Question about RO/DI

craftedpacket · 10/18/2007, 08:55 PM

I have a 5 stage RO/DI system from AirWaterIce. There is a sediment filter, 2 coconut type filters a filmtec 75gph membrane and then the DI cartridge.

My tap water tests at 750+ppm...sadly enough its not even well water but city provided water. Out of the filters and membrane the water is testing around 250ppm. Needless to say i go through DI resin very quickly. Is there anyway to optimize my system to get more life out of my DI resin?

AZDesertRat · 10/18/2007, 10:19 PM

How old is the membrane? You should be seeing an RO only TDS of no more than 15-20 maximum out of the 75 GPD Dow even with a tap water TDS of 750. My tap is 835 and I average 5 to 6 TDS with RO only using a Spectrapure Select hand tested RO membrane.

craftedpacket · 10/18/2007, 10:30 PM

Thank you for the reply. My membrane is around a year old now, it is the original one I purchased when setting up my tank.

craftedpacket · 10/18/2007, 10:34 PM

I am not sure what they are called but I guess it is the device that does the rejection? I have 2 of them labeled "organic" with a number 550 on them.

AZDesertRat · 10/18/2007, 10:36 PM

Have you moved or dropped the unit at some point which could cause the membrane to become unseated? If water bypasses the membrane it can lead to high TDS. You might try removing the membrane from its housing and reinstalling it making sure it extends down into the housing all the way, they go in further than you think.
How much water do you estimate you have made and how long has it been since you changed the prefilter and carbons? Normall the prefilter and carbon have little to no effect on final TDS except if the carbon has been exhausted and you have passed chlorine on to the RO membrane.

AZDesertRat · 10/18/2007, 10:40 PM

You are talking about the flow restrictor. You should have one of those installed in the waste line so it causes enough restriction to force water through the membrane.
Speaking of restrictors have you times the flow from both the good and waste lines to ensure you have a 4:1 waste ratio? You need 4 gallons to waste fro every 1 gallon of good water to keep the membrane flushed, any less and the membrane goes bad prematurely. Try timing the flows with a watch and a measuring cup and tell us what they each are in a one minute period.

old salty · 10/18/2007, 11:51 PM

I have the same unit and have had problems with it for almost 2 years (and went through lots of filters). After talking with Russ from BFS, I ended up changing my RO housing when I changed my RO filter. I don't remember the additional cost for this, but I know it wasn't much. I think this is where the issue was all along and it just never occurred to me.

Anyhow, I now use a booster pump as well as an adjustable flow restriction device (a ball valve) in addition to a pressure gauge and a TDS meter. With a 4:1 waste to good water ratio, it makes 180 gallons per day with a 98% rejection rate. I used to go through lots of DI resin; probably a cartridge per month. I've had the same DI cartridge for 10 weeks and it doesn't look any different than the first day; no noticeable color change.

craftedpacket · 10/19/2007, 12:09 AM

Thank you for your replies.

With the test in one minute i produced exactly 4 cups of waste water and 2/3 cups of good water.

I just replaced all 3 pre filters about 1 month ago.

I actually have 2 flow restrictors connected with a Y fitting.

craftedpacket · 10/19/2007, 12:10 AM

Old salty, what is BFS?

craftedpacket · 10/19/2007, 12:22 AM

I opened the membrane housing....but minus getting medevil with a pair of plyers I could not remove the membrane from its housing.

I did follow the way the tube runs...the prefilters run into the membrane and out of it either goes to the waste drain or the DI cartridge...so it looks like water would have to flow through the membrane to get to the DI. But I am just going by the way the tubing runs.

Coming in:
Pre filter ---> pressure shut off valve ---> membrane

Out:
Membrane ---> shut off valve ---> DI
Membrane ---> flow restrictors --> waste drain

I currently use refillable cartridges with mixed bed color changing DI resin....I make top off for my 140 gallon...say around 2-5 gallons a day depending on temperature and make 25-30 gallons every week to every other week for water changes.

I am lucky to get 1 month on a DI fill.

