Can you use the waste water from ro/di to feed the ro/di

[shamoo]

Hi al :wavehand:

My current ro/di set is pretty good, i'm getting 0ppm (tds) pressure (pumped) at about 100psi and 2:1 gallons of waste. i have stored the waste water and my question is, could i use that water to feed back into the ro/di unit to limit the amount of waste?
in the instuctions of the unit it said not to do this, but did not explain why, has anyone else tried/done this or know why we shouldn't?

thanks

 

[Member No. 1]

You can run a second RO cartridge in series to produce about twice the water.
BRS sells a kit.
Watch these videos on this page:
https://www.bulkreefsupply.com/brs-150-gpd-water-saver-upgrade-kit.html

And this:
https://www.bulkreefsupply.com/video/view/week-7-how-to-produce-the-best-water-possible/

 

[ReefkeeperZ]

the reason for not re filtering the waste water is it already has ghigher concentrations of the things you are using your RO to remove, so you will simply be working harder for less gains and need more maintinence on the membrane and exhaust the membrane faster, the cleaner (lower total PPM) your source water has the longer your filter will last.

 

[jamie1981]

If you have low TDS water to start you could. For example if you have 100 TDS tap water you could run the same water through 3 times and still use less filter life up than someone who has 400 TDS out of the tap. It's really up to you to determine how long you want to go before requiring a filter change. Cost wise I'm not so sure you will save anything.

 

[shamoo]

thanks everyone, my tap water is about 400 ppm, i will test the waste water and compare it.

 

[bertoni]

I suspect that it's not worth the effort, given the higher level of DI media consumption involved, but if you have a pressurization pump, you could give it a shot.

 

[ReefkeeperZ]

I suspect that it's not worth the effort, given the higher level of DI media consumption involved, but if you have a pressurization pump, you could give it a shot.

I'm not sure extra DI consumption would be an issue (something to look into) since Ions pass through the RO membrane there should not be higher (or significantly higher) concentrations of Ions in the waste water than the source water because they arent getting rejected by the RO membrane. and only water that passes the RO membrane goes to the Di filter so it's only getting De-ionized once even if it was say a third pass. unless they are tagging along with other elements rejected by the Ro membrane. now you have my curiosity up.

 

[Dan_P]

Interesting question. It almost sounds like a "œsomething for nothing idea" but I think the cost of doing this is increased pressure with increased TDS or salinity. A desalination unit runs at a higher pressure than a freshwater low TDS system.

If you are mechanically inclined, maybe you could recycle your water until the rejection water is like seawater. The possible catch is that as you concentrate the ions, precipitation might occur, fouling your equipment if you don't filter out the salts. Calcium and irons salts come to mind.

Back to your idea, I would just do an experiment with the equipment you have. Measure the rejection rate and the TDS of the purified water for every recycle. So, you would run 50 or 100 gallons of new water, take your measurements and run the rejected water through the RO system again. Repeat until you get bored of recycling or the rejection rate is unacceptable, or your prefilter is clogged. I would guess that at some point you will not have enough pressure to remove the water from the high TDS recycled water. Maybe that is 1 or 10 recycles.

Sounds like fun. Let us know how the experiment turns out.

 

[bobt2]

I use the waste water in the garden, or to feed my hard freshwater tank

 

[cpballer]

I use my waste water for water changes for my breeding pair of julidichromis trascriptus.

 

[bertoni]

RO membranes are imperfect, and they will pass a proportion of the input contaminants through them. I'd expect the TDS to rise something like 50% if the input is 50% higher in TDS. That might vary somewhat based on what's actually in the water, though. Very large particle or larger compounds might be filtered more effectively than something like carbon dioxide, for example.

 

[Member No. 1]

I'm running my RO/DO with two 75gal/day membranes in series. These are feed with a 8800 booster pump, pressure is running at 90 psi.
My input water, which is well water, the TDS is ~145
I have a (3) probe TDS meter installed.
I have (1) installed on the effluent output on each RO
Primary RO TDS is 4
Secondary RO TDS is 5
The effluent fills a 55 gallon container which I run a air stone to degas the excess Co2 before I pump it thru my 3 stage DI
Flow thru is : Cation---->Anion---->Mixed Bed
If I don't degas the high levels of Co2 from my well water before sending the RO effluent thru the DI resin, it will deplete the Cation resin very quickly.

Watch the video in the link I posted earlier in this thread.
I am using the same principle.
https://www.bulkreefsupply.com/video/view/week-7-how-to-produce-the-best-water-possible/

 

[bertoni]

Carbon dioxide is a significant problem in RO systems because it's small enough to get through RO membranes fairly well. That's the opposite end of the spectrum from something like larger insecticide compounds and the like.

 

[shamoo]

Just a quick update, the TDS from my water source is around 380-400 ppm the waster from my ro/di machine is around 700ppm. I'll use that for storage for the garden rather than putting extra strain on the filters

 

[bertoni]

That sounds like a good plan to me.

 

[GTR]

I'd always used the waste water in the garden. Once we installed a water softener I ran it directly to the drain since salt content is to high for most plants. Sort of a catch 22 I guess. Soft water is much easier on the membrane in the long run without the calcium and magnesium.