RODI Waste

[ph33nyx]

I was looking at my RODI filter the other day and was wondering if the waste water was clean enough to use for my freshwater tank.
Any thoughts? It has to be cleaner than what comes out of the faucet.

 

[bjohanson1234]

It has to be cleaner than what comes out of the faucet.

Actually, it is probably dirtier from a TDS aspect. Let us do some math!!!!:^:

Say you have 100ppm TDS water from the faucet and 0 TDS water coming out of the unit. Let us also say that for every gallon of RO water you make creates 5 gallons of waste water. Now since the RO water is at 0ppm, the 100ppm of the water will get spread over to the 5 gallons of waste water. The output in this situation should be about 120ppm.

However, since the water goes through your sediment filter, there won't be as much sediment in it.

 

[ph33nyx]

So the fact that the waste goes through 3 of the 4 filters has nothing to do with it?

 

[bjohanson1234]

Those first filters are mainly sediment filters. They don't really remove many dissolved solids. Then the RO membrane actually will concentrate them in the waste water.

 

[ph33nyx]

Guess it's time to get a TDS meter

 

[Buckeye Field Supply]

Your waste water will have a TDS about 20% higher than your feedwater, but it will have had the sediment removed and the chlorine removed.

Russ

 

[poksal]

OK.. now ..someone explain how to read what value at the TDS meter. }}}-----> Please

 

[Buckeye Field Supply]

?? I don't understand your question...

 

[poksal]

?? I don't understand your question...

So you.. install a TDS meter to both sides of your RODI.. what is it supposed to read.. or what value do you look for.. ?? ("splain it Ricky")

 

[Ted]

you can tell what your base water tds going in is compare to your water coming out. tells you kinda how hard the unit is working. Some people test before di stage and after. To me I would think that after reading the base water going in once would be good enough. The important one is the water coming out of the di. In my thinking...

 

[Buckeye Field Supply]

Ideally you check/monitor the TDS in three locations:
1. feedwater
2. RO water
3. DI water


You use Nos. 1 & 2 to calculate your rejection rate. Compare that to the factory spec rejection rate for your membrane so you know how well your membrane is working.

So for instance, let's say you have a 75 gpd Filmtec membrane, your feedwater TDS is 467, and your RO water TDS is 14. Your rejection rate is about 97%. Factory spec on the membrane is 96 to 98%, so your membrane is working ok.

You measured your DI TDS and found it to be 1 ppm last week, and this week it is 3 ppm. Anything higher than 1 ppm tells you its time to change the DI resin.

Russ

 

[poksal]

you can tell what your base water tds going in is compare to your water coming out. tells you kinda how hard the unit is working. Some people test before di stage and after. To me I would think that after reading the base water going in once would be good enough. The important one is the water coming out of the di. In my thinking...

OK, I get that it reads different before and after the filter device it is bridging (I don't have one and that may be why I don't get it, but I had one before). But no one seems to be able to give an answer that sounds "scientific" enough. So, IMO, I'm not understanding.

The instrument measures conductivity of water (or a liquid). Pure water does not conduct electricity. So the reading "reads" impurities... which do cause water to conduct electricity accordingly to how they ionize in water… so in truth it is a specialized ohm meter. But… shaking my head… “WE” use it to tell us when to change filters. ..... ok.. but when...?

I’m getting the feeling that “we” look at the meter and say to ourselves, “oh, look the reading is different going in than going out. Wow, now I have tangent proof that my filter is doing something”. Then when the difference is less (some un-tangent amount) we say, “oh, I need to change my xxxx filter material”.

Does someone have some numbers to expect to read on the meter?? Or something more tangable? Then I will buy this new toy…because then I can see a clear benefit.

Trust me, my extremely logical mind will be a pain at times but we as a group absolutely will gain from it often together. So.. wink... work with me.

Thanx for listening
-confused-

 

[poksal]

Ideally you check/monitor the TDS in three locations:
1. feedwater
2. RO water
3. DI water


You use Nos. 1 & 2 to calculate your rejection rate. Compare that to the factory spec rejection rate for your membrane so you know how well your membrane is working.

So for instance, let's say you have a 75 gpd Filmtec membrane, your feedwater TDS is 467, and your RO water TDS is 14. Your rejection rate is about 97%. Factory spec on the membrane is 96 to 98%, so your membrane is working ok.

You measured your DI TDS and found it to be 1 ppm last week, and this week it is 3 ppm. Anything higher than 1 ppm tells you its time to change the DI resin.

Russ

>>>>>.. YES..<<<
that is what I needed...

So Russ, do you like to run two meters to sample before & after both the membrane and the DI? Could be nice to test the sediment too... what is the usual accepted method?

THANK YOU, Russ!

-much less confused, randy-

 

[poksal]

Russ?

So, to feed my change water tank. Would you rather "Y" your output from your RODI or split off after the sediment filters and add a second set of RODI? I haven't done that yet and was interested in your opinion and ideas.

 

[Civicdemon]

My waste water usually reads the same tds as the water going in the unit. My good water reads 4 tds