Date of Award

2024

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil and Environmental Engineering

First Advisor

Amber Doiron

Abstract

Forward osmosis (FO) is the term given to osmosis in water filtration applications. FO has many advantages to conventional membrane filtration processes. The lack of external pressure needed to force solvent through the membrane is dramatically decreased in FO, resulting in a lower cost of operation compared to reverse osmosis. Lower external pressures also result in decreased fouling on the membrane surface and improved permeate flux. Fouling is one of the foremost challenges within the membrane filtration industry and is one of the biggest contributors to operating costs. While FO results in less fouling than RO, fouling remains a major concern and results in significant expenses to operate FO. Many techniques exist to combat fouling, such as back washing, flushing, and chemical cleaning, however these techniques can be cost intensive and harmful to membrane integrity and performance. As a result, there is great interest in less intrusive cleaning techniques such as acoustic cleaning or electric fields that can be applied to mitigate fouling without compromising the membrane. Electric cleaning has shown great promise as an in-situ cleaning method, offering increased performance in membrane flux.Electric field membrane cleaning involves applying an electric field perpendicular to the membrane surface, resulting in the movement of charged particles towards the electrodes at either side of the filtration channel, reducing the occurrence of fouling. Most electric field membrane cleaning techniques use a direct current (DC) electric field to cause this motion, called electroosmosis. DC cleaning has various drawbacks, such as electrolysis at the electrodes, corrosion of the electrodes, and further damage to the membrane surface which hinders DC cleaning performance. There is currently limited literature involving the use of alternating current (AC) fields for membrane cleaning. The aim of this study was to examine the feasibility of AC fields as an in-situ cleaning technique in FO application. Flux performance was assessed using bovine serum albumin (BSA) and sodium alginate as model foulants. Flux was measured over a 6 to 8-hour filtration period using a pulsed AC field applied every 2-hours, and a continuous AC field applied over the duration of filtration. Sodium chloride was used as a draw agent. Results from these experiments indicate that AC electric fields are an effective method for in-situ organic fouling mitigation in FO process. Continuous and pulsed fields of various frequencies, conducted with foulant material in the feed solution, have demonstrated to improve flux retention to levels comparable to clean water flux conditions with no foulants. Normalized flux in the presence of foulants was raised from as low as 40% of initial flux at the conclusion of the trial to as high as 90% of initial flux with the application of electric field. Pulsed AC field application appeared to be more effective than continuous field, both in terms of fouling mitigation and lower energy input requirement

Language

en

Number of Pages

77 p.

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