Presentation on International Desalination Asociation World Conference in 2015 at San Diego on reverse osmosis membranes oxidation.

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RELATIONSHIPBETWEENHYDRAULICPROPERTIESANDSURFACECHARACTERIZATIONOF OXIDIZED
MEMBRANESIN SEAWATER
Jorge J. Malfeito
15WC:51662

2. World Congress RenewableWaterResources toMeetGlobal Needs August 30 – September4,2015 |San Diego California
1. Objective.
2. Problem statement.
3. Experimental conditions.
4. Hydraulic properties.
5. ATR-FTIR.
6. XPS.
7. Rf-GD-ToFMS.
8. SEM.
9. AFM.
10. Conclusions.

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To study the degradation process of the active layer of
TFC membranes in seawater caused by oxidants
commonly employed in desalination.
To introduce some analytical techniques useful in order
to carry out membrane degradation studies in seawater.

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TFC membranes’ active layer is composed by aromatic
polyamide, which is degraded in contact with the most commonly
employed oxidants in desalination processes.
¿What is the role of 𝑂𝐵𝑟−
in the degradation of the active
layer?
𝐵𝑟− + 𝐻𝑂𝐶𝑙 → 𝐻𝑂𝐵𝑟 + 𝐶𝑙−
𝐻𝑂𝐵𝑟 ← 𝑂𝐵𝑟− + 𝐻+
Kwon et al., Desalination (2011) 280, 80-86

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Fujiwara test is employed in RO membranes’ autopsies in order to detect
exposure to halogenating agents.
Spectroscopic techniques can detect oxidation before than Fujiwara test.
Desalin. Water Treat. (2013) 15, 1-3, 198-204
For an oxidized membrane, the relationship between hydraulic properties and
the surface characterization by means of spectroscopic techniques allows
knowing:
Which spectroscopic technique is faster in terms of oxidation detection.
Which chemical specie is the main responsible for oxidation in seawater.

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Accelerated degradation assays. Samples of a commercial TFC membrane
immersed in seawater with controlled additions of the oxidant agents:
Sodium hypochlorite (NaClO).
Chlorine dioxide (ClO2).
Sampling each hour.
Oxidation experiments in static conditions
10𝑁𝑎𝐶𝑙𝑂2 + 5𝐻2 𝑆𝑂4 ← 8𝐶𝑙𝑂2 + 5𝑁𝑎2 𝑆𝑂4 + 2𝐻𝐶𝑙 + 4𝐻2 𝑂
Standard Method 4500-ClO2-B

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Hydraulic properties related with the following analytical techniques results:
Fujiwara test
FTIR-ATR
XPS
rf-GD-ToFMS
SEM
AFM
Spectroscopic techniques
Morphological techniques
Chemical - Qualitative test

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0 2 4 6 8 10 12 14
96
97
98
99
100
Initial
NaClO (-)
NaClO (+)
ClO2 (-)
ClO2 (+)
Saltrejection[%]
Exposure time [h]
Monitorization of salt rejection values during testing.
Fujiwara test performance in each sample obtained.

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Oxidant agent Exposure time (h) Salt rejection (%)
NaClO 3 98,37
ClO2 13 97,63
Fujiwara test positive results conditions
Degradation (halogenation) of the membarne is faster with NaClO
than with ClO2.
Fujiwara test point of detection when employing ClO2 requires,
approximately, a 5 % lower salt rejection value than the required
value with NaClO.

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Study of the evolution of the aromatic polyamide characteristic
bands intensity during the oxidation process, by means of the
Degradation Index (DI).
1700 1650 1600 1550 1500
50
60
70
80
90
100
1587 cm
-1
Transmittance(%)
wavenumber (cm-1)
virgin membrane
degraded membrane
1541 cm
-1
Polysulfone
Polyamide
Desalin. Water Treat. (2013) 15,
1-3, 198-204
DI=
𝑇 𝑁
1541
𝑇 𝑁
1587 𝑠𝑎𝑚𝑝𝑙𝑒
−
𝑇 𝑁
1541
𝑇 𝑁
1587 𝑣𝑖𝑟𝑔𝑖𝑛
𝑇 𝑁
1541
𝑇 𝑁
1587 𝑣𝑖𝑟𝑔𝑖𝑛

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Samples’ oxidation detection following the evolution of
DI values.
Exposure time (h)
Exposure time (h)

12. World Congress RenewableWaterResources toMeetGlobal Needs August 30 – September4,2015 |San Diego California
Oxidant agent
Exposure time
(h)
Salt rejection
(%)
NaClO 1 (3) 99,27 (98,37)
ClO2 7 (13) 98,47 (97,63)
Oxidation detection by DI values
In terms of DI, degradation caused by NaClO is faster than the one
made by ClO2.
In both cases, salt rejection values are higher than the ones
required by Fujiwara test in order to detect oxidation.
Thus, ATR-FTIR detects membrane degradation earlier than
Fujiwara test.

