ro water saving idea

[purelyh2o]

Someone put alot of thought into this

Someone put alot of thought into this

This is really good in theory and will work for a while.
We in long term use have found that this method causes premature failure in the primary membrane. I do understand your math in the concentrate side but answer a very simple lamens question so that everyone can understand. If the required rejection for one membrane is 400 ml per minute and you have 2 membranes that need a flow area of 800 ml per minute and are still faced with the exact same pressure downstream no matter what. How will each membrane be able to clean itself when the concentrate stream is cut in half with a waste allowance of only 400 ml per minute down stream. This is a good answer if the consumer chooses to sacrifice membrane life for water consumption but Im still faced with the fact that no 2 TFCs are alike and there will be variables in the flow streams that are not anticipated. My prefered method is to split the supply line to feed each membrane separately, only because I know this way the membranes will be able to perform the best that each individual membrane can. Using the method above would be catastrophic given the failure of either element.

 

[jdieck]

Re: Someone put alot of thought into this

Re: Someone put alot of thought into this

<a href=showthread.php?s=&postid=7560345#post7560345 target=_blank>Originally posted</a> by purelyh2o
How will each membrane be able to clean itself when the concentrate stream is cut in half with a waste allowance of only 400 ml per minute down stream. This is a good answer if the consumer chooses to sacrifice membrane life for water consumption but Im still faced with the fact that no 2 TFCs are alike and there will be variables in the flow streams that are not anticipated.

The interesting thing is that the concentrate stream is not cut in half. Actually the concentrate stream on the first membrane increases by 20% and the concentrate stream for the second membrane remains the same.

In other words, the amount of water that pass trough the restrictor is the same if you use one or two membranes.
the difference is that in the two membrane scenario the restriction (back pressure) to the first membrane provided by the restrictor is reduced by the permeability of the second membrane. This drop in back pressure is what creates the additional flow in the first membrane, that additional flow is equivalent to the flow that comes out of the second membrane.

So really what we are doing is not reducing the concentrate flow to one half but using the same flow to clean two membranes, one first and from there to the second. I agree that the second membrane in this case is washed with 466 ppm water rather than 400 ppm, how significant it is in the life of the membrane? I do not see it as very relevant considering that we get more variability than that in our tap water.

As far as the two membranes are of equal rated capacity (in other words require the same restrictor when used separately) the difference of +/-15% in manufacturer specifications will equally affect two membranes connected in parallel than connected in series. And because in both cases you are mixing the product out of both the resultant effect will be the same if one membrane fails and not the other.

 

[purelyh2o]

?

?

Were are you getting your data?

Not to be rude but these just dont comply with my data.
Maybe Im missing something.

 

[Roland Jacques]

Dude, you guys are smart. so will it work?

 

[RobbyG]

Bryan your sitting on a crap load of RO stuff , why not test this out, we all would love to know if it works..

BTW guys this is a good one, really interesting.

 

[purelyh2o]

Well

Well

I was trying to elude to that in a nice way


It doesnt work well long term
Thats why I was saying it is a toss up for efficiency and production.

The membranes will not function full tilt.

 

[dtaranath]

Re: Water temp

Re: Water temp

<a href=showthread.php?s=&postid=7559092#post7559092 target=_blank>Originally posted</a> by purelyh2o
Very true,
Flushing the membrane is a very important feature at any temp or pressure. The one problem I see happen fairly often when adjusting the temp on the system is that when you go above the 75 degree point you begin to lower the rejection rate of the membrane. The opposite is true when you lower the temp so it is a toss up really as to what is more important to you, Performance or production.

Bryan, do you not recommend increasing the temp of the incoming water? My water is 50-60 degrees, and I'm wondering if I should be heating the incoming water with 10 feet of coil in heated water like someone mentioned. But then it seems that there might be a drop in pressure from the coil....

 

[purelyh2o]

We have tried it

We have tried it

each way, and We have just found better membrane life and productivity using the dual feed than the series method.

 

[purelyh2o]

Well

Well

I cant say I dont condone it as you would have a well performing membrane at 75 degrees. The thing is though are you making enough water? Is the system performing fast enough for you. If so running the system at a colder temp is actually making the system better able to achieve a high rejection.

 

[Savatage]

Let us look at something else here. Lets go back to the beginning of this thread. Put this one on the scales and weigh it out once..........

