RO/DI Resin and membrane

[bluwtr]

I just installed a ro/di system I was given (new filters, membrane and resin) and I seem to remember reading about having to flush the membrane. My system has three filters, then the membrane then the resin. I turn the system on and shut down my restrictor valve to force all of the pressure through the output side. I noticed that the begining edge of my resin is already changing color. Several questions about all of this:
1. How do I flush the membrane?
2. How do I determine my rejection rate and flow through my system--in other words how much waste to output?
3. Should my resin be getting used that fast?

A little more background it is an old AquaSafe system.

Thanks for all of the help.

Wes

 

[NobleSun27]

Its normal for the resin to change a little. You need to get a TDS meter to make sure your filters are good and make sure you change the first carbon filter often that will keep the membrane and resin lasting longer. I change mine at least once a month. You can check your waste to output by putting your output to fill a gallon jug and the waste to a 5 gallon bucket, as soon as you fill the gallon jug check the 5 gallon bucket and see what you got.

 

[AZDesertRat]

When you first got the system you should have cleaned and disinfected the housings then flushed each filter in sequence before installing the next. You start out with all empty housings including the RO membrane housing and DI if you are replacing those too.
After disinfecting the system, install ONLY the sediment filter and screw all the remaining empty housings back on then disconnect the 1/4" line between the carbon block and the RO membrane and stick the line in the sink or a bucket. Open the tap water and let the wate run through the sediment filter for a couple minutes to flush out all the glues and binders from the mnufacturing process so it does not clog or foul the carbon pores. Next unscrew the first carbon housing and install the first carbon block and agin flush the sediment and carbon for a few minutes to flush out the carbon fines or dust present from the extrusion of the carbon block (I hope it is a carbon block and not granular carbon) . Next install the second carbon block and do another several minutes so all three prefilters, sediment and 2 carbons, are clean and ready to use.

Now install the RO membrane and reinstall the 1/4" line from the carbon to the RO membrane. Open the tap water and overthe next hour or two send 3 to 5 gallons of RO water down the drain until a handheld TDS meter shows the effluent TDS has dropped as low as it will go, it should be around 98% lower than the tap water TDS with a new RO membrane. Finally install the DI cartridge and run the system until the RO/DI TDS is 0 and you are ready to go.

By not doing these steps you have shortened the life of all components by sending the glues, binders, dust and antimicrobial agents from he manufacturing to each component downstream.

You determine the rejection rate using the tap water TDS and the RO only (taken between the RO membrane and the DI filter, not the final RO/DI TDS)TDS numbers. DO NOT confuse Rejection Rate with Waste Ratio which you are doing in question 2. Rejection Rate if the removal efficiency of the RO membrane, Waste Ratio is the amount of waste water versus treated water to keep the membrane flushed and usable.

For rejection rate you take your tap water TDS and subtract the RO only TDS then divide that result by the original tap TDS and multiply by 100. A quick example would be say you have a tap TDS of 100 and your RO only TDS is 4. 100-4=96, 96/100= 0.96, 0.96x100 = 96% rejection rate or removal efficiency. Not good but not bd, you want to be at around 98% or better with a new membrane.

For waste ratio you use a measuring cup and a clock or watch and time the flow from the waste line then the treated line for exactly the same time period. Take the measuring cup and measure the waste flow for exactly one minute and write down the ounces or m/L, dump it and do the same from the treated line then compare thetwo results. You want the waste ratio to be very close to 4:1 or 4 times as much waste as treated. If you have 500 m/L of waste then you should have around 125 m/L or treated etc. The exact amounts will vary depending on the membrane, your tap water TDS, your water temperature and your water pressure but you still want about 4:1 in the end. If it is not close to that I would suggest a new capillary tube flow restrictor you the end user can trim or adjust to fit your exact conditions for around $5-$6.

Good sediment and carbon filters should last 6 months under normal conditions. The RO membrane will last 18 months to 10 years or more depending on the quality of your sediment and carbons, how well you keep up with the 6 month replacements and if you do at least and annual disinfection. DI resin is entirely dependent on the quality and freshness of the resin, how well the resin is packed in the cartridge, how you make water, by that mean frequent small batches are bad while less frequent long filter runs are good and if you have CO2 present in your water. It can be 3 months or a year or anywhere in between. Under normal conditions you can expect 3000 to 6000 total TDS per pound (16oz) of fresh DI resin. If your rejection rate is not good and your RO only TDS is say 10-15 you can expect shorter TDS life than if your RO is very efficient and your RO TDS is only 2 or 3.

