Ancient oxygen purifier
From The Stargate Omnipedia
One of three nodes aboard the Destiny responsible for absorbing carbon dioxide and releasing fresh air back into the ship. The device is flexible enough to accept several different materials to process oxygen.
One node can be found in the Destiny gate room behind a push-button grate.
KEY EPISODES
Air, Part 2 - After failing to reset life support, Dr. Rush orders Lt. Scott and Sgt. Greer to the gate room, where they discover an Ancient oxygen purifier overflowing with deadly amounts of alkaline.
Air, Part 3 - An expedition to a desert planet yields a supply of lime, which is brought back to the ship and fed into the air purifiers, restoring life support.