Improving MFI-UF constant flux to more accurately predict particulate fouling in RO systems: Quantifying the effect of membrane surface porosity

Abstract
This study aimed to quantify the effect of membrane surface porosity on particulate fouling predicted by the MFI-UF method at constant flux. Firstly, the surface porosity of polyethersulfone UF membranes (5–100 kDa) was determined using ultra-high resolution SEM. Thereafter, the MFI-UF was measured using suspensions of polystyrene particles (75 nm), which were pre-washed to remove surfactant and particle fractions smaller than the pores of MFI-UF membranes, thus ensuring complete retention of particles during MFI-UF measurements. Consequently, the MFI-UF values of washed polystyrene particle suspensions were independent of the pore size and depended only on the surface porosity of MFI-UF membrane. The results showed that the membrane surface porosity decreased with MWCO from 10.5% (100 kDa) to 0.6% (5 kDa), and consequently the MFI-UF increased from 3700 to 8700 s/L2, respectively. This increase in MFI-UF was attributed to the non-uniform distribution of membrane pores, which is exacerbated as surface porosity decreases. Consequently, preliminary correction factors of 0.4–1.0 were proposed for MFI-UF measured with UF membranes in the range 5–100 kDa. Finally, the surface porosity correction was applied to predict particulate fouling in a full-scale RO plant. However, additional research is required to establish correction factors for different types of feed water.

Citation
Abunada, M., Dhakal, N., Andyar, W. Z., Ajok, P., Smit, H., Ghaffour, N., Schippers, J. C., & Kennedy, M. D. (2022). Improving MFI-UF constant flux to more accurately predict particulate fouling in RO systems: Quantifying the effect of membrane surface porosity. Journal of Membrane Science, 660, 120854. https://doi.org/10.1016/j.memsci.2022.120854

Acknowledgements
This study has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 820906 and the Department of Biotechnology (Government of India, Project No. BT/IN/EU-WR/40/AM/2018). The authors would like to acknowledge Alla Alpatova from King Abdullah University of Science and Technology (KAUST) for her contribution in imaging the UF membrane surfaces by SEM. Thanks also to Alma Imamovic from IHE-Delft Institute for Water Education (IT department) for her help in taking the pictures of the membrane holder support pad.

Publisher
Elsevier BV

Journal
Journal of Membrane Science

DOI
10.1016/j.memsci.2022.120854

Additional Links
https://linkinghub.elsevier.com/retrieve/pii/S0376738822005993

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