May 172 min read

TECH INC TIPS: ALL THINGS FLAT SHEET MEMBRANES

Pre-Conditioning, Use, and Preservation

What is membrane preconditioning and why is it recommended to precondition new flat sheet or spiral wound membranes prior to use?

Membrane preconditioning is a filtration step using deionized water as feed solution and is typically performed at a pressure equal to or higher than the anticipated testing pressure. During this process membrane pores are wetted and the membrane structure may go through compaction or swelling, affecting both the permeate flux and the rejection values. Preconditioning will help ensure that the membrane performs according to the specs provided by the manufacturer.

Will my membrane flux data compare to that of an element?

Flow characteristics for a spiral element and flat sheet membrane are significantly different and are really only comparable on a qualitative basis. Variability in the membrane manufacturing process, differences in water composition, test procedures, and test equipment used in a factory, laboratory, or elsewhere, will impact water flux results. The flux data, as given for flat sheet membranes, should be considered as approximate.

How do I clean and store my membrane after use?

In general, caustic solutions (for example 0.01 to 0.05% aqueous sodium hydroxide solutions) are used for organic foulants and acidic solutions (for example 0.1 to 0.2% aqueous HCL solutions) are used for inorganic foulants. It is important to perform the caustic cleaning first to remove organic foulants since some organics can be irreversibly linked to the membrane at low pH.

Proper storage is essential to preserving the quality of flat sheet membranes after use. Used flat sheet membranes must always remain wet, including during storage. Membranes that are allowed to dry will irreversibly lose water permeability. To prevent microbial growth, the membranes can be stored in a 0.5% solution of formaldehyde. Alternatively, the membranes can be stored in a 1.0% solution of sodium metabisulfite (SMBS). To maintain efficacy, the SMBS solution should be replaced monthly. Or the membranes can be stored in UPDI water that is replaced weekly.

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