350 PPM TDS before RO, 10 PPM after RO, 0 PPM after DI - Chewing through Resin

[Chocobo]

Originally Posted by OrionN

I don’t think you can run membrane in series. The output of the first membrane is too low to go into the second membrane. It you use two 99% rejection membrane in series then you only keep 1/10000 of the volume you put through your RO filter. ( rejected 99% of the 1 % that go through the first membrane)

I understand where you are getting your numbers but it simply does not work like that in regards to 99% rejection vs 1%. 99% rejection does not mean that it rejects 99% of the water - but that it rejects 99% of the contaminates.

You definitely can run them in series and this is common - running them in parallel is not so common but still doable. Simplicity let's use round numbers - and say your source water is 1,000 TDS. After the first membrane at 99% rejection you should have permeate that has 10 TDS. At 75 GPD [~200 ml/min] and 800 ml/min rejection you'd have 1:4 permeate:waste. That waste water will be ~20% concentrated due to the permeate that was taken out in the first step giving you ~1188 TDS input to the second membrane. At 99% rejection you'd be getting ~11.88 TDS permeate and 1,425.6 TDS waste out of the second membrane.

In short you would get 10 TDS from the first membrane and 11.88 TDS from the second membrane. A little higher than a single membrane - but you'll save water - because you're still only wasting 80% of the water passed through the system be it single or dual membrane while the output will be what two membranes can output - at about 400 ml/min.

Originally Posted by OrionN

However I’d you use the 500 instead of the 800ml/min then your rejection rate going to be a lot less. This is the problem in your case.

I do believe the restrictor is my issue at this point.

I just tested a single membrane and my TDS after the membrane once TDS creep settles is 7 TDS. With dual membranes in series it's 9 TDS which is 22% higher but not a huge amount of TDS overall.

I tested the source water just prior and it is ~247 TDS.

This works out to 97.1% Rejection Rate with a single membrane and 96.3% rejection with dual membranes if my math is right - so I am really starting to think the biggest issue here is not having a properly sized restrictor. The membranes I am using are Dow Filmtec High Rejection 99% Membranes - so I really should be getting closer to 99% IMHO.

As soon as I have an 800 ML/hour restrictor to test I will test dual-in-series membranes, single membrane, and will also test dual parallel for completeness. I wonder if there is anywhere local that I can purchase one ...

[FPSD]

Originally Posted by Chocobo

The membranes I have are 99% Rejection rate [newer Dow Filmtec HR membranes]. I really think the reason I'm at 97% is due to running the membranes in series as well as a 550 ML/min restrictor instead of an 800 ML/min.

Just waiting on parts to show up to do testing.

You can’t do that. I have been through talk of this. I can help you if you can answer my questions. Believe me I searched too. First step is remove the dual r/o. It produces higher tds as a byproduct of saving water.
Where does your water come from? Well? Lake? Community well?
Water pressure
?

[FPSD]

Originally Posted by Chocobo

I understand where you are getting your numbers but it simply does not work like that in regards to 99% rejection vs 1%. 99% rejection does not mean that it rejects 99% of the water - but that it rejects 99% of the contaminates.

You definitely can run them in series and this is common - running them in parallel is not so common but still doable. Simplicity let's use round numbers - and say your source water is 1,000 TDS. After the first membrane at 99% rejection you should have permeate that has 10 TDS. At 75 GPD [~200 ml/min] and 800 ml/min rejection you'd have 1:4 permeate:waste. That waste water will be ~20% concentrated due to the permeate that was taken out in the first step giving you ~1188 TDS input to the second membrane. At 99% rejection you'd be getting ~11.88 TDS permeate and 1,425.6 TDS waste out of the second membrane.



In short you would get 10 TDS from the first membrane and 11.88 TDS from the second membrane. A little higher than a single membrane - but you'll save water - because you're still only wasting 80% of the water passed through the system be it single or dual membrane while the output will be what two membranes can output - at about 400 ml/min.

I do believe the restrictor is my issue at this point.

I just tested a single membrane and my TDS after the membrane once TDS creep settles is 7 TDS. With dual membranes in series it's 9 TDS which is 22% higher but not a huge amount of TDS overall.

I tested the source water just prior and it is ~247 TDS.

This works out to 97.1% Rejection Rate with a single membrane and 96.3% rejection with dual membranes if my math is right - so I am really starting to think the biggest issue here is not having a properly sized restrictor. The membranes I am using are Dow Filmtec High Rejection 99% Membranes - so I really should be getting closer to 99% IMHO.

As soon as I have an 800 ML/hour restrictor to test I will test dual-in-series membranes, single membrane, and will also test dual parallel for completeness. I wonder if there is anywhere local that I can purchase one ...

Parallel won’t work. Tried it with a booster pump. Just doesn’t work. I fixed my issue by know what I am dealing with water wise. If you answer what I asked I. An help you without wasting money hopefully.

[Chocobo]

Originally Posted by FPSD

Where are you at? I am in NW Indiana. I had same issues. Are you on a well or ?

