The water toilet is truly one of the greatest miracles of modern life, a frothy disappearing act; now you see it… now you don’t. But washing human waste away requires huge sewage treatment infrastructures in cities, and extensive home septic systems for rural dwellers. Compost toilets, though in their essence as old as human civilization, have evolved to a point of technological sophistication whereby they tackle the minutiae of composting details to create optimal conditions for recycling human waste.
Take a look at the compost toilet tech out there for the non-flushers among us.
The Basic Outhouse
In a basic outhouse, or pit-toilet, waste composts (at least a little bit) as bacteria digest raw material and transform it into more benign stuff. But it may not compost fully, or as quickly as in a more advanced system, where the waste can be turned, aerated and heated.
Modern compost toilets control the process of waste breakdown by enclosing waste, sometimes adding heat to evaporate extra liquids or water to keep compost moist, and allowing for finished compost to be removed.
Double-Hole Toilet System
Another option is to separate urine out at the very beginning with a double-hole toilet system like this one. Keeping liquid out reduces odor and allows the solid waste to compost better.
Self-Contained Compost Toilet
A self-contained compost toilet stores composting waste inside the body of the toilet. To keep the poo out of view, most self-contained toilets have a trap door that covers the seat opening when not in use. A little electricity (if available) drives fans that help dry out liquids and circulate air. A long vent pipe sucks odors up and out.
Inside the Aeration Process
Human waste compost, just like garden compost, needs oxygen for its bacteria and other little digesters to work properly. To help aeration, newer model toilets usually include either a central stirrer, a rotating drum or a manual rake (like this one).
Hands-Off Process (It’s a Good Thing)
Some toilets, like this Biolet, make the process even more hands-off by doing the stirring for you with electric interior mixer bars, which are activated when you sit on, and then release, the toilet’s seat. Automatic trap doors over the bowl also open when you sit down, which may confuse some stand-up male users.
As waste is composted and dries out, it falls down into a tray at the bottom of the toilet. There it dries out even more, and once or twice a year (depending on use) you pull it out and dump it somewhere to continue breaking down in the great outdoors.
Simple Separated System
More extensive systems move the composting away from the toilet bowl itself – separating you from your poo. In a simple separated system, gravity and a little bit of water carry waste down to a basement or crawl space composting tank where everything proceeds as described in the previous slide.
Vacuum Toilet Tech
At the cutting edge of home compost toilet technology are toilets that use a vacuum to suck the waste into a composting tank. With a vacuum, the tank can be placed on the same level or even slightly above the toilet, meaning you can still enjoy some distance from your composting waste, even without a basement or lower space to keep the tank in.
For larger industrial applications – think airport or office building restrooms – you need a composter that can handle the waste from multiple toilets or stalls. Large systems like this one, built by Clivus Multrum, are designed to order for as many users as necessary.
In the case of large separated tank systems, using a compost toilet is almost like using any old toilet. This one even flushes with a foamy soap solution discharged when you press a button.