Date of Award

Spring 2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Environmental Engineering - (Ph.D.)

Department

Civil and Environmental Engineering

First Advisor

Taha F. Marhaba

Second Advisor

Tanapon Phenrat

Third Advisor

Sima Bagheri

Fourth Advisor

Robert Dresnack

Fifth Advisor

Hsin Neng Hsieh

Abstract

Engineered nanoparticles, such as titanium dioxide (TiO2), are important building blocks for the evolution of nanotechnology in industries and commercial products. Ever so increasing use of the engineered nanoparticles is bound to result in a substantial fraction of these nanoparticles ending up in wastewater; or surface water and groundwater, which are sources of intake for drinking water treatment. Removal of these engineered nanoparticles in wastewater and drinking water treatment processes is a very important step towards the protection of environmental and public health as well as protecting water treatment units from fouling and other issues.

Experimental studies showed TiO2 removal efficiency of up to 75% using conventional coagulation and flocculation, but only with very high coagulant dosage and prolonged settling time. Clearly, conventional treatment will prove to be costly and impractical to treat TiO2 in water. This research presents a method of using cationic surfactant-modified magnetite nanoparticles to enhance removal efficiency of TiO2 nanoparticles in coagulation and flocculation. Magnetite nanoparticles can be recovered using an organic solvent (such as: cyclohexane) and recycled to minimize cost. Furthermore, effect of modeled parameters: pH, coagulant dose and type, settling time, and initial TiO2 nanoparticle concentration on removal efficiency using the proposed method is also presented. Finally, the best operating ranges for values of modeled parameters, which if maintained will maximize removal efficiency were obtained for both conventional and proposed method.

The method employed herein was able to increase the removal up to 90%+ at much lower coagulant dosage as compared to conventional coagulation and flocculation. The increase in removal efficiency is due to magnetic seeding aggregation. The outcome also indicated that the use of cationic surfactant-modified magnetite nanoparticles makes the coagulation and flocculation not only practical, but also cost efficient for removal of TiO2 engineered nanoparticles. The results of this work will provide water and wastewater authorities with better understanding of the behavior of TiO2 engineered nanoparticles in process streams and will help them come up with a better removal mechanism for TiO2 engineered nanoparticles with least possible or no additional cost.

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