 

[bluwtr]

Thanks for all of the information. Sorry I wasn't as clear as I should have been. I did clean the system very well and I have all brand new filters. I bought my resin from BRS and the filters from another company. I have flushed the prefilters (sed, car,CCC) and then the membrane. According to the manufacturer they recommend a 3:1 ratio as set by the restrictor valve. I believe I have it closer to 4:1. I am not ready to make water for my tank yet so an upstream and downstream TDS meters are next. Given this I'm not overly concerned about what my rate is but will measure it when the time comes. I was more concerned about the resin seeming to change quickly but it settled down.

Again thanks for the outstanding information and for the clarifications. Much appreciated.

W

 

[AZDesertRat]

I have tried every resin on the market and will only buy from Spectrapure now, the difference was quite dramatic from any other I tried previously. I also will not buy color changing resins since they are very unreliable, they may change in streaks, top to bottom, bottom to top, not at all, all at once etc. It is far better to use a handheld TDS meter and not rely on color change. Inline TDS meters lack the accuracy of a good $25 handheld since they are not ATC temperature compensated and cannot be calibrated. Plus they cannot be used portable so lack the versatility of a single handheld which can test tap water, RO only, RO/DI, your ATO storage, LFS water, bottled water, your buddies water and more. I own two dual inlines but never even turn them on anymore since they never agree with the handhelds.

Your waste ratio per membrane manufacturers should be 4:1. If you have softened water and lower than normal tap TDS then it can be cut to 3:1 or in rare cases 2:1 otherwise stick with 4:1 if you want decent membrane and DI life. What restrictor valve? Does your system have an adjustable needle valve on the waste line? Most vendors use preset or fixed type restrictors and some better vendors use capillary tubes you cut to length to adjust the waste. There are some needle valves but you have to watch them closely as they tend to plug and then the membane gets fouled due to too little waste.

 

[bluwtr]

Do you buy directly from Spectrapure? I bought the color changing just for visual reference and not as an end all be all. As far as the meters I actually plan on getting the dual inline but also a handheld. With my background and what I do I believe in reliablity and repeatability. As far as the ratio I adjusted up a little as I thought it was too low as well, so I think I'm closer to the 4:1 even though I've not measured it yet. I ordered the flow restrictor valve from Aquasafe that is inline and adjustable.

 

[AZDesertRat]

I do buy directly from Spectrapure so I am sure it has not been sitting on a shelf somewhere. Previously I bought directly from Resin Depot and other wholesalers but the blends and useful life were not the same.
You will find in a very short time you will not use the inline TDS meter so I wouldn't waste the money. My unit came with two of them for 4 measuring points but I would not get them again.
Watch the adjustable flow restrictor, it is probably a needle valve and will plug if not paid attention to. When it plugs the waste goes down and the membrane fouls, been there done that.

I am a certified water treatment plant operator, and manager by profession with almost 40 years in the industry so I am anal about its quality. Having owned 6 different systems personally and working with literally hundreds over the 30 years or so I learned there really is a difference so spend the extra couple $$ up front to get only the best and it saves much more than that over its lifespan.

 

[bluwtr]

Thanks again for the awesome info and I will take your advice on the TDS meters.

Which handheld unit would you recommend?

I am always appreciative of someone who can back up their opinions/recommendations etc. with real world experience. I'm a fisheries biologist and it can get aggravating when you give someone advice and they want to argue a point. Granted, no one is 100% correct all of the time but geez!

 

[AZDesertRat]

I used to use the HM Digital TDS-4TM and it was a great choice but I upgraded to the HM COM-100 which is much more sensitive and can be calibrated and used in several different modes including conductivity and keep the new HM AP-1 as a back up. I have two of the DM-1 dual inlines bit would not recommend them for anything other than ballpark accuracy. The COM-100 is a little more $$ but well worth it in my opinion. Over the last 15+ years I have kept log books on my RO/DI systems performance and filter changes so they are well documented, not just opinion or personal preference.

I have a distant cousin who is a cold water fisheries biologist and was a Professor at the University of Alaska-Fairbanks. Never met him though because he was in Alaska which is a fair piece from Arizona. Lots of cousins that are Drs. and I'm just a dumb old treatment plant operator working for a top 10 engineering firm.

 

[PCygni]

I used to use the HM Digital TDS-4TM and it was a great choice but I upgraded to the HM COM-100 which is much more sensitive and can be calibrated and used in several different modes including conductivity and keep the new HM AP-1 as a back up. I have two of the DM-1 dual inlines bit would not recommend them for anything other than ballpark accuracy. The COM-100 is a little more $$ but well worth it in my opinion. Over the last 15+ years I have kept log books on my RO/DI systems performance and filter changes so they are well documented, not just opinion or personal preference.

I have a distant cousin who is a cold water fisheries biologist and was a Professor at the University of Alaska-Fairbanks. Never met him though because he was in Alaska which is a fair piece from Arizona. Lots of cousins that are Drs. and I'm just a dumb old treatment plant operator working for a top 10 engineering firm.