AZDesertRat · 10/19/2007, 08:52 AM

Sounds like you are close to the 4:1 waste ratio. I still don't understand why you have two flow restrictors though, one correct sized one is all you need.
It sounds to me like you have a bad membrane or a bad housing or both as Salty suggested. With RO only TDS like that there is nothing you can do to improve the DI life much, even better DI will still exhaust quickly. You can probably get a new membrane and housing for around $50-$60 and that should solve your problems. With a tap water TDS in the 750 range I would highly recommend looking at a Spectrapure Select 98+% rejection rate hand tested membrane. I am averaging 99.23% rejection rate from mine so DI last much longer. A good rule of thumb is for every 2% you increase the RO efficiency you double the life of the DI resin so it pays for itself rather quickly if you make much water at all. I was getting 150 gallons of DI per 20oz cartridge with a normal 75 GPD Dow Filmtec membrane, now I get 630 gallons per cartridge so it really paid off for me.

craftedpacket · 10/19/2007, 11:30 PM

Is there a specific one you recomend?

AZDesertRat · 10/20/2007, 08:12 AM

The Dow Filmtec 75 GPD is the most widely used membrane and is pretty good at 96-98% rejection. Off the shelf membranes are not tested though and you get what you get, they can vary by 15% or so.
Spectrapure goes a few steps beyond the normal Dow with their select series membranes. Each and every one is individually hand tested and guaranteed to be 98+% rejection and will produce 90 GPD at 60 psi and 77 degrees F. You pay for this service and gauarantee but with hight TDS water like you and I have its well worth the difference in DI savings alone. They also ship their membranes wet in a special pickling solution ulike anyone else, this maintains its efficiency.

craftedpacket · 10/20/2007, 04:48 PM

Thanks for the info...is this the one you were referring too?

MEM-S-0090 90 (340) 2" x 12" $99.99 1 / 0.45

Should it fit in my housing I have now with my filmtec? or should I get a new housing as well.

old salty · 10/20/2007, 08:36 PM

Here it is; it's the first item and is ten bucks:

http://buckeyefieldsupply.com/showpr...owspecials=153

If you decide to get a new RO housing, you will reuse the fittings from the old one. One of them has a check valve installed, so do not swap them accidentally.

Buckeye Hydro · 10/21/2007, 07:35 AM

CP - With the waste to permeate ratio you report I suspect your membrane is properly seated and your RO membrane housing is ok.

You may just need to replace the membrane. We have wet tested 75 gpd Filmtec membranes in stock.

You're dual flow restrictor is an unusual/odd configuration, but it is yielding an appropriate waste to permeate ratio so it's ok.

What is your water pressure and water temperature?

Go ahead and get physical with the membrane - grip the plastic stem with pliants and twist and pull - get it out of the housing and report what you see on the label.

Russ

craftedpacket · 10/21/2007, 09:38 PM

Its a filmtec membrane
model TW30-1812-100

Buckeye Hydro · 10/22/2007, 03:45 AM

With that membrane you should be seeing about 75 ppm in the RO water. That is still very high, and you'd go through resin pretty quickly.

If you went with either a 75 gpd, or a 150 gpd replacement membrane, your RO water would be 15 to 25.

Russ

craftedpacket · 10/22/2007, 09:25 AM

Will I need a different flow restrictor? does the 75gpd perform better then the 150?

Buckeye Hydro · 10/22/2007, 05:47 PM

If your new membrane has a different capacity than your existing membrane -- yes, you'd want a new, matched flow restrictor.

Both the 75 and 150 gpd membranes have a rejection rate of 96 to 98+%

Russ

craftedpacket · 10/22/2007, 09:42 PM

sorry for all the questions....so if they both perform the same...why even make the 75?

Buckeye Hydro · 10/23/2007, 03:24 AM

The 50 gpd is also a high rejection membrane.

Higher production membranes are a bit more expensive than lower production membranes.

Some situations (e.g., a residential drinking water system) might only heen a very low capacity membrane.

The 50, 75, and 100 do well with 50+ psi. With the 150 you'll want 60+ psi.

10/18/2007, 08:55 PM	#1
craftedpacket Registered Member Join Date: Oct 2006 Location: Odessa, TX Posts: 239	Question about RO/DI I have a 5 stage RO/DI system from AirWaterIce. There is a sediment filter, 2 coconut type filters a filmtec 75gph membrane and then the DI cartridge. My tap water tests at 750+ppm...sadly enough its not even well water but city provided water. Out of the filters and membrane the water is testing around 250ppm. Needless to say i go through DI resin very quickly. Is there anyway to optimize my system to get more life out of my DI resin?

