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Title: Investigation on the hydrodynamics of a circular crossflow membrane filtration for purification of drinking water
Author: Shamsuddin, Norazanita
ISNI:       0000 0004 7971 0442
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2015
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With increasing frequency and intensity of disasters reported around the world, no doubt the developing countries would suffer considerable damages such as environmental, infrastructure, economy, population displacement, etc., compared to the developed countries. It is well known that in the events of emergency situations, e.g., natural disasters, one of the most basic requirements for human survival is the supply of clean and safe drinking water. However, it is impossible to supply when the facilities and infrastructures required are not functioning effectively. Hence, there is an urgency to develop a decentralized water treatment system to answer such problems in the aftermath of disasters, which undoubtedly require immediate response while waiting for aid to arrive. In order to address these issues, experiments involving contaminants which are commonly found in natural waters (e.g. clay, humic acid, and bacteria) were carried out using commercially available microfiltration (MF) and ultrafiltration (UF) membranes. Membrane module configurations can have a noticeable impact on filtration processes, hence, it is essential to investigate which configuration performs better with respect to hydrodynamics (Reynolds number, Dean number, membrane surface shear, etc.) and operating conditions such as feed concentration, pH, filtration pressures, etc. Two experimental set-ups were investigated, namely, circular crossflow and stirred dead end. Filtration experiments of humic acid solution using UF membranes with both set-ups were first investigated. Another sets of experimental procedures were also conducted where filtration of clay suspension using MF membranes were carried out. The results have shown that the rejection (both the observed and the true rejection) in the case of circular crossflow were higher than in the case of dead end flow. Mass transfer coefficients were determined for both set-ups where the values are higher in circular crossflow than stirred dead end system. These are significant results because in the circular crossflow, the presence of Dean vortices (under certain circumstances) in the circular channel path disrupt solute build-up on membrane surface hence, minimizes the effect of concentration polarization. This, in turn, causes the effect of fouling to be delayed, and as a result prolongs the lifespan of the membrane. It has been proven in the experiments conducted throughout the study. A computational fluid dynamics (CFD) model was built using COMSOL Multiphysics computer software in order to study the hydrodynamics on the circular crossflow system. It was found that the Dean number increased as the filtration pressure was increased, as well as the production rate of clean water and the shear stress on the membrane surface. With the design of the spiral channels it was found that increasing the number of spiral turns would increase the permeation rates, and also improve Dean numbers meaning that the system could be less susceptible to fouling due to impact of Dean vortices. Increasing the size of the device was also found to increase the permeation rates and consequently the Dean number. Hence, based on the modelling predictions, a prototype design was proposed. A prototype was developed which incorporated the circular crossflow configuration. The hydrodynamics of the prototype was investigated with different spiral turn configurations, namely, 2.15, 4.15 and 7.72. MF and UF experiments have been carried out to test the performance of the prototype with regards to permeate flow rate, Dean number, shear stress and removal efficiency of the membranes. From the results gathered, MF of clay suspension and bacteria show promising results, where the spiral turn of 7.72 indicates the best filtration performances (high flowrates, low permeate turbidity readings, high log removal value (LRV) and high removal efficiency) when compared with the spiral turns of 2.15 and 4.15. However, further work is still required to improve the design specifications of the prototype especially with UF experiments. It is believed that this prototype, once finalized, could be deployed in developing countries to help provide them with clean and safe water for short term relief.
Supervisor: Not available Sponsor: Brunei Government
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemical Engineering not elsewhere classified ; Membrane filtration ; Circular crossflow ; Dean vortices ; Hydrodynamics of system ; Prototype design ; Drinking water purification.