Abstract

Membrane processes are currently used in several ways to purify water and wastewater. Because of their high performance and smaller footprint, membranes are likely to grow in importance as compared to other conventional technologies. Therefore, there is a critical need for development of improved membranes that have higher flux, greater selectivity, and are less prone to fouling. Recently, multiwalled carbon nanotube (MWNT) electrochemical (EC) filter was reported to be extremely effective as a point-of-use technology in achieving complete removal and inactivation of pathogens. In order to scale-up the electrochemical filtration technology to utilize it in a plant-scale centralized water treatment plant, conductive nano-composite ultrafiltration membranes were developed in this project, through incorporating amine and carboxylic functionalized MWNTs (MWNT-NH2, MWNT-COOH) into polysulfone (PSf) substrates. A novel fabrication method, vacuum-assisted layer-by-layer self-assembly was used for surface modification of polysulfone ultrafiltration membrane.

First, the polysulfone membrane was functionalized with oxygen containing negatively charged functional groups through oxygen plasma treatment. In order to optimize the degree of functionalization of polysulfone membrane with increasing plasma duration, a comprehensive physicochemical characterization of the plasma treated membrane was performed by using ATR-FTIR, XPS, contact angle, EKA and SEM analyses. Water permeability test was also conducted to investigate the differential performance of the plasma-treated membrane with increase in plasma treatment duration. The ATR-FTIR analyses revealed the peaks at specific wavelengths for hydroxyl, carboxyl and carbonyl functional groups, while the XPS results showed an increase in oxygen content of the pristine polysulfone from 18.6% to 30.7%, after being plasma treated. The contact angle of the plasma-treated membrane dropped down to 44.2? from 68.6? of the pristine membrane and the EKA showed an increase in surface zeta potential from -22.5mV to -42.8mV for varying plasma duration. Based on these analyses, 60s plasma treatment time was set as optimum for further modification of PSf membrane with MWNT.

The MWNT modified PSf membrane was characterized with a SEM that showed the uniform distribution of MWNTs throughout the membrane thickness as well as a linear growth in membrane thickness with increasing number of MWNT bilayers. The water contact angle analyses revealed that the modified membrane became more hydrophobic with increasing number of bilayers. The modified membrane exhibited reasonable permeability, higher conductivity and high antifouling properties due to application of very low DC potential (0V-3V). Due to high conductivity of the MWNT modified membrane an application of 3V DC voltage showed almost 100% inactivation of E. coli inactivation suggesting the effectiveness of the MWNT modified polysulfone membrane in controlling the biofouling in electrofiltration system. Moreover, this study showed over 99% degradation of methyl orange during electrofiltration that could contribute to reducing the organic fouling of the modified membrane. Overall, the new MWNT modified polysulfone membrane has huge potential to be used in large scale electrofiltration systems.