Help with water purification decsion

[jdieck]

Carlo:
What controls the ratio of waste to product is not the membrane nor the amount you pump in but how much you restrict the waste. In other words it is the restrictor which for a given inlet pressure dictates how much water is wasted.
A single membrane working with an inlet pressure of 70 psi with a restrictor which is adjusted to produce a backpressure such as to force one gal trough the membrane and let 4 gallons pass to the waste will create almost the same back pressure and allow the same flow to the waste. I say almost because in the second case it will see a pressure of 64 to 65 psi rather than 70 due to the pressure drop from the first membrane to the second.
In round numbers the second membrane sees 4:1 because the restrictor will let pass 4 (as before with a single membrane) The first membrane sees 5:1 because it sees the 4 of waste that the restrictor lets pass plus the 1 that goes as product trough the second membrane.

In round numbers The inlet to the first membrane is 6, the product of the first is 1 and the waste of the first is 5. The inlet to the second membrane is 5, the product of the second membrane is 1 and the waste from the second is 4
Overall you input 6, produce 2 and waste 4 so in round numbers you gate on the overall a waste of 4:2 (2:1) rather than the 4:1 you will get with a single membrane.
Again as mentioned before these are round numbers and the ratio will vary depending on the specific membranes, TDS input, temperature and adjustments for discharge pressure of the booster pump, I have seen anything from 1.75:1 to 2.5:1

 

[A.T.T.R]

about piggy back membranes. i have at work 3 of them piggy backed using ONE 90 gpd style restrictor ( most ppl use 3 for some reason)

and i get 96 percent rejection ( same as if single membrain trust me iv tried it)

just get a better booster pump and throw on some more membrane and call it done....

and btw the slightly higher tds input to the second membrane dosnt matter its not that much more

ill post a pict if i remember to brign a camera to work tommorow.

anyways.

buy two sperate di resins from spectra pure ( one cation one anion ) and put them in seperate chambers... taht way you can run acid in one and caustic soda in the other and save alot of money on ro di recharge ( again. what i do at work.. we use any where from 100 to 300 gallons perday and the system is no where near capacity)

 

[jnarowe]

I would like to learn more about the re-charging aspect as I just throw mine out right now. Is there a good place to get info. on that?

Currently my two systems are fed from a "Y" on my inlet water. Are you guys suggesting that I change to have them inline instead of fed "seperately"?

 

[cayars]

<a href=showthread.php?s=&postid=10520396#post10520396 target=_blank>Originally posted</a> by jdieck
In round numbers The inlet to the first membrane is 6, the product of the first is 1 and the waste of the first is 5. The inlet to the second membrane is 5, the product of the second membrane is 1 and the waste from the second is 4
Overall you input 6, produce 2 and waste 4 so in round numbers you gate on the overall a waste of 4:2 (2:1) rather than the 4:1 you will get with a single membrane.
Again as mentioned before these are round numbers and the ratio will vary depending on the specific membranes, TDS input, temperature and adjustments for discharge pressure of the booster pump, I have seen anything from 1.75:1 to 2.5:1 [/B]

I guess I don't understand the math you're using because If I were using a single membrane I'd say it's 20% effective (1 out of 5 total gallons). With the two membranes I'd get 2 gallons out of a total 6 gallons which is approximately 33.3% effective use of water.

That's pretty close to what I said originally (but actually worse) when you said it doesn't work that way. Either way it doesn't save 1/2 the waist water flowing though the unit which was the intent of my original post. IE going from 1 out of 5 to 1 out of 3 (2/6). It's a definite improvement non-the-less!

Carlo

 

[A.T.T.R]

ill get you that info in a few days

or there is a thread around here some where about it


i personaly just recharget ehm where they sit and dont bother removing htem..
but w/e

 

[jdieck]

<a href=showthread.php?s=&postid=10521455#post10521455 target=_blank>Originally posted</a> by cayars
I guess I don't understand the math you're using because If I were using a single membrane I'd say it's 20% effective (1 out of 5 total gallons). With the two membranes I'd get 2 gallons out of a total 6 gallons which is approximately 33.3% effective use of water.

