Flow field in fouling spiral wound reverse osmosis membrane modules using MRI velocimetry

Abstract
Magnetic Resonance Imaging (MRI) velocimetry was applied to study non-invasively the water flow field inside a spiral-wound desalination membrane module (diameter: 2.5 in.; length: 18.5 in.), located in a pressure vessel, at typical practice operational conditions as a function of alginate fouling, simulating extracellular polymeric substances (EPS). Cross-sectional velocity images were acquired at an in-plane spatial resolution of 0.137 mm at multiple locations along the length of the reverse osmosis module and were acquired as a function of alginate concentration. At a total system alginate concentration of 3.25 mg/l, significant changes in the cross-sectional velocity map were observed near the module inlet due to alginate fouling, with limited changes observed in the middle and outlet regions of the module. When the total system alginate concentration was increased to 75 mg/l, it caused the module brine seal to fail resulting in significant local water flow by-passing the membrane module. This was clearly discernible in this opaque membrane system using MRI and resulting in dramatic changes in fluid velocity distribution through the membrane module. These observations of significant flow field heterogeneity as fouling develops are consistent with ‘irreversible’ fouling effects noted frequently in practice by the water treatment industry.

Citation
Bristow, N. W., Vogt, S. J., O’Neill, K. T., Vrouwenvelder, J. S., Johns, M. L., & Fridjonsson, E. O. (2020). Flow field in fouling spiral wound reverse osmosis membrane modules using MRI velocimetry. Desalination, 491, 114508. doi:10.1016/j.desal.2020.114508

Acknowledgements
The authors acknowledge Mr. Ryuta Ujihara's assistance setting up the flow loop used in this work for the MRI measurements. The authors acknowledge Mr. David Amm's assistance and expertise in design and fabrication of the various custom parts used in this work. The authors acknowledge Dr. Kirk Feindel, the Centre for Microscopy and Characterisation and analysis (CMCA) at UWA and the Australian National Imaging Facility (NIF) for use of 9.4T MRI instrument used in this work. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Publisher
Elsevier BV

Journal
Desalination

DOI
10.1016/j.desal.2020.114508

Additional Links
https://linkinghub.elsevier.com/retrieve/pii/S001191642030151X

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