Figure 2.

A proposed bioregenerative life support system. Water from a primary source (darker blue arrow) or purified from urine (light blue arrow) is supplied to a fermentor, together with extracted urea and mineral salts (purple arrow). Respired carbon dioxide is converted to ethanol either via chemical synthesis or by using an ethanologenic bacterium (black arrow). Ethanol is fed into the same fermentor as the water, urea, and mineral salts. No other complex organic chemicals are required. Regenerated oxygen (red arrow) is also provided to the fermentor. Saccharomyces yeast is inoculated into the fermentor and grows aerobically by utilizing the ethanol, urea, and minerals. The yeast biomass that is produced provides sugars, amino acids, lipids, vitamins, and other nutrient compounds for downstream food production.