RO membrane life?

[Raznyc79]

how and when do you know the RO membrane needs to be chage. I have an 150 gpd dual ro unit from from BRS. Tap water here in AZ run 450 tds. It seem barely much water going into my coletion bin. I changed the filter and carbon last week. I looked at the waste line and the water is flowing at what seems to be very good flow. Could it be because. The ro membrane is done? Thank you for your help

 

[Forsaken77]

You should have a psi gauge inline right before the membrane. You need at least 60 psi. If not, you need a booster pump. Sounds like you either don't have enough pressure pushing the water THROUGH the membranes, and it's going around them, or you don't have a flow restrictor to enable pressure.

Any water that goes around the membrane goes down the drain. Only water that goes through ends up in the bin.

 

[mjlash22]

You should have a psi gauge inline right before the membrane. You need at least 60 psi. If not, you need a booster pump. Sounds like you either don't have enough pressure pushing the water THROUGH the membranes, and it's going around them, or you don't have a flow restrictor to enable pressure.

Any water that goes around the membrane goes down the drain. Only water that goes through ends up in the bin.

+1 If you have the "plus" model that comes with the pressure gauge and TDS meter, check your water pressure. Also, are you sure you don't have it in flush mode? Most membranes will last up 2 years depending on the amount of water you run through it. Take note of your average pressure when the membranes/filters are new. When you start seeing it drop, that is when you should look into replacing them.

High TDS will be an indicator that your cartridges/DI needs to be changed, low pressure (as compared to average pressure) is an indicator that your membranes are clogged and need to be replaced.

 

[Raznyc79]

The pressure is 55 as its always been at. The flow regular is in the off positon as well. What i noticed the last week was the water did not stop flowing even when the collection container was full. When I lift the float with my hand to test, the water does not stop flowing thru the black waste line. The filter and carbon is new last week. DI need change but i dont think it matter as far as preasures. Could the ro membrane need change or could it be the piece the shuts off the water when the collection bin is full?

 

[JoshH]

The pressure is 55 as its always been at. The flow regular is in the off positon as well. What i noticed the last week was the water did not stop flowing even when the collection container was full. When I lift the float with my hand to test, the water does not stop flowing thru the black waste line. The filter and carbon is new last week. DI need change but i dont think it matter as far as preasures. Could the ro membrane need change or could it be the piece the shuts off the water when the collection bin is full?

A float valve on your collection container will not shut the flow off to your RODI filter. All it will do is stop water from overflowing your collection container. When this happens it closes off your clean water outlet and your unit will stop producing clean water but it will not stop the flow through your unit so all your water goes straight out the waste line. What you need to stop the production of water altogether is a solenoid valve either before the RO or the sediment/carbon filters. And run the valve either with a controller or another timing device.

 

[Raznyc79]

My unit has an auto shut off valve which used to turn off the water flowing thur the unit when the float valve would close . That was my understanding of how the auto shut valve works....

 

[EmdeReef]

How old is the membrane and what's the tds of purified water after flushing the membrane 15-20mins? You could also measure before it goes through the DI resin. Pre-DI you'd expect a tds of under 10 but not much higher than ~20 depending on the system and your tap water.

 

[JoshH]

My unit has an auto shut off valve which used to turn off the water flowing thur the unit when the float valve would close . That was my understanding of how the auto shut valve works....

Yeah if you do have an auto shutoff that is rather unusual waste is still coming out.

 

[Raznyc79]

The unit and membrane new aprox 10 months, water pre DI after flushing 10 min is 20-21 ppm and post DI 3ppm. Tap water here in AZ is aprox 450ppm

 

[Greybeard]

ASOV (Auto shut off valves) are notorious for failing. If you're blocking clean output and still getting waste water, get a new one.

In my experience, when the RO membrane fails, it doesn't produce extra waste, but lets more and more 'stuff' through the membrane. TDS rises to 8 or 9 after the RO membrane, I change the carbon and sediment. About every 3 months. (well water, no chlorine/chloramine to deal with). If TDS stays high after changing sediment and carbon filters, it's time to change the membrane. I've been running the same membrane for just over 2 years. My last one lasted me about that long. DI carts, I just watch the color change and TDS meter, and refill them as needed. About once every other month.

 

[chipmunkofdoom2]

It sounds like there are several issues here that need to be addressed.

First is pressure. You need higher than 55PSI to run two membranes. 50 PSI is fine for running one membrane, but not two. As for how much pressure, you'll need to ask BRS or Dow, but you likely need a booster pump to make your dual membrane setup work. Perhaps try unhooking one of the membranes and see if that solves your flow problem.

