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

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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)

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(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:

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(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

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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

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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

THANK YOU

http://www.fsr.ecm.uwa.edu.au

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)