Combine air, warmth, moisture, and food for oxygen-loving (aerobic) bacteria, which consume waste. Done right, the compost emits an earthy aroma, carbon dioxide, and water, and leaves minerals and humus behind. Some models, such as Envirolet’s Basic Plus or Biolan’s Composting Toilet, compost without added energy. Electric fans or heaters, however, aid evaporation and keep compost warm. The Envirolet DC12, for example, runs two 0.24 amp fans, which can be operated by battery or solar power. But what really distinguishes one composter from another is the mixing-aerating system: Rotating arms in a BioLet (below) and a tumbling drum in a Sun-Mar are two of many mechanisms.
The good : Shrinks waste to less than a tenth of its original volume. Uses little or no water. Produces humus to fertilize trees or perennials.
The bad: Toilet owners must actively manage decomposition, encouraging good microbes and discouraging bad ones. Get it wrong, and the bad bugs (which are “anaerobic,” because they thrive in low oxygen) raise a stink.
The ugly: Signs of anaerobic apocalypse (and other microbial failures), as reported by cottagers: “residual brown tar,” “mush,” and “like espresso, but smells much worse.”
The ick factor: Many folks don’t like “sitting over a pile of poop,” admits cottager Lloyd Alter. Some toilets come with retractable doors that open when you settle in place. With some, you can add bulking agent (a dry, carbon-rich material) to cover deposits, reduce odour, and aid composting.