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View Full Version : RODI system. A few questions.


shovelnose
06/26/2013, 05:05 PM
Ok I am looking at getting an rodi system. I can't seem to use the search function even though I am logged in.

I have been doing some research however, my main concerns are these. Cost of replacement filters, the waste to good water ratio and the ability to tap into the water after the RO membrane but before the DI system for drinking water. Also could I use the dirty water for my fresh water tanks?

My LFS has this system for sale for $230=tax with extra cartridges. I am in Canada so I was wondering if this is a fair price? http://www.aquaticlife.com/products/356#1 It is only 60 gpd but has low waste ratio. Again I am not sure of the ability to tap into the system for drinking water.

Any help is appreciated. Thanks, Kevin.

Denbf58
06/26/2013, 05:20 PM
http://www.bulkreefsupply.com/brs-5-stage-plus-ro-di-system-75gpd.html check out bulk reef supply this is the unit i went with and yes you can t off a line before the di unit for drinking water also i would not use waste water for you freshwater tank but to can be used for watering plants replacement filters run about $ 35.00

James77
06/26/2013, 07:46 PM
I would not purchase what you linked Kevin...too fancy IMO. Any of the sponsors here provide great RODI at a cheaper price, most of them are very comparable in price and filter replacement price. BuckEyeField Supply is my favorite, Russ is very helpful. Close runner ups are BulkReefSupply and thefilterguys.

The waste water is not "dirty", and should be better thought of as flush water. It actually has been run through carbon and sediment blocks so it is somewhat cleaner than the input water in that sense...but it has higher TDS since the membrane has raised it by about 20% or whatever the fraction would be. If your TDS is not high (mine is about 60-70 going in) I would have zero problem using it for a freshwater tank.

The waste/flush water ratio is what keeps the membrane working. The manufacturers recommend a certain ratio for best performance and life. I tried a "double the output" upgrade kit last year that added a membrane and kept the same waste restriction....and ended up with bacteria fouled membranes. I ditched them and returned to the standard 4 to 1 ratio.

Boosting the pressure can increase the product to flush ratio....but really look at how much water costs for you. For myself, I am not in an area where water is a limited resource...so conservation only really helps in the cost. For water and sewer...both based on water volume...I pay about $5 for 1,000 gallons. For the price of a booster pump, I could buy enough water to filter for water changes and top off for my tanks for probably a decade :). If water is a tight or expensive resource for you, or you really object to the waste, look at some of the systems offered by SpectraPure. More expensive, but they cut down waste.

Here is a quote for Buckeye Field Supply:

The "optimum" pressure for RODI systems seems to be an issue that keeps coming up on RC. There's a few things to consider here, including the best pressure for the membrane, and the pressure ratings for other system components.

Filmtec 75 gpd membranes are spec'ed with a max pressure of 300 psi. In general, the higher the pressure the better the membrane will perform in terms of how fast it produces clean water, and how clean the water is (the rejection curve goes pretty flat however at less than 100 psi). Now, in practical terms, no one has pressure approaching 300 psi in their plumbing. How about if you have a booster pump? Chances are it will max out at 120 psi or less.

I can hear the question already - "I thought the optimum pressure for Filmtec membranes was 50 psi - that's what the manufacturer says." Well, not really. What Filmtec says is that if you provide a 75 gpd membrane feedwater at 50 psi, 77 degrees F, and 250 ppm; and configure the system to run at 15% recovery, it will produce 75 gallons per day, plus or minus 20%, at the spec'ed rejection rate. Is 50 psi the "optimum" pressure? No. It just happens to be one of the standard test conditions used by the manufacturer in their testing. Most membrane manufacturers other than Filmtec use a test pressure of 60 psi.

Remember that your flow restrictor is designed to provide about a 4:1 ratio of concentrate to permeate assuming you have "standard conditions" (50 or 60 psi, 77 degree water, ...). So if you operate your system at much higher pressure, you may have to adjust/change your flow restrictor so that you stay near the recommended 4:1 ratio.

Also be aware that other components in your RO or RODI system can't handle anything close to the 300 psi your membrane can. The weakest link in most systems in terms of ability to withstand pressure is the clear housings. This is why we always recommend installation of booster pumps after the prefilters.

Russ

thegrun
06/27/2013, 06:39 AM
I like the nposted BRS system, I use all the added fancy features on a regular basis (flush valve, duel TDS meter, water gauge).

dkeller_nc
06/27/2013, 07:26 AM
I can't answer whether $230 is a "good deal" on the Aquatic Life unit in Canada, as I've no idea what taxes/duties, etc... are in the North Country.

