Feedback on Night Soil: Composting Human Waste

One reader writes in to answer a question about composting human waste into fertilizer, and a second reader offers recommendations for venting an outhouse.

Night Soil - Privy - Fotolia

Composting human waste — aka "Night Soil" — can be easily done in a way that also controls any problems with flies or odor. 


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In MOTHER EARTH NEWS Edith Little asked for information about using yeast in a privy to decompose and deodorize feces or "night soil." I don't know of any yeast that will serve this purpose, but I do know that composting human waste can be done very nicely. There will be little objectionable odor ... much less than from the average privy where waste is allowed to pile up and putrefy, creating unhealthy conditions. Flies will also be eliminated and the resulting fertilizer will be of very high quality: an odorless, crumbly black gold for the garden.

In order to compost effectively and efficiently, night soil must be mixed with material that is high in cellulose or carbon. I find that sawdust, wood chips, pine needles or old leaves—in a ratio of four or five parts sawdust or whatever to one part excrement by volume—seem to work best. Straw or hay isn't satisfactory, for it tends to pack down and is difficult to turn over later on.

The sawdust should be dumped down the hole of the privy after each use to completely cover your latest "gift to the earth". Use more if necessary, to insure that flies cannot get down into the night soil to lay their eggs. The mixture should be kept damp but not sopping wet.

After a period of time, as the pile builds up in volume, it will begin to heat. At this point the material should be turned over with a long-handled pitchfork every two or three days, depending on how much the privy is used. This will keep the pile cookin' by supplying air to the aerobic bacteria responsible for the composting process ... and will also insure that any stray fly larvae on the surface of the mass get dug into the hot center and destroyed.

The heat is caused by the work of beneficial microorganisms which break down the night soil-sawdust mixture. If conditions are right, the temperature will be high enough (at least 150° F for about 24 hours) to render the compost completely free of any disease-causing bacteria. As an added safeguard, I would not use the fertilizer on plants that will be eaten raw until the dressing has aged for at least one year.

It would be advantageous if the privy were designed to allow easy access to the composting chamber for turning and removal of the contents. The facility could be as simple as a tarp strung over a three-foot-deep pit in the ground ... all that's needed is something to keep the pile from getting too wet.

After the pit is full the privy should be moved to another location ... or, if this is impractical, the compost dug out and re-piled elsewhere. You should continue to mix and water the material until it's cool to the touch. At this time you could throw in some red wriggler earthworms (which can be obtained from your local bait dealer or ordered through the classified section of Gardening and Farming magazine) to further insure that the end product will be nothing like what you started with. The heap should then be covered with a tarp or sheet of plastic to prevent leaching, and allowed to age for one year (unless the fertilizer is to be used on fruit trees or crops that will be thoroughly cooked, in which case it could be spread as is).

In MOTHER EARTH NEWS Milton Wend suggests using night soil which has merely been treated with hydrated lime. I myself would be wary of fertilizing crops with human waste unless it had heated up to 150° F in a controlled composting operation and/or aged for at least one year buried in a pit. The Chinese used to get around this precaution by never eating any vegetables raw (see Farmers of Forty Centuries by F. H. King).

Further and more detailed information on composting night soil can be found in the book Composting by Harold Gotoos. The author also gives a nice set of plans for a community-size methane generator.

Bruce Martin
Ponca, Arkansas

An innovation that I've seen lately—and that I would surely include in the building/remodeling of a privy—is the use of a vent pipe running from the vent or waste area to above the roof. It keeps the air inside the privy fresh and successfully eliminates the inside odor ... even when nothing else is used.

Harold & Grace Brown
Yarmouth, Maine

You're right, Harold and Grace ... and the article, "Privies, Old and New" contains cutaway drawings of two versions of outhouses built with such vents.—MOTHER EARTH NEWS.