RO based desalination :its current developments,Challenges & future prospects

1. REVERSE OSMOSIS BASED
DESALINATION: CURRENT
DEVELOPMENTS, CHALLENGES AND
FUTURE PROSPECTS
A Presentation by,
ANOOPA ANN THOMAS
M180294CH 1

2. 2
CONTENT
1. Introduction
2. Desalination techniques
I. Classification
II. Importance of RO based desalination
3. Reverse osmosis
I. Definition
II. Process description
III. Comparison
IV. Advantages and Disadvantages
4. RO membrane
I. Cellulose acetate membrane
i. Introduction
ii. Advantages and short comings
II. Thin film composite (TFC) membrane
i. Current developments
ii. Challenges
III. Thin film nanocomposite (TFN) membrane
i. Property enhancement using nanoparticle
5. Conclusions
6. References

3. WATER, WATER EVERYWHERE BUT NOT A DROP
TO DRINK !
3

4. What we need ?
Sustainable technological solutions that would meet increasing
water consumption.
4

5. WAYS TO OBTAIN POTABLE WATER
1. Wastewater reclamation
2. Rainwater harvesting
3. Seawater desalination
5

6. WHY SEAWATER DESALINATION ???
 Depletion of reserves
 Alternatives are not always available
 To meet the demand
6

7. WHERE DESALINATION IS USED ???
 Arid areas with scarcity of freshwater ,contaminated
groundwater or brackish groundwater.
 Power availability in abundance and cost of power is low.
 Some major RO based desalination projects in INDIA
 Minjur – Chennai (100 mld )
 Nemmeli - Chennai (100 mld )
7

8. Desalination techniques......
Desalination
Distillation
Multi-stage flash distillation
(MSF)
Multiple effect distillation (MED)
Vapour Compression
Freezing desalination
Geothermal desalination
Solar desalination
Ion-exchange
Membrane processes
Electrodialysis reversal
Nano-filtration
Reverse osmosis
Membrane distillation
8

9. 9

10. DEMAND vs SUPPLY
Ref:- IDA world congress 2015, held at San Diego
10

11. What?
Why?
11

12. A process by which a solvent passes through a porous
membrane in the direction opposite to that for natural osmosis
when subjected to a hydrostatic pressure greater than the
osmotic pressure.
REVERSE OSMOSIS
12

13. 13

14. Advantages
 Suitable for desalinating both sea water as well as brackish ground
water.
 Flexibility in regards of quantity and quality.
 Requires less energy than thermal processes (absence of an
evaporation step).
 Operating cost is comparatively low with respect to thermal
processes.
 Less environmental impact.
14

15. Table(1.a) – Energy cost comparison of desalination processes
Table (1.b) – Cost comparison for produced water 15

16. Disadvantages
 More pre-treatment required
 Maintenance cost is high
 Membrane fouling
 Direct effect of salinity
16

17. SEMI-PERMEABLE MEMBRANE: Heart of RO
 Factors that defines effectiveness of membrane based desalination
process
 Flux across the membrane
 Salt rejection
 Asymmetric cellulose acetate membrane developed by Loeb and
Sourirajan in 1963.
17

18. CELLULOSE ACETATE MEMBRANE
c/s of Loeb & Sourirajan
asymmetric membrane
 Feed solution - 52,500 mg/L NaCl
 Pressure - 1500 to 2000 psig
 Flux - 9 to 19 LMH
 NaCl rejection - 99.5%
18

19.  Cellulose acetate (CA) is made by acetylation of cellulose.
 The degree of acetylation can range from 0-3.
 Degree of acetylation has a large effect on membrane properties.
1. High degree of acetylation results in high salt rejection
but low permeability.
2. Low degree of acetylation results in lower salt rejection
but higher flux.
 Degree of acetylation of commercial CA membrane is about 2.7.
19

20. Advantages
 Easy to make.
 Excellent mechanical properties.
 Resistant to attack by chlorine.
20

21. Short comings
 Tend to hydrolyze over time.
 Stable only in pH ranges of 4 to 6.
 Thermally labile.
21

22. THIN FILM COMPOSITE
MEMBRANE
22

23. Membrane Type CA based Polyamide TFC
Feed (mg/L NaCl) 2000 2000
Pressure (psig) 425 225
Flux (GFD) 22 27
NaCl rejection (%) 97.5 99.5
Comparison of CA and polyamide TFC membrane
Source:-fundamentals of membranes for water treatment, Alyson Sagle
23