But, I can comment on the waste/reject ratio. As James77 noted, almost all non-powered RODI units are configured to give you about 15% product/85% waste. That configuration is set based on an average incoming water hardness value and is designed to stay below the precipitation limit of so-called "hard water ions". These ions are typically calcium and magnesium.

If the reject ratio is changed such that more product water to waste water is produced, the danger is that the calcium and magnesium concentration will be raised to the point that their solubility limit is exceeded and they precipitate onto the RO membrane. If that occurs, the RO membrane will be quickly rendered useless.

If, however, your incoming water is relatively soft (a TDS of < 200ppm, for example), the product/waste ratio can be altered to yield more product water without fouling the RO membrane.

Calcium/magnesium fouling is why commercial systems are almost always configured with a water softener pre-treatment. The water softener replaces the calcium and magnesium ions with sodium, which has a very high solubility limit in water. So such a system can run a product/waste ratio of close to 1:1 or even better. Some systems that have water softeners and anti-foulant injection pumps can yield up to 90% product water.

All municipalities in the US are required to publish water test analysis data, so you can look that data up and figure out whether your tap water is relatively soft. If it is, you can use a higher pressure flow restrictor that will boost your product to waste ratio.

Fizz71
06/27/2013, 08:00 AM
Ok I am looking at getting an rodi system. I can't seem to use the search function even though I am logged in.

I have been doing some research however, my main concerns are these. Cost of replacement filters, the waste to good water ratio and the ability to tap into the water after the RO membrane but before the DI system for drinking water. Also could I use the dirty water for my fresh water tanks?

My LFS has this system for sale for $230=tax with extra cartridges. I am in Canada so I was wondering if this is a fair price? http://www.aquaticlife.com/products/356#1 It is only 60 gpd but has low waste ratio. Again I am not sure of the ability to tap into the system for drinking water.


When it comes to RO the filters are everything...the RO unit itself is just a few chambers and tubes so I personally get it as cheap as I can and make sure refilling/replacing the cartridges are cheap and easy to do. I like the BRS ones too because you can buy just carbon and resin and not have to buy the whole cartridge. I also like color changing DI that I can see rather than relying on testing but not everybody cares about that.

I can't tell by the specs if the DI resin is refillable or if you have to buy a whole new cartridge which would be another turnoff to me. Although when you replace it you should be able to buy a refillable cartridge from BRS that going forward is refillable to save a little money.

I also prefer 3 stages before my RO membrane, that one only has 2.

To answer your question of being able to tap into the RO and not the DI I'd have to say yes you can, BUT you'll need to drill some holes in that pretty case. You'd need to cut the line from the RO to the DI and run it out of the case to a series of valves and T's to either tap from there or send it back in to complete it's path through the DI and out the normal exit.

Bottom line...I think that unit is nice looking, but not really what you want. Atleast I wouldn't want it. :)

As for using the waste water for other purposes...that all depends how bad the water is going in. If your TDS isn't all that bad (20s to 30s) then your waste water will be better than some people's regular water. I had to practically chew the well water in my last house (over 200)...my current home's RO waste water has a lower TDS than my old house's main line.

LJLKRL
06/27/2013, 08:49 AM
I bought a spectrapure 4 stage 90 GPD RODI refurbished system for $130 from spectrapure
It works fine and I cannot see what is refurbished about it.

chrisfont23
06/27/2013, 09:58 AM
Check out the filterguyz. They have some good stuff

tallball158
06/27/2013, 02:25 PM
+1 on BRS. I love my unit

shovelnose
06/27/2013, 04:22 PM
Thanks for the responses. Looked at my city water report. Not sure about TDS. Couldn't find it. Around 100 ppm hardness. .5 ppm Nitrate. The water itself costs about 12.6 cents per cubic foot. $62 last month just me and my son. Not sure how that compares to others here.

Holy crap James77! I pay about $60 per 1000 gallons.

Anyone running a powered Ro system? Opinions?

So am I to believe that the replacement cartridges are the same for all units? I find that hard to believe.

The more I read the more my head hurts lol!

Also the unit I was looking at is regarded highly here. http://saltaquarium.about.com/od/toppicks/tp/tprodiunits.htm

shovelnose
06/27/2013, 04:27 PM
I can get this unit for $340 to my door. http://www.bulkreefsupply.com/brs-5-stage-water-saver-plus-ro-di-system-150gpd.html. This should cut down on waste water. I don't mind paying more in the short term for savings in the long term. I can get extra membranes(uses 2) carbon cartriges(2) and sediment filter for $460. (includes taxes and shipping about $100) I'm thinking I may as well order extra stuff as the shipping is minimal for the extra stuff vs ordering it later.

