RODI question

[MzFixIt]

For a lack of knowing where to post this I chose this DIY section.

Ok, so I know some of you reading this will gasp at my thoughts....but I have to ask/discuss anyway because it's truly bugging me not finding a good answer.

I have had a 4 stage "plus" RODI system from BRS for a little over 3 years. With the "plus" I am supposed to be getting more water than the standard 4 stage, but whatever. For the past few years I have paid my increased water bill due to the fact that for every 1 gallon of RODI water I successfully get, I lose 1 to 1.5 gallons as "waste" water. When I started my system up each time I used to set the valve to go out the waste only and wait for that to show "0" TDS output then I would turn it over to go into my storage bin with "0" TDS as well because that was the way I was instructed to do it. It took me about a year of wasting a lot of water to realize I didn't really have to do that initial step of turning it all to waste first and started running it into the storage bin upon turning the system on. I found that the "in" for the storage container was starting out at "0" TDS anyway so I no longer wanted to waste that initial water in the beginning.

A couple of months ago I called BRS because I had an aha moment and I wanted clarification. In my pea brain the way I see it, just like with water filters and purifiers for human consumption drinking water, once the water goes through the filter it is then "clean" and acceptable to use and there is no "waste" water that gets poured out. So I asked the rep why there is waste water on the RODI systems if in theory the water is "clean" after it has passed through the filters. His explanation was that the water that goes out through the waste line is filled with all the bad stuff one wants to rid themselves of, or in our cases rid our fish of, and only the good RODI water goes forward into the storage bin. I suppose that would not be so bad for a small amount of water usage, however, I have an aquarium room with several large tanks (I do both fresh and salt tanks) and I have been sending a little over 200 gallons of "waste" water down my driveway every week now for the past few years, hence the high water bills.

Because I still couldn't wrap my little pea brain around the BRS explanation I decided to do an experiment for myself. Over the past two weeks I have ran the "waste" water line into buckets and the RODI "good" line into my normal storage tank. I have used my TDS meter to test each bucket of "waste" water and have found that just as I suspected they are reading "0" TDS on the meter as well with only a small exception of the 1st bit of run off when I start things up I might get a small reading of 6 to 16 depending on how much is in that bucket.

So my question for discussion and hopefully get some clarification for myself is why is there "bad runoff water" if it tests out to be zero TDS? Isn't that what it's supposed to be? Is there something in that waste water one should be concerned about that will not show up on the TDS meter? I am feeling like I may start to run all my water into my storage bin, both "waste" and "good" lines and perhaps as an added safety measure pour a little Seachem Prime in there "just in case." When I started my first salt tank I used tap water and used Prime when mixing my salt water and never really had any issues....but I got caught up in the fact that everyone kept saying "you have to do that for salt tanks" so I gave in and bought my RODI system. I now use the RODI water for both my fresh and salt tanks. I am just struggling with all this "waste" water from the RODI system getting flushed out even when it's testing out to be zero TDS.

Any feedback? Theories? Concerns? Explanations?

 

[DiefsReef]

Very interesting question as I to struggle with the amount of water wasted. If no TDS then why is the water waste? I dont know but I hope someone here can give some answers. thx for posting! (watching)

 

[bg2311]

The in-line TDS meters you see on the RODI units take maybe 10 minutes or so of the system running before you get an accurate reading I believe. They also have to be aligned properly in the T fitting to get a good reading. Every hour or so of making water you will want to flush the water saver membrane (s) on your plus system for 15-20 seconds. You can do this by hand by opening the valve by the membrane directing all the flow to the waste line briefly, you will see the pressure gauge drop sharply). They also make auto-flush kits that will do it for you if you make lots of water at once and don't want to be there to poke it every hour. The higher the pressure the more efficient your RODI unit will be so if you are low on water pressure, you can add a booster pump. For every gallon of clean water you make, less waste water will be produced at higher pressure (to a point). Low temperature will also affect this efficiency so if possible keep the RODI unit inside, ideally somewhere at least partially climate controlled vs. outside or in an uninsulated basement.

 

[bg2311]

The "waste" water is in fact as I understand it drinkable, just with a higher amount of dissolved solids than the output water. You can use it for watering plants as well.

This is the auto-flush unit I mentioned above: https://www.bulkreefsupply.com/aquatec-auto-flush-flow-restrictor.html
It uses the same power as the booster pump. The higher pressure from the pump improves your overall system efficiency and you will end up with less gallons of "waste" water produced. We use our BRS 150 water saver system with the 6800 booster pump. Our water pressure before was around 32PSI which is below the recommended range and produced a lot of waste water prior to us adding the booster pump. Now we're around 55-60psi and it's much more efficient.

