Humic acid fouling on an ultrafiltration membrane: Towards nanocomposite-based self-cleaning membranes.

摘要

In water treatment and purification processes, membrane fouling severely limits membrane performance and increases the cost of separation in terms of both water and energy use. This research contributes to an understanding of the mechanism of humic substance fouling on a polysulfone ultrafiltration membrane. To achieve this goal, the first focus was a study of humic substances and their colloidal or aggregation behavior. The dynamic nature of humic aggregates solutions at low electrolyte concentration is not well understood and this research provides important new information relevant to dynamic behavior at different concentrations. Dynamic light scattering methods and zeta potential techniques were applied. These results are important due to the effect of humic substance aggregate size and electrical surface charges on membrane fouling.;In the second part of this research, humic acid (HA) fouling mechanisms for polysulfone membranes at two scales, intrinsic and operational, were studied. Isotherm adsorption techniques and permeability test techniques were applied to investigate fouling mechanisms. A hypothesis is postulated as the new fouling mechanism for humic substances fouling based on dynamic aggregation of HA in PSF pore structures. The effects of humic acid concentration and filtration time on fouling mechanism were analyzed using dynamic light scattering, adsorption isotherms based on HA fluorescence and permeability studies.;The understanding of humic acid/polysulfone behavior and their interactions is leveraged to explore the case of a nanocomposite membrane formed from titanium dioxide (TiO2)/multiwall carbon nanotube (MWCNT) and polysulfone focusing on self-cleaning and synergistic anti-fouling performance. Different ratios of TiO2 and MWCNT were embedded as a mixture in polysulfone membranes via a phase inversion fabrication method. The effect of nanoparticles on membrane pore size, pore morphology and surface hydrophilicity were characterized. Moreover, the performance of all the nanocomposite membranes in terms of permeability, antifouling and total organic carbon rejection were evaluated. Based on the results, an optimum ratio of the paired nanoparticle complex in the porous PSF membrane is shown, balancing membrane performance in terms of permeability, anti-fouling and rejection.