Loss of salt rejection due to fouling in seawater reverse osmosis SWRO desalination processes

1
Loss of salt rejection due to fouling in seawater
reverse osmosis (SWRO) desalination processes

• Suhan Kim1,2, Sungyun Lee1, Eunkyung Lee1, Sarper
  Sarp1,
• Eric M. V. Hoek3, and Jaeweon Cho1,2
• 1 Department of Environmental Science and
  Engineering, GIST, Gwangju, Korea
• 2 Center for Seawater Desalination Plant,
  Gwangju, Korea
• 3 Department of Civil and Environmental
  Engineering, UCLA

2
Backgrounds

• Unexpected loss of salt rejection can be a big
  problem.
• SWRO system design should satisfy the desired
  permeate water quality.
• Salt rejection is a function of permeation
  velocity and may be affected by fouling.

3
Backgrounds

• Factors affecting performance decline in SWRO
  system

(Ref) Khedr G et al., Desalination Water Reuse
10/3 (2000)
4
Objective Hypothesis
Objective

• To more systematically understand factors
  affecting salt rejection in SWRO system.
• - Effect of TMP and permeation velocity
• - Effect of fouling

Hypothesis

• Permeation velocity is a key factor to determine
  salt rejection.
• Fouling may affect salt passage by decreasing
  permeation velocity and interaction b/w fouling
  layer and salt CP layer.

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Theory

• Concentration Polarization Convection and
  Diffusion balance, Film theory

Cb , fb
g0
y
k
D
x
v, Cp Cm(1Ri)
(ref) Kim Hoek, Desalination 186 (2005) 111
6
Theory

• Permeate concentration increases as TMP decreases.

lt Seawater gt
lt Membrane gt
lt Permeate gt
Water
- Symbols -
Salt
(Ref) M. Mulder, Basic Principles of Membrane
Technology 2nd Ed., Kluwer Academic Publishers
7
Theory

• Cake layer enhances osmotic pressure drop and
  salt passage Cake enhanced CP (CECP)

(ref) Hoek Elimelech, Environ. Sci. Technol. 37
(2003) 5581
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Experimental Conditions

• Foulants
• Organic matter
• HA (Humic Acid, Aldrich),
• SA (Sodium Alginate, Aldrich)
• Nanoparticle
• S120 (Silica nano particle, d120nm)

• Membrane
• SR (Saehan, RO)

• Operation conditions
• Hydrodynamic condition
• Cross-flow Re 190
• Cross-flow velocity 0.05 m/s
• Initial TMP 850 psi 5.9 MPa
• Temperature
• T 25?C

Seawater - Source Masan Bay, Korea - pH 8.0
8.1 - DOC 2 mg/L
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Membrane Characteristics
lt Top view SEM image gt
lt AFM image gt
lt Zeta Potential gt

• lt Basic Properties gt
• Type Thin film composite
• Material Polyamide
• - Membrane resistance Rm ? 2.6?1014 m-1
• Contact Angle 57 ? 2? (water)

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Flux VS Salt Rejection

• Salt rejection increases as flux increases.

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HA Fouling VS Salt Rejection

• HA Concentration 960 mg/l as DOC
• Fouling degrades water quality 22

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SA Fouling VS Salt Rejection

• SA Concentration 170 mg/L, 75 mg/L as DOC
• Fouling degrades water quality 16

13
S120 Fouling VS Salt Rejection

• S120 Concentration 500 mg/l
• Fouling degrades water quality 35

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Effect of fouling on rejection

• SA, HA Increase of salt rejection (additional
  salt rejection by organic fouling layer)
• S120 Loss of salt rejection (CECP) starting at
  the very early stage

15
Key Findings Future works
Key findings

• Fouling affects salt rejection by two different
  ways (1) additional salt rejection (2) CECP
• Organic fouling increases salt rejection in SWRO.
• Nanoparticle sized 100 nm as diameter can
  severely degrade permeate water quality in SWRO.

Future works

• More applications including biofoulng study
• Development of more systematic model

16
Acknowledgements

• Financial support KOSEF
• This work was supported by a grant (No.
  R01-2006-000-10993-0) from the Basic Research
  Program of the Korea Science and Engineering
  Foundation (KOSEF)

• Prof. Chos research group at GIST, Korea.
• Prof. Hoeks research group at UCLA, USA.
• Center for Seawater Desalination Plant, Gwangju,
  Korea