Effect of Ozone Treatment on Nano-Sized Silver Sulfide in Wastewater Effluent

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• 作者：Basilius Thalmann ; Andreas Voegelin ; Urs von Gunten ; Renata Behra ; Eberhard Morgenroth ; Ralf Kaegi
• 刊名：Environmental Science & Technology
• 出版年：2015
• 出版时间：September 15, 2015
• 年：2015
• 卷：49
• 期：18
• 页码：10911-10919
• 全文大小：415K
• ISSN：1520-5851

文摘

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^{鈥?/sup>) with ozone. The second-order rate constant for the reaction of nano-Ag₂S with ozone (k = 3.1 脳 104 M鈥? s鈥?) 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.}