Ralf Kägi

Dr. Ralf Kägi

Department Process Engineering

About Me

Research Interests

  • Detection and fate of engineered nanoparticles in the natural environment and engineered systems
  • Transformation of Silver Nanoparticles in urban wastewater systems
  • Development of new analytical methods for nanoparticle detection
  • Characterization of the structure of environmental colloids and particles using microscopic and spectroscopic methods
  • Optimization of sampling and fractionation procedures for colloids and nano scale materials

Research statement
Nano-materials (including engineered nanoparticles(NP), as well as nano-structure materials) are increasingly used in many consumer products due to their ‘beneficial’ properties. However, while these materials are certainly beneficial regarding their respective application, they might not be as beneficial in the aquatic environment. The (unintended) release and the fate of these nano-materials in the aquatic environment are only poorly understood mainly due to the he lack of adequate analytical techniques to detect and characterize these materials in the environment. My research therefore, aims at combining well established standard characterization methods from colloidal sciences, with new methods from materials science and with own developments to detect, quantify and understand the effects of the ‘nano-materials’ in the aquatic environment. The following research areas are of particular interest:

Detection and fate of engineered nanoparticles in the natural environment and engineered systems.
Although a large variety of analytical methods exist to characterize nano scale materials (and especially nanoparticles) mainly developed for materials science applications. these methods are capable of detecting pure substances in high concentrations (such as Ag-NP in concentrated stock solutions), but cannot handle polydisperse and dilute systems. However, natural systems are polydispers and dilute; we therefore try to fractionate aquatic colloids, including engineered NP, into monodisperse size fractions using field flow fractionation techniques. Individual size fractions can be further be analyzed using light scattering, mass spectroscopic or microscopic techniques.

Development of new analytical techniques to detect NP
Commercially available particle detection systems are not designed to detect particles down to the nano scale. A very promising laser based method (Laser Induced Breakdown Detection, LIBD) capable of detecting particles down to about 10nm at low concentrations has been developed almost 20 years ago by Japanese researchers. The technique never had it huge break-through (for several reasons) and thus no commercial LIBD systems are available. However, for certain applications, such as drinking water monitoring, the technique seems to be well suited. We therefore developed our own LIBD prototype in collaboration with the FZ-Karlsruhe, which is being continuously refined.

Characterization of the structure of environmental colloids and particles using microscopic and spectroscopic methods

Within this branch of research I am using state-of-the-art electron
microscopes (SEM and TEM) to characterize particles, such as natural and
experimentally produced aquatic colloids, as well as particles recovered from
ice cores. This part of my research has the rather unspecific goal of seeking any
kind of information stored in the particles that was not accessible with
‘older’ instruments. This exploratory work is vital to my function as head of
the particle laboratory at the Eawag, where I support / advise different
‘users’ on a variety of different materials.

Particle Laboratory

Apart from my own research outlined above I also run the particle laboratory at Eawag. The particle laboratory is a contact-point for all sorts of particle-related questions, especially concerning microscopic work. My engagement in different projects covers all ranges from simple advice over a few measurements for a feasibility study up to solid collaborations. Thanks to very good contacts to the electron microscopy centers at ETHZ and Empa, experts on any kind of materials can be consulted if necessary.

Affiliation with professional societies
Swiss Society for Optics and Microscopy (SSOM), American Geophysical Union (AGU), International Water Association (IWA), Society of Environmental Toxicology and Chemistry (SETAC)

Management Committee:

  • Chair of the IWA specialist group: ‘Nano and water, Nanotechnology for the water sector’ (2012 – 2014)
  • Chair of the Norman WG4: ‘Engineered nanoparticles in the environment’ (2012 – present)
  • Swiss delegate in the management committee of COST action ES1205: ‘Engineered Nanomaterials - from wastewater Treatment & StormwatEr to Rivers? (ENTER)’ (2012 – present).
  • Chair of the Cost action ES1205, WG1: Fate and behavior of ENMs. (2012 – present)

Conference and workshop organization

  • Conference chair of the IWA specialist conference: ‘Nano and water, Nanotechnology for the water sector’, 15.05. – 18.05.2011, Monte Verita, Switzerland (Organiser)
  • Workshop organizer ‘Engineered nanoparticles in the environment’ NORMAN WG4; Zurich 18. – 19. 10.2012
  • Member of the program committee of the IWA Symposium on Environmental Nanotechnology, Nanjing, China, 2013
  • Member of the scientific committee of the 8th International Conference on the Environmental Effects of Nanoparticles and Nanomaterials. Aix en Provence, France, 2013
  • Member of the organizing committee of the Micropol & Ecohazard Conference, Zürich, Switzerland, 2013.
  • Convener of Session 18I: Environmental Application of Engineered Nanomaterials: Benefits and Risks, Goldschmidt Conference, Florence, Italy, 2013

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Curriculum Vitae

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Selected publications

Kaegi, R.; Voegelin, A.; Ort, C.; Sinnet, B.; Thalmann, B.; Krismer, J.; Hagendorfer, H.; Elumelu, M.; Mueller, E. (2013) Fate and transformation of silver nanoparticles in urban wastewater systems, Water Research, 47(12), 3866-3877, doi:10.1016/j.watres.2012.11.060, Institutional Repository
Kaegi, R.; Voegelin, A.; Sinnet, B.; Zuleeg, S.; Hagendorfer, H.; Burkhardt, M.; Siegrist, H. (2011) Behavior of metallic silver nanoparticles in a pilot wastewater treatment plant, Environmental Science and Technology, 45(9), 3902-3908, doi:10.1021/es1041892, Institutional Repository
Kaegi, R.; Voegelin, A.; Sinnet, B.; Zuleeg, S.; Siegrist, H.; Burkhardt, M. (2015) Transformation of AgCl nanoparticles in a sewer system — a field study, Science of the Total Environment, 535, 20-27, doi:10.1016/j.scitotenv.2014.12.075, Institutional Repository
Thalmann, B.; Voegelin, A.; von Gunten, U.; Behra, R.; Morgenroth, E.; Kaegi, R. (2015) Effect of ozone treatment on nano-sized silver sulfide in wastewater effluent, Environmental Science and Technology, 49(18), 10911-10919, doi:10.1021/acs.est.5b02194, Institutional Repository

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Phone: +41 58 765 5273
Fax: +41 58 765 5802
Address: Eawag
Überlandstrasse 133
8600 Dübendorf
Office: BU B17

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Expert of


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