M.Sc Thesis


M.Sc StudentYu Xu
SubjectThe Effect of Surfactant on Membrane Fouling During
Separation of Oil/Water Emulsions
DepartmentDepartment of Civil and Environmental Engineering
Supervisors ASSOCIATE PROF. Guy Ramon
PROF. Jiaping Paul Chen


Abstract

Oily wastewater, generated from a wide range of industries, brings great risk to the environment. Treatment of oily wastewater is necessary and broadly researched; however, when it comes to emulsified oily wastewater with an oil size of 20 µm or even lower, the problem becomes challenging since traditional approaches may become less efficient. Filtration membranes, as a versatile and simple tool, meet the need and performs effectively towards this issue. However, deterioration of the membrane’s filtration capability during the treatment process, known as membrane fouling, remains a major drawback. Much research has been aimed at trying to understand the mechanism that causes membrane fouling during emulsion separation, particularly using ultrafiltration (UF) membranes. Interestingly, while many studies pointed out that the emulsifier, namely surfactant, is the main source of fouling in nanofiltration and reverse osmosis, oil fouling is generally regarded as the main foulant in UF. To understand whether surfactant or oil causes fouling of membrane during UF of emulsion, and reveal the fouling mechanism behind, the present study uses commercial UF membranes to separate a series of oil/water emulsions stabilized by surfactants, which are different in charge and size. In addition, a solution containing only surfactant is also permeated through the UF membranes. The flux data of these experiments shows that although oil causes some level of irreversible fouling, surfactants are the main source of fouling in ultrafiltration, and the degree of fouling is closely related the properties of the surfactant. To further prove that oil coverage is not directly related to flux reduction, confocal microscopy is used to conduct real time monitoring of oil fouling. The result confirms that variation of oil coverage on the membrane during the filtration is not consistent with the fluctuation of the flux. Fouling from surfactant alone is less considered in ultrafiltration and this study provides clear evidence that more emphasis should be placed on avoiding surfactant fouling, rather than oil fouling, when UF membranes are used for emulsion separation.