Which one costs more. Water or resin? If we disconnect our RO and run straight to the DI, we have no waste water. In the long-term are we spending more on the water going down the drain or on the resin?

The only real question that concerns me is, how would this effect the TDS difference???? Does the RO unit remove the TDS or does the DI part remove the TDS?

Lets talk about this idea for a while. Give us pros and cons on this one. I think it's the best way to go because of this reason...... Anthony Calfo (if I'm not mistaken) only runs a DI and no RO. He has had no problems that I know of. I only wish we could get him in on this thread.

 

[jdieck]

Re: ?

Re: ?

<a href=showthread.php?s=&postid=7561074#post7561074 target=_blank>Originally posted</a> by purelyh2o
Were are you getting your data?

Not to be rude but these just dont comply with my data.
Maybe Im missing something.

Provably the missing part is the assumption that there is a significant pressure drop across the first membrane but given the slow flow and the large pressure differential between the membranes casings and the waste line after the restrictor (50 to 70 psi range) the pressure drop across the first membrane is relatively low.
The data comes from my own system. I have been using this configuration for 18 months now and the rejection has not drop a bit.
I use two ultra high rejection membranes (99%+) tested before purchase, booster pump, auto purge and auto backflush.
Tap TDS is relatively low changing depending on the season from 160 to 220 ppm. inlet pressure 73 psi from the booster installed after the carbon before the membranes. The TDS of the product water before DI stages is below the detection level of the in line meter I use to monitor the rejection, and below the lowest detection level (0.3 ppm) of the monitor installed after the first DI cartridge and before the two subsequent DI cartridges.
Production rate is 163 gpd with a waste rate of 385 gpd
By the way I did not invented the procedure.
http://spectrapure.com/huds/DUAL.pdf

 

[jdieck]

<a href=showthread.php?s=&postid=7562070#post7562070 target=_blank>Originally posted</a> by Savatage
Let us look at something else here. Lets go back to the beginning of this thread. Put this one on the scales and weigh it out once..........

Which one costs more. Water or resin? If we disconnect our RO and run straight to the DI, we have no waste water. In the long-term are we spending more on the water going down the drain or on the resin?

The only real question that concerns me is, how would this effect the TDS difference???? Does the RO unit remove the TDS or does the DI part remove the TDS?

Lets talk about this idea for a while. Give us pros and cons on this one. I think it's the best way to go because of this reason...... Anthony Calfo (if I'm not mistaken) only runs a DI and no RO. He has had no problems that I know of. I only wish we could get him in on this thread.

Yes, when Tony had his farm he used industrial sized DI only filters with regenerable resin.
Both remove TDS, one wastes water the other don't but has increased cost of regeneration labor and materials. One is more economical at lower volume of usage but the economies revert as the volume is increased, the cross point depends on the kind and amount of contaminants need to be removed and the total volume of water required to be processed.

 

[purelyh2o]

Hmmm...

Hmmm...

Im gonna play with this for a bit..

Its going to take some convincing for me to believe this is more efficient than a dedicated feed but we will see.

Hey jdieck, you need a job

 

[jdieck]

Re: Hmmm...

Re: Hmmm...

<a href=showthread.php?s=&postid=7562236#post7562236 target=_blank>Originally posted</a> by purelyh2o
Im gonna play with this for a bit..

Hey jdieck, you need a job

It is really easy, measure pressure at inlet of membrane 1 in between membranes 1 and 2 and after membrane 2 but before restrictor.
I measure the production by timing a graduated 5 gal bucket.
I have two dual TDS meters (Which by the way I do not trust much) one measures the tap and the final product, the other one the inlet of the membranes and the output of the membranes and I have a monitor to measure the output of the first DI cartridge to know when to replace.
For added info, Thanks that I have almost no sediment I am able to use 0.5u absolute gradient sediment filter and 0.5u carbon block.
My tap water is treated with chloarmines that is why the extra DI cartridge.

Thanks for the job offer :lol: If I like I'll get my points by the end of this year so why not I might consider it

 

[AnnArborBuck]

It is common to run membranes in series as jdieck mentions when desalinating water. But the reason for that is because the pre-treatment of the water (before RO) is very expensive, so the extra cost in energy (pumps, etc) and membranes is smaller compared to the water costs. In this situation I really doubt anybody's water really costs that much to warrant two membranes.


jdieck system is slightly unique in that he has a very good psi and a full flushing system which is very important. As RO membranes seperate the solids from the water a layer of scale forms on the membrane. This scale actually reduces the size of the pores (their not pores but it is easier to think that way) so the membrane becomes more and more restrictive, thus more waste water. Eventually, this scale can become so thick that all flow stops and the pressure builds up. I know a guy that has a car wash and one of his membranes actually exploded because he never flushed it or changed it (it was like 5 or 10 years old, very used).