24.  TFC RO membranes are prepared via interfacial polymerization
by forming a polyamide (PA) thin selective layer on the surface of
a porous membrane.
 PA monomers are
m-phenylene diamine (MPD)
Trimesoyl chloride (TMC)
 Monomers and their chemical properties play an important role to
determine the pore dimension, thickness, roughness and
hydrophilicity of active thin film.
ACTIVE LAYER
24

25. Current developments........
1. Use of pyridine tricarboxylic acid chloride (PTC) reduced
bacterial attachment.
Flux (L/m2 h) Salt rejection (%)
PTC with TMC 52.7 93
PTC without TMC 42.5 94
2. Use of MPD and disulphonated bis sulphone
 Improve flux but decreases salt rejection
 Reduced Chlorine tolerance
25

26. SUBSTRATE LAYER
 Substrate should be hydrophilic.
Poly sulfone is used in conventional TFC RO membrane.
 Support/substrate layer is prepared by phase inversion technique.
 Support membrane with high hydrophilicity with the largest pore
size showed an optimum separation performance.
 Smooth surface is less desirable
26

27. Current developments........
1. Development of polyamide (PA) thin film / carboxylated
polysulfones (CPSf )
 CPSf is synthesized via direct polysulfone
functionalization.
 The functionalization had increased the wettability
and decreased the mechanical strength.
 High porosity and hydrophilicity.
27

28. 2. Development of a new material to fabricate substrate layer
 Substrate from sulfonated polyphenylene sulfones of various
degrees of sulfonation.
 Impact of sulfonation on water flux and hydrophilicity were
studied.
 The water and salt permeability obtained from the
pressurized tests was in good correlation with the RO data.
28

29. CHALLENGES OF TFC-RO MEMBRANES
IN DESALINATION INDUSTRY
I. Sensitivity to fouling
II. Sensitivity to chlorine attacks
III. Inadequate boron rejection efficiency
29

30. FOULING
 The process of deposition of particles on a membrane surface or in
membrane pores so that the membrane’s performance is degraded.
 Fouling is unavoidable in all pressure-driven membrane water
separation processes.
 Four types
I. Inorganic fouling
II. Colloidal fouling
III. Organic fouling
IV. Biofouling
30

31.  Adhesion of microorganisms and / or organic matters onto the PA
surface promotes the development of microbial which later on
forms extra-cellular polymeric substances (EPS) on membrane
surface.
 Increase in membrane resistance leads to low water productivity.
 The production of acidic by-product by microorganisms enhances
membrane degradation
 Higher energy consumption
 Declines in both permeate flux and salt rejection were primarily
due to biofilm - enhanced osmotic pressure (BEOP) effect.
31

32. CHLORINE ATTACK
 Chlorine attacks amide linkage.
 Factors upon which membrane degradation depends on
I. Chlorine concentration in feed
II. Exposure time in feed water /seawater
III. Independent of feed pH
32

33. fig(a) – permeability of TFC RO
membrane under active and passive
conditions
fig(b) – salt rejection of TFC RO
membrane under active and passive
conditions
33

34. BORON REJECTION
 Rejection of boron in seawater reverse osmosis (SWRO) is
challenging and based on the current standard set by WHO on
drinking water boron concentration is < 0.5 mg B/L.
 Boron rejection efficiency of TFC RO membrane is relatively low
compared to other dissolved ions.
 Boron which naturally presents in seawater can easily form as an
uncharged boric acid (B(OH)3).
pH < 9 boric acid easily permeates through
34

35. Distribution of B(OH)3 & B(OH)4
- vs Feed pH
35

36. Factors that influence boric acid dissociation
 Feed pH
 Operating temperature
 Pressure
 Ionic strength of sea water
 Intrinsic properties of membrane
36

