Pneumatic Down Flow Aeration / Oxygenation
In some cases, subsidizing dissolved oxygen availability is most reliable using either pure oxygen or compressed air containing a greater fraction of oxygen than atmospheric air (21% oxygen). Pure oxygen has been used in some parts of the US to maintain dissolved oxygen downstream of a reservoir dam release (to maintain fishery habitat) and where oxygen demand is extreme. Early systems used mechanical/electrical pumps underwater, which required underwater pump maintenance and resulted in significant down time. Ecosystem Consulting Service modified the geometry of several of its aerators to create a pneumatically-driven downflow contact reactor.
Designed for use with compressed air, pure oxygen, or 'enriched air', this approach makes bubbles slowly move downward with no electrical or mechanical parts underwater! As a result, the contact time between fluid and gas is very long, making the technology much more efficient than other oxygenation approaches (and there are no underwater electrical or mechanical parts to require expensive repairs).
Integrated approaches which use compressed air to drive the air-lift pumping of water, and which use an oxygen source to subsidize dissolved oxygen input can be most effective in water bodies that exhibit a very high oxygen demand. Such systems can be 'Side-Stream Oxygenation' tapped into in-lake aerators (oxygenation equipment is readily accessed on land for maintenance), or oxygen feed systems to increase the oxygen content of 'air gas' sent to aerators. Air contains 21% oxygen. If the compressed air, or side-stream feed, doubles the oxygen delivery then the scale of in-lake equipment is reduced to half. Two aerators can accomplish the oxygen input of four! The oxygen source can be Liquid Oxygen, or an on-site oxygen generator that concentrates oxygen from air.