Composting is the controlled aerobic (atmospheric oxygen-using) biological decomposition of moist organic solid matter to produce a soil conditioner. Because it requires molecular oxygen, it cannot be immersed in water (saturated).

The emphasis is on “controlled.” This sets it apart from the uncontrolled decomposition that occurs in the natural environment. A leaf falls from a tree branch to the forest floor, and microbes transform it into a nutrient form that the tree can consume. The biochemical process is the same.

In a composting toilet, the objective is to transform potentially harmful residuals — mostly human excrement — into a stable, oxidized form.

The primary microorganisms responsible for composting are bacteria, actinomycetes, and fungi. However, algae, mixomycetes (slime molds), viruses, lichens, and mycoplasmas are other organisms present in the compost process. Soil organisms, such as protozoa, amoeba, nematodes, earthworms, and arthropods, also perform major roles by degrading surface litter — consuming bacteria and assisting in aeration.