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Fate of Silica Nanoparticles in Simulated Primary Wastewater Treatment

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Helen P. Jarvie*^†, Hisham Al-Obaidi^‡, Stephen M. King^§, Michael J. Bowes^†, M. Jayne Lawrence^‡, Alex F. Drake^‡, Mark A. Green and Peter J. Dobson

NERC Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Crowmarsh Gifford, Wallingford OX10 8BB, U.K., Pharmaceutical Science Division, King’s College London, Franklin-Wilkins Building, Stamford Street, London SE1 9NH, U.K., STFC ISIS Facility, Rutherford Appleton Laboratory, Harwell Science & Innovation Campus, Didcot OX11 0QX, U.K., Department of Physics, King’s College London, Strand, London WC2R 2LS, U.K., and Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, U.K.

Environ. Sci. Technol., 2009, 43 (22), pp 8622–8628

DOI: 10.1021/es901399q

Publication Date (Web): November 15, 2009

* Corresponding author phone: +44 1491 692260; fax: +44 1491 692424; e-mail: hpj@ceh.ac.uk., †

NERC Centre for Ecology and Hydrology.

, ‡

Pharmaceutical Science Division.

, §

STFC ISIS Facility, Rutherford Appleton Laboratory.

Department of Physics, King’s College London.

University of Oxford.

Section:

Waste Treatment and Disposal

Abstract

Through novel application of small-angle neutron scattering, we examined the fate of silica nanoparticles (SiO₂NPs) during simulated primary wastewater treatment, by measuring, in real time, the colloidal behavior of SiO₂NPs in wastewater (sewage). We examined the effects of surface functionality on SiO₂NP fate in wastewater, by comparing both unfunctionalized (uncoated or “bare”) SiO₂NPs and SiO₂NPs functionalized with a thin coating of a nonionic surfactant (Tween 20), which is widely used in personal care and household product formulations containing engineered oxide nanoparticles. Our results show new evidence that the surface functionality of SiO₂NPs plays a crucial role in their flocculation and sedimentation behavior in wastewater, and thus the likely efficacy of their removal from the effluent stream during primary wastewater treatment. Uncoated SiO₂NPs did not flocculate in wastewater over typical residence times for primary treatment. Conversely, surface-functionalized (Tween-coated) SiO₂NPs underwent rapid flocculation in wastewater. Our results show that the surface-functionalized SiO₂NPs are likely to be removed by sedimentation to sewage sludge (typically recycled to land), whereas uncoated SiO₂NPs will continue through the effluent stream. While nanoparticle design is driven by use purpose, this study shows new potential for exploiting surface functionalization of nanoparticles to modify their environmental pathways.