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Colloidal fouling in a microfluidic membrane mimic device
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- Author / Creator
- Debnath, Nandini
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With the advancement in microfabrication technology, on-chip membrane fouling study has undergone significant development and improvement for the last two decades. A single-chip microfluidic filtration platform integrates the benefits of both microfluidics and membrane technology. In this regard, a microfluidic membrane mimic (MMM) device can be used as a micron-sized tool to investigate the fouling phenomena at the pore scale. In this dissertation, fouling experiments were performed in an MMM device to investigate colloidal, organic, and combined fouling using synthetic wastewater such as polystyrene particle solution, polyacrylamide polymer solution, and a mixture of these two solutions, respectively. Four major categories of microscopic fouling were observed: (1) cake layer fouling at upstream, (2) pore fouling (inside the pores), (3) colloidal aggregation (downstream) and (4) colloidal streamer fouling (downstream). We discussed the new kind of downstream fouling and the timescales of colloidal streamer formation. We also showed that the streamer formation is the result of flow of polystyrene and polyacrylamide mixture only. Furthermore, experimental analysis revealed that the colloidal streamer formation is likely the result of flocculation of the PS beads. The flow regimes under which colloidal streamer formation was observed was quantified through state diagrams. Our microfluidic experiments showed that downstream colloidal aggregation and streamer fouling have a significant influence on overall membrane fouling, which were not studied before. Streamer formation has led to the maximum flux decline among all.
We have also performed constant-pressure dead-end filtration by varying particle size with silica (SiO2). Interestingly, SiO2 only resulted in cake layer fouling while PS, which caused cake layer fouling along with downstream colloidal aggregation. Fouling experimental results by varying ionic concentrations suggested that the energy barrier and secondary energy minimum play an essential role in mitigating membrane fouling. Calculating membrane and foulant interaction energies by extended DLVO (XDLVO) approach showed a growing depth of secondary energy minimum with increasing ionic strength. On the other hand, a decrease in the ionic strength resulted in release of foulants from the secondary energy minimum to the bulk, suggesting an increase in the energy barrier. Additionally, back-washing experiments showed that the majority of the PS particles were released from the cake layer by water channel formation while in case of SiO2, the creation of water channel was not prominent. At last, a summary of all significant findings, the potential of microfluidic devices to investigate the microfiltration process at pore scale, and the future trends are provided. -
- Graduation date
- Spring 2020
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
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