Membrane Selection, Testing and Evaluation

The choice of membranes is critical and this requires careful evaluation. To save costs of testing, many operators try to perform bench-scale rather than pilot-scale experiments for an initial process evaluation. Stirred cell systems are commonly used for research purposes. 

DiGiano (1996) suggested a batch-recycle membrane test as an alternative. The test operates in batch mode by recirculating both feed and permeate. The advantage of this test is the lower feed volume required (3 L versus 60 to 200 L for the RBSMT). Moulin (1993) described a dynamic membrane test, that allows determination of the suitability of a membrane to obtain the required health standards (cytotoxicity). 

The characteristics of eleven different NF membranes were summarised by Rautenbach and Groschl (1990). Traditional softening membranes were compared to high flux tyfpe membranes. Fu et al. (1995) characterised eight membranes from different manufacturers and of various materials. Trisep TS80 and Nitto Denko NTR7450 were chosen for pilot studies. Performances were comparable, but the latter membrane was better for removal of trihalomethane precursors (THMPs). 

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