Air bubbles are a promising means of controlling fouling for a range of applications, particularly delaying fouling in marine environments. This work investigates the mechanism by which the collision of an air bubble with a solid removes adsorbed bacteria. A key feature of the work is that the numbers of bacteria were monitored via video microscopy throughout the collision, so we were able to explore the mechanism of bacteria removal. When a bubble collides with a solid, an air–water interface crosses the solid twice, and we were able to distinguish the effects of the first and second air–water interface. The bacterium Pseudomonas aeruginosa was allowed to adhere to smooth polydimethylsiloxane (PDMS) and then a collision with a bubble was investigated for one of three different approach geometries: perpendicular, parallel, and oscillating parallel to the solid surface. Other factors examined were the speed of the bubble, the duration of bacterial adhesion on the solid surface, and the wettability of the solid. Surface wettability was identified as the most significant factor. When the solid dewets, almost all bacteria were removed from hydrophobic surfaces upon the passage of the first air–liquid interface. In contrast, when a thin liquid film remained between the solid and the bubble (a hydrophilic solid), variable amounts of bacteria remained. Although almost all bacteria were initially removed from hydrophobic solids, many bacteria were redeposited on hydrophobic surfaces upon the passage of the second air–liquid interface, especially when the first and second air–liquid interfaces moved in opposite directions. As described previously, a lower velocity of the bubble allows more time for the thin liquid film to drain, and improved removal efficiency on hydrophilic solids. A rougher solid (8 µm diameter hemispherical protrusions) decreased the detachment efficiency because bacteria and liquid were able to shelter in concavities. Air bubbles are capable of removing bacteria over a range of conditions and are a potentially efficient means of combating biofilm growth for practical applications. / Master of Science / A major problem for equipment submerged in seawater is their eventual coverage in marine organisms including bacteria, barnacles, seaweed, and algae. This work investigates how effectively an air bubble removes bacteria adhered to a submerged solid. Adhered bacteria were observed and counted throughout the interaction of a bubble with a solid. When a bubble collides with a solid and is then removed, the bubble edge passes over the solid twice. The edge of the bubble is referred to as an air–liquid interface. The effects on adhered bacteria removal of the first and second passes of the bubble air–liquid interface were observed. Pseudomonas aeruginosa, a bacterial species common to both marine and medical environments, was allowed to adhere to flat solids made up of the polymer polydimethylsiloxane (PDMS) prior to a collision with an air bubble. The air bubble was collided with the solid in three distinct ways: directly from above, across the solid surface in one direction, and across the solid surface in one direction before being pulled back in the other direction. The speed of the bubble, the amount of time bacteria were adhered to the solid prior to bubble collision, and the extent to which the solid could be wet were all also examined for their effects on adhered bacteria removal. The extent to which a solid surface could be dewetted was identified as the most significant factor. For solids that are easily dewetted, almost all adhered bacteria were removed with the passage of the first air–liquid interface. Many bacteria were then redeposited back onto the solid surface upon the passage of the second air–liquid interface, especially when it moved in a direction opposite to the first. In contrast, for solids that are easily wet by water, variable amounts of bacteria remained after the first air–liquid interface swept across its surface. Slower moving air–liquid interfaces were also shown to be more effective at removing adhered bacteria. Solid surfaces with rough patterning made it more difficult to remove bacteria. Air bubbles can be an effective method to combat adhered bacteria and potentially prevent eventual biological growth on different types of underwater applications.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/93527 |
| Date | 10 September 2019 |
| Creators | Kriegel, Alex Timothy |
| Contributors | Chemical Engineering, Ducker, William A., Goldstein, Aaron S., Bortner, Michael J. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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