northbay-reefer
Active member
fahz ... thanks for the test, this is eye opening ... I know that I was saving water by doing it this way the last 5 years, but never measured to see how much
ro water saving idea
- Thread starter little_squid
- Start date
jdieck
New member
Nice data and besides confirming the savings it also show (as would be expected) that as pressure drops the waste to product ratio increases.
Pressure drop 5 psi 7.7%
Production reduction 8.4%
Waste product ratio at 65 psi 1.62 : 1
Waste product ratio at 60 psi 1.75 : 1
ALthough product decreased by 8.4% waste volume reduction was 1.4% which I think was to be expected given the normal behaviour and response of membranes to pressure changes.
Roland Jacques
Premium Member
Jim
thats great info. im defenetly going this route. again RC members shine. the 2 psi drop across the membrane was the final missing piece. thanks guys
yeah my water is like yours tap TDS 50. DI only did not work that well for me. im working up to needing about 800 gallons / mo of water, recharging DI took way to much time. plus im on a septic tank. for me this clearly is the ticket, im going to try 3 membranes. im looking at the parts i need right now
thats great info. im defenetly going this route. again RC members shine. the 2 psi drop across the membrane was the final missing piece. thanks guys
yeah my water is like yours tap TDS 50. DI only did not work that well for me. im working up to needing about 800 gallons / mo of water, recharging DI took way to much time. plus im on a septic tank. for me this clearly is the ticket, im going to try 3 membranes. im looking at the parts i need right now
Roland Jacques
Premium Member
jdieck
like you say try and see.
oops.
Waste product ratio at 100 psi 1.25 : 1
Waste product ratio at 65 psi 1.62 : 1
Waste product ratio at 60 psi 1.75 : 1
like you say try and see.
oops.
Waste product ratio at 100 psi 1.25 : 1
Waste product ratio at 65 psi 1.62 : 1
Waste product ratio at 60 psi 1.75 : 1
jdieck
New member
Sorry I missed your question before.
Because this configuration degrades the purity of the water at the ouput of the membrane, using low rejection membranes which already cause more consumption of DI cartridges will make the consumption of DI cartridges or resin even worst but if you have a cheap source of resin or are willing to regenerate it might be feasible but I think the cost in DIs even regenarating will be higher than the cost diferential between high rejection and low rejection membranes.
Roland Jacques
Premium Member
jdieck
thanks, thiers no reason other than a higher grade of water that you recomend the ultra high rejection membrane Right?
i was going to use filmtec membranes i assume that they sell only one type. i dont no what catagory they fall in. Again i assume low rejection rate.
my other thought is for 3 membranes do you think i should use 3/8 hose or will 1/4" flow enough water.
thanks, thiers no reason other than a higher grade of water that you recomend the ultra high rejection membrane Right?
i was going to use filmtec membranes i assume that they sell only one type. i dont no what catagory they fall in. Again i assume low rejection rate.
my other thought is for 3 membranes do you think i should use 3/8 hose or will 1/4" flow enough water.
jdieck
New member
The actual reason is expense in DI cartridges, the lower the purity of the water out of the membranes the higher the cost of DI replacement.
Assuming say a membrane with 90% rejection and TDS on tap of 200 ppm you will have a theorethical purity at the output (with one membrane) of 20 ppm, with a high rejection membrane of 98% you will get 4 ppm this means that with low rejection you will be changing five cartridges of DI for each cartridge you would have changed with a high rejection one. Because rejection specs are rather loose (+/- 15%) this ratio of increased cost in DI could be as low as 3 to 1 and as high as 20 to 1. That is why I recomend high rejection even when using a single membrane.
Filmtec produces both. Usually the 100 gpd membranes are rated for 90% rejection while 75 gpd or lower are rated fro 98%+ rejection.
By the way the membranes cost almost the same if not the same.
Regarding the tubing diameter 3/8" it is a good idea pressure wise but I am afraid you will find all kind of issues in adapting it to a standard system, all residential cartridges and membrane housings I know out there are prepared for 1/4" connectors.
Post edit note: I forgot you have 50 ppm TDS in your tap. That will be 5 ppm vs 1 ppm so the ratios are also valid.
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So are you saying that if a person doesn't really require too much water anyway, that it would be more benificial to use only the DI part?
I only go through about 50 gallons a month, give or take 10 gallons. Are you saying it would be more logical to just use the DI part????
fahz
Premium Member
1/4" versus 3/8" tubing: were dealing with such small amounts of tubing friction loss isn't a real issue. I was very suprised the system performed so well at lower pressures. The FilmTec 75 GPD membrane would be the membrane of choice because of its lower operating pressure besides the rejection rate.
Jim
Jim
jdieck
New member
No it is the opposite, DI only systems are justified only with large consumption
Again each situation is different depending not only on the volume of water but also in the purity. In general the things that DI alone does not remove are not an issue for reef aquariums but lets go trough some cost engineering here:
Say your tap water has 150 ppm tds, you do not regenerate, the cost of replacing the resin only (not the whole cartridge) on the DI cartridge cost $10.00 and it can remove 7000 ppm and you use 50 gallons per month or 12 gallons per week.
