How long does your RO membrane last?
 

I currently have a Filmtec 75gpd RO membrane and it only last for about 700g. Is this normal? I'm not sure.

WOW, something isn't right. It is impossible to say how long a R/O membrane will last because it is a filter. Garbage in/ Garbage out. Unless you have well water, and your TDS is out of site I'd say there is no way to exhaust a membane after only 700 gallons. I'd say 10 times minimum that would be closer to normal. Perhaps much more. What are your TDS out of the mebrane now? How about out of your tap?

Its definitely not normal!!!! I'm going on 2 yrs with my RO unit with the original membrane. Do you have a TDS meter? I have a hand held one you could borrow if you want. Pm me if you like

Some people run warm water through their ro, so it ready for top off. That will damage the membrane.

You running barebones w no prefilters??
 

Are you running at least 1 and hopefully two stages before the Membrane???????????????

If you are barebones with no carbon block and no pre-filter in 1 and .05 micron then you will hammer your membrane fast. IE the membrane is doing all the work.

(1/2 micron is not required and is probably excessive by most BTW)

For example MY RO/DI setup.
I have 1micron, then 1 micron carbon, and 1/2 micron then membrane, then DI stage 1 and DI stage 2

OR do you have the tubes going the correct route. Get up to 4 and 5 stages and same color tubing and in a hurry during setup you could have bypassed other stages.

???

Why do you think the membrane has gone bad?

Russ

Because my DI resin goes bad really quick.

I would borrow Cove's meter and test
 

I would take Cove Beach up on his TDS meter offer. I would remove DI resin out of that stage.

Then I would charge it back up and let 10 or so gallons go through then test the output to double check the RO membranes output before you bring in a verdict.

Thanks for the offer. I have a TDS meter myself. If the membrane is bad, the water coming out without the DI stage would essentially read the same as the tap water, right? If it is still good, what reading should I approximately get? Thanks for everyones input!

If you have the 75g filmtec membrane and it is in good working order and you have 300ppm coming out of your tap, you should have about 6-10 ppm after the RO membrane. After DI it should be 0ppm.

math sounds good

The thing that kills RO membranes is chlorine, then particulate matter that fouls it. How old is your carbon stage and have you tested the post-carbon water for chlorine breakthrough? Do you have a solid carbon block or a granulated carbon filter?

The other thing that can kill your RO membrane is letting it dry out.

The carbon blocks are solid. I have the typical 5 stage RO/DI system. How can I ensure that the membrane stays wet? I have a 30g trash can that I fill with water when it gets empty. I fill it about once every 1.5 weeks. Is there a problem in doing this. Can the membrane dry out during this period.

Measure the pre and post RO TDS. See what percent it is removing.

TDS meter wont read chlorine or chloramine.

More likely you just need to replace the DI resin.

Russ from BFS (posted above) really knows his stuff.

I also only run mine about twice a month but its hooked to water supply the whole time with a ball valve on the supply I use to turn it off.

If you unhooked it like from a faucet adapter it maybe able to drain back? I know the pure water outlet on mine is always open, and it doesn't seem to drain.

[QUOTE][i]<a href=showthread.php?s=&postid=11045438#post11045438 target=_blank>Originally posted</a> by sohal1025 [/i]
[B]Some people run warm water through their ro, so it ready for top off. That will damage the membrane. [/B][/QUOTE]

Where did you hear that? The club had a professional filtration expert out about a year ago to do a speech at a meeting. He stated that they preheat the water going into the RO units to get optimal production. It should be 70-77 degrees if possible. If the water is cooler it will have a higher rejection rate as it makes the pores on the RO membrane close up tighter.
I have a 100ft coil of tubing inside my sump before the RO unit to help bring the input temp up from the underground temps and it also helps cool the tank water.

77 degrees is perfect. You can run into trouble if folks are imprecise in heating the water and occassionally feed HOT water to the membrane.

Russ

As said above, report your tap water tds and your RO water tds. Also - what is your waste to permeate ratio?

Russ

[QUOTE][i]<a href=showthread.php?s=&postid=11058507#post11058507 target=_blank>Originally posted</a> by itZme [/i]
[B]Where did you hear that? The club had a professional filtration expert out about a year ago to do a speech at a meeting. He stated that they preheat the water going into the RO units to get optimal production. It should be 70-77 degrees if possible. If the water is cooler it will have a higher rejection rate as it makes the pores on the RO membrane close up tighter.
I have a 100ft coil of tubing inside my sump before the RO unit to help bring the input temp up from the underground temps and it also helps cool the tank water. [/B][/QUOTE]

Interesting....guess I should go to more meetings. Since mine's hooked up to my sink, I wonder if the cost of heating the water to decrease the rejection rate is worth wasting less water? I'm guessing not. Kevin has a nice way of making it work though!

I just wish the tubing I have in the sump was titanium instead of plastic tubing :)
I'm guessing it doesn't transfer heat very well.

Found[url=http://www.excelwater.com/eng/b2c/water_tech_5.php?WL_Session=abdd38c643c88c355d3d4898d60f12d8] this[/url] to answer your question about mixing hot/cold water.

"Membrane performance is based on feedwater temperature of 25°C. For every 1°C below 25°C product water quantity is reduced by 3%. When feedwater temperature is regularly below 25°C, it is recommended that hot and cold water are mixed to increase the temperature to 25°C. Feedwater which is greater than 35° will damage most membranes. "

Just guessing that the input water temp from the cold water supply line would hover around 50F in the winter means that 50F= 10C. 25C- 10C= 15C difference from optimal temp. 15C x 3% reduction in product water per degree = 45% reduction in output water :eek:
To me it seems that it may pay off to run some hot and some cold in your case.

just a note if you mix hot and cold and somone flushes the toilet or anything it will change and burn your membrance rate up i found out the hard way, also now that i run pure cold water i dont notice much more waste so just run cold water and put a heater in it,

my tds out of tap is about 130-145 and after the membrance i see 0-1tds i quit using the di unit sense i am just a fowlr no sense in paying all that in refill for di as it dont last long for some reason?

Hope i helped a little

There is a nice [url=http://buckeyefieldsupply.com/calc.asp]calculator[/URL] available where you can plug in your water temperature and water pressure and it will calculate what your membrane should be producing.

Russ

Running the tubing through the sump first is a great ideal But unless you're dealing with heavy evaporation, I doubt it would do much cooling. Doesn't matter that the tube is made of plastic because the flowrate through the tube is so slow. I'm sure that the water in the tube is heating up very close to aquarium temperature before hitting the membrane.