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Magnetic Resonance Imaging of Membrane Fouling
Dr Einar Fridjonsson
Fluid Science & ResourcesSchool of Mechanical and Chemical Engineering
University of Western Australia
Mobile NMR technology Research Areas:
Low field NMR (Remote Operations):
Oil & Gas industry(1) Emulsion & oil discharge monitoring
Oil & Gas industry(2) Multi-phase flow metering
Mining & Coal seam gas industries(3) Well logging
Desalination industry(4) Membrane fouling (Desalination)
• 87 million m3/day desalination capacity (2015).• 18,426 desalination plants worldwide.• Globally more than 300million people rely on desalination.
(Source: IDA - International Desalination Association)
Reverse Osmosis Membranes: NEED
Sources: UNESCO, IFPRI
Local motivation
47% of Perth‘s water comes from desalination!
4
Fig. 1. (a) Kwinana desalination plant in Perth, Western Australia; (b) an example of a heavily biofouled desalination membrane module, the dark regions are due to biofilm.
Feed
Feed spacer
Feed water
Permeate
ROCore
Permeate
Concentrate
Reverse Osmosis Membranes: Construction
Bio-fouling is a major limitation for ROMs
Research aims:• Direct evidence that spacers host biofilm growth and loss of membrane performance• Direct measurement of ROM cleaning potential• Early detection of membrane bio-fouling• Development of low-cost MRI solution for monitoring membrane fouling.
NMR/MRI Studies
High-field(Superconducting)
(Cost > $1M)
Bench-top(Permanent Magnet)
(Cost > $100k)
Mobile(Permanent or No Magnet)
(Cost < $10k)
Tap water
Flow controller
Differential pressure transmitter
Pressure regulator
Carbon filter
RO module
ΔP
Nutrients Pump
Discharge
Schematic: Flow loop for spiral wound membrane fouling
Imaging Biomass Accumulation (High-field)Unfouled
Fouled
Velocimetry
Imaging Biomass Accumulation (High-field)
Graf von der Schulenburg, D.A., Vrouwenvelder, J.S., Creber, S.A., van Loosdrecht, M.C.M and Johns, M.L. (2008), Nuclear Magnetic Resonance Microscopy Studies of Membrane Biofouling, J. Memb. Sci., 323(1), 37-44.
Imaging Biomass Accumulation – Model System
16 mm37 mm
xyz
pH 12 NaOH at 45°C, 100 mL/min for 1.5 h
Structural
Velocity
0.05 m/s
-0.01 m/s
Imaging Biofouling cleaning processes - Example
0.05 m/s
-0.01 m/s
• A variety of cleaning protocols assessed and effectiveness relatedto original fouling structure
Creber, S.A., Vrouwenvelder, J.S., van Loosdrecht, M.C.M and Johns, M.L. (2010), Chemical cleaning of biofouling in reverse osmosis membranes evaluated using magnetic resonance imaging, J. Memb. Sci. 362(1-2), 202-210.
Front
Middle
End
Clean Fouled
55 mm
55 m
m
(a)
(c) (d)
(b)
On-line Analysis?
On-line NMR/MRI tool should be simple, robust and low cost.
Superconducting Magnets Permanent Magnets
Even Simpler System: Mobile NMR/MRI
Nuclear Magnetic Resonance (NMR) measurements conducted using Earth’s magnetic field as the external (B0) magnetic field.
NMR experiments conducted at end of each fouling stage (indicated by arrows):
Fridjonsson et al. J. Memb. Sci. 489 (2015): 227-236.
High Field MRI (400MHz)
Before Fouling After Fouling
Before Fouling After Fouling
Flat Sheet Membrane:
Spiral Wound Membrane:
Observations:
Fouling causes a backbone (Channeling) flow occurs within membrane system:
Results in stagnant (slow) flow regions
&
Flowing regions to flow at higher velocity.
High field MRI - Observations
No Fouling:Linear decrease in NMR signalwith increasing velocity:
Fouling Stage 3:Negligible decrease in NMR signalas function of increasing velocity.
NMR signal measured has increased.
2/0 1 ET TE
dd
T US S eL
− −
Low field NMR - Observations
“Outflow” effect
=
Results consistent with high field NMR observations:
Fouling causes stagnation (low flow)regions to form, resulting in increased total signal,and independence of increasing flow rate.
Fridjonsson et al. J. Memb. Sci. 489 (2015): 227-236.
