Manufacturing and Performance of Activated Carbon-Coated Nanofiltration Membranes

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Tomkiewicz, Johanna Elizabeth
Hatzell, Marta C.
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Membrane-based desalination is becoming increasingly important due to rising global water scarcity. Both membrane systems and adsorption-based technologies are critical for most water treatment processes. Membranes are effective at removing total dissolved salts and particulate matter from water and adsorption-based technologies are ideal for removing organic and inorganic compounds. By combining adsorption and membranes together, there may be potential to create a lower energy treatment process with reduced system complexity, and therefore reduced cost. Merging adsorption and membranes together may also alleviate some of the limitations associated with each technology. Specifically, commercial membranes require high pressures and their salt removal capabilities tend to decline in harsh conditions. Activated Carbon (AC) is a highly adsorptive material that is used in wastewater treatment, but processing it with the wastewater can be a time-consuming and expensive process. Therefore, combining membrane technology and activated carbon adsorption into a single step may increase wastewater treatment efficiency and improve membrane performance. This thesis seeks to understand the feasibility of manufacturing an activated carbon-coated commercial Nanofiltration (NF) membrane in order to improve water treatment performance. Several coating methods were tested, including film coating and vacuum filtration coating, to determine the most suitable method for manufacturing the activated carbon-coated membranes. The concentration of activated carbon was varied to investigate the coating thickness’s impact on membrane flux and salt rejection; these performance tests were carried out in a Sterlitech HP4750 dead-end cell with an aqueous magnesium sulfate solution as the feed solution. Characterization tests such as contact angle testing and Scanning Electron Microscopy (SEM) were carried out to develop a comprehensive understanding of the modified membranes. The primary discovery is that activated carbon reduces a membrane’s magnesium sulfate removal capabilities. Correlations between membrane performance and the concentration of coating on the membrane are reported. Testing showed that as the concentration of activated carbon in the coating increased, the flux through the membrane decreased. In addition, the salt rejection decreased with higher concentrations of activated carbon, and it was determined that this decreased rejection was likely due to the phenomenon of concentration polarization. Using lower concentrations of activated carbon for coating the surface of nanofiltration membranes led to the formation of an inhomogeneous AC-coated surface, resulting in less statistically significant data. In addition, contact angle testing proved that as the concentration of activated carbon increased, the membranes became more hydrophilic. The findings from this research can guide future experiments seeking to use coated membranes for other contaminant removal applications, such as the removal of pharmaceuticals or other micropollutants from wastewater.
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