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Dynamics of bacterial streamers and impact on biofouling of microfluidic filtration system
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- Author / Creator
- Biswas, Ishita
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Biofouling refers to the undesirable accumulation and growth of biological substances on a artificial surface with time. Biofilm on the surfaces occurs due to bacterial aggregation and extracellular polymeric substance (EPS) that acts as the construction material of biofilm. EPS consists of long-chain biomolecules such as polysaccharide, protein, and DNA. An interesting phenomenon in the observation that form filamentous bacterial aggregates in continuous flow regime that is called streamer. In this dissertation, two different modes of failure of bacterial streamers have been investigated and quantified in a microfluidic device in a creeping flow regime. In both analyses, the quantification of streamer deformation and failure behavior was performed by using 200 nm fluorescent polystyrene beads, which firmly embed in the EPS and act as tracers. In the first mode of failure, this bacterial streamers, which form soon after the commencement of flow begin to deviate from an apparently quiescent fully formed state in spite of steady background flow and limited mass accretion indicating significant mechanical nonlinearity. This nonlinear behavior shows distinct phases of deformation with mutually different characteristic times and comes to an end with a distinct localized failure of the streamer. A simplified nonlinear analytical model has been developed to describe the experimentally observed instability phenomena assuming a necking route to instability. The model leads to a power law relation between the critical strain at failure and the fluid velocity scale exhibit excellent qualitative and quantitative agreement with the experimental rupture behavior. The second mode of failure has been investigated and quantified where streamers break due to the growth of voids and cracks in the biomass. This failure occurs in thick bacterial streamers in a microfluidic device with micro-pillars and stands in strong contrast to necking-type instability observed in the thin bacterial streamer. Void/crack growth time-scales could be characterized as short-time scales, and long time-scales and the void/crack propagation showed several instances of fracture-arrest ultimately leading to a catastrophic failure of the entire streamer structure. Amongst the different application domains that bacterial streamers can impact, is the domain of biofouling of membranes. The effect of biofouling in a microfluidic filtration system has been investigated by using a microfluidic filtration device consists of cylindrical microposts with a pore-spacing of 2 µm, thus mimicking a microfiltration membrane system operating in a dead-end mode. The existence of a critical pressure difference above which pronounced streamer formation was observed, which eventually leads to rapid clogging of the device with an accompanying exponential decrease in permeate flow. Moreover, the de-clogging of pores also occurs intermittently, which leads to small time scale fluctuations (O(101 seconds)) superimposed upon the large time-scale (O(102 minutes)) clogging of the system. These de-clogging phenomena leads to a sharp increase in water permeation through the membrane, but deteriorates the water quality as biomass debris is transported in the permeate. It has also been observed that the pH of the feed solution strongly affects biofouling of the microfluidic filtration system.
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- Graduation date
- Fall 2018
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.