Abstract

The increasing commercial use of engineered zinc oxide nanomaterials necessitates a thorough understanding of their behavior following their release into wastewater. Herein, the fates of zinc oxide nanoparticles (ZnO NPs) and ionic Zn in a real primary sludge collected from a municipal wastewater system are studied via stable isotope tracing at an environmentally relevant spiking concentration of 15.2 µg g−1. Due to rapid dissolution, nanoparticulate ZnO does not impart particle‐specific effects, and the Zn ions from NP dissolution and ionic Zn display indistinguishable behavior as they partition equally between the solid, liquid, and ultrafiltrate phases of the sludge over a 4‐h incubation period. This work provides important constraints on the behavior of engineered ZnO nanomaterials in primary sludge—the first barrier in a wastewater treatment plant—at low, realistic concentrations. As the calculated solid–liquid partition coefficients are significantly lower than those reported in prior studies that employ unreasonably high spiking concentrations, this work highlights the importance of using low, environmentally relevant doses of engineered nanomaterials in experiments to obtain accurate risk assessments.

Highlights

  • For such a scenario, it has been suggested that most released ZnO NPs will partition into the sludge—Zinc oxide nanoparticles (ZnO NPs) have attracted a vast quan- amounting to an estimated concentration of ≈24 μg g−1—that tity of research owing to their wide range of optoelectronic is subsequently amended to soils as biosolids or fertilizer.[5,6]and electrical properties, including transparency in the visible Some of the particles (≈2.3 μg L−1) may discharge into freshwaters as effluents

  • Transmission electron microscopy (TEM) images show that the synthesized 68ZnO nanomaterials were mostly spherical in shape with an average diameter of 7.6 ± 1.7 nm (Figure 1A)

  • Monitoring of two Zn species revealed that Zn from the ZnO NPs distributed in exactly the same manner as the ionic Zn derived from the ZnCl2 in the solid, liquid, and ultrafiltrate phases of the sludge within 30 min

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Summary

Introduction

It has been suggested that most released ZnO NPs will partition into the sludge—. Within the detection limits of the employed techniques relative to the Zn background These studies indicate that ZnO NPs in environmental media transform to several different phases, including ZnS and Zn3(PO4), and can associate with FeOOH under both acidic and neutral pH conditions. Single particle—inductively coupled plasma mass spectrometry (ICP-MS) is one of the few techniques that can detect low, environmentally relevant concentrations of ZnO NMs and subsequent dissolved species.[13] One report showed that size exclusion chromatography (SEC) coupled with ICP-MS can separate ZnO NPs from the released metal ions in environmental waters for quantification, with high recoveries (>97%) of the ions.[14] An additional advantage of this technique is that it provides information about which compartment (i.e., liquid or solid matrix) of the sludge the particles and ions partition into, allowing prediction of their fate in the stages of WWTPs, that is, if they discharge into treated effluent to the aquatic environment or are amended from sewage sludge to soil.

Results and Discussion
Conclusions
Experimental Section
Data Availability Statement
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