That's pretty close to what I said originally (but actually worse) when you said it doesn't work that way. Either way it doesn't save 1/2 the waist water flowing though the unit which was the intent of my original post. IE going from 1 out of 5 to 1 out of 3 (2/6). It's a definite improvement non-the-less!

Carlo

OK let's try again...
Your confusion seems from the use of input to product rather than waste to product.
Note that the ratio is a reference of Waste to Product water (Not input to product water). 4:1 means 4 wasted for each 1 of produced. (In your book it will be 5 input 1 product or 20% produced for each input) In other words for every 5 you input you get 4 of waste and 1 of product.

Again the membrane on itself does not establish nor determines the waste to product ratio on by itself. The waste to product ratio is an operational parameter that you adjust via the restrictor. You can adjust a system to any waste to product ratios by adjusting or calibrating the restrictor, higher than 4:1 the membrane will last longer but there is increased waste water, lower than 4:1 will shorten the life of the membrane by forcing more precipitation on the membrane's surface plugging it.
In other words, if you remove the restrictor you will get all waste and no product. If you install a closed valve instead of a restrictor (Or shut off the restrictor if adjustable) you get all product and no waste (Although the membrane will not last long). So the restrictor is adjusted to get the ratio specified by the membrane manufacturer.

In our case the first membrane without restrictor will pass as much water as the second membrane takes and it takes 5 as it's restrictor rated for 4:1 will waste 4 for the overall system.

So as in your book the first scenario you input 5 you get 1 in the second you input 6 you get 2, your production relative to input goes from 20% to 33% (if you want to see it other way, your additional 1 is produced at no additional waste), your product doubles (2) and your waste remain the same (4) so the waste to product ratio went from 4:1 to 4:2 or same waste double product. In other words half the waste for equivalent production.

Seen it in even another way: If you consume 10 gallon per day, in the first scenario with one membrane you wasted 40 and in the second scenario (with two membranes n series) you wasted 20 as the ten gallons you consume will be produced in half the time before you shut down.

So yes you increased the production rate from 20% to 33% (from 1 to 2) and by doing so without additional waste your waste will be half of what it was before as you will need to operate the system half the time.

 

[jnarowe]

You guys know I'm retarded right? I am going to have to re-read that like 5 times. Based on what you are writing then, do you feel membranes in parallel or series is the best option? (OK, so I don't want to re-read it )

 

[jdieck]

<a href=showthread.php?s=&postid=10522921#post10522921 target=_blank>Originally posted</a> by jnarowe
You guys know I'm retarded right? I am going to have to re-read that like 5 times. Based on what you are writing then, do you feel membranes in parallel or series is the best option? (OK, so I don't want to re-read it )

Both have advantages and disadvantages.

In parallel, you double production and waste (so no gain in that area as you will still waste the same for the same volume of production) but the membranes will last their purposed life and you get slightly less TDS in your RO (before DI)

In series you waste half the water (For the same production volume) but the second membrane will see a slight increase in TDS whit slight increase in DI consumption and you must have a booster pump if your tap pressure is below 65 psi
The increase in TDS is almost insignificant if your TDS input is not very high (Say higher than 200 TDS)

After DI both systems will produce basically the same water quality.

 

[cayars]

<a href=showthread.php?s=&postid=10522867#post10522867 target=_blank>Originally posted</a> by jdieck
OK let's try again...
Your confusion seems from the use of input to product rather than waste to product.
Note that the ratio is a reference of Waste to Product water (Not input to product water). 4:1 means 4 wasted for each 1 of produced. (In your book it will be 5 input 1 product or 20% produced for each input) In other words for every 5 you input you get 4 of waste and 1 of product.

Again the membrane on itself does not establish nor determines the waste to product ratio on by itself. The waste to product ratio is an operational parameter that you adjust via the restrictor. You can adjust a system to any waste to product ratios by adjusting or calibrating the restrictor, higher than 4:1 the membrane will last longer but there is increased waste water, lower than 4:1 will shorten the life of the membrane by forcing more precipitation on the membrane's surface plugging it.
In other words, if you remove the restrictor you will get all waste and no product. If you install a closed valve instead of a restrictor (Or shut off the restrictor if adjustable) you get all product and no waste (Although the membrane will not last long). So the restrictor is adjusted to get the ratio specified by the membrane manufacturer.

