The majority of pure silver nanoparticles in consumer products are likely released into sewer systems and usually end up in wastewater treatment plants (WWTPs). Research investigating the reduction in nanoscale silver particles (n-Ag-Ps) has focused on the biological treatment process, generally in controlled laboratory experiments. This study, analyzing the field-collected samples from nine municipal WWTPs in Germany, is the first to evaluate the reduction in n-Ag-Ps by mechanical and biological treatments in sequence in WWTPs. Additionally, the concentration of n-Ag-Ps in effluent was determined through two different methods that are presented here: novel ionic exchange resin (IER) and cloud point extraction (CPE) methods. The n-Ag-Ps concentrations in influent were all low (<1.5 μg/L) and decreased (average removal efficiency of ∼35%) significantly after mechanical treatment, indicating that the mechanical treatment contributes to the n-Ag-Ps removal. Afterward, more than 72% of the remaining n-Ag-Ps in the semi-treated wastewater (i.e., wastewater after mechanical treatment) were reduced by biological treatment. Together, these processes reduced 95% of the n-Ag-Ps that entered WWTPs, which resulted in low concentration of n-Ag-Ps in the effluents (<12 ng/L). For a WWTP with 520,000 t/d treatment capacity, we estimated that the daily n-Ag-Ps load in effluent discharge equated to about 4.4 g/d. Obviously, WWTPs are not potential point sources for n-Ag-Ps in the aquatic environment.

Silver-based nanoparticles (Ag-b-NPs) emitted by wastewater treatment plants (WWTPs) are considered to be widely present in the natural environment. However, there is much that is unknown about the effect of WWTP effluent on the occurrence of Ag-b-NPs in surface waters. On the basis of field analysis of representative WWTPs in Germany, we demonstrate that more than 96.4% of Ag-b-NPs from wastewater influent are removed through WWTPs, even though influent contains Ag-b-NP concentrations of tens to hundreds ng L(-1), resulting in effluent Ag-b-NP concentrations of 0.7-11.1 ng L(-1) over the seasons. The estimated flux of Ag-b-NPs associated with WWTPs effluent discharge is ∼33 kg y(-1) in Germany. WWTPs effluent increases Ag-b-NP levels of the River Isar to 2.0-8.6 ng L(-1), while remarkable decreases are observed at sites ∼1.5 km downstream of each discharge point, and Ag-b-NP levels then keep stable (0.9-2.3 ng L(-1)) until the next discharge point, showing subtle differences in Ag-b-NP levels between the river and reference lakes without industrial sources and WWTPs effluent discharge. Our results demonstrate that WWTPs effluent can exert a clear influence on the occurrence of Ag-b-NPs in surface waters.

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Capable of preserving the size and shape of nanoparticles, a novel method to effectively and selectively extract noble metal nanoparticles even at the 80 ng L(-1) level from real environmental water was designed and performed using a noncovalent reversible adsorption onto an ionic exchange resin.

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