At this point, the water looks like chocolate milk. We use microorganisms to clean the water for us, the same way the river cleans water.
The microorganisms are important for two reasons:
They eat the solids (feces and food) out of the water.
They break down the ammonia from our urine, completing the nitrogen cycle. In order to accomplish this, we pump compressed air into some of our tanks. Bacteria help replace the hydrogens in the ammonia from our urine with oxygen, creating nitrates. In our anoxic tanks (not much oxygen) heterotrophic bacteria strip off the oxygens and release nitrogen gas as well as carbon dioxide. (click here to learn more about the nitrogen cycle.)