37. Where we reached ?
37

38. THIN FILM NANOCOMPOSITE (TFN)
MEMBRANE
When nanoscale materials are used in TFC-RO
membranes it paved the way to the development of thin
film nanocomposite membrane.
 It is possible to tune membrane properties by using
nanoparticles.
38

39. Widely used nanoscale particles for membrane
property enhancement are
 Zeolite
 Carbon nanotubes ( CNTs )
 Titanium dioxide ( TiO2 )
 Silica
 Silver
39

40. 1. ZEOLITE
TFN –RO membranes that consist of a zeolite PA active layer
and a zeolite PSf substrate exhibited certain properties
superior to TFC-RO membrane like
• Smooth and hydrophilic membrane surface
• Higher water permeability
• Better salt rejection
• Improved resistance to physical compaction
• Improved fouling resistance
40

41. Fig (a) TFN membranes embedded
with zeolite nanoparticles
Fig (b) TFN membranes embedded
with CNTs
41

42. Membrane Type TFC Zeolite loaded
TFN
Flux (L/m2 h) ~ 33 37- 42
Salt rejection (%) 99.3 95.7-99.5
Comparison of TFN and zeolite loaded TFC
membranes when tested using 32,000 ppm NaCl
solution at 5.5 MPa
42

43. 2. Silica
Addition of 1-2 wt% silica into membrane matrix , membranes
with promising performances with respect to flux and rejection
could be fabricated.
3.Titanium dioxide (TiO2)
 TiO2 nanoparticles layed in active PA layer have
reduced biofouling of membrane.
 Utilization of photocatalytic activity of TiO2
nanoparticles.
43

44. 4. Silver
Silver nanoparticles integrated with the active layer of TFC
membrane is found to release silver ions which reacts with
thiol groups of microbial cells.
5. MW-CNTs
 One of the latest research
 Aims to embed multi-wall CNTs into PA membrane
 Enhance membrane performance and eliminate the
tradeoff between permeability and selectivity.
44

45. CONCLUSIONS
I. Seawater desalination is one of the potent source of potable
water.
II. Reverse osmosis (a membrane based process ) is the most
efficient process for desalination.
III.Use of Thin film nanocomposite membrane will mitigate
most of all the shortcomings of conventional RO
membranes.
45

46. References:-
1. A.F. Ismail, M. Padaki, N. Hilal, T. Matsuura,W.J. Lau,Thin film
composite membrane-Recent development and future potential, The
International Journal on the Science and Technology of Desalting
and Water Purification,356(2015)140-148.
2. N. Misdan, W.J. Lau, A.F. Ismail,Seawater Reverse Osmosis
(SWRO) desalination by thin-film composite membrane-current
development, challenges and future prospects, The International
Journal on the Science and Technology of Desalting and Water
Purification,287 (2012)228-237.
3. R.W.Baker, Membrane technology and applications,2nd ed,John
Wiley & Sons,Ltd.,New york 2004.
46

47. 4. I.G.Wenten , Khoiruddin (2015),Reverse osmosis applications:
Prospects and challenges, The International Journal on the
Science and Technology of Desalting and Water Purification, xxx
(2015) xxx-xxx.
5. Kah Peng Lee, Tom C. Arnot, Davide Mattia, A review of
reverse osmsosis membrane materials for desalination-
Development to date and future potential, Journal of Membrane
Science,370(2011) 1-22.
6. B.H.Jeong,E.M.V.Hoek,Y.S.Yan,A.Subramani,X.F.Huang,
G.Hurwitz ,A.K.Ghosh,A.Jawor, Interfacial polymerization of
thin film nanocomposites:a new concept for reverse osmsois,
Journal of Membrane Science,294 (2007)1-7.
47

48. 7. Alyson Sagle, Benny Freeman, Fundamentals of membranes for
water treatment, The future of desalination in Texas,2004.
8. Asif Matin , Z. Khan, S.M.J. Zaidi, M.C. Boyce ,Biofouling in
reverse osmosis membranes for seawater desalination:
Phenomena and prevention, The International Journal on the
Science and Technology of Desalting and Water Purification,281
(2011) 1-16.
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49. “The wars of the twenty-first century will be
fought over water “
Ismail Serageldin
Quotes!!!!
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51. Queries.......
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