NanoFASE Case study - Removal of Ag and CeO2 NP by a pilot WWTP

We spiked selected Silver and Cerium NPs (50 nm AgNP and ~10-30 nm CeO2 NP) to a pilot waste water treatment plant (WWTP) and determined crucial NP characteristics (e.g., size, chemical speciation) as well as NP removal efficiencies over a period of 86 days. 

Release scenario


AgNP are released from consumer products and anti-microbial coatings and enter WWTP via the wastewater stream.

CeO2 NPs are expected to be released from catalyst, chemical-mechanical planarization (CMP) and coating-/paint applications to the wastewater stream and enter WWTPs.

  1. ENM release from the WWTP is mainly governed by the amount of total suspended solids released from the WWTP. Elimination efficiencies were >99%, regardless of the ENM type.
  2. The size of the particles that were emitted through the effluent over the experiment duration was rather constant and comparable to the particle size of the initial material for CeO2 (~30 nm), but Ag(2S) particles showed considerable variations, possibly as a result of the sulfidation process already occurred in the activated sludge. 
  3. In the digested sludge, Silver NP were sulfidized. Ce NP agglomerates detected in the digested sludge showed sizes ~50 nm to >100 nm. 
  4. Ce in the digested sludge was occurring to 40% as a Ce(III) phase after 86 days.


Emitted to

  1. Size distribution of NP emitted from the WWTP via the effluent
  2. Removal efficiency of the WWTP for the different NP
  3. Speciation of Ce in the sludge after the experimental period of 86d (assessed using XAS)



Surface water

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Read also


Visit the NanoFASE Library.

Kägi et al. (2019) Fate of NanoParticles in Managed Waste Facilities

B. Vriens, A. Voegelin, S. J. Hug, R. Kaegi, L. H. Winkel, A. M. Buser and M. Berg, Quantification of Element Fluxes in Wastewaters: A Nationwide Survey in Switzerland, Environ. Sci. Technol., 2017, 51, 10943-10953.




Ralf Kägi

EAWAG, Switzerland




Alexander Gogos

EAWAG, Switzerland