Refiltering RO/DI Waste Water ??

[j2quinn]

Hi i was wondering if i can do the following: I want to use for instance two HDPE or alike 30 G+ containers. Use one 100GPD modified aquasafe unit and a booster pump. Basically one container contains tap water and a booster pump will pump water from the tap water container to the RO/DI aquasafe unit. The waste water is put back into the tap water container and the purified RO/DI water is placed into the other HDPE container. All that is required is that i top off the tap water container once in a while. Would this theoretical approach to a self containing RO/DI system work? Any suggests would be welcomed. And yes i did try search but failed to find the answer i was looking for.

[ajx22]

No - as you have a 4 to 1 ratio of brine to product + you can't recycle the brine (waste water) - as it will be ~4x the tap water TDS.

ie = if you have 200ppm TDS @ your tap - you will have >500ppm TDS in the waste line - plus, it contains all the things that you DON'T want - and trying to force the brine back through the filter will destroy the filters in days.

[j2quinn]

No - as you have a 4 to 1 ratio of brine to product + you can't recycle the brine (waste water) - as it will be ~4x the tap water TDS.

ie = if you have 200ppm TDS @ your tap - you will have >500ppm TDS in the waste line - plus, it contains all the things that you DON'T want - and trying to force the brine back through the filter will destroy the filters in days.

Ok good point. Something i should have realized. Ok thanks man.

[msobon]

No - as you have a 4 to 1 ratio of brine to product + you can't recycle the brine (waste water) - as it will be ~4x the tap water TDS.

ie = if you have 200ppm TDS @ your tap - you will have >500ppm TDS in the waste line - plus, it contains all the things that you DON'T want - and trying to force the brine back through the filter will destroy the filters in days.

I don't get it.

You have the tap water go through the filters, then t's passed onto the RO memberane, the waste water is water that has not been put to the RO membrane because of the pressure valve, this water will have same tds it came with.. or less as it went through the first line of filters before the RO.
I don't see where you will get the 500 tds... unless you decide to flush the RO mebrane or something.
The water recycled would probably be more cleaner on the RO membrane since the pass through the first set of filters might bring it down from 200ppm ->180ppm->160ppm.. etc as it loops through until it hits the RO membrane where it goes close to 0 ppm and then DI filter which makes it to 0ppm.

Is there something I'm missing? If anything you would be saving the filters?

[ajx22]

I don't get it.

You have the tap water go through the filters, then t's passed onto the RO memberane, the waste water is water that has not been put to the RO membrane because of the pressure valve, this water will have same tds it came with.. or less as it went through the first line of filters before the RO.
I don't see where you will get the 500 tds... unless you decide to flush the RO mebrane or something.
The water recycled would probably be more cleaner on the RO membrane since the pass through the first set of filters might bring it down from 200ppm ->180ppm->160ppm.. etc as it loops through until it hits the RO membrane where it goes close to 0 ppm and then DI filter which makes it to 0ppm.

Is there something I'm missing? If anything you would be saving the filters?


Unfortunately - that's not the way that RO units work.

Read the links RO/DI <-- it explains the whole process of the TFC membrane.

There are 2-bodies of water traveling through the TFC membrane at the same time.

If you have (just a number) 200ppm TDS going into the TFC (post prefilters that have already removed the sediment and VOC's )- the unit produces product (permeate) water at a ratio of 4 Gallons of brine (waste) to 1 Gallon product (permeate/good). The TFC membrane and the DI resin are the only ones to really remove any TDS...the prefilter and the carbon stage don't address TDS - but sediment which isn't a dissolved solid; and VOC 's - also not a Dissolved solid). If the output of the TFC is (just for ease) now down to 10 ppm TDS - there was 190 ppm TDS stripped out - and flushed out the waste line with the 2nd body of water that isn't forced through the TFC membrane. This is the whole reason for the 4 to 1 ratio - as the waste water is constantly flushing out the removed TDS - thus is a brine - being a mixture of the 200 ppm TDS from the tap + the 190 ppm TDS that you removed...totaling ~390 ppm TDS out of the waste line. The 10ppm TDS would be charged minerals and the like, that the TFC can't remove - that the DI stage does. Each stage targets a specific thing (listed in the RO/DI link).

So now - if you try to reuse this water - you are feeding the TFC membrane with nearly DOUBLE the TDS as the tap water has/had - and it's all the worst stuff that has already been rejected by the TFC membrane.

Flushing of the TFC Membrane only removes built up deposits like calcium, etc. from the membrane, to help ensure that the holes in the semi-permeable membrane are all open to allow water to pass through (get filtered).

Hope this makes more sense now that you have a little more understanding of the way RO/DI units work.

:cheers2:

[Sydney]

Out of curiosity what are you trying to gain with this set up?

[SaltNurEye]

For the cost of fresh water in Canada, I dont see why you would want to do this? Sounds like a great idea to cut back on water and waste but this hobby is money and water hungry. The costs of membranes and filters are going to be much greater than extra water off your main line.

[SaltNurEye]

If the idea is to cutback on waste water, I know many people use tee's that run into their washing machines. You can also use the waste water for house plants and the garden. Hope that helps

[bigtyguyy]

Hi i was wondering if i can do the following: I want to use for instance two HDPE or alike 30 G+ containers. Use one 100GPD modified aquasafe unit and a booster pump. Basically one container contains tap water and a booster pump will pump water from the tap water container to the RO/DI aquasafe unit. The waste water is put back into the tap water container and the purified RO/DI water is placed into the other HDPE container. All that is required is that i top off the tap water container once in a while. Would this theoretical approach to a self containing RO/DI system work? Any suggests would be welcomed. And yes i did try search but failed to find the answer i was looking for.


I can get you some containers if you want! cheap.. A few guys here picked up some really nice ones..


No - as you have a 4 to 1 ratio of brine to product + you can't recycle the brine (waste water) - as it will be ~4x the tap water TDS.

ie = if you have 200ppm TDS @ your tap - you will have >500ppm TDS in the waste line - plus, it contains all the things that you DON'T want - and trying to force the brine back through the filter will destroy the filters in days.


and AJ is right i tested my waste and it was 377 and the water going into the purely H2O unit is 260.. soo its tough watching it wash away but its the way it goes!:cheers2:

[saltsa]

Does the aquipure system not use this principle, no waste line out...???:giggle:

---------- Post added March 9th, 2012 at 12:51 PM ----------

Also, good explanation AJ, makes sense, I run 2 x prefilters, and 2 x charcoal, before 1 TFC..