Question for all you dialysis water experts. A local vendor wants to place 3 in-series mixed bed DI tanks post RO in our small hospital unit(currently there is two). There is a audible/visual quality alarms before and after the last tank. The vendors want to place a audible/visual alarm after the second tank. Their rationale for three tanks is that the tanks won't exhaust as quickly, requiring less frequent deliveries.

My thoughts on this is, I don't really like three tanks in series, and I think there should be al least a quality light between the first and second tank. The first tank will exhaust first regardless, then this first exhausted tank will release all the captured ions quickly making the water worse than if was not in place in the first place. Am I off base here? The vendors don't agree.
Thanks Beancounter

beancounter,

If they are planning to use 3 mixed beds then you are 100% correct and you should find a new vendor that knows what they are doing. The third tank will serve no purpose at all other than to be a bacterial breeding ground.

In instances where DI is the only treatment being used (not polishing post RO), 3 tanks are frequently used (in addition to carbon) but one is a cation, the next an anion then followed by a mixed bed. The systems such as this that I have used have had two monitors, one before the mixed bed and the other after.

[This message has been edited by Chuck W (edited 10-21-2002).]

Theoretically, the vendor is correct .... the first tank would exhaust COMPLETELY and the second tank would exhaust nearly completely before activating the lamp indicator. HOWEVER; Chuck is also correct. The additional tank provides additional breeding ground for bacteria. The trend nationally is to get DI tanks out all together. If your RO system is functioning properly, the use of DI is redundant anyway, and a system without DI polish is far less likely to grow bacteria. I have seen MANY units, particularly hospital units, going with two ROs (either alternating or running simultaneously) if they want the protection of having back up availability. In any case, if your RO is working & maintained properly, you don't need DI on site. Many centers are leaving tank access in line & having local vendor deliver emergency tanks only if the RO goes down.
I'd be happy to answer any other questions you may have. You may reach me directly @ 502-548-0594, or you may leave a message for me @ Isopure HQ, 800-280-PURE(7873).

Good Luck!