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Reduce Biofouling of Reverse Osmosis Membranes by Surface Modification

Reduce Biofouling of Reverse Osmosis Membranes by Surface Modification. Abhijit Sarkar, Adrian Merrington, Joseph L. Rousseau, Tracy Zhang, Apurba Chakrabarti, Peter I. Carver, Beena Thomas, Steven E. Keinath and Petar R. Dvornic. Michigan Molecular Institute. Midland, MI. Abstract.

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Reduce Biofouling of Reverse Osmosis Membranes by Surface Modification

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  1. Reduce Biofouling of Reverse Osmosis Membranes by Surface Modification Abhijit Sarkar, Adrian Merrington, Joseph L. Rousseau, Tracy Zhang, Apurba Chakrabarti, Peter I. Carver, Beena Thomas, Steven E. Keinath and Petar R. Dvornic Michigan Molecular Institute Midland, MI

  2. Abstract The applications for Reverse Osmosis (RO) are numerous and varied. Desalination of seawater or brackish water for drinking purposes, wastewater recovery, food and beverage processing, biomedical separations, purification of home drinking water and industrial process water are some of these applications. However, membrane fouling caused by the growth of bacteria on the membrane surface often leads to significant permeate flux decline and loss of product quality in RO systems. Thus, prevention of biofouling of RO membranes has become most imperative. MMI has developed a unique coating system for RO membranes that make the surface extremely hydrophilic. This, in turn, provides protection of the RO membranes from biofouling. Most importantly, the increase in antifouling property via surface modification does not compromise the permeate flux and salt rejection efficiencies of the membranes.

  3. Water Purification Methods • Screening and preconditioning (Screen filters: nylon, PP, steel) • Coagulation and flocculation (Al sulfate: Fe sulfate, Fe chloride) • Tank-type pressure filters (activated carbon, anthracite coal, sand bed) • Disinfection (chlorine, UV, ozone) • Ion exchange systems (zeolite resin) • Distillation • Electrodialysis (need to treat with RO membrane first) • Cross-flow filtration systems

  4. Crossflow Membrane Membranes have small pores that will plug and blind off instantly, unless they are run in the crossflow mode.

  5. Classes of Crossflow Membranes Four categories of membranes defined on the basis of size of the materials they can remove from the carrier liquid. Reverse osmosis (RO) Nanofiltration (NF) Ultrafiltration (UF) Microfiltration (MF)

  6. Membrane Filter Types

  7. Desalination: Facts Extensive use of desalination will be required to meet the needs of a growing world population. • At present, • Middle East: 52% capacity • North America: 16% • Asia: 12% • Europe: 13% • Africa: 4% • Central America: 3% • Ships exclusively use RO technology for fresh water requirements. Desalination Technology Energy Requirement Reverse Osmosis (RO; 44%) 4.7-5.7 kWh/m3 Multi-Stage Flash distillation (MSF; 40%) 23-27 kWh/m3

  8. Reverse Osmosis

  9. RO Membranes: Structure

  10. Time Versus Flux Time Versus Flux 35 35 30 30 25 25 Flux (mL/min) Flux (mL/min) 20 20 15 15 10 10 5 LE 100 LE 250 XLE100 XLE250 5 0 0 0 2 4 6 8 10 0 2 4 6 8 10 Time (hours) Time (hours) Commercial RO Membranes Evaluation of FilmTec RO Membranes for Selectivity and Flux (b) (a) Rejection rate versus time at 100 psi and 250 psi for (a) LE and (b) XLE membranes (c) (d) Flux versus time at 100 psi and 250 psi for (c) LE and (d) XLE membranes

  11. Membrane Fouling • Fouling layer exerts hydraulic resistance to permeate flow and causes flux decline • Sources of fouling: • Scale • Silt • Organic matter • Bacteria Fouling by model colloids: 20 nm and 110 nm

  12. Surface Modification by Formation of HBP-PEG Thin Network Film

  13. HBP-PEG Thin Network Filmon RO Membrane Substrate • FilmTec LE and XLE RO membranes were cut into appropriate dimensions and taped onto a glass plate • HBP and PEG reagents in water were mixed in a pre-determined and optimized ratio • The solution thus obtained was used to coat the membrane surfaces • Films were cured at room temperature and subsequent evaluations of hydrophilicity were carried out by contact angle measurements • The surface modified membranes were evaluated for dynamic (flux and salt exclusion) properties

  14. Surface Morphology Characterization SEM photomicrograph of an LEmembrane coated with HBP-PEG network. SEM photomicrograph of an uncoated LE membrane.

  15. Evaluation of RO Membranes Hydrophilicity, flux and selectivity of surface modified FimTec membranes Flux and salt rejection for FilmTec’s LE RO membrane, surface modified with HBP-PEG polymer network coating. Average values of dynamic membrane properties from 5 measurements were obtained at 100 psi. Flux and salt rejection for FilmTec’s XLE RO membrane, surface modified with HBP-PEG polymer network coating. Average values of dynamic membrane properties from 5 measurements were obtained at 100 psi.

  16. Summary • RO membrane surfaces were successfully modified with novel HBP-PEG polymer network based coating system • Following RO membrane surface modification, their hydrophilicity significantly increased • The dynamic properties (flux and salt exclusion) of surface modified RO membranes were not very much compromised • Evaluation of antifouling activity of surface modified RO membranes is in progress

  17. Acknowledgements • The funding for this program was provided by DARPA Grant No. W911SR-05-C-0026 • LE and XLE RO membranes were kindly provided by FilmTec Corporation.

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