Graduation Year

2006

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Civil Engineering

Major Professor

Robert P. Carnahan, Ph.D.

Keywords

Scaling, Concentration polarization, Clay, Salt, Permeate

Abstract

This dissertation describes the investigation of the fouling of a reverse osmosis membrane under different operating conditions. A mass transfer model to predict the permeate flux decline is defined. These studies used kaolin clay and bentonite clay as the fouling particles. As the membranes, thin film Low fouling Composite 1 polyamide reverse osmosis flat sheet membranes were used. Baseline experiments using only kaolin in D.I. water were conducted. At an operating pressure of approximately 1,380 kPa, no flux decline was observed. These results established the effects of a membrane-particle interaction. For the fouling experiments with kaolin clay, experiments show a linear relationship between the mass of the deposited foulant layer and total permeate flux decline. The increased concentration of scale forming salts such as calcium chloride and sodium carbonate combined with clay particles has been found to increase flux decline. It also leads to the formation of a less porous cake layer on the membrane surface, which may be due to the particle surface charge. The increase in transmembrane pressure leads to the formation of a well compacted, less porous, cake layer on the membrane surface. The reduced porosity results in the deterioration of the permeate quality, which is a direct result of reduced back diffusion of the salt solution.A fouling model that combines a resistance-in-series model and a simplified-mass-transport relationship were used to predict the transient stage permeate flux of a reverse osmosis membrane. This model contains a constant which is a function of the operating condition and the ionic species in the feed solution. It was found that the results from the model agreed with the experimental results.

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