RO - expected mineral content?

[Mer-man]

I have found an affordable RO system that uses a TFC-75F membrane (http://aquafilter.com/download/461436_TFC.pdf), so I can give up boiling.

I read on a random page that RO reduces mineral ion content to about one-ninth of the starting point.
My water spreadsheet has a default RO profile but I think a filter (even a fancy membrane) would have an efficacy threshold and only remove a certain proportion of minerals. Or perhaps I misunderstand the technology?

This Cornell paper (http://waterquality.cce.cornell.edu/publications/CCEWQ-04-ReverseOsmosisWtrTrt.pdf) says the reduction rate depends on the filter and conditions, but I cannot find reduction rate for the filter.


Is there a reliable method for estimating post-filtration content, or do I need to send a sample to a lab?

Thanks!

 

[Mer-man]

Cough

 

[Spartan1979]

Get a TDS meter. They're pretty cheap and it will tell you how much is still in your water. It won't tell you what is there, only how much in total. It's also good for monitoring if your system is still working.

My tap water is usually around 278 ppm. After the RO system I usually get 8-12ppm. It's pretty immaterial.

 

[ajdelange]

Using the TFC you can just assume 95% rejection for everything and probably not be too far off. If you are concerned about a particular ion assume 90% to be conservative and if you are really concerned do an analysis for that ion

Many RO sytem owners here obtain an inexpensive TDS meter and use that to check overall rejection i.e.1 - outputTDS/inputTDS. If you do this with a brand new system right after installation you can use this simple test to keep an eye on system performance. If the membrane degrades you will spot it with this overall rejection test.

 

[Mer-man]

Thanks guys!

I will use 90% to be conservative.

I appreciate that I can use a TDS meter to gauge effectiveness, too.

Happy Danish summer (i.e. it's 16 and drizzling)!

 

[mabrungard]

Rejection rate is ion specific. However, there are broad estimates that can be applied based on the ion diameter. In general, monovalent ions pass through RO membranes at a higher rate than divalent ions. So, sodium and chloride tend to have less favorable rejection than calcium or magnesium and a little more of the water's original Na and Cl content may make it through into the product water. I've shown a table on typical membrane passage rates (which is the inverse of rejection rate) on the Water Knowledge page of the Bru'n Water website. Those rates came from my college water treatment class notes and from GE (they sell membranes).

 

[Mer-man]

Ok, I'll check it out.

The 95% and your table, Martin, come close enough to each other that they are probably within my margin of error.

Cheers!