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Current IssueJuly 25, 2014
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Ask The Expert: Testing the condition of membranes
02/01/2008 
 
Question:

I would like to know if there is a machine that can be used totest the condition of a membrane. Im asking this because I have an RO system thatuses 16 membranes and Im going to have to replace all of them, unless some of them are still healthy; but I dont know howto findout.

Sergio Guimera: sergio@adiego.com

 

Answer: 

I would like to know if there is a machine that can be used totest the condition of a membrane. Im asking this because I have an RO system thatuses 16 membranes and Im going to have to replace all of them, unless some of them are still healthy; but I dont know howto findout.

Sergio Guimera: sergio@adiego.com

The easiest way to test an RO membranes performance is to evaluate its TDS reduction. Many commercial units are designed to allow the user to test each membrane (or bank of membranes) individually. This really needs to be part of the complete RO system design; that is, to have a sample port for each membrane in order to isolate it for this type of evaluation.

If this commercial unit does not have this built-in capability, then what you may be able to do is disconnect individual permeate ports off of each RO membrane vessel and take a sample of the water coming out from that RO membrane. Use a five-gallon bucket (or so) and fill the entire bucket. Then use a TDS meter to determine the membranes reduction capability.

As to an actual test machine, I am sure the manufacturers of the membranes have them, but the shipping cost to do this would not be worth the test. It would be better to just get all new membranes than to start shipping wet commercial ones around.

Shannon Murphy, Watts Premier, Inc.

I concur with Murphy and would add that unless the problems have just started to occur,they are all probably bad. In addition to testing the permeate TDS from each vessel, when the permeate fitting is removed, it is possible to insert a length of quarter-inch tubing into the permeate tube in order to check the permeate from each membrane. This is valuable in cases of suspended solids fouling (feed end) or precipitated solids (concentrate end).

Peter S. Cartwright, PE, Cartwright Consulting Co.

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