DI Units pros...cons...etc

[DiscusOnly]

that is a lot of waste. can the waste be circulate back and go through the RO process again? have to rethink this.

Yes you can to get a better ratio. I run two 100gpd filmtec membrane on mine but remember that when you start slowing down the flow through the membrane, you may get premature wear on it (membrane is the most expensive part in an RO system).

Van

[Buckeye Field Supply]

What folks in this hobby call "waste water," might be better thought of as "flush water" in that it flushes away from the membrane all the things the membrane doesn't allow to pass through. The 4:1 ratio comes from the recommendations of the membrane manufacturers.

You can change that ratio with a little $4 flow restrictor, but as mentioned above you risk prematurely building up scale in the membrane. If you have very low TDS feedwater (we talked to a customer today with feedwater at 35 ppm), or softened feedwater, you'll be more successful with a ratio lower than 4 to 1.

Russ

[pennex1]

Russ, i have another question regarding the "flush water". Is the flush water purer than the straight tap water?

[Buckeye Field Supply]

The waste water has been through a sediment filter and a carbon block, but the TDS of the waste water will be about 20% higher than the tap water.

Russ

[DiscusOnly]

The waste water is perfectly fine to use if you don't mind the hight TDS (some uses it to raise discus). Remember that since it's been through the carbon block, chlorine is removed so no need to use water conditioner (if chlorine is what's in your tap).

[pennex1]

The waste water has been through a sediment filter and a carbon block, but the TDS of the waste water will be about 20% higher than the tap water.

Russ

Not sure if i understand this correctly. I should of been more specific. What i meant to ask is, the waste water from the RO/DI unit should be cleaner than what comes out of my tap before going into the RO/DI unit, is this correct? or is it going to have higher tds than then the pre RO/DI water, if so, why?

thanks

[DiscusOnly]

Not sure if i understand this correctly. I should of been more specific. What i meant to ask is, the waste water from the RO/DI unit should be cleaner than what comes out of my tap before going into the RO/DI unit, is this correct? or is it going to have higher tds than then the pre RO/DI water, if so, why?

thanks

In a 4:1 RO unit (for example: 4 gallons of waste for 1 gallon of RO water). What's left (the 4 gallons of waste water) is going to end up with a higher TDS because there is less water but the same amount of TDS. The 20% increase is from the TDS that was originally with the 1 gallon of now RO water. That's just a rough number, actual number is probably a little less on a new membrane.

Van

[Buckeye Field Supply]

Van's got it right...

Pennex - "cleaner" in what way? The waste water will have less sediment than the tap water, and it will have had the VOC's including chlorine removed by the carbon block, BUT it will have higher TDS than the tap water. Not sure if you want to call that "cleaner" or not.

Russ

[Sean Buehrle]

Not sure if i understand this correctly. I should of been more specific. What i meant to ask is, the waste water from the RO/DI unit should be cleaner than what comes out of my tap before going into the RO/DI unit, is this correct? or is it going to have higher tds than then the pre RO/DI water, if so, why?

thanks

The only way your waste water is going to be cleaner is because it went through a sediment filter and carbon blocks.
Sediments will be lowered or gone and chlorine removed.
TDS in waste water is going to be higher because the dissolved solids that were rejected by the ro membrane are being washed out with the waste water.

[TURQ64]

I use my RO reject water (the phrase originally used by RO manufacturors) waste to the newer crowd, to balance my mineral content to whatever spec I'm looking for. Although I have additives for mineral replacement, I seldom use them due to the predictablity of the reject water..I've used it for many years with nothing but great results..Gary