I think I read that di material you want to be fresh. Is that correct?

billdogg
06/27/2013, 04:41 PM
I'm going to chime in for Buckeye field supply as well (www.buckeyefieldsupply.com) I wanted to do just as you do and run a line to my frig after the RO unit. I shopped around and found what I thought was going to be the perfect setup, but still had a couple questions. I emailed BFS on a Saturday morning, expecting an answer sometime the following week. About 2 hours after I clicked send, my phone rang. It was Russ from BFS. I explained what I was wanting to do, he patiently explained a better method. I ended up having them custom build one for me that was almost $200 cheaper than what I thought I needed. I gave him my visa# and the deal was done. On Tuesday it was on my porch when I got home from work. It has been about 18 months, I'm still on my original cartridges (although I have purchased replacements to have on hand).

Bottom line? Great service. Great price. Excellent value for my hard earned $$$

Cozwey
06/27/2013, 05:23 PM
I purchased a 50 gpd system and now wish I had gone for the 100 gpd. Feels like all I do is make water now.

bnumair
06/27/2013, 05:32 PM
I purchased a 50 gpd system and now wish I had gone for the 100 gpd. Feels like all I do is make water now.

lol i have 2 x 75 gal per day ro/di units from BRS and it seem like i all i do is make water but automatically. i have rvoc system that monitors bin turn rodi units on/off.
OP BRS units best for the buck and replacement filters are cheap too.
http://i1105.photobucket.com/albums/h353/bnumair/20130205_205306_zps4317d39f.jpg

tatuaje08
06/27/2013, 10:24 PM
Spectrapure is the best in the biz. They also sell a drinking water add-on kit.

jwwalker
06/28/2013, 01:39 AM
+1 on Spectrapure. I have the Maxcap 90gpd and it works great.

tallball158
06/28/2013, 06:12 AM
I think I read that di material you want to be fresh. Is that correct?

Yes you will want the DI resin to be fresh, and if you purchase refills, make sure that it is from someone that sells a lot, to ensure that you are not getting some junk that someone had laying on the shelf for a while.

Fizz71
06/28/2013, 06:45 AM
Anyone running a powered Ro system? Opinions?


A powered RO can be useful, but it depends what it does. Some powered units are nothing more than a booster pump on your source water line. This is only needed if your house pressure is really low. Other units have the booster pump AND can do an automated flush every time the unit powers on. This is really cool, but again the booster is only needed if you have poor pressure.

I've owned all three types (booster only, booster and auto flush, and no power). I don't need a booster anymore since my current house has such strong water pressure I regret not tapping in after the home's reducer. I miss the autoflush, but the booster pump is a waste for me now.

dkeller_nc
06/28/2013, 11:20 AM
Thanks for the responses. Looked at my city water report. Not sure about TDS. Couldn't find it. Around 100 ppm hardness. .5 ppm Nitrate. The water itself costs about 12.6 cents per cubic foot. $62 last month just me and my son. Not sure how that compares to others here.

Essentially, your total hardness of 100 ppm is the TDS. While the precise definition of TDS includes non-ionizable substances in addition to calcium, magnesium, sodium, potassium, etc..., for treated municipal water the TDS is pretty much the same as total hardness. 100 ppm is more than reasonable, so RO membrane fouling is unlikely in your case.

And, while I can't say for sure, something seems a bit "off" on the price you quoted. One cubic foot of water is equal to about 7.5 gallons, and paying 12.6 cents for that is exhorbitant. For most municipalities in the Eastern half of the US, the rate is usually around 2-3 cents per cubic foot

silverwolf72
06/28/2013, 12:50 PM
You just need a T before the DI that runs to a storage tank that can be used for drinking water. I actually T mine off right before the RO membrane and skip the need for the storage tank

shovelnose
06/28/2013, 02:09 PM
Yes you will want the DI resin to be fresh, and if you purchase refills, make sure that it is from someone that sells a lot, to ensure that you are not getting some junk that someone had laying on the shelf for a while. That is what I was asking. Thanks!

[QUOTE=dkeller_nc And, while I can't say for sure, something seems a bit "off" on the price you quoted. One cubic foot of water is equal to about 7.5 gallons, and paying 12.6 cents for that is exhorbitant. For most municipalities in the Eastern half of the US, the rate is usually around 2-3 cents per cubic foot.[/QUOTE] That's what I pay. We have high rates. Plus sewer charges and infrastructure charges and tax lol! It's a scam. Good to know that the membrane will last.

silverwolf72 I would like a t and a valve after the ro membrane to fill 5 gallon jugs for my water cooler. That's about all I need.

http://www.bulkreefsupply.com/brs-5-stage-water-saver-plus-ro-di-system-150gpd.html Again this unit is supposed to have less water waste. Anyone have it? Do you like it?