City water. I'm south west of Indy about ~20 miles.

[Chocobo]

Originally Posted by FPSD

Parallel won’t work. Tried it with a booster pump. Just doesn’t work. I fixed my issue by know what I am dealing with water wise. If you answer what I asked I. An help you without wasting money hopefully.

Just answered the only two questions I see from you - if I missed one let me know.

That said - the parallel thing is more for testing sake - if it doesn't work it doesn't work . I really think that I'm using too small of a restrictor right now and forcing too much through the membrane that should be going down the drain.

[FPSD]

Originally Posted by Chocobo

City water. I'm south west of Indy about ~20 miles.

Ok. Not sure where they get their water from. Wells usually eat up DI do to CO2. I would use one 75 r/o unit. I will say this. I had one unit that wouldn’t
Go under teens in tds. The other I am running and get 5 out of r/o. Do you have a booster pump? Temp and pressure affect water tds

[FPSD]

Change to run one r/o unit. That will get your tds cut in half. Then report results. Are you flushing r/o before you send water thru di? Makes a huge difference.

[Chocobo]

Originally Posted by FPSD

Change to run one r/o unit. That will get your tds cut in half. Then report results. Are you flushing r/o before you send water thru di? Makes a huge difference.

Single unit is 7 tds dual is 9 tds.

I really believe it’s the restrictor forcing too much through the membrane.

[slief]

Originally Posted by Chocobo

I understand where you are getting your numbers but it simply does not work like that in regards to 99% rejection vs 1%. 99% rejection does not mean that it rejects 99% of the water - but that it rejects 99% of the contaminates.

You definitely can run them in series and this is common - running them in parallel is not so common but still doable. Simplicity let's use round numbers - and say your source water is 1,000 TDS. After the first membrane at 99% rejection you should have permeate that has 10 TDS. At 75 GPD [~200 ml/min] and 800 ml/min rejection you'd have 1:4 permeate:waste. That waste water will be ~20% concentrated due to the permeate that was taken out in the first step giving you ~1188 TDS input to the second membrane. At 99% rejection you'd be getting ~11.88 TDS permeate and 1,425.6 TDS waste out of the second membrane.

In short you would get 10 TDS from the first membrane and 11.88 TDS from the second membrane. A little higher than a single membrane - but you'll save water - because you're still only wasting 80% of the water passed through the system be it single or dual membrane while the output will be what two membranes can output - at about 400 ml/min.

I do believe the restrictor is my issue at this point.

I just tested a single membrane and my TDS after the membrane once TDS creep settles is 7 TDS. With dual membranes in series it's 9 TDS which is 22% higher but not a huge amount of TDS overall.

I tested the source water just prior and it is ~247 TDS.

This works out to 97.1% Rejection Rate with a single membrane and 96.3% rejection with dual membranes if my math is right - so I am really starting to think the biggest issue here is not having a properly sized restrictor. The membranes I am using are Dow Filmtec High Rejection 99% Membranes - so I really should be getting closer to 99% IMHO.

As soon as I have an 800 ML/hour restrictor to test I will test dual-in-series membranes, single membrane, and will also test dual parallel for completeness. I wonder if there is anywhere local that I can purchase one ...

I didn’t see it mentioned but I also didn’t read all the comments. What is your water pressure? Ideal is around 80 psi for best performance in terms of rejection ratio, membrane life and DI water output. This is why pretty much all high end RODI’s include booster pumps. Also, flushing can be very helpful as mentioned above FPSD. Many high end ones include an Auto Flush. Mine automatically flushes with RODI water every 30 or so gallons. Lastly, RODI’s should be run in larger batches for best cartridge life. I run a minimum of 30 gallons at a time for this reason. If you only run your RODI for a handful of gallons, you will burn through cartridges MUCH quicker.

[Chocobo]

Originally Posted by slief

I didn’t see it mentioned but I also didn’t read all the comments. What is your water pressure? Ideal is around 80 psi for best performance in terms of rejection ratio, membrane life and DI water output. This is why pretty much all high end RODI’s include booster pumps. Also, flushing can be very helpful as mentioned above FPSD. Many high end ones include an Auto Flush. Mine automatically flushes with RODI water every 30 or so gallons. Lastly, RODI’s should be run in larger batches for best cartridge life. I run a minimum of 30 gallons at a time for this reason. If you only run your RODI for a handful of gallons, you will burn through cartridges MUCH quicker.

I am using a booster and do have it set to 80 PSI [tap pressure is 60]. I am presently doing batches of 14 gallons [that's all the storage I have right now] but my 55 gallon drums will be here tomorrow .

I should also have my 800 ml/min restrictor tomorrow or the day after.

[FPSD]

You never said how fast you go though resin. I burn thru real fast (CO2). I just went to separate DI’s. Anion in first two and cation in second two. I get 200gal out of one anion cart.
I accept I have CO2 so not worried. Sometimes if you don’t pack di tight it depletes faster too.