AZ, you are the undisputed King of RO/DI. I have steadily applied all your suggestions (to the extent I can) into practice. Just wanted to thank you for your input through the years.

 

[bluwtr]

AZ I didn't mean to imply that your advice was just an opinion. Sorry if you took offense as none was meant. I was just saying it's always nice to get the views of an expert. That is amazingly awesome that you've kept a journal that long. I've kept a journal for my tank with my parameters since I began the tank and I feel it has helped me id any issues etc. I don't keep up with it as well as I once did as I work two jobs and have three little ones at home, but it is still a very handy reference.

I've met more than my fair share of PhD's and trade workers and I promise you I would take the trade worker any day. Almost every "smart" person I've met are either self absorbed jerks (being polite) or are dumb as a bag of rocks. I'll take commen sense and pratical experience over book smarts any day!:bigsmile:

 

[AZDesertRat]

No offense taken. I just try to back up my observations with data. Having been in water treatment for almost 40 years I find it carries more weight than simple statements with nothing to back it up. My clients as well as the regulators demand it.

 

[bluwtr]

Glad none was taken!

 

[sir bonkers]

When you first got the system you should have cleaned and disinfected the housings then flushed each filter in sequence before installing the next. You start out with all empty housings including the RO membrane housing and DI if you are replacing those too.
After disinfecting the system, install ONLY the sediment filter and screw all the remaining empty housings back on then disconnect the 1/4" line between the carbon block and the RO membrane and stick the line in the sink or a bucket. Open the tap water and let the wate run through the sediment filter for a couple minutes to flush out all the glues and binders from the mnufacturing process so it does not clog or foul the carbon pores. Next unscrew the first carbon housing and install the first carbon block and agin flush the sediment and carbon for a few minutes to flush out the carbon fines or dust present from the extrusion of the carbon block (I hope it is a carbon block and not granular carbon) . Next install the second carbon block and do another several minutes so all three prefilters, sediment and 2 carbons, are clean and ready to use.

Now install the RO membrane and reinstall the 1/4" line from the carbon to the RO membrane. Open the tap water and overthe next hour or two send 3 to 5 gallons of RO water down the drain until a handheld TDS meter shows the effluent TDS has dropped as low as it will go, it should be around 98% lower than the tap water TDS with a new RO membrane. Finally install the DI cartridge and run the system until the RO/DI TDS is 0 and you are ready to go.

By not doing these steps you have shortened the life of all components by sending the glues, binders, dust and antimicrobial agents from he manufacturing to each component downstream.

You determine the rejection rate using the tap water TDS and the RO only (taken between the RO membrane and the DI filter, not the final RO/DI TDS)TDS numbers. DO NOT confuse Rejection Rate with Waste Ratio which you are doing in question 2. Rejection Rate if the removal efficiency of the RO membrane, Waste Ratio is the amount of waste water versus treated water to keep the membrane flushed and usable.

For rejection rate you take your tap water TDS and subtract the RO only TDS then divide that result by the original tap TDS and multiply by 100. A quick example would be say you have a tap TDS of 100 and your RO only TDS is 4. 100-4=96, 96/100= 0.96, 0.96x100 = 96% rejection rate or removal efficiency. Not good but not bd, you want to be at around 98% or better with a new membrane.

For waste ratio you use a measuring cup and a clock or watch and time the flow from the waste line then the treated line for exactly the same time period. Take the measuring cup and measure the waste flow for exactly one minute and write down the ounces or m/L, dump it and do the same from the treated line then compare thetwo results. You want the waste ratio to be very close to 4:1 or 4 times as much waste as treated. If you have 500 m/L of waste then you should have around 125 m/L or treated etc. The exact amounts will vary depending on the membrane, your tap water TDS, your water temperature and your water pressure but you still want about 4:1 in the end. If it is not close to that I would suggest a new capillary tube flow restrictor you the end user can trim or adjust to fit your exact conditions for around $5-$6.

Good sediment and carbon filters should last 6 months under normal conditions. The RO membrane will last 18 months to 10 years or more depending on the quality of your sediment and carbons, how well you keep up with the 6 month replacements and if you do at least and annual disinfection. DI resin is entirely dependent on the quality and freshness of the resin, how well the resin is packed in the cartridge, how you make water, by that mean frequent small batches are bad while less frequent long filter runs are good and if you have CO2 present in your water. It can be 3 months or a year or anywhere in between. Under normal conditions you can expect 3000 to 6000 total TDS per pound (16oz) of fresh DI resin. If your rejection rate is not good and your RO only TDS is say 10-15 you can expect shorter TDS life than if your RO is very efficient and your RO TDS is only 2 or 3.

I just installed new filters and a membrane in my system yesterday. I had no idea there was a procedure to a simple filter/resin change. Guess Ill be replacing them again soon. This is great advice and Im gonna make sure I do this next time around!