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Item Summary

Authors:Chun, Cherisse Kanani
Contributors:Jun, Soojin (advisor)
Food Science (department)
Keywords:Food science
Drinking Water
Escherichia coli
Insulator-Based Dielectrophoresis
show 2 moreNon-Uniform Electric Field
Water Treatment
show less
Date Issued:Dec 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:Since water is vital to all forms of life, achieving basic water security for all human beings remains a top priority. However, millions of people around the world, especially those living in least developed countries, do not consume water from a reliable potable water source. As a result, contaminated water has been the cause of a wide range of diseases such as hepatitis A, cholera, typhoid, polio, dysentery, and diarrhea. Water stress is brought on by a variety of social, environmental, and economic factors that threaten the health and well-being of a large number of individuals. The World Health Organization predicts that by the year 2025, half of the population will live in water-scarce areas that will need to implement progressive strategies for water re-use and management.
Water intended for drinking contains undesirable pollutants such as organic and inorganic contaminants, as well as pathogens like bacteria, viruses, and protozoa. Although water sanitation has improved greatly over the past few decades, the technologies currently being used to enhance the safety of water have a number of disadvantages. For instance, chemical disinfection with the addition of chlorine can result in the production of carcinogenic disinfection by-products that are linked to heart disease, liver and kidney cancer, and sometimes death. In addition, pressure-driven filtration methods, such as reverse osmosis and nanofiltration, are energy inefficient and prone to fouling. These drawbacks have been heavily documented and can lead to steep increases in the general cost to run the system.
As an alternative to filtration, a cell manipulation method known as dielectrophoresis (DEP) has garnered interest in the scientific community as a means to remove bioparticles from tap water. DEP is the net translational movement of a polarizable particle that occurs when it is subject to a non-uniform electric field. Positive-DEP occurs when the particle moves towards the region of high electric field, whereas negative-DEP describes the motion of a particle when it moves away from the high field region. There are two dominant forms of separation DEP: migration and retention. In migration DEP, particles are able to migrate to either weak or strong electric field areas; while in retention DEP, DEP forces are made to compete with fluid-flow forces to trap particles in place and prevent them from moving out of the channel. DEP has been shown to separate, trap, and sort a wide range of bioparticles, including bacteria, proteins, viruses, DNA, and blood cells.
To test the hypothesis that DEP can influence bacterial cells so that they may be separated from tap water, this thesis describes two different types of DEP devices that were fabricated for bacterial removal from a continuous stream of water. The main objective of this study was to design a single-stage dielectrophoresis device that could separate Escherichia coli K12, a target bacterium and fecal indicator organism, from contaminated tap water. Next, the device fabricated using relatively inexpensive materials and simple procedures was tested for its efficacy using a combination of different experimental parameters such as varying voltages, flow rates, and dielectric bead sizes. The fabrication methods, materials and surfaces, and possible applications for both devices were discussed.
The second chapter of this thesis discusses the first DEP device design that was microfluidic and utilized a standard pin-and-plane electrode configuration. Based on a previous design from Dr. Jun’s research lab, this new device was intended to address and resolve issues such as the large channel width and short electrodes. The channel width was decreased since high electric field is only produced in the narrow electrode gap directly near the edges of the electrodes. Consequently, the strength of the DEP force is greatly reduced as the distance from the electrodes increases in a wide channel. Also, by elongating the electrodes, the bacterial cells are subject to a longer period of DEP influence so that they have more time to move across the channel. The device’s Y-junction channel used migration-based DEP to draw the E. coli K12 cells towards one outlet, leaving the other outlet with a reduced microbial load. Polydimethylsiloxane (PDMS) was used to construct the device, and the pin and base electrodes were made out of titanium. A syringe pump created a continuous flow of E. coli solution through the device, and a frequency generator and voltage amplifier were used to produce the non-uniform electric field that was monitored on an oscilloscope. Different voltages and flow rates were applied to see which combination resulted in the highest separation efficiency. The greatest separation yield was 67.3% with the device set at 60V and 1 MHz, paired with a 0.1 mL/min flow rate. This yield was slightly greater than the 47% that was achieved with the former graduate student’s device, but was still under a 1-log reduction.
To achieve a greater separation efficiency, a new design approach was taken. The third chapter of this thesis explains how the shortcomings of the first DEP device were resolved using an alternative to traditional DEP, called insulator-based DEP (iDEP). A millifluidic iDEP device was packed with dielectric glass beads that altered the electric field distribution so that there were a greater number of high electric field regions. Instead of migration DEP, retention DEP occurred by trapping the bacteria on the surface of the glass beads, as well as at the contact points, where the electric field was greatest. The device channel was printed on a stereolithography 3D printer and coated with PDMS. Stainless steel plates surrounded both sides of the rectangular channel to form the electrodes. The same experimental set-up used in the second chapter was utilized, and the applied voltages, flow rates, and glass bead sizes were varied. The highest percent reduction of E. coli K12 was 99.9% with a combination of 60 V, 200 µm bead size, and a 1.0 mL/min flow rate. Greater applied voltages, slower flow rates, and smaller bead sizes seemed to lead to a greater reduction of the bacteria.
These studies showed that iDEP serves as a practical alternative to traditional DEP that has a limited throughput and is generally intended for microfluidic applications. Since this study acted as a basic proof-of-concept, further research should be conducted to determine the potential for iDEP to be scaled-up and serve as a method of filtration that is not prone to fouling and is more energy efficient. The potential uses of DEP span far beyond the current biomedical applications that are already studied at length. DEP may also have a variety of food processing functions that should be evaluated, including the removal of yeast from beer and contaminants from milk or juice without the application of heat.
Description:M.S. Thesis. University of Hawaiʻi at Mānoa 2018.
Pages/Duration:120 pages
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: M.S. - Food Science

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