 

[MzFixIt]

Very interesting question as I to struggle with the amount of water wasted. If no TDS then why is the water waste? I dont know but I hope someone here can give some answers. thx for posting! (watching)

I also posted on R2R and had several "your TDS meter must be bad", however, I don't agree with that, as I get readings with my tap water. Also, my BRS RODI system has a built in TDS meter and it too reads zero TDS after a few minutes of running.

I have read posts where people use their RODI water even when it's reading low amounts of 1 to 3 TDS. My point being is that I still don't "get it" when it comes to dumping so much water that is reading zero TDS just because it's going out of the "dump" side of the system. After reading many "well I think it's this...or that" I'm at the point of following my gut and as long as it has no TDS I'm going to use it. I "might" regret it later perhaps but my pea brain just can't see that happening now that I know the numbers. I have every gadget sold for testing water in the hobby and my "waste" water has no TDS, copper, nitrates, nitrites, ammonia or anything else I can test for....that in theory would be "bad" for my fish family. Considering I used to use tap water without any repercussions (I did use Prime) I'm feeling pretty confident at this point.

If, however, in a few months I find something is off and the only change I have made is this "waste" water addition I will be sure to post so others then know it's been tried at least. I'll also make a point to post in a few months if/when I find that things are doing fine and I'm no longer wasting over 150 gallons of our precious water source.

 

[timeconsumer]

Okay I want to clarify something. I feel like you're using the term wastewater to describe two very different things. The wastewater line that exits the RO membrane is going to have a TDS very similar to tapwater as it hasn't run through the RO membrane which does about 95% of the work in purifying our tapwater. All the prefilters before the RO membrane are really about removing chlorine and large particles to keep the membrane from being damaged. These prefilters are basically the same thing as a Brita filter or a filter on your refrigerator door, mostly all they do is remove chlorine, they don't really do anything else so the TDS before and after these should be almost exactly the same.

The water that exits your membrane I will simply refer to as RO water, this is different from RODI water, which is what happens after it passes through your DI canister and exits the system at 0 TDS, ready for use. Now it sounds like you are using a DI bypass valve to get rid of the RO water when first starting up a system, this is a common tactic to help preserve the life of DI resin which is very expensive. When a system sits for a long time you get ions bypassing the membrane slowly and if you turn the system back on those run through your expensive DI resin and deplete it faster (ish, more on this later) However it will still leave the DI stage at 0 TDS and be fine for use. This does not really make it wastewater though, wastewater is still coming from a different hose and is not the same thing.

Now if you are telling me the wastewater line exiting your RO unit is reading 0 TDS that's where I get confused. Unless your tap water is very close to that, there must be something wrong. And in our area our tapwater (well I'm Cobb County but very very close to Woodstock) is astonishingly good compared to most of the US. I am getting under 50 TDS, but my waste water is still around the same, it just has no chlorine anymore. This very low TDS actually means the problem referred to above with TDS creep really isn't a big issue for us. Our DI resin lasts so long anyway since our RO water should be exiting the membrane around 1 TDS that it just doesn't matter that much.

Now here's where I am getting very confused with what you're describing:

"Also, my BRS RODI system has a built in TDS meter and it too reads zero TDS after a few minutes of running."

Okay, your BRS RODI wouldn't have the built-in TDS meter running on the wastewater line. It would be in 2 (sometimes 3) places. Source water, basically your tap water, RO water, so the water out of the membrane but before the DI, around the same location as your bypass valve, and lastly on the very end of the line, the DI water. If you're using the BRS meter to measure the TDS of your wastewater line, well then you aren't measuring your wastewater, because they wouldn't install that on the waste line. More than likely you're measuring the TDS of the RO water.

 

[ichthyoid]

Most freshwater sources here in N Georgia are pretty ‘soft’ (ie- low dissolved mineral content). About 40-70 ppm.

It is for this reason that I do not run an RO membrane for my water system. I only use particle, carbon & 2x DI resin stages for filtration.

When everyone jumped on the RO bandwagon years ago, I was working in R&D. We had huge Millipore RO/DI systems that produced a LOT of 20+ meg ohm pure water, but didn’t need to get serviced very often. So, I began to think about usage, investigated the facts & decided on what I’ve got.