10/18/2007, 11:51 PM	#7
old salty Genius Join Date: Jun 2005 Location: The Island of Misfit Toys Posts: 3,131	I have the same unit and have had problems with it for almost 2 years (and went through lots of filters). After talking with Russ from BFS, I ended up changing my RO housing when I changed my RO filter. I don't remember the additional cost for this, but I know it wasn't much. I think this is where the issue was all along and it just never occurred to me. Anyhow, I now use a booster pump as well as an adjustable flow restriction device (a ball valve) in addition to a pressure gauge and a TDS meter. With a 4:1 waste to good water ratio, it makes 180 gallons per day with a 98% rejection rate. I used to go through lots of DI resin; probably a cartridge per month. I've had the same DI cartridge for 10 weeks and it doesn't look any different than the first day; no noticeable color change. __________________ "The man who reads nothing at all is better educated than the man who reads nothing but newspapers." Thomas Jefferson Current Tank Info: Out of the marine aquarium hobby

10/20/2007, 08:36 PM	#15
old salty Genius Join Date: Jun 2005 Location: The Island of Misfit Toys Posts: 3,131	Here it is; it's the first item and is ten bucks: http://buckeyefieldsupply.com/showpr...owspecials=153 If you decide to get a new RO housing, you will reuse the fittings from the old one. One of them has a check valve installed, so do not swap them accidentally. __________________ "The man who reads nothing at all is better educated than the man who reads nothing but newspapers." Thomas Jefferson Current Tank Info: Out of the marine aquarium hobby

10/18/2007, 10:19 PM	#2
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	How old is the membrane? You should be seeing an RO only TDS of no more than 15-20 maximum out of the 75 GPD Dow even with a tap water TDS of 750. My tap is 835 and I average 5 to 6 TDS with RO only using a Spectrapure Select hand tested RO membrane.

10/18/2007, 10:30 PM	#3
craftedpacket Registered Member Join Date: Oct 2006 Location: Odessa, TX Posts: 239	Thank you for the reply. My membrane is around a year old now, it is the original one I purchased when setting up my tank.

10/18/2007, 10:34 PM	#4
craftedpacket Registered Member Join Date: Oct 2006 Location: Odessa, TX Posts: 239	I am not sure what they are called but I guess it is the device that does the rejection? I have 2 of them labeled "organic" with a number 550 on them.

10/18/2007, 10:36 PM	#5
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	Have you moved or dropped the unit at some point which could cause the membrane to become unseated? If water bypasses the membrane it can lead to high TDS. You might try removing the membrane from its housing and reinstalling it making sure it extends down into the housing all the way, they go in further than you think. How much water do you estimate you have made and how long has it been since you changed the prefilter and carbons? Normall the prefilter and carbon have little to no effect on final TDS except if the carbon has been exhausted and you have passed chlorine on to the RO membrane.

10/18/2007, 10:40 PM	#6
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	You are talking about the flow restrictor. You should have one of those installed in the waste line so it causes enough restriction to force water through the membrane. Speaking of restrictors have you times the flow from both the good and waste lines to ensure you have a 4:1 waste ratio? You need 4 gallons to waste fro every 1 gallon of good water to keep the membrane flushed, any less and the membrane goes bad prematurely. Try timing the flows with a watch and a measuring cup and tell us what they each are in a one minute period.

10/19/2007, 12:09 AM	#8
craftedpacket Registered Member Join Date: Oct 2006 Location: Odessa, TX Posts: 239	Thank you for your replies. With the test in one minute i produced exactly 4 cups of waste water and 2/3 cups of good water. I just replaced all 3 pre filters about 1 month ago. I actually have 2 flow restrictors connected with a Y fitting.

10/19/2007, 12:10 AM	#9
craftedpacket Registered Member Join Date: Oct 2006 Location: Odessa, TX Posts: 239	Old salty, what is BFS?

10/19/2007, 12:22 AM	#10
craftedpacket Registered Member Join Date: Oct 2006 Location: Odessa, TX Posts: 239	I opened the membrane housing....but minus getting medevil with a pair of plyers I could not remove the membrane from its housing. I did follow the way the tube runs...the prefilters run into the membrane and out of it either goes to the waste drain or the DI cartridge...so it looks like water would have to flow through the membrane to get to the DI. But I am just going by the way the tubing runs. Coming in: Pre filter ---> pressure shut off valve ---> membrane Out: Membrane ---> shut off valve ---> DI Membrane ---> flow restrictors --> waste drain I currently use refillable cartridges with mixed bed color changing DI resin....I make top off for my 140 gallon...say around 2-5 gallons a day depending on temperature and make 25-30 gallons every week to every other week for water changes. I am lucky to get 1 month on a DI fill.

