Reef Central Online Community - View Single Post

PurdueWaterGuy · 05/13/2010, 09:06 PM

Kind of ironic, isn't it? There's typically a lot of CO2 in well water. It goes right thru the RO membrane like it isn't even there, uses up the ion exchange resin, and then we bubble CO2 back into the water in the calcium reactor to raise the alkalinity.

You could try the Kold Steril system, which would leave the calcium and CO2 intact.

In big commercial systems sodium hydroxide is injected into the RO feed to raise the pH, which causes the CO2 to change into bicarbonate and carbonate ions which are well rejected by the RO membrane. Another alternative are membrane contactors, where the water flows over tiny hollow fibers, which typically have a vacuum on one end and nitrogen fed into the other. The CO2 diffuses thru the fiber and out of the water. As you might guess, neither of these techniques is cheap.

At work we use membrane contactors to degas the RO water before it gets to the electrodeionization stacks. It took five years to get the system "tuned up" but it looks like we will be using about 90 cubic feet less of ion exchange resin this year, which should save about $18,000.

If I wasn't so far behind I'd post a few pictures.

To get back to the original question, if you have a pressurization pump for the RO, you could let the water sit in an open container for a few days, let the CO2 equilibrate with the surrounding air, and then run it thru the RO. As a bonus, the Fe++ or soluble iron, will oxidize to insoluble Fe+++ and settle out in the bottom of the tank, keeping it out of the RO membrane.

Let me know if you give that a try and if so, how it works out.

05/13/2010, 09:06 PM	#3
PurdueWaterGuy Registered Member Join Date: May 2010 Location: Lafayette, IN Posts: 196	Kind of ironic, isn't it? There's typically a lot of CO2 in well water. It goes right thru the RO membrane like it isn't even there, uses up the ion exchange resin, and then we bubble CO2 back into the water in the calcium reactor to raise the alkalinity. You could try the Kold Steril system, which would leave the calcium and CO2 intact. In big commercial systems sodium hydroxide is injected into the RO feed to raise the pH, which causes the CO2 to change into bicarbonate and carbonate ions which are well rejected by the RO membrane. Another alternative are membrane contactors, where the water flows over tiny hollow fibers, which typically have a vacuum on one end and nitrogen fed into the other. The CO2 diffuses thru the fiber and out of the water. As you might guess, neither of these techniques is cheap. At work we use membrane contactors to degas the RO water before it gets to the electrodeionization stacks. It took five years to get the system "tuned up" but it looks like we will be using about 90 cubic feet less of ion exchange resin this year, which should save about $18,000. If I wasn't so far behind I'd post a few pictures. To get back to the original question, if you have a pressurization pump for the RO, you could let the water sit in an open container for a few days, let the CO2 equilibrate with the surrounding air, and then run it thru the RO. As a bonus, the Fe++ or soluble iron, will oxidize to insoluble Fe+++ and settle out in the bottom of the tank, keeping it out of the RO membrane. Let me know if you give that a try and if so, how it works out.