Effect of Ozone Treatment on Nano-Sized Silver Sulfide in Wastewater Effluent.
Silver nanoparticles used in consumer products are likely to be released into municipal wastewater. Transformation reactions, most importantly sulfidation, lead to the formation of nanoscale silver sulfide (nano-Ag2S) particles. In wastewater treatment plants (WWTP), ozonation can enhance the effluent quality by eliminating organic micropollutants. The effect of ozonation on the fate of nano-Ag2S, however, is currently unknown. In this study, we investigate the interaction of ozone with nano-Ag2S and evaluate the effect of ozonation on the short-term toxicity of WWTP effluent spiked with nano-Ag2S. The oxidation of nano-Ag2S by ozone resulted in a stoichiometric factor (number of moles of ozone required to oxidize one mole of sulfide to sulfate) of 2.91, which is comparable to the results obtained for the reaction of bisulfide (HS(-)) with ozone. The second-order rate constant for the reaction of nano-Ag2S with ozone (k = 3.1 × 10(4) M(-1) s(-1)) is comparable to the rate constant of fast-reacting micropollutants. Analysis of the ozonation products of nano-Ag2S by transmission electron microscopy (TEM) and X-ray absorption spectroscopy (XAS) revealed that ozonation dominantly led to the formation of silver chloride in WWTP effluent. After ozonation of the Ag2S-spiked effluent, the short-term toxicity for the green algae Chlamydomonas reinhardtii increased and reached EC50 values comparable to Ag(+). This study thus reveals that ozone treatment of WWTP effluent results in the oxidation of Ag2S and, hence, an increase of the Ag toxicity in the effluent, which may become relevant at elevated Ag concentrations.
Eawag, Swiss Federal Institute of Aquatic Science and Technology , Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.|Institute of Environmental Engineering, ETH Zürich , CH-8093 Zürich, Switzerland.
Basilius
B
Thalmann
Eawag, Swiss Federal Institute of Aquatic Science and Technology , Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.
Andreas
A
Voegelin
Eawag, Swiss Federal Institute of Aquatic Science and Technology , Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.|Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich , CH-8092 Zürich, Switzerland.|School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.
Urs
U
von Gunten
Eawag, Swiss Federal Institute of Aquatic Science and Technology , Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.|Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich , CH-8092 Zürich, Switzerland.
Renata
R
Behra
Eawag, Swiss Federal Institute of Aquatic Science and Technology , Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.|Institute of Environmental Engineering, ETH Zürich , CH-8093 Zürich, Switzerland.
Eberhard
E
Morgenroth
Eawag, Swiss Federal Institute of Aquatic Science and Technology , Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.
Ralf
R
Kaegi
D016825:Chlamydomonas reinhardtii / Q000187:drug effects; D000460:Chlorophyta; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry*; D012834:Silver / Q000737:chemistry; D018030:Silver Compounds / Q000737:chemistry* / Q000633:toxicity; D013440:Sulfides / Q000737:chemistry; D018675:Toxicity Tests / Q000379:methods; D062065:Wastewater / Q000737:chemistry* / Q000633:toxicity; D056928:X-Ray Absorption Spectroscopy
D010126:Ozone; D012834:Silver; D018030:Silver Compounds; D013440:Sulfides; D062065:Wastewater; C013251:silver sulfide; C037548:silver chloride