In our case the first membrane without restrictor will pass as much water as the second membrane takes and it takes 5 as it's restrictor rated for 4:1 will waste 4 for the overall system.

Agreed so far but one could say the 1st membrane has a resistor via the second membrane. Regardless of there the restrictor is there is still the required back pressure. We agree thus far.

So as in your book the first scenario you input 5 you get 1 in the second you input 6 you get 2, your production relative to input goes from 20% to 33% (if you want to see it other way, your additional 1 is produced at no additional waste), your product doubles (2) and your waste remain the same (4) so the waste to product ratio went from 4:1 to 4:2 or same waste double product. In other words half the waste for equivalent production.

Here is where you lost me. If you only pass 5 gallons into the first membrane and get one good gallon with 4 going into the second you'll get 0.8 gallons good with 3.2 gallons going to waist from the second membrane. Total of 1.8 good gallons, 3.2 bad.

So looking at the waist ratio you would have 3.2:1.8 and not 6:2 or 3:1. Either way it's not a 50% savings in waist but more like 20%.

I just can't see how adding another membrane is going to do anything but save 20% of the waist from the previous membrane because it itself needs a 4:1 ratio or put another way will make 1 good gallon out of each 5 going through it assuming your running a 4:1.

Seen it in even another way: If you consume 10 gallon per day, in the first scenario with one membrane you wasted 40 and in the second scenario (with two membranes n series) you wasted 20 as the ten gallons you consume will be produced in half the time before you shut down.

I disagree, in the first you'll get 10 gallons with 40 going to waist and with 2 membranes you'll get 10 good and 27.8 going to waist (3.2:1.8).

So yes you increased the production rate from 20% to 33% (from 1 to 2) and by doing so without additional waste your waste will be half of what it was before as you will need to operate the system half the time.

I understand you're not going to have more waist but per the same amount of water running through the system but you won't get double the amount of production either since the 2nd membrane get's 20% less water running through it (production of first membrane).

BTW I think the production rate would be 4:1 = 1/5 = 20% for 1 membrane and 3.2:1.8 = 1.8/5 = 36% for two membranes in series.

Honestly we're just looking at the numbers different ways but I think we both got how it works. Obviously if the 2nd membrane get's less water passing through it then the first then the true production rate can't double but going from 20% to 36% is good enough.

Carlo

 

[jnarowe]

<a href=showthread.php?s=&postid=10522974#post10522974 target=_blank>Originally posted</a> by jdieck
Both have advantages and disadvantages.

In parallel, you double production and waste (so no gain in that area as you will still waste the same for the same volume of production) but the membranes will last their purposed life and you get slightly less TDS in your RO (before DI)

In series you waste half the water (For the same production volume) but the second membrane will see a slight increase in TDS whit slight increase in DI consumption and you must have a booster pump if your tap pressure is below 65 psi
The increase in TDS is almost insignificant if your TDS input is not very high (Say higher than 200 TDS)

After DI both systems will produce basically the same water quality.

Seems like in series would be simpler to build and maintain, and I need a booster pump anyway, but are you implying that membrane life might not be as good?

 

[jdieck]

In general the higher the inlet TDS the lower the membrane life but because the membranes operate well on a wide range of TDS input, the increased TDS for the second will be neglegible performance wise unless your TDS are really excessive.
Say your water has 200 TDS the second membrane in series will be seeing around 240 TDS an increase of 40 TDS which membrane wise will not make much of a difference but if you TDS is too high, say 800 TDS then the second membrane will see around 960 TDS, now 160 TDS increase at those high levels could make a difference.

In your case with those low TDS I would expect membrane life in the 5 year plus if not exposed to free chlorine and back flushed regularly.

 

[jdieck]

<a href=showthread.php?s=&postid=10526297#post10526297 target=_blank>Originally posted</a> by cayars
Here is where you lost me. If you only pass 5 gallons into the first membrane ....
Carlo

You will not pass 5... it will take 6 by itself as the first membrane sees less restriction than the second membrane because of the reduced pressure due to part of the water passing trough the second membrane and not only the restrictor.
In any case, as they say seeing is believing, install it, test your ratios and calculate the new waste to product ratio, you may be pleasantly surprised.

