Development of Corrugated Polyvinylidene Fluoride (PVDF) Membranes for Fouling Control in Membrane Bioreactors (MBR) and Membrane Distillation (MD)

Student thesis: Master's Thesis

Abstract

Membrane fouling reduction in membrane bioreactors (MBRs) is mostly performed by improving sludge quality, applying high shear rates on the membrane surface and improving membrane properties. The latter is generally done by increasing both membrane hydrophilicity and porosity. In the first section of this thesis, corrugated membranes were fabricated, characterized and tested in a lab-scale MBR to improve their filterability. An imprinting step was successfully included into preparation procedure to form corrugations on the membrane surface. Corrugation consisted of valleys-and-hills topography which increased membrane effective surface area (AE of ~50%) and acted as turbulence promoter. It also enlarged membrane mean flow pore size (PS) because of changes in formation mechanism. Both higher AE and larger PS increased membrane permeability to about 5-6x compared to a flat membrane. Surface corrugations enhanced membrane fouling propensity as observed from the flux-stepping and the long-term filtration tests, without affecting permeate quality. In membrane distillation (MD), fouling and scaling reduction can be achieved by controlled surface topography through surface modification. In the second part of this thesis, a two layer corrugated flat sheet polyvinylidenefluoride (PVDF) membrane (corrugated composite membrane) was fabricated, characterized and tested in a lab-scale direct contact MD (DCMD) system for improved fouling and scaling resistance. The first layer was used to control the overall pore size while the second devoted to the formation of surface corrugation and hydrophobicity. Tested with both seawater and concentrated seawater against non-corrugated composite membrane, the corrugated composite membrane showed much higher fouling and scaling resistances identified by only 10.7% reduction in permeate flux after 103 hrs of exposure to seawater, compared to 66.6% for the non-corrugated membrane. DCMD experiment with concentrated seawater proved the effectiveness of corrugations even at high feed concentrations when the corrugated membrane performed as good as it was with seawater exposure, while the non-corrugated membrane had even worse performance reaching a zero-flux after 93 hrs of experiment and proving scaling and wetting were exacerbated by increased feed salinity. SEM images of the post-MD membranes also confirmed the advantage of corrugations over the flat surface when the corrugated membrane experienced small amount of salts deposition leaving most of the membrane pores open while the non-corrugated membrane experienced severe scaling and salt depositions forming a thick layer at the membrane surface and blocking most of the pores.
Date of AwardMay 2015
Original languageAmerican English
SupervisorHassan Arafat (Supervisor)

Keywords

  • Membrane Fouling Reduction
  • Membrane Bioreactors
  • Corrugated Membranes
  • Membrane Permeability
  • Membrane Distillation.

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