December 2008, Vol. 20, No.12

Research Notes

Study Suggests Cerium Dioxide Could Elude Treatment

Cerium dioxide, used by industries to grind computer components, mobile phone camera lenses, and lasers in CD players, has found its way into the environment and into wastewater, according to a new study conducted by the Institute for Chemical and Bioengineering, a laboratory of the Swiss Federal Institute of Technology Zurich (ETH Zurich; Zurich, Switzerland). More cerium dioxide particles than originally was assumed have been found to pass through the biological separation stage in wastewater treatment, the study concludes.

Scientists expect nanoparticles to be bound in solids, which then can be removed from the water, and that is what was expected for this study, according to an article published in ETH Life magazine on July 15. “Intuitively, we presumed that practically 100% of the cerium oxide particles would remain trapped in the [solids],” said assistant professor Wendelin Stark, who led the research group that conducted the study. “After all, the particles should form clumps and sink to the bottom.” However, the study found that while the majority of cerium dioxide particles bind to the surface of bacteria in wastewater, up to 6% by weight of the particles were found in the exit stream.

The research group performed experiments in a test wastewater plant with nanoparticle concentrations of 100 ppm. According to the article, because this concentration is relatively high, the researchers expect agglomeration of the cerium dioxide to solids to be hindered even more at lower concentrations.

A series of experiments, performed by researchers from ETH Zurich, University of Applied Sciences Wädenswil (Switzerland), and BMG Engineering AG Co. (Schlieren–Zurich, Switzerland), found that bacteria living in the activated sludge excrete soaplike substances that avoid forming clumps and result in a proportion of material that is not sufficiently agglomerated. This enables oxide nanoparticles to leave wastewater treatment plants practically unchanged, according to the ETH Zurich article.

“The particles disperse astonishingly well and do not agglomerate entirely as was assumed,” Stark said. “However, we are still at the beginning of nanosafety research. Further investigations must follow.”