Second is the auto shutoff. The auto shutoff should be after the second membrane. The product water line should go into the top of the valve, where it says "IN", and the output should be going out the top of the valve were it says "OUT". The waste valve from your second RO membrane should go into the bottom of the switch on the IN side, and the waste line to your drain should go in the bottom of the OUT side.

Third is your unit's age and the carbon blocks. You mention that you just replaced the carbon blocks recently. If your RO/DI unit has been running for 10 months on the same carbon blocks, it's possible that the old blocks were no longer able to process the chlorine/chloramine in your water. If this is the case, both your membranes could be fried. Chlorine is especially damaging to RO membranes and can ruin them in short order. Chloramine is actually a little less harmful to RO membranes, but it can still ruin them given enough exposure. Personally, I would test each membrane, one at a time, to make sure they're still meeting the advertised rejection rate of 96% or higher. Hook each membrane up one at a time. Test the TDS before and after the membrane. If your tap water is 450 ppm TDS, the water after each membrane should be 18 ppm or less. If it's not, that membrane is no longer meeting the specified rejection rates and could benefit from being replaced. To prevent damage to your membranes in the future, always replace the carbon blocks and prefilters every 6 months on a schedule.

Fourth is the DI resin. If your product water ever reads more than 0 ppm TDS, the DI resin needs to be replaced, regardless of what the rest of your RO/DI system is doing.

 

[Greybeard]

Excellent post, Chipmunk

I would disagree on this one...

...replace the carbon blocks and prefilters every 6 months on a schedule.

How long those filters will last depends on what you feed through them, and how much volume. No way mine will last 6 months. I change them out every 3 months or so.

 

[chipmunkofdoom2]

How long those filters will last depends on what you feed through them, and how much volume. No way mine will last 6 months. I change them out every 3 months or so.

Thanks Greybeard, I appreciate it. You're right, 6 months is a bit of a generalization. They may last shorter or longer periods of time. You could be more smart about it and replace as needed, but it requires testing and diligence.

To know when the prefilter needs to be replaced, you have to monitor pressure before and after the prefilters. When there's a pressure drop, at least the prefilter needs to be replaced. Depending on the quality and size of the prefilter, the carbon blocks may need to be replaced too, as they can plug up with small particulate matter also.

To know when the carbon blocks need to be replaced, really the only good metric that I know of is chlorine breakthrough. If you test your membrane waste water and find any chlorine or chloramines, your carbon blocks need to be replaced immediately. You mentioned you don't have chlorine because you're on well water, but for all other reefers, chlorine will ruin an RO membrane in very short order, so it's sort of a "stop everything and replace this filter before making any more water" deal, which can be pretty inconvenient.

If a reefer is willing to deal with the hassle of testing the pressure and chlorine/chloramine breakthrough, then the 6 month rule doesn't apply. You'd probably save a lot of money replacing when you need to as opposed to just blindly replacing every six months (this is what I do, I test and replace as necessary). But, it requires constant vigilance or you're going to potentially fry your RO membrane (again, for those with chlorine/chloramine in their water).

 

[Whipples]

@Greybeard excellent point. Those filters are cheap enough and with the right pressure and good replacement protocol for carbon/sediment a membrane should last 2-3 years, or more, depending on the brand. You can check by measuring tds after the membrane but before DI media to see what the rejection rate is, if you are not within 2-3% of what the manufacturer states at your pressure rating it indicates a replacement may be necessary.

 

[Greybeard]

My father in law, may he rest in peace, told me long ago to buy furnace filters by the case, as cheap as you can find, and replace them monthly. He was a HVAC guy... I like his advice. I use the same advice on sediment and carbon blocks. Buy 'em cheap, replace 'em often. I pay like $2 for sediment filters, $5 and change for 5 micron carbon blocks. An expired carbon block or sediment filter can ruin a perfectly good $40 membrane in no time at all, especially if you have chlorine in your water supply (no, I don't).

I use RO water for drinking water and to feed my icemaker and chilled water in the fridge. Not DI, mind you, but RO. Stored in a 5g pressure tank. Useage for drinking, cooking, icemaking, far exceeds usage for ATO and 30 gallon bi-weekly water changes for my ~150g aquarium.

 

[LiquidFunk]

I am hoping you RO folks can help me. I seem to only get about 500 gallons from an RO membrane. I have a whole house filter that uses 4x20" pre and carbon filters as well as the prefilters on the RODI.

