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The Worm Composting Toilet E-mail
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Sunday, 11 September 2005

by S. Zorba Frankel

A worm composting toilet is a beautiful thing and a marvel to behold when it has been designed well and, consequently, is operating smoothly. Fortunately, correct operation only requires an understanding of general, basic worm composting and only infrequent maintenance. This article will guide you in the construction of a simple outhouse, and give basic operating instructions for a worm composting toilet.

Operating a worm composting toilet is very easy. One of life’s great satisfactions is the ability to close the organics loop in making our daily deposit at the “worm bank.” In return, redworms present us with “black gold” for our trees.

As easy as the vermicomposting toilet is to operate, it’s better to get experience first operating a worm bin for kitchen scraps. After managing (and troubleshooting) your worm bin, you’ll find it easy to run a worm composting toilet. So, give it a try!

The worm bin
The worm bin is the heart of my worm composting toilet and it is set into, or under an outhouse. In my outhouse, the worm bin is simply a 2’ wide by three foot long by two feet high bin built of half-inch plywood. The bin is used by one person, year round, and requires emptying twice a year. Size your bin larger or smaller,depending on how many it will serve. For two people, just double the surface area of the bin.

Bin maintenance
The worm bin should be operated like any worm bin. The moisture, temperature and aeration needs are the same. One difference is that human waste has a Carbon to Nitrogen ratio of 20:1 and so it needs a high carbon material added to decompose best. I use decomposed leaves. Our City collects and will delivers these leaves each fall in seven-yard loads. Several months later, I have a very carbon-rich leaf mold. This balances the high nitrogen levels of human waste nicely, and adds lots of organisms as well.

Insulating the bin
This is a very simple worm composting toilet design for temperate climates, where average winter temperatures don’t fall too far below freezing. Our Pacific Northwest (USA) climate is temperate. Winters rarely see temperatures below about 30°F, and temperatures usually remain in the 40s. Since 40s are well below the preferred vermicomposting temperatures (65-80°F), I insulate the bin in the late fall. The bin’s contents stay in the 50s through most of the winter, much nearer the perfect processing temperature. I also pack straw all around the bin to keep it warmer.
For even colder climes, you’ll want to insulate the composting bin even more. Straw, hay and styrofoam all work well. You may even want to use an underground bin. If it’s going to be wet down there, you’ll want a worm bin that doesn’t leak, so as not to contaminate the soil or groundwater with not-yet-decomposed human waste.

The beauty of outhouses
There is an art to outhouses. They have been built for generations, and given their a special look, with a crescent moon at the top. Take great care in your design and construction, and it will forever be a beauty to behold. Your outhouse deserves this kind of attention, after all, as it provides a necessary function to your family and guests.

There’s another reason to make the outhouse as inviting as possible. In my experience, many guests approach using a composting toilet with great apprehension. (I don’t tell these folks that it’s a worm composting toilet as they’re nervous enough already.)

A few words about pathogens
There are a number of disease causing organisms that may be found in human waste from individuals carrying these diseases. In composting human waste, these organisms can pose a health hazard when they are not killed. The only way to be absolutely sure that they are killed is to use a hot composting process. “The EPA’s ‘Process to Further Reduce Pathogens’ (PFRP) (for in-vessel or aerated static-pile composting of biosolids) requires maintaining a temperature of 55°C (131°F) or higher for three days. Using the windrow method, a temperature of 55°C or higher must be maintained for 15 days or longer with at least five turnings of the windrow in that time period.” This treatment produces what is called Grade A Compost or Biosolids.

There is preliminary research pointing out that, in controlled vermicomposting situations, pathogens are killed off and grade A compost is produced. For my own safety, these are the precautions I take to be insure that I’m producing a pathogen-free (or nearly pathogen-free) product:

• I make sure the worm population remains high (at least one pound per square foot, and closer to two pounds) by keeping the system moist, well aerated and reasonably warm.

• I let the material decompose for a year longer after it is removed from the worm bin (and leave a large population of worms in the “aging” box of vermicompost)

• I use the finished vermicompost on trees only, and always put a thick layer of leaves over the freshly-added vermicompost


My Outhouse Materials List:

  • Foundation: nine small (reused) concrete pieces.
  • Base: Two large (3' x 4') pallets, joined by 2 x 4s so they won’t flex. On top of pallets: one 4' x 6' sheet of plywood.
  • Worm bin: a regular 2' x 3' wooden bin made of exterior grade plywood
  • Bench: one sturdy board, just larger than the 2' x 3' bin it sits on. Oval hole, below...
  • Toilet seat: a handsome, oak seat. A garage sale find.
  • Walls: fence boards from a neighbor’s fence replacement. Begin at 3' height in back, so worm bin can slide out back.
  • Front door: Old garden gate, from a neighbor’s fence.
    Has an attractive green moss growing all over it.
  • Roof: A thin piece of plywood, bent into a nice curve. (Next time, I think I’d use cedar shakes, instead.)

A group of home-schooled children came by to paint the sides, back, top of the roof, and the front ornamental top. That top was cut with a traditional crescent moon. Turned out beautiful, wouldn’t you say?


Worm Digest issues #8 and #9 feature composting and worm composting of human waste. Available online in our back issues section.

Nature Calls: The History, Lore and Charm of Outhouses, by Dottie booth available through Ten Speed Press.. A tour of 75 old outhouses that’s going to give you plenty of creative ideas.

The Humanure Handbook, by Joseph Jenkins (302 pages) An awesome practical guide to dealing with our own waste. Full text of this book is available on the publisher’s website.

The Composting Toilet System Book: A Practical Guide to Choosing, Planning and Maintaining Composting Toilet Systems, by David del Porto and Carol Steinfeld. An excellent and complete resource book on composting toilet systems (234 pages)

The Toilet Papers: Designs to Recycle Human Waste and Water: Dry Toilets, Greywater Systems & Urban Sewage, by Sim Van der Ryn (c) 2000, 127 pages. An excellent book on the subject of human waste.
Last Updated ( Sunday, 18 September 2005 )
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