner, T.J., Hintermann, M.A., Muller, M., Gunther, D., Stark, W.J, Oxide nanoparticle uptake in human lung fibroblasts: Effects of particle size, agglomeration, and diffusion at low concentrations, (2005) Env. Sci. Technol 39, 9370-9376.