[Zalick]

Originally Posted by Chocobo

I am going to try running both 75 GPD membranes in parallel. I will have more waste water per minute but will maintain 1:4 ratio. I estimate each membrane should be able to produce 200 ml/min clean water for a total of 400 / min.

This hopefully will help it make sense.

1. City water enters the booster pump
2. Water passes through sediment filter
3. Water passes through carbon block 1
4. Water passes through carbon block 2
5. Water split into two lines - each feeding a membrane.

RO filtered water output from membranes is joined back together into a single line and enters de-ionization and then RO/DI storage.

Waste water leaves each membrane and each goes to a different restrictor - one 800 ml/minute normal restrictor on one line and one 800 ml/minute auto flushing restrictor on the other line.

The waste lines are joined together before the restrictor pair so that when the auto flush happens both membranes get flushed through this line. When the auto flush is not flushing a combined 1600 ml/minute will be going down the drain.

Each membrane should in theory produce 200 ml/minute of filtered water before DI and 800 ml of waste water for a 1:4 ratio.

Booster pump should be able to push the pressure to make running this in parallel feasible.

I expect to have the parts needed to test this by Tuesday and will definitely update this thread.

If anybody has any suggestions or questions let me know. I don’t pretend to be an expert but I think I understand this well enough to experiment with this a bit.

I doubt this explains your rejection ratio, but why do you have the booster pump before the sediment filter and carbon block? Every setup I've seen and what SpectraPure says to do, is have the booster pump immediately before the RO membrane.

[Chocobo]

Originally Posted by Zalick

I doubt this explains your rejection ratio, but why do you have the booster pump before the sediment filter and carbon block? Every setup I've seen and what SpectraPure says to do, is have the booster pump immediately before the RO membrane.

Pressure at the membrane is 80psi. I can turn it up or down as needed.

I have a small strainer filter before the pump and the fittings and filters can handle the pressure.

[Chocobo]

Originally Posted by FPSD

You never said how fast you go though resin. I burn thru real fast (CO2). I just went to separate DI’s. Anion in first two and cation in second two. I get 200gal out of one anion cart.
I accept I have CO2 so not worried. Sometimes if you don’t pack di tight it depletes faster too.

I'm going through it about 10x faster at my office than I do at my house. It looks like I'll get 200~250 gallons per 10" mixed bed resin. I easily got 3,000 gallons [or more] at my house.

[Chocobo]

I went to 5 stages of deionization. Cation - Anion - Mixed 1 - Mixed 2 - Mixed 3.

I have TDS monitoring before DI, between each DI stage, and after.

Whatever gets used up the fastest I’ll double up on be it cation or anion and will drop to two stages of mixed.

[Chocobo]

[earwicker7]

Originally Posted by 45commando

OP, have you researched "TDS creep" ? Basically, the RO water produced at start up can be very high in TDS & then drops off as more RO water is produced. If this initial water is going into your DI resin, it will exhaust the resin faster. An in-line TDS meter on the output RO line will show you when it is ok to then divert to the DI resin. Please ignore if you are already aware of this HTH

This.

If you use an auto top off which pulls straight from your RO/DI (as opposed to a reservoir), each time it starts you are going to get high TDS going into the DI resin.

I was going through huge amounts until I programmed my Apex controller to only turn the auto top off on
for fifteen minutes every six hours.

[Chocobo]

Originally Posted by earwicker7

This.

If you use an auto top off which pulls straight from your RO/DI (as opposed to a reservoir), each time it starts you are going to get high TDS going into the DI resin.

I was going through huge amounts until I programmed my Apex controller to only turn the auto top off on
for fifteen minutes every six hours.

I am not using an ATO from the RO system. I am using a 55 Gallon Drum that I fill and then turn off the RO system until that drum is empty - and I am flushing the permeate to the drain until the TDS drops down to ~7 PPM. I can visibly see the mixed bed resin color changing as I make 55 gallons - I use about half a cartridge making a single barrel.

I have since, as per my last update, switched to cation, anion, and then mixed.

[earwicker7]

Originally Posted by Chocobo

I am not using an ATO from the RO system. I am using a 55 Gallon Drum that I fill and then turn off the RO system until that drum is empty - and I am flushing the permeate to the drain until the TDS drops down to ~7 PPM. I can visibly see the mixed bed resin color changing as I make 55 gallons - I use about half a cartridge making a single barrel.

I have since, as per my last update, switched to cation, anion, and then mixed.

Half a barrel is a lot.

[Chocobo]

Originally Posted by earwicker7

Half a barrel is a lot.

I got 1,000+ gallons out of a single mixed bed cartridge at my old place on the same water company...

[earwicker7]

Originally Posted by Chocobo

I got 1,000+ gallons out of a single mixed bed cartridge at my old place on the same water company...

Meant to say half a cartridge is a lot... d'oh!

[Chocobo]

Originally Posted by earwicker7

Meant to say half a cartridge is a lot... d'oh!

.