Below is a link to a water hardness map -

Water Hardness Map of the United States – H2O Distributors

Water Hardness Map of the United States, Water Hardness Table of Classifications and links to more information about water softening and effects.

www.h2odistributors.com

 

[Gabridge83]

What is your TDS straight out of the tap?

 

[MzFixIt]

What is your TDS straight out of the tap?

Averages around 54

 

[ichthyoid]

Averages around 54

I live just north of you and have seen similar levels. Which, as stated above, led me to use GAC & DI resin only as the means to remove dissolved substances from water.

Wasting 50+% of the treated water isn’t acceptable to me. However, some people use the RO waste water in gardens, etc. Most just send it down a drain.

 

[Gabridge83]

I live just north of you and have seen similar levels. Which, as stated above, led me to use GAC & DI resin only as the means to remove dissolved substances from water.

Wasting 50+% of the treated water isn’t acceptable to me. However, some people use the RO waste water in gardens, etc. Most just send it down a drain.

We are at 40 out of the tap and we have been trying to figure out how to use the waste water. With that low of TDS I don’t want to waste it

 

[jcook54]

I really don't like wasting all of the water either and I've got 110g of storage that my wastwater line empties in to so I can water the plants outside. It's a lot harder this time of year because there's not a lot of watering that needs to be done. The water going into the RO membrane at my house is 38-42 TDS and the idea of using resin only is one that I'm going to investigate.

 

[ichthyoid]

You can buy the the refillable cartridges and bulk resin, which saves some money.

Another thing is, RO membranes are more efficient during winter, when temps are lower. That makes the membrane contract & mean pore size shrinks. So, filtration efficiency goes up because it captures smaller substances/more of the solute.

 

[ZapataInc]

I really don't like wasting all of the water either and I've got 110g of storage that my wastwater line empties in to so I can water the plants outside. It's a lot harder this time of year because there's not a lot of watering that needs to be done. The water going into the RO membrane at my house is 38-42 TDS and the idea of using resin only is one that I'm going to investigate.

Yeah i like the idea of not having "waste" water. Ill check my TDS from the Tap when i get home. @ichthyoid if i run a batch of water without the RO and just through my filter, carbon, and DI and it comes out 0TDS...then it should be good to go?

 

[ichthyoid]

Yeah i like the idea of not having "waste" water. Ill check my TDS from the Tap when i get home. @ichthyoid if i run a batch of water without the RO and just through my filter, carbon, and DI and it comes out 0TDS...then it should be good to go?

Yes Zap, it should.

Just run it slowly, if possible. Give the GAC & DI resin a chance to work.

TDS is a poor way to evaluate water quality, because it doesn’t tell you what’s in it. Just how much of ‘something’ there is.

 

[ZapataInc]

So what pressure do you run through it?

Yes Zap, it should.

Just run it slowly, if possible. Give the GAC & DI resin a chance to work.

TDS is a poor way to evaluate water quality, because it doesn’t tell you what’s in it. Just how much of ‘something’ there is.

 

[db366]

Just curious, what would happen if you ran your waste water back through the unit with a pump? Would it all run back out or would you get say another 50% out of it?

 

[ichthyoid]

Just curious, what would happen if you ran your waste water back through the unit with a pump? Would it all run back out or would you get say another 50% out of it?

You would get a little less than whatever percent you got the first pass.

 

[ichthyoid]

So what pressure do you run through it?

It's not so much about pressure, but about how long the water takes to pass through the filter media.
The longer it takes, the more effective the deionization, but only up to a point of course.
If you are plumbed with 1/4 inch tubing you may not have much to worry about.

 

[RedRad]

Most freshwater sources here in N Georgia are pretty ‘soft’ (ie- low dissolved mineral content). About 40-70 ppm.

It is for this reason that I do not run an RO membrane for my water system. I only use particle, carbon & 2x DI resin stages for filtration.

When everyone jumped on the RO bandwagon years ago, I was working in R&D. We had huge Millipore RO/DI systems that produced a LOT of 20+ meg ohm pure water, but didn’t need to get serviced very often. So, I began to think about usage, investigated the facts & decided on what I’ve got.

Below is a link to a water hardness map -

Water Hardness Map of the United States – H2O Distributors

Water Hardness Map of the United States, Water Hardness Table of Classifications and links to more information about water softening and effects.

www.h2odistributors.com

That is interesting. Not running membranes would completely eliminate wastewater which would be huge. I noticed that my TDS reads zero before it enters the first DI stage. So I know my DI filters are doing pretty much nothing. But I never though of measuring the TDS right before the membranes. It might already be super low coming out of the carbons. Pretty awesome idea.