RO/DI effeciency

[joelespinoza]

If your worry is about waste water, why not sell your unit and get a kati ani unit? They are a bit more spendy, but from my understanding they have 0 waste water, so will probably be cheaper in the long run. The filter guys sell them.

[DamonG]

Not a bad suggestion at all. But I could be wrong, but wasn't there something with the recharge or replenishment cost when they exhausted? That was years ago, but there was something about them that kept them from selling heavily? I really cannot remember?

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[thor109]

Sediment and carbon filters have nothing to do with the final output tds. Both simply keep the membrane from being damaged by sediment (clogged) and chlorine (damaged). With very HIGH TDS input water and even 98% rejection, one may need to change DI several times before a sed or carbon replacement is needed.
Color changing resin is misleading and somewhat useless. What is important is to monitor the output TDS. Monitor the output of the RO membrane so that you can tell when the membrane needs replaced.


I agree.
My understanding is its simply a cost thing. Your prefilters are cheap and easy to replace, therefore they do the bulk of the work. Next is membrane, its gets your water near perfect but it is expensive. One thing on tfe membranes is chlorine will destroy them. That is the main purpose of carbon. That is why two carbon filters are used and should be changed every six months. Again chlorine will destroy your tfe membrane. Last and most costly is di, the most expensive and the last step.
As much as good water is needed in a tank its not really a determining factor but more a solid foundation on which to build on.

[Buckeye Hydro]

Originally Posted by thor109

I agree.
One thing on tfe membranes is chlorine will destroy them. That is the main purpose of carbon. That is why two carbon filters are used...

I understand the line of thinking here (if one carbon block is good, two must be better), but two carbon blocks are really not necessary. If this were years ago and you were using GAC in your carbon stages, 2 would be a good idea. However, if you're using a good quality carbon block - only one is needed.

We recommend two carbon stages for people with chloramines in their tap water, but not for tapwater with chlorine.

Russ

[thor109]

You are one of the few that only uses one. I understand what you are saying. I think with the cost of membranes its more of an insurance policy. I change my filters in Jan and July. Many people forget to do these things. I have about 400 gallons of water I maintain.

[Buckeye Hydro]

Yep - us and Spectrapure.

What we tell people is to start with a 4 stage RODI consisting of
sediment->carbon->membrane->DI

Then add additional stages only if needed for specific purposes. For instance, you might want to add a sediment filter if you have heavy sediment loads. You might want to add a carbon stage if you have chloramines. You might want to add a DI stage if you have very high TDS feedwater, or CO2 issues, or chloramines.

If a customer doesn't pay attention and leaves a carbon block in too long, then yes - additional carbon stages may be warranted. Same line of thinking goes for DI stages. But in this case nothing says only two carbons or DI's will be enough! The trick is to use a single carbon stage with a chlorine capacity well higher than you'll use in six months, and change your prefilters every 6 months. The carbon block in our Premium Series systems for instance has a 20,000 gallon chlorine capacity.

On this schedule, its good practice to sanitize the system every other filter change.

Using two carbon stages as a default is typically either a holdover from the days when the carbon prefilters were GAC, or a measure to make a system appear more robust when low quality carbon blocks are used (you can see these on ebay), or a vendor's attempt to address some buyer's feeling that "a system with more stages is better." The worst case of this is systems we often see on ebay with a GAC Taste and Odor Filter (that contains GAC) AFTER the DI. What a hoot.

Russ

[thor109]

Makes since to customize based on actual needs rather than to produce a "cookie cutter" system for everyone.
I guess I use about 300 gallons of ro a month. Total water through my filters is a little less than 10,000 every 6 months, plenty of room for error.

[Buckeye Hydro]

IF you use a good carbon block. There are standard-sized (10" x 2.5" nominal) carbon blocks out there with 1,000 gallon capacity - so we always encourage people to "read the labels" on carbon blocks. If a vendor doesn't provide the spec's on their carbon blocks (pore size, chlorine capacity) - there's probably a reason for that. Buyer beware!

Russ

[joelespinoza]

Originally Posted by DamonG

Not a bad suggestion at all. But I could be wrong, but wasn't there something with the recharge or replenishment cost when they exhausted? That was years ago, but there was something about them that kept them from selling heavily? I really cannot remember?

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Its hard to say, I think most people are afraid of them because they are a high initial investment, and they are not incredibly common.

Here is the filter guys article about them: http://www.thefilterguys.biz/kati_ani_di-onizer.htm

They need hydrochloric acid (31%) and lye to recharge them, both are somewhat hazardous if you are not careful, but both are very common, and from my understanding they dont have to be recharged THAT often, I have heard every 6 months, but I assume it would vary wildly based on useage and incomming water quality.

[Buckeye Hydro]

If someone want's to go down that road, realize that all those units are are a container of cation resin, and another container of anion resin (rather than a mixed bed resin like you all are used to). You don't need the huge clear acrylic containers that the KAti-Ani units come with...

Russ

[Buckeye Hydro]

double post

[BeanAnimal]

Originally Posted by DamonG

Actually, they do, as the whole premise is to send the pre-filtered water to the membranes so that the membranes don't take a beating, thus speeding the demise of your membranes

The function and need of pre-filtration is not what was being disagreed with. My point of contention was your statement that the carbon block and prefilters needed to be changed with every DI change, and that is simply not true or even close to being a "rule of thumb".

As for the "RO/DI lesson", thanks but I am already well versed in the physics and chemistry that govern the function of an RO/DI unit


Kati-Ani:

Recharge costs can vary depending on many factors but in the end, most folks just don't want to deal with the mess and with high TDS source water, recharges will be frequent. Pre-filtering is still important and output PH can be a problem depending on the choice and ratio of resins chosen.