Biological wastewater treatment
Wastewater treatment is a group of methods to free water from biological and chemical pollution.
Most water treatment systems include a number of steps for waste water treatment. Screening, filtering, biological treatment and chemical filtration. Some systems also include Ultra-violet and ozonation.
Water treatment units
Screening removes large objects such as vegetable matter or sanitary napkins from the water stream in order to avoid clogging the system. It is usually accomplished using wire mesh screen, bar meshes, rotating drums or other mechanical means, configured for continuous operations.
Particles are removed by controlling the velocity of the flow and providing impingement surfaces in order to favorise the settlement of particles into the bottom of the cremoval section.
Equalisers regulate flow in order provide continuous flow to treatment systems and reduce turbulence, favoring settlement.
Fat and grease removal
Skimmers are used to remove floating grease and oils from the water stream, as these materials are lighter than water and tend to rose to the surface.
Primary treatment usually consists of settlement chambers where oils rise to the top and sludge falls to the bottom. The sludge is removed mechanically and transferred to a separate treatment stream.
Secondary treatment uses aerobic biological processes to degrade the waste and bind particles together to increase settlement rates. Oxygen is often injected to increase the biological production. Media is provided as a surface to promote the growth of the biota.
Tertiary treatment will be required on Mars, as the habitat ecosystem is not large enough to absorb the contaminants left over from secondary treatment. Chlorination, UV and ozone are all possible technologies. Sand filtration is another possibility, as well as membrane filtration.
Energy and space requirements
The active littoral zone
a long term alternative to standard water treatment is to use the active littoral zone of lakes and ponds. The littoral zone of a lake is the shallow part, where water plants and a great variety of small animals and microbes are living. It is biological active, that is, it has a cleaning effect upon the water. Even pharmaceuticals are digested. However, the cleaning capacity is limited.
Such a lake could eventually be an important part of the waste water treatment in a Martian settlement. Lakes and ponds on Mars would require enclosure in a pressure vessel to avoid freezing and evaporating.