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210 205 200 195
10000
15000
20000
25000
30000
35000
40000
45000
50000
55000
60000
65000
70000
75000
80000
85000
90000
95000
VirginNaCl
VirginNaBr
MQ,NaClO
NaCl,NaClO
Seawater,NaClO
MQ,ClO2
NaCl,ClO2
Seawater,ClO2
Cl-C
Cl
-
Intensity(cps)
Binding Energy (eV)
Cl2p

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80 75 70 65 60
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
Virgin with NaBr
Seawater with NaClO
Seawater with ClO2
Br-C
Br
-
Intensity[u.a.]
Bond energy [eV]
The covalent bond C-Br( 70,6 eV) predominates in all samples oxidized in seawater
with both oxidant agents.

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Surface Cl atomic percentage and Br atomic percentage of all
membrane samples exposed to NaClO and ClO2 at different
exposure times.
Cl-C is present in the virgin sample.
Chlorination
Exposure time (h)
Bromination
Exposure time (h)

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Cl content remains stable over time, while Br content increases
linearly with the exposure time to both oxidant agents.
Bromination is detected from the first sampling (1 h of contact
time with both oxidant agents).
Quantitatively, a more intensive halogenation is observed with
the use of NaClO than employing ClO2.

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Depth profile of the
elements present in the
sample is what
determines the extent
of the oxidant agent
attack to the membrane
structure.
Polyamide active layer composition is registered during the first 20 s of the glow discharge.
C
• Cl is present in the virgin sample
O
N
Cl
S
Virgin membrane sample
Time (s)
IntensityN,O,C(IU)
IntensityS,Cl,Br(IU)

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Depth profile of membrane
samples in contact with NaClO and
ClO2 in seawater.
Br is incorporated in the active
layer of the sample.
The oxidative attack is focused in
the membrane surface, in both
cases.
O
N
Cl
S
C
Br
Time (s)
0,00E+00
1,00E+06
2,00E+06
3,00E+06
4,00E+06
5,00E+06
6,00E+06
7,00E+06
8,00E+06
0,00E+00
2,00E+06
4,00E+06
6,00E+06
8,00E+06
1,00E+07
1,20E+07
1,40E+07
0 20 40 60 80 100 120 140 160 180
IntensidadBr,Cl,S(cps)
IntensidadN,O,C,Na(cps) Tiempo (s)
ClO2 - 7 horas
C:12
N:14
O:16/4
Na:23
S:34
Cl:35
Br:79
O
N
Cl S
C
Br
IntensityN,O,C(IU)
IntensityS,Cl,Br(IU)
Time (s)
NaClO
ClO2

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The Surface roughness is characteristic for TFC membranes prepared by interfacial
polymerization.
NaClO
ClO2
1h 3h 7h
1h 7h 13h
Virgin membrane
surface micrography
 No changes were observed in the degraded membrane samples in comparison with the
virgin one.

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From the Peaks and Valleys intensity registered, the surface roughness is
quantified in the membrane samples.
Oxidant agent Exposure time (h) Surface roughness
(nm)
None - 1571
NaClO
1 1441
3 1481
7 1351
ClO2
1 1521
7 1411
13 1541
 No significant roughness change was produced in the membrane surface
after degradation in the present conditions.

21. World Congress RenewableWaterResources toMeetGlobal Needs August 30 – September4,2015 |San Diego California
Spectroscopic techniques may be employed in the field of membrane autopsy in order to clarify the
reason that produces decrease in salt rejection in a significant advance compared to the Fujiwara test.
FTIR-ATR can monitor the degradation process, by means of the evolution of the DI parameter.
XPS is the most sensible analytical technique studied in the present work because it is the first in
detecting degradation.
Rf-GD-ToFMS provides specific information about the species involved in the degradation process
and the extent of the attack to the active layer.
The combination of the evidence obtained by XPS and rf-GD-TOFMS confirm that the mechanism of
degradation of aromatic polyamide membranes with ClO2 or NaClO in seawater is based on the effect
of hypobromite ion.

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R. Sandín, E. Ferrero, C. Repollés, S. Navea, J. P.
Espinós, N. Bordel, C. González