10/19/2007, 08:52 AM	#11
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	Sounds like you are close to the 4:1 waste ratio. I still don't understand why you have two flow restrictors though, one correct sized one is all you need. It sounds to me like you have a bad membrane or a bad housing or both as Salty suggested. With RO only TDS like that there is nothing you can do to improve the DI life much, even better DI will still exhaust quickly. You can probably get a new membrane and housing for around $50-$60 and that should solve your problems. With a tap water TDS in the 750 range I would highly recommend looking at a Spectrapure Select 98+% rejection rate hand tested membrane. I am averaging 99.23% rejection rate from mine so DI last much longer. A good rule of thumb is for every 2% you increase the RO efficiency you double the life of the DI resin so it pays for itself rather quickly if you make much water at all. I was getting 150 gallons of DI per 20oz cartridge with a normal 75 GPD Dow Filmtec membrane, now I get 630 gallons per cartridge so it really paid off for me.

10/19/2007, 11:30 PM	#12
craftedpacket Registered Member Join Date: Oct 2006 Location: Odessa, TX Posts: 239	Is there a specific one you recomend?

10/20/2007, 08:12 AM	#13
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	The Dow Filmtec 75 GPD is the most widely used membrane and is pretty good at 96-98% rejection. Off the shelf membranes are not tested though and you get what you get, they can vary by 15% or so. Spectrapure goes a few steps beyond the normal Dow with their select series membranes. Each and every one is individually hand tested and guaranteed to be 98+% rejection and will produce 90 GPD at 60 psi and 77 degrees F. You pay for this service and gauarantee but with hight TDS water like you and I have its well worth the difference in DI savings alone. They also ship their membranes wet in a special pickling solution ulike anyone else, this maintains its efficiency.

10/20/2007, 04:48 PM	#14
craftedpacket Registered Member Join Date: Oct 2006 Location: Odessa, TX Posts: 239	Thanks for the info...is this the one you were referring too? MEM-S-0090 90 (340) 2" x 12" $99.99 1 / 0.45 Should it fit in my housing I have now with my filmtec? or should I get a new housing as well.

10/21/2007, 07:35 AM	#16
Buckeye Hydro .Registered Member Join Date: Sep 2006 Location: Cincinnati, Ohio Posts: 4,857	CP - With the waste to permeate ratio you report I suspect your membrane is properly seated and your RO membrane housing is ok. You may just need to replace the membrane. We have wet tested 75 gpd Filmtec membranes in stock. You're dual flow restrictor is an unusual/odd configuration, but it is yielding an appropriate waste to permeate ratio so it's ok. What is your water pressure and water temperature? Go ahead and get physical with the membrane - grip the plastic stem with pliants and twist and pull - get it out of the housing and report what you see on the label. Russ

10/21/2007, 09:38 PM	#17
craftedpacket Registered Member Join Date: Oct 2006 Location: Odessa, TX Posts: 239	Its a filmtec membrane model TW30-1812-100

10/22/2007, 03:45 AM	#18
Buckeye Hydro .Registered Member Join Date: Sep 2006 Location: Cincinnati, Ohio Posts: 4,857	With that membrane you should be seeing about 75 ppm in the RO water. That is still very high, and you'd go through resin pretty quickly. If you went with either a 75 gpd, or a 150 gpd replacement membrane, your RO water would be 15 to 25. Russ

10/22/2007, 09:25 AM	#19
craftedpacket Registered Member Join Date: Oct 2006 Location: Odessa, TX Posts: 239	Will I need a different flow restrictor? does the 75gpd perform better then the 150?

10/22/2007, 05:47 PM	#20
Buckeye Hydro .Registered Member Join Date: Sep 2006 Location: Cincinnati, Ohio Posts: 4,857	If your new membrane has a different capacity than your existing membrane -- yes, you'd want a new, matched flow restrictor. Both the 75 and 150 gpd membranes have a rejection rate of 96 to 98+% Russ

10/22/2007, 09:42 PM	#21
craftedpacket Registered Member Join Date: Oct 2006 Location: Odessa, TX Posts: 239	sorry for all the questions....so if they both perform the same...why even make the 75?

10/23/2007, 03:24 AM	#22
Buckeye Hydro .Registered Member Join Date: Sep 2006 Location: Cincinnati, Ohio Posts: 4,857	The 50 gpd is also a high rejection membrane. Higher production membranes are a bit more expensive than lower production membranes. Some situations (e.g., a residential drinking water system) might only heen a very low capacity membrane. The 50, 75, and 100 do well with 50+ psi. With the 150 you'll want 60+ psi.