 

[A.T.T.R]

in series you double production and cut waste
like i said i have 3 hooked up this way. ( waste of one membrain goes to the input of the other)

 

[jnarowe]

Thanks for the posts. I will be doing a re-design soon.

 

[cayars]

<a href=showthread.php?s=&postid=10526453#post10526453 target=_blank>Originally posted</a> by jdieck
You will not pass 5... it will take 6 by itself as the first membrane sees less restriction than the second membrane because of the reduced pressure due to part of the water passing trough the second membrane and not only the restrictor.
In any case, as they say seeing is believing, install it, test your ratios and calculate the new waste to product ratio, you may be pleasantly surprised.

I'm not trying to be a pain, but want to fully understand the optimal operation of running them in series.

If the 1st membrane is seeing less restriction then won't you loose more to concentrate/waist on the 1st membrane? If so wouldn't this membrane then be operating at worse then 4:1 (1/5)? I'd assume the 2nd membrane still works at 4:1 correct?

So if I got this right you're saying if you pass 6 gallons into the unit the 1st membrane will output 1 gallon of good water with 5 gallons flowing into the 2nd membrane. The 2nd membrane at 4:1 with 5 gallons will end up with 1 gallon of good water for a total of 2 gallons out of 6. = 6:2 or 3:1 ratio.

Let me ask this. Would it help to put a valve inline between the two unit and begin closing it a bit to create back pressure and measuring the first membrane waist to good and adjust valve until you get to 4:1?

Curious what happens if you run the normal flow restrictors on both membranes but still run them in series. Will the first membrane have excessive pressure and put out way to much good water and clog the membrane to fast? What does this do overall?

Is it possible to run 2 (or more) membranes in series if they are of different flow rates. IE one 75gpd and one 150gpd. Is so how what would be preferred order and restrictor?

Thanks a bunch,

Carlo

 

[A.T.T.R]

two membrains will use the same restrictor as one ( so 2 90 gpds will use one 90 gpds restrictor)


so if you pass 4 gallons into the system the first membrain will pull out one and the second will pull out another ( appx) so you get same water usage but more good water
and no you dont need anything between the membrains as the restrictor will make the back pressure (hopfully) i know using 3 membrains my pressure is so low ( really low to begin with less then 30) that i needed a booster pump.


and yes you can run two in series that are of different type .. use the higher rated ones restrictor and put it first
but the 75 gpd may run a lil wierd ( less waer output then normal

 

[jdieck]

It is OK to operate a membrane at higer than 4:1 as far as you are not wasting more water; 5:1 in this case for the first membrane, they even last longer. What is not OK is to operate an individual membrane at lower than 4:1
If you put a restrictor or valve in between the membranes the second membrane will have a lot less production.
Although different membranes will work I recommend two equal sized for optimal production

 

[cayars]

<a href=showthread.php?s=&postid=10535109#post10535109 target=_blank>Originally posted</a> by A.T.T.R

and yes you can run two in series that are of different type .. use the higher rated ones restrictor and put it first
but the 75 gpd may run a lil wierd ( less waer output then normal

So if you had a 75/90 and 150 you would have the 150 first followed by the 75/90 and then the restrictor which would be matched up to the 150 correct?

So with the use of a pump I may be able to do 150, 150,75/90 as long as the restrictor is from the 150 and pressure is good enough correct? Of course I'd want to check to make sure I'm actually getting more from the 3 then I would from the 2 over X amount of time.

Carlo

PS this is tomorrows project so I'm trying to soak as much in now as possible.

 

[cayars]

<a href=showthread.php?s=&postid=10461796#post10461796 target=_blank>Originally posted</a> by jnarowe

This is my ne 200g fiberglass RO/DI tank I need to plumb into the system:

This tank comes with plenty of BHs as well as a nice electronic float switch.

Can you tell me what storage tank that is and/or where you got it?

Thanks,
Carlo

 

[jnarowe]

It's a Barnstead and I got it from a guy down the road that was getting rid of an old medical water making system.