|
[Last updated:
February 17, 2010
]
Research Activities and Highlights
- The recent colloidal fouling phenomena - Cake Enhanced Osmotic Pressure (CEOP) was first to be applied to bacterial cells in RO biofilms (See in: Herzberg M. and Elimelech M. (2007) "Biofouling of reverse osmosis membranes: Role of biofilm-enhanced osmotic pressure". Journal of Membrane Science 295: 11-20.)
|
|
Normalized flux decline (a) and salt passage (b) upon deposition of formaldehyde fixed PA01 dead cells (initial concentration of 109 cells/mL) and PA01 biofilm growth (initial concentration of 107 cells/mL) on the RO membrane in a synthetic wastewater medium (ionic strength of 14.6 mM and pH 7.4). Flux decline is also shown for P. aeruginosa PA01 dead cells (initial concentration of 109 cells/mL) in DI water supplemented with 0.01 mM LaCl3 at pH 5.8.
|
- While cells were found to induce a trans-membrane osmotic pressure, EPS was found to induce hydraulic resistance (manuscript in preparation):
|
|
Permeate flux upon deposition of EPS (extracted from a biofilm of P. aeruginosa PAO1 grown in LB batch cultures) and upon deposition of formaldehyde fixed P. aeruginosa PAO1 dead cells (initial concentration of 109 cells per mL) on RO membrane. Fouling experiments were conducted in a synthetic wastewater medium (ionic strength of 14.6 mM and pH 7.4) and in DI water supplemented with 0.01 mM LaCl3 at pH 5.8. Initial permeate flux in the EPS fouling was 1.17 (± 0.06) ª 10?5 m/s (42.1 L/m2-h or 24.8 gal/ft2-day) and in the dead cells fouling was 1.12 (± 0.04) ª 10?5 m/s (40.3 L/m2-h or 23.7 gal/ft2-day). Crossflow velocity was 8.5 cm/s and initial EPS concentration was 16 mg per liter as TOC. |
- Under limiting growth conditions of the biofilm in the RO unit, a distinct distribution of viable and dead cells were observed upon filtration of secondary effluents. In the biofouling layer, more viable cells were analyzed close to the RO membrane interface and more dead cells were analyzed close to the bulk liquid side (this project is in collaboration with Menachem Elimelech from Yale University and Lutgarde Raskin from the University of Michigan).
|
 |
|
|
|
|
-
Gene expression in RO biofilms (consisting Pseudomonas aeruginosa PAO1 as a model strain) has been analyzed with DNA microarrays. The RO unit was operated when a faster growth of the RO sessile cells was obtained in comparison to the planktonic cells in the unit. In contrast to findings recently reported in gene expression studies of P. aeruginosa biofilms, genes related to stress, adaptation, chemotaxis, and resistance to antibacterial agents were induced in the planktonic cells in the RO system. In agreement with the findings of previous P. aeruginosa biofilm studies, motility and attachment related genes were repressed in the RO P. aeruginosa biofilm. Supported by the microarray data, an increase in both motility and chemotaxis phenotypes was observed in the suspended cells. The increase in nutrient concentration in close proximity to the membrane is suggested to enhance biofouling by chemotaxis response of the suspended cells and their swimming toward the membrane surface (manuscript submitted to ISME journal - NPG group).
|
|
|
|
^ Top of Page |
