Anyone tell me what the ebct on portable machines is?

Same as a main unit water treatment system. 6 minutes for chlorine and 10 minutes for chloramine.

The preference is 2 carbon tanks and a 10 minute EBCT. Acute patients deserve as much protection as a chronic patient. And, in many cases, acute patients are less capable of coping with a premature chlorine break. But, currently AAMI RD62 says "Carbon adsorption systems used to prepare water for home dialysis or for portable dialysis systems are exempt from the requirement for the second carbon and a 10-minute EBCT, provided that removal of chloramines to below 0.1 mg/L is verified before each treatment." I say current because RD62 is under revision and the new version should be released soon. The revised RD62 says "Carbon adsorption systems used to prepare water for portable dialysis systems are exempt from the requirement for the second carbon and a 10-minute EBCT, provided that removal of chloramines to below 0.1 mg/L is verified before each treatment." Home dialysis was removed from the exemption. The AAMI guidelines do not mention the 6 minute EBCT anymore.

But....AAMI is currently writing an Appendix to RD52 entitled "Water Treatment Requirements for Acute Hemodialysis". This DRAFT document currently says "Initially, the requirement for two carbon adsorption beds in series and a 10-minute Empty Bed Contact Time (EBCT) was waived for portable dialysis systems because of the impracticality of providing these features while retaining the portability of the system. However, after studying the issue, the committee felt that because of lower flows and available technology, attaining a 10-minute EBCT was easily accomplished. For example, many portable RO manufacturers employ two adsorption beds with a 0.25 or 0.50 cu/ft granular activated carbon (GAC) tank inline on the outside of the RO unit and a 10” dense carbon block inside the RO as a polisher. This configuration easily meets the 10-minute EBCT as long as only one dialysis machine is attached to the portable water treatment system."

Florian, could you please show the calculation for obtaining an EBCT of 10 minutes with two tanks of 0.25 cu. ft. carbon? Our Millenium RO's have an average flow of a little over 1 GPM. The per cent recovery is not adjustable. Thanks.

EBCT = cuft of carbon x 7.48/total flow through the carbon in gpm. Therefore, 2 x 0.25 x 7.48/1 gpm = 3.74 minutes.

If you want an EBCT of 10 minutes, you will need more carbon. cuft of carbon = EBCT x total flow through the carbon/7.48

10 minutes x 1 gpm/7.48 = 1.34 cuft carbon

Florian,
Thanks for the heads up on the new acute standards. On the portable ro, do you think the 10min ebct will become the standard?

Also, on the ebct equation, do you need to add in the reject flow of at least another 1gpm, because it's also passing thru the carbon?

Thanks for your help.

In the near future, I would see the 10 minute EBCT for portable ROs being more of a recommended practice. If you are setting up a new system, it would be a good time to design a 10 minute EBCT into the system. But, you also need to make it portable. If you are currently using two 0.25 cuft carbon tanks, it shouldn't be much of a physical change to upgrade to 0.5 cuft and it wouldn't add much weight. The upcoming revision to RD62 still says that portale dialysis is exempt from needing 2 carbon tanks and a 10 minute EBCT. But, as mentioned before, an appendix to RD52 is being writting to encourage 2 carbon tanks and a 10 minute EBCT. In any case, you must maintain the chlorine below 0.1 ppm. If you don't have 2 carbon tanks and a 10 minute EBCT, you might want to check the chlorine more often.

As for the reject flow, you must use the TOTAL flow that is going through the carbon, which includes the reject flow. Typically, for an indirect feed system in a clinic, the amount of flow through the carbon is equal to the RO Product flow + the RO reject flow. For a direct feed system, this is not the case since some of the RO Product Flow comes back to the inlet of the RO (doesn't go through the carbon again). The same may be true for some portable ROs. Some portable ROs dump any excess RO product flow to the drain, therefore the total flow through the carbon is the RO product flow + the RO reject flow. But, some portable ROs return any excess RO product flow back to the inlet of the RO. Returning it back to the inlet of the RO causes less flow through the carbon and therefore requires less carbon to get to a 10 minute EBCT. If you don't know how your RO is configured, you can put a flowmeter on the carbon to measure the flow.

Florian,
good point. i didn't think about the product recirc.
i just wanted to make sure they used total flow vs product only.

thanks again.