Living in an underwater habitat requires gas treatment; an input of oxygen and the disposal of carbon dioxide and pollutants. Industrial divers live in a pressure complex on a support vessel and all air treating is done outside the habitat on the vessel. It seems there are not too many references of air being treated inside an underwater habitat. If we are mistaken do not hesitate to comment this article accordingly.
The rough solutions would be:
- a constant flow of fresh air: air is pumped from the surface/shore into the habitat while redundant air bubbles out from the entrance pool. No filtering mechanism is necessary, but the flow of air has to be undisrupted. Since the fresh air travels through long pipes there should be preventive steps to avoid odours from the pipe material and moisture. The air inside the habitat should be exchanged all 60-90 minutes completely. Aquarius habitat uses compressors in the life support buoy pumping the air into the habitat.
- compressed air tanks: the air is stored in huge tanks to provide a constant flow of air. These tanks are generally located outside the habitat not to waste precious space, and due to difficulties and risks during refilling and handling, that might damage the integrity of the hull. The tanks can be filled via hoses from compressors on the surface or completely exchanged when empty. This system requires lots of tanks (the deeper the more) while its handling is difficult. On the other hand there is no carbon dioxide filtering necessary
- oxygen tanks: produced carbon dioxide is filtered out and replaced by oxygen stored in tanks. This system requires oxygen-clean equipment (since oxygen promotes rapid combustion, valves should be oil-free etc.) and atmosphere measuring/blending devices.
These solutions could be used for the first stages of the habitat. But after a while we should consider air treatment inside the habitat.
Here are some proposals for processing the atmosphere inside the habitat.
In standard dry scrubbers polluted air is led through a canister of absorbent like sodalime (see SodaSorb by Amron) which filters out the carbon dioxide and releases clean air. The absorbent has to be replaced frequently in huge amounts.
Aquanaut and adventurer Lloyd Godson used a biocoil for gas treatment in his BioSub project. In this system chlorella algae in a transparent tubeare supposed to convert carbon dioxide into oxygen. Though a very impressive idea the system failed to work satisfactory. See all details about the biocoil on our former article. Still the idea deserves to be followed-up. Maybe there is a way to make it function.
Amine Gas Treating
A typical amine gas treating process includes an absorber unit and a regenerator unit as well as accessory equipment. In the absorber, the downflowing amine solution absorbs H2S and CO2 from the upflowing sour gas to produce a sweetened gas stream (i.e., a gas free of hydrogen sulfide and carbon dioxide) as a product and an amine solution rich in the absorbed acid gases. The resultant “rich” amine is then routed into the regenerator (a stripper with a reboiler) to produce regenerated or “lean” amine that is recycled for reuse in the absorber. The stripped overhead gas from the regenerator is concentrated H2S and CO2. (Source: Wikipedia)
Systems like this are used in nuclear submarines like in the USS Nautilus. One major concern is the case of a leaky separator that would produce a chemical aerosol that might harm the aquanauts health.
Image Source: [GFDL (http://www.gnu.org/copyleft/fdl.html) oder CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons, User Mbeychok
Gas Treatment by using Sea Water
Another alternative we are just considering is the question if it would be possible to clean air by leading it through a spray of seawater? Seawater is available and disposable without limits.
to be continued…