 

[Roland Jacques]

Re: Re: Well

Re: Re: Well

<a href=showthread.php?s=&postid=7559956#post7559956 target=_blank>Originally posted</a> by jdieck
Lets run some excercise here:

Tap water 400 ppm TDS
Two equal capacity high rejection 98.5% membranes
Restrictor for a 5:1 ratio
One membrane will waste 5 gallons for every gallon of product so require 6 gallons of feed.
The same 5 gallons of waste will pass trough the restrictor using two membranes but by effectively doubling the membrane area there are 2 gallons produced so require feed of 7 gallons.

How the TDS will be affected:
7 gallons of 400 ppm enter the first membrane and 6 get out.
The product TDS of the first membrane is:

(1-.985)*400=6 ppm

The TDS waste output of the first membrane is:

(6*400+400*.985)/6=2794/6=466 ppm

So the TDS of the product of the second membrane is:

(1-98.5)*466=7ppm

So the tds of the combine product is (6+7)/2=6.5 ppm

And the TDS of the overall waste will be:

(5*400+466*.985)/5=2459/5=492 ppm

In summary:
With one membrane:
Waste 5 gallons per gallon of product
Product tds 6 ppm
Waste tds 466 ppm
Production 75 gpd
Waste 375 gpd

With two membranes
Waste 2.5 gallons per gallon of product
Product tds 6.5 ppm
Waste tds 492 ppm
Production 150 gpd
waste 375 gpd

If we use say 75 gallons per day we operate the system half the time with two membranes effectively save 375 gallons per day of water consumption at a penalty of 1/2 ppm increase in the TDS of the product which equals to an 8% increase (6.5ppm/6ppm=8% incr) in the consumption of DI cartridges.

If we use two low rejection (90%) membranes the increase in TDS of the combined product water will be from 40 ppm to 43ppm also ~8% but it is to note that although the increase in DI consumption is the same in % we will be adding insult to outrage because at 40 tds we are already using about 7 times more cartridges (vs 6ppm) so adding another 8% will be just making a bad situation worst.

thanks for all the details

i think the confusion with the math came from going from 6 gallons in, to 7 gallons in. it may have been more clear to have kept it as 6 gallons in and worked from thier. but 6 or half dozen your math looks good to me, and well thought.

it seems to me that the main question is, what pressure drop actualy occures from the membrane before the restictor?

this can very easly be anserwed with a few pressure gauges. bryan if you sell housings, membranes, and gauges seperatly pm me. id like to see if this works like i think it will.

 

[Roland Jacques]

jdieck
what defferance dose the ultra high rejection membranes make when use this configuation?

i have to start refreshing my screen more often.

 

[AZDesertRat]

Yes it is common to run membranes in series in large applications but there are major differences. One is the feed antifouling chemicals continously in the process. But the biggest difference is they are using hollow fiber membranes and not spiral wound membranes like smaller units use. These are periodically removed and cleaned unlike or home use membranes. They are also much less efficient to begin with and would never work for what we are doing here with reefkeeping.

 

[fahz]

jdieck test results are in after reading your thread I went and built a system. Single 75 GPD Filmtec system before conversion Waste 4:1 after RO TDS 1.

Jim


TEST RESULTS

Two 75 GPD Filmtec membranes in series
One 75 GPD 600 mL flow restrictor
Aquatec Booster pump producing 100 psi
Tap water temp 68 degrees
Tap water TDS 59 ppm
Waste water TDS 114 ppm
TDS after RO 2 ppm
DI TDS 0
Production water 1 gallon
Waste water 1 1/4 gallons

 

[fahz]

The system is actually over producing which customers report with booster pumps anyway. I had to go back to get GPD rate as I was just interested in production to waste. The conversion took maybe ten minutes and I already use the Aquatec 8800 booster pump.

Jim

TEST RESULTS

Production water 7.5 GPH or 180 GPD
Waste water 9.37 GPH or 225 GPD
Gallons of water saved 495