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Sludge concentration, shear rate and nanoparticle size determine silver nanoparticle removal during wastewater treatment

Abstract

Wastewater treatment (WWT) is generally efficient in removing nanoparticles (NPs) from sewage effluent, but the variety in the removal rates has not yet been explained. WWT parameters such as activated sludge (AS) concentration, shear rate and ionic strength were varied in kinetic batch attachment and sedimentation studies using silver NPs having nominal 20 or 80 nm sizes and citrate or PEG coatings. Fitted attachment and detachment rate constants and the resulting distribution ratios at steady state varied with WWT process parameters, but most notably with the NP size, which was also found to influence the settling rates most. NP coating molecule had a limited or no effect. A meta-analysis of literature distribution ratios (attached/detached concentration) of NPs composed of Ag and other materials showed NP (aggregate) size as the only significant parameter. However, while the distribution ratio of silver NPs to AS increased linearly with AS concentration, the final effect of NP effluent concentrations is partly offset by decreased sedimentation rates. The results thus confirm that a WWT process is efficient in removing NPs from wastewater, but relatively small (< 20 nm) non-aggregated NPs are somewhat more likely to exit a WWT process via the effluent into aquatic compartments compared to relatively larger NPs, that nearly entirely leave the WWT plants with AS to soils, incineration plants or landfills.

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Publication details

The article was received on 08 Aug 2017, accepted on 29 Sep 2017 and first published on 04 Oct 2017


Article type: Paper
DOI: 10.1039/C7EN00734E
Citation: Environ. Sci.: Nano, 2017, Accepted Manuscript
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    Sludge concentration, shear rate and nanoparticle size determine silver nanoparticle removal during wastewater treatment

    G. Cornelis, A. Forsberg-Grivogiannis, N. Sköld, S. Rauch and J. Perez-Holmberg, Environ. Sci.: Nano, 2017, Accepted Manuscript , DOI: 10.1039/C7EN00734E

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