I change my prefilters very regularly. So frequently the prefilter is usually bone white still, because of that I have recently gone to 2x Carbon instead of floss to try and preserve the membrane.

Any thoughts on the cause of my membrane failures? I have been buying replacements 1-2 times per year. I do have ridiculously high silicates, but I am not aware of this being a problem for membranes.

 

[Whipples]

What rejection rate are you running? Run your system for a minute and measure the product water and waste water. You should have a ratio of product to waste of 1:3 or 1:4.

How much PSI are you running through the membrane?

Have you tested your water for chloramines? Those can slip by standard carbon filters and eat away your membranes.

Also having significant co2 in the water can cause premature membrane failure.

 

[chipmunkofdoom2]

I am hoping you RO folks can help me. I seem to only get about 500 gallons from an RO membrane. I have a whole house filter that uses 4x20" pre and carbon filters as well as the prefilters on the RODI.

I change my prefilters very regularly. So frequently the prefilter is usually bone white still, because of that I have recently gone to 2x Carbon instead of floss to try and preserve the membrane.

Any thoughts on the cause of my membrane failures? I have been buying replacements 1-2 times per year. I do have ridiculously high silicates, but I am not aware of this being a problem for membranes.

How do you determine that your RO membrane is "shot?" Do you test TDS before and after the membrane? If so, what are your numbers, and when do you change the membrane?

Also worth asking, what is your waste to product ratio? With the kinds of TFC membranes that we use, ideally you want to produce around 4 gallons of waste water for every gallon of product water. This is to keep the membrane clean: as the waste water flows over the membrane and down the drain, it carries all the stuff that doesn't go into your product water with it. If you have a low waste to product ratio, this could help to explain why the membranes are failing prematurely.

 

[LiquidFunk]

What rejection rate are you running? Run your system for a minute and measure the product water and waste water. You should have a ratio of product to waste of 1:3 or 1:4.

How much PSI are you running through the membrane?

Have you tested your water for chloramines? Those can slip by standard carbon filters and eat away your membranes.

Also having significant co2 in the water can cause premature membrane failure.

It is probably 1:200, I have a 100gpd membrane producing water via drips every 5-10 seconds. Certainly not what it did when it was new. To be clear I have been in this hobby professionally for 14 years but I have never come across RO membranes “clogging”. I am very aware of what kind of flow is typical for a 100gpd and I am no where near it. It’s only been an issue at my newer residence on different municipal water.

I have not tested for chloremines, nor am I using a chloramine specific carbon prefilter.
PSI is about 65.

How do you determine that your RO membrane is "shot?" Do you test TDS before and after the membrane? If so, what are your numbers, and when do you change the membrane?

Also worth asking, what is your waste to product ratio? With the kinds of TFC membranes that we use, ideally you want to produce around 4 gallons of waste water for every gallon of product water. This is to keep the membrane clean: as the waste water flows over the membrane and down the drain, it carries all the stuff that doesn't go into your product water with it. If you have a low waste to product ratio, this could help to explain why the membranes are failing prematurely.

Membrane is shot because my rejection rate is probably 200:1. I am not producing RO water. The rejection rate is typical, a steady pressurized stream out of the 1/4” line.

It takes a week to fill a 55gallon drum, while wasting thousands of gallons.

My TDS meter is shot, but I probably have a handheld around. My incoming TDS is around 600 when I tested it a few years ago. (Which sucks, my old house has single digit TDS)


Oh and lastly, I have checked my flow restricter and it appears fine, it’s the capilary style on the ejection line. It acts like I don’t have one. I purchaed a new one with my membrane which is due to land in 2 days.

 

[chipmunkofdoom2]

Oh and lastly, I have checked my flow restricter and it appears fine, it’s the capilary style on the ejection line. It acts like I don’t have one. I purchaed a new one with my membrane which is due to land in 2 days.

How do you know the restrictor is fine? It sounds like the restrictor is your problem. RO membranes only produce water out the product line if you force water through them. This is why you need a restrictor on the waste line, to pressurize the water and force water through the TFC film. If you don't have a restrictor on the waste line, water will simply drip out of your product line, or it might not come out at all. The path of least resistance is out of the unrestricted waste line, so given the choice, the water will go that way.

Also, by rejection rate, I mean how much of the solids in the water are rejected (read: sent out of the membrane housing in the brine). To calculate this, you would need to measure the TDS of the water coming out of your tap, then the TDS of the water coming out the RO membrane but before the DI resin.

I think your problem is the restrictor though.