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Membrane Performance Enhancement Using Electrically Conducting Membranes

Creative Commons 'BY' version 4.0 license

Water shortage is a pervasive problem which has plagued societies for centuries. Recently, membrane technology has offered an effective and robust water treatment method for water sustainability due to great improvements in membrane performance. Depending on the intended applications, microfiltration (MF), ultrafiltration (UF), nano-filtration (NF) or reverse osmosis (RO) membranes can be used individually or in combination to achieve a specific water quality goal. However, a major challenge facing these technologies is membrane fouling, where particulates in the feed stream are deposited or developed on the membrane surface during the filtration process. Membrane fouling results in performance deterioration, lifetime shortening, and ultimately, increased operational costs. Therefore, membrane cleaning and fouling control or prevention are critical research topics for membrane development.

The goal of this dissertation is to demonstrate fouling prevention and foulant removal on carbon nanotube-modified (CNT) electrically conductive UF, NF and RO membranes. First, mineral scaling was prevented and removed by applying an external anodic electrical potential to an electrically conducting CNT – polyamide RO membrane. The results demonstrate that CaCO3 scaling was efficiently removed by the intermittent application of 2.5V and CaSO4 scaling can be prevented by the continuous application of 1.5V with the membrane as the anode. Second, biofouling and organic fouling were prevented while treating anaerobic sequencing batch reactor effluent by using electrically conducting UF and NF membranes. The continuous application of negative 5V to the UF membrane surface prevents organic fouling and allows good membrane performance while treating complex wastewater streams for long periods of time. The application of positive potentials to the NF membranes has also been shown to increase fouling and hinder cleaning and recovery. Third, a highly conductive and anodically stable polyaniline coated UF membrane was designed and used as a flow through electrode. Results show that the polyaniline coated CNT membrane had a significantly reduced degradation rate under high anodic potentials in a pH controlled environment when compared with polyvinyl alcohol crosslinked CNT membrane. The modified membrane can be used to degrade organic compounds and perform in situ oxidative cleaning of the fouled membrane without any additional oxidizing chemical reagents.

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