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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

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

slide2

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.

slide3

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
slide4

Crossflow Membrane

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

slide5

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)

slide8

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

slide11

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

membrane fouling
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

slide14

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
slide15

Surface Morphology Characterization

SEM photomicrograph of an LEmembrane coated with HBP-PEG network.

SEM photomicrograph of an uncoated LE membrane.

slide16

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.

slide17

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
slide18

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.