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Transparent exopolymer particles (TEP) and their precursors in reverse osmosis (RO) systems: quantification, fouling potential and cleaning

Li, Xu (2018) Transparent exopolymer particles (TEP) and their precursors in reverse osmosis (RO) systems: quantification, fouling potential and cleaning. PhD thesis, Murdoch University.

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Transparent exopolymer particles (TEP) and their precursors have been identified as critical causal factors in fouling of desalination and other water treatment membranes. TEP and the fractions thereof are composed of a wide variety of organic constituents and size fractions and have conventionally been only quantified by an operational method, specifically, Alcian Blue measurement. For fouling control and mitigation purposes, it is important to accurately measure the amount of both TEP and TEP precursors, their fouling capacity, and their response to cleaning. However, these issues are not well understood nor are there generally accepted methods for undertaking comparative studies to address this lack of understanding. In this study, a three-stage research study was undertaken to evaluate (1) TEP and TEP precursors quantification methods, (2) TEP and TEP precursors fouling potential on seawater reverse osmosis (SWRO) membranes, and (3) hydrogen peroxide (H2O2) cleaning performance on TEP fouled SWRO membranes. It was found that the concentrations of TEP may only represent ~10% of the total mass; while TEP precursors represent ~80% of the total TEP. This highlights the importance of measuring, reporting, and operationally considering both TEP and TEP precursors for membrane biofouling studies. A reliable, adaptable statistical method using the T-test was developed to quantify and develop a criterion for differentiating fouling behaviour of different TEP surrogates and TEP fractions. Similar fouling potential was measured with total TEP, TEP, and TEP precursors at the same concentrations. Therefore, TEP concentrations rather than TEP sizes were correlated to membrane fouling. It highlighted the importance of developing new advanced pre-treatment techniques for TEP precursors removal. H2O2 cleaning enhanced water flux, possibly due to re-compaction/re-attachment of xanthan gum on the membrane surface following its breakdown into smaller fragments. The hypothesis of membrane degradation due to exposure to H2O2 during cycles of fouling and cleaning-in-place (CIP) was not supported by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), salt flux, and salt rejection results. The work strongly suggests peroxide cleaning be further evaluated with field trials as an alternative to commonly used, but more destructive, cleaning techniques.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Engineering and Information Technology
Supervisor(s): Ela, Wendell and Li, Linda
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