Research Project Full Title: GOALI: In situ generation of two-phase flows to eliminate membrane concentration polarization and fouling
Principal Investigator(s): Manish Kumar, PI
Sponsor(s): National Science Foundation
Full Abstract: Membrane technologies, especially reverse osmosis (RO), are now at the forefront of water purification from lower-quality water sources such as seawater, brackish water, and wastewater. The objective of this project is to minimize membrane fouling by producing oxygen at the membrane surface to impede the growth of biofilms on the membrane. Biofouling has the largest negative impact on desalination membrane performance. This fundamental research has the potential to transform membrane performance by significantly decreasing the energy use of membranes and increasing their usable lifetime.
Numerous efforts have focused on improving RO efficiency by pretreatment, minimizing concentration polarization (CP), and mitigating fouling. Current methods have not overcome the problem in a feasible manner, especially for concentration polarization; however, no study has been reported on the application of microbubbles generated in situ to disturb the CP boundary layer. The hypothesis is that catalytically generating microbubbles at a membrane surface will produce localized micromixing, which will significantly reduce both concentration polarization and particle-bacteria-organic fouling. To test the overall hypothesis and meet the objective, three important fundamental questions must be answered, and form the intellectual merit of this research: 1) What is the rate of microbubble formation, and the microbubble size distribution, given a particular catalyst type, catalyst loading fraction, hydrogen peroxide (H2O2) dosing profile, and local pressure (i.e., must exceed Henry’s law solubility)? 2) For a given microbubble production rate and size distribution, what is the increase in water effluent due to the different mechanisms of micromixing for concentration polarization, and liftoff for membrane fouling species? and 3) For a given microbubble production rate, what is the disinfection capacity for biofilm-forming microorganisms using the produced oxidant (reactive oxygen species), at production levels that avoid membrane damage? The approach is to incorporate catalysts in the membrane module (either membrane surface or spacers), and then during the operation of the membrane, to inject pulses of H2O2 or other reactants that will produce microbubbles at the membrane surface. A primary figure of merit for this work is an increased water flux through the membrane over time. The broader impacts of this proposal focus on educating Ph.D. students (including internships with Dow Chemical, our NSF GOALI partner) and undergrads, as well as technological commercialization (with partner Dow Chemical). Producing microbubbles and generating localized micromixing could be achieved at commercial scale. Ph.D. and undergrad education as well as internships and entrepreneurship training will form part of the student experience.