In the previous post I did not discuss particular technologies to purify waste water and to turn it into clean water. One way to remove minerals from waste water are algae.
As orbital space settlements will get most of the energy from solar power, there is little use for biofuel. However, algae have a lot of other useful applications.
Since algae remove phosphates and nitrates from waste water, dried algae are usable as a fertilizer. This way phosphates and nitrates could be recycled and reduce the need for mining.
Another use of algae is the production of textile. Algae are rich in cellulose – an important note is that cotton is more or less pure cellulose – and hence could be utilized as a feedstock for textile and paper.
As algae are rich in oil and protein, they are also a great source for food. For instance FollowYourHeart has developed an egg replacer made of algae protein.
A related food application, is algae butter. In combination with algae based egg replacers, this use of algaculture will reduce the demand for livestock, i.e. cattle and chickens.
The examples above are just a few potential applications, but they show that the combination of waste water treatment and algaculture could be profitable. Any revenue raised bu the sale of algae products, will reduce the need for levying sewer fees to the public.
Algae containing bioreactors could be located at the outside of an orbital space habitat (source: NASA).