The total ppm in 12 gallons of water will be 6,813 parts (12gal x 3.7854 lts/gal x 200 parts/lt) so you will have to replace the resin in average 0.97 times per week or roughly 4 times per month or $40.00 per month.
Assume in the same scenario using an RO/DI unit with 98% rejection your TDS out of the membrane will be 3 ppm so you will have to replace the resin every 12.3 months (7000 parts/3 parts per lt / 3.7854 lt/gal / 50 gal/mo.) or $0.81 / Mo.
You will also have to replace the sediment and carbon filters
but they last aprox every 6,000 Gal for the carbon and assume 3,000 for the sediment. That is every 60 months for the sediment at $8.00 per filter that is $0.13 / Mo. for sediment and it is every 120 months for carbon at $15.00 per filter that is $0.125 / Mo. for carbon. Assume you also need to change the membrane every 5 years at $75.00 that is $1.25 / Mo.
Assuming a waste to product ratio of 4:1 you will be wasting 200 gals of water per month. Assuming your water cost (including drainage charges) at 0.5 cents per gallon your increased water cost will be $1.00 per month so total monthly operating cost of the membrane will be:
DI $0.81
Carbon $0.125
Sediment $0.13
Membrane $1.25
Waste Water $1.00
Total: $3.315
versus $40.00 running DI only that will be aprox savings of $36.68 per month. If the membrane system costs $250.00 (fairly good one) you will pay back for the RO/DI units in just under 7 months.
Regenerating may take the cost of the resin replacement down which makes the DI system feasible for large requirements of pure water and worth the hassle of regenerating.
So there you go I hope I responded your question.
jdieck
New member
Some clarification.. Rejection is the amount of TDS that a membrane removes from the input water and is expressed as a percentage of the total amount incoming into the membrane.
Assume you have 100 ppm TDS in the input water, a 98% rejection membrane will "reject" (remove) 98 ppm TDS (100 x .98) and let 2 ppm pass thru to the product water.
The restrictor is just that, a calibrated orifice that prevents free flow of water. That resistance to the free flow creates higher pressure inside the membrane so the water passes thru it.
A possible methaphor will be a reduction in lines in the express way that creates a trafic jam before the reduction, some of the cars will start taking the exits of the express way before the restriction. Here the line restriction (the orange cones
) are the restrictor, the cars the water flow and the express exits is the membrane. Crude but can give you an idea.The more restriction there is the more water passes thru the membrane but also more contaminants the less restriction the more pure the water but the production is reduced while the waste increases so there is a point that balances this two factors, that is a point where the restrictor let pass about 4 volumes of waste water for each volume of product water.
Some restrictors are very obvious like the white one in the pic above (C) but some others can not be seen as they are installed inside the waste line (inserted at point B in the pic above) and look like a 1/16" diameter transparent tubing. The water is forced to pass thru such small diameter which is what creates the restriction. In this case the amount of restriction is obtained by making this tubing shorter (less restriction) or longer (more restriction)
For adding a second membrane of the same capacity use the same restrictor you would use with a single membrane, there is no need to change the capacity of the restrictor or try to adjust it.
In other words if you are using two 75 gpd capacity membranes use the restrictoryou would use for a single 75 gpd membrane unit.
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My restrictor is identical looking to the one in the photo. It has the (three sections) look to it. Can I restrict it a little more to slow the waste rate or will that hurt the unit? I think I should just leave it alone and use it the way it was built.
I bought my RO/DI unit through The Filter Guys. I like it and it does a great job, but I just don't like wasting so much water.
As for this other stuff about setting up multiple RO Membranes, I am confused a little. Good or not good????? Some people say it is working fine and some say not because of something with preassure.
I tested my home lines for preassure everywhere I could. At the end of a 50foot garden hose I had 82psi and at the wash sink in the basement 85psi. I have my RO/DI hooked up to the 85psi. Am I correct in hooking the unit up to the highest pressure I can in the house???
I bought my RO/DI unit through The Filter Guys. I like it and it does a great job, but I just don't like wasting so much water.
As for this other stuff about setting up multiple RO Membranes, I am confused a little. Good or not good????? Some people say it is working fine and some say not because of something with preassure.
I tested my home lines for preassure everywhere I could. At the end of a 50foot garden hose I had 82psi and at the wash sink in the basement 85psi. I have my RO/DI hooked up to the 85psi. Am I correct in hooking the unit up to the highest pressure I can in the house???
fahz
Premium Member
Savatage you are correct and your flow restrictor is for 4:1. Adding a second membrane would be ideal for you and cut your waste just like the tests show. Jdieck said he has run his setup for 18 months with no problems which caught my eye right away. Your pressure @82 psi would make a retro with an extra membrane hum right along. I don't know if it's in the thread but the pressure drop between membranes is very small.
Jim
Jim
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