DaFit
y
x
Spatial domain Frequency domain, S
x
Σy
kx
ky
Frequency domain, φ
kx kx
kx
ky
ln(S/Smax) φ
Fourier transform
Acquire only the moments of the signal distribution - Test
Fridjonsson et al., J. Magn. Reson. 252 (2015): 145-150.
2 2
max
S(k) 1ln kS 2
σ≈ −
0.5
0.6
0.7
0.8
0.9
1
1.1
40
60
80
100
120
140
0 10 20 30 40
2nd M
omen
t - σ
2 -(c
m2 ) Pressure D
rop (kPa)
Fouling Time (Days)
Pressure Drop
2nd Moment
2 2
max
S(k) 1ln kS 2
σ≈ −
Magnetic Resonance Signal Moment Determination using the Earth’s Magnetic Field
Future Work: Modelling of Outflow (EF NMR)
EF MRI
26
400MHz MRI
Figure 1: Typical model outputwith model prediction, (solid blueline) and NMR output (blackcrosses). It can be seen that thereis good agreement between themodel prediction and the NMRsignal measured.
EF NMR
Future Work - Signal Enhancement & Customisation
Miniaturizing Hardware(NMR Spectrometer)
(i) Dynamic Nuclear Polarization(DNP)
(ii) Compressed Sensing
(iii) Bayesian Analysis
Signal Enhancement:
Custom Built NMR coils:
NMR-CUFF (Windt et al. 2011)
CUFF – Cut-open, Uniform, Force Free
A phenomenon whereby the flux through the membrane is controlled by the film mass transfer resistance on the feed-side rather than purely the resistance of the membrane itself.
Measuring Concentration Polarisation
Feed
Permeate
Permeate
boundary layer
solute molecules
Sodium (23Na) MRI (High-field)
29
(a) 1H image and (b) 23Na MRI images of a flat sheet membrane module(resolution 0.01 by 1mm2). (c) Shows a sodium profile of the operatingmembrane module (b), with concentration polarisation evident at interface.
Flat sheet membrane system:
- Monitor interplay of fouling and concentration polarisation using sodium MRI.
Spiral wound membrane module:
- Use 23Na MRI techniques to monitor concentration polarisation and fouling.
Membrane module geometries:
30
(ii) Hollow fiber(i) Spiral wound
Hollow Fibre Membranes (HFM):
Non-invasive performance measurement of membrane distillation hollow fibre modules – Four different arrangements tested.
Collaboration with: Singapore Membrane Technology Centre.
Bench-top NMR
19mm
Optical MRI
10mm
10mL/min 20mL/min 30mL/min 40mL/min 50mL/min
100mL/min 400mL/min 1000mL/min 1500mL/min 2500mL/min
Yang et al. J. Memb. Sci., 451, 46-54 (2014).
Ultrafiltration (UF) HF membranes
Module type: SIP-1013Material (membrane & housing): polysulfone (C27H22O4S)n
Membranes no.: 400ID: 0.8 mm; Length : 205 mm
32
2-D MRI (Bench-top)
33
In-plane resolution:180µm x 180µm
Slice thickness: 1.42cm
Acquisition time:2.3hrs
Aim:Monitoring effect of foulingon membrane performanceusing velocity images.
46 mm
Permeate
ConcentrateFeed water
CapillariesOuter shell
0.06 m/s
-0.02 m/sFlow
13 m
m
(a)
(b)
13 m
m
2-D MRI (High-field MRI)
Biofouled HFM – impact on flow distribution
35
13 m
m
(a) (b)
0.06
-0.02 Flow
13 m
m
(a) (b)
Clean Fouled
Acknowledgements
36
Mike JohnsSarah CreberDaniel Graf von der SchulenbergWiktor BalinskiRyuta UjiharaNicholas BristowAndrew SedermanDan HollandSzilard BucsHans VrouwenvelderMark von Loosdrecht
Funding/Support from
37
Mobile NMR and MRI
38
NMR Measurements:
Velocity:
Proton density: T1 & T2 Relaxation:
0
0.1
0.2
0.3
0.4
-100 0 100 200 300am
plitu
defrequency / Hz
Chemical Shift:Diffusion/DSD:
0.00
0.05
0.10
0.15
0.20
0.0 5.0 10.0
Droplet size (µm)
Oil
Water
Free Water
Water (surface interacting)
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