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Yttrium Residues in MWCNT Enable Assessment of MWCNT Removal during Wastewater Treatment

1
Nanosystems Engineering Research Center for Nanotechnology Enabled Water Treatment, School of Sustainable Engineering and The Built Environment, Arizona State University, Tempe, AZ 85287-3005, USA
2
Department of Civil and Environmental Engineering, University of Nevada, Reno, NV 89557-0258, USA
3
School of Molecular Sciences, Arizona State University, Tempe, AZ 85287-1604, USA
*
Author to whom correspondence should be addressed.
Nanomaterials 2019, 9(5), 670; https://doi.org/10.3390/nano9050670
Received: 19 March 2019 / Revised: 23 April 2019 / Accepted: 25 April 2019 / Published: 1 May 2019
(This article belongs to the Special Issue Sustainable and Safe Nano-Enabled Water Treatment Applications)
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Abstract

Many analytical techniques have limited sensitivity to quantify multi-walled carbon nanotubes (MWCNTs) at environmentally relevant exposure concentrations in wastewaters. We found that trace metals (e.g., Y, Co, Fe) used in MWCNT synthesis correlated with MWCNT concentrations. Because of low background yttrium (Y) concentrations in wastewater, Y was used to track MWCNT removal by wastewater biomass. Transmission electron microscopy (TEM) imaging and dissolution studies indicated that the residual trace metals were strongly embedded within the MWCNTs. For our specific MWCNT, Y concentration in MWCNTs was 76 µg g−1, and single particle mode inductively coupled plasma mass spectrometry (spICP-MS) was shown viable to detect Y-associated MWCNTs. The detection limit of the specific MWCNTs was 0.82 µg L−1 using Y as a surrogate, compared with >100 µg L−1 for other techniques applied for MWCNT quantification in wastewater biomass. MWCNT removal at wastewater treatment plants (WWTPs) was assessed by dosing MWCNTs (100 µg L−1) in water containing a range of biomass concentrations obtained from wastewater return activated sludge (RAS) collected from a local WWTP. Using high volume to surface area reactors (to limit artifacts of MWCNT loss due to adsorption to vessel walls) and adding 5 g L−1 of total suspended solids (TSS) of RAS (3-h mixing) reduced the MWCNT concentrations from 100 µg L−1 to 2 µg L−1. The results provide an environmentally relevant insight into the fate of MWCNTs across their end of life cycle and aid in regulatory permits that require estimates of engineered nanomaterial removal at WWTPs upon accidental release into sewers from manufacturing facilities. View Full-Text
Keywords: MWCNTs; wastewater treatment; yttrium; RAS; spICP-MS; ICP-MS MWCNTs; wastewater treatment; yttrium; RAS; spICP-MS; ICP-MS
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Kidd, J.; Bi, Y.; Hanigan, D.; Herckes, P.; Westerhoff, P. Yttrium Residues in MWCNT Enable Assessment of MWCNT Removal during Wastewater Treatment. Nanomaterials 2019, 9, 670.

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