We use DI tanks to polish our water after RO. We are looking into getting rid of the DI tanks because of the cost. I have done aami water test of the product water everything came back ok. Is there anything else we should be looking at? We are thinking about going with 2 RO one for backup. I was wondering if more dialysis center run with out DI or more with DI?

Tom,

The only thing we use DI for is our home patients. I know some units do polish with it but with todays membranes, most people feel that polishing is overkill.

RO machines are very simple and reliable. I wouldn't go through the trouble, routine maintenance or expense of having a second RO just for back-up. Instead, why not just arrange with your vendor to have DI brought in if needed.

We Are currently using our DI's as polishers and back-ups In case the RO goes down. We also have considered the cost associated with running DI's as polishers, but it does save your hide in an emergency. Also, you have to consider the reaction time of your vendor. If your R.O. breaks down will your unit be completely without water for a few hours or days?

We use DI's as back up's and for off site satellite's. We wanted a backup RO, but due to monetary constraints, we went with DI instead. This way if the RO fails, we switch to DI, while we do the repairs.
We're a 50 station unit running 24/7, so we can't afford to have any down-time, while waiting for the vendor to deliver tanks.

If you are in a relatively rural area you may have some delay in response time to get DI , but any reasonably sized market you can usually get DI within a couple of hours (I have made agreements with vendors guaranteeing delivery with set up within 2-4 hours). I agree with chuck, DI is overkill and can present problems as well, as far as a second RO if you do go that route make sure it is run regularly and properly cleaned and disinfected. The truth is a properly maintained RO will give you little or no problems and if they go down they are relatively easy to troubleshoot and repair.

We felt that even 2-4 hours was too long for our unit to be down. If your RO goes down in the middle of the first shift, you have 50+ patients who have to quit their treatments early, plus all following shifts get their schedules altered. We'd rather have the hassle of DI's and the security of not having to worry. We designed the system so 6 times a day, it automatically diverts to the DI tanks, and then back to the RO after 30 minutes. Plus we heat clean the RO and loop every night, to remove possiblity of bact growth in less moving sections of the loop.
We found that the DI's were worth it, even though we need them maybe once eevery two years or so

Tom,

In most cases if you RO machine is operating above a 90% rejection rate, your permeate water quality will be within the AAMI recommendations, but it does depend on the quality of your feed water. Most facilities that are polishing with DI�s are not doing it because they have to do so to meet the AAMI recommendations. Some are doing so because they feel that it�s cheap insurance should they have a premature membrane failure or a drastic unexpected increase in the quality of the feed water.

If you do take the DI tanks off line it will be very important for you to closely monitor your feed water quality. Remember that just because your RO membranes are running a high rejection rate does not mean that the permeate water quality is within the AAMI guidelines. Many municipalities will change their water source or their method of treatment form time to time. To that end, you can find that the feed water conductivity or TDS can double or sometimes triple from one day to the next, or the feed water pH can increase well above 9. Even if the change in the feed water does not interfere with the RO membranes rejection capabilities, the permeate quality can sometimes double or triple and your RO machine will still register a high percent rejection.

Some facilities, by the request of the medical director or because of their water treatment vendor�s response time will keep DI�s in the facility and will polish with them to help keep them fresh. In some cases they�re not used as polishers but are on standby, flushed routinely and changed every 2-3 months. If this is the case, they should be cultured at least monthly.

In your situation as well as most, seeing that the concern of keeping DI tanks in the facility is cost and bacteria control, you may want to look at setting up a split stream system. With a split stream system you can divert a portion of the RO water through the DI tanks. With doing so you will maintain a constant flow of water through the DI�s which will help to keep them fresh and at the same time greatly reducing the frequency of the DI resin exhaustion. If done correctly and depending on the permeate water quality, a 3.6 cubic feet, mixed bed tank can last over 90 days.

No matter what you do, please remember that DI�s can be your best friend in your time of need, but your worst enemy if not properly monitored and maintained.