The fate and transport of engineered nanoparticles in wastewater treatment systems

Date
2016
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Publisher
University of Delaware
Abstract
To comprehend the engineered nanoparticle release to waster, soil, and air, it is important to understand the discharge from specific points of release. And as a point of release, wastewater treatment plants play a critical role in the collection and redistribution of nanoparticles in municipal waste streams. So to better understand its fate and transport, the current study focuses on three major subjects regarding the quantification, particle-particle interaction, and particle-organic sorption of engineered nanoparticles in wastewater treatment plants. ☐ To quantify engineered nanoparticles, a novel pretreatment method was developed for ICP-OES analysis. Samples were collected from various locations in the treatment plant, mainly to verify the transport pathway, and mass balance of each sedimentation basins. A concentration profile was mapped out, to visualize the distribution of engineered nanoparticles throughout the treatment plant. Additional aspects such as the mass flux, particle to organic ratio, and seasonal variations were also mapped out for further analysis. Results showed an overall 80% removal of titanium and 68% removal of zinc through primary and secondary sludge particulates, respectively, indicating the importance of activated sludge in the fate of engineered nanoparticles. Seasonal effects showed elevated amounts through summer and winter, matching the seasonal consumption patterns of nanoparticle imbedded products. ☐ To understand the mechanism behind the fate of engineered nanoparticles in the wastewater treatment plants, the next sections were focused on the interactions of the particles. The first mechanism observed, was the particle-particle interaction of nanoparticles under high concentrations of dissolved organic matter. The main purpose of the observation was to understand the transport characteristics of nanoparticles through attachment efficiency experiments. The uniqueness of the current study was the fact that experimental conditions were set to simulate field conditions, where dissolved organic matter from field-operated plants were tested under TOC concentrations that match the inflow of wastewater treatment plants. Results showed the influence of organic concentration on the stability of particles, where higher organic loading will increase the stability. The second mechanism observed was the interaction of engineered nanoparticles and wastewater sludge. Based on the distribution results in the wastewater treatment plants, particle-organic sorption experiments were conducted with primary and secondary sludge particulates. The main object was to understand the attachment of engineered nanoparticles to wastewater sludge. Sedimentation experiments were conducted to measure the attachment of both suspended materials under various conditions. Conditions such as ionic strength, organic loading, and nanoparticle compositions were tested to verify the impacts of field conditions. Results showed elevated sorption of ENP under lower organic loads, lower ionic strengths and strongly hydrophobic nanoparticles. The knowledge acquired from the current research, can be a basis for future research and policy regulations.
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