Should You Compost Your Poop?

Is it safe to compost human feces? We look at the science.

October 9, 2015
toilet in garden

While many of the nutrients we eat are released in a convenient liquid form (which is why diluted urine is great for immediate use in the garden or compost pile), the residual bulk and nutrients are delivered in a somewhat more problematic form: poop. Why problematic? Well, it's heavy, bulky, and smelly, but, most importantly, in its raw form, poop is significantly more likely to contain microorganisms that can make us sick than urine is. 

But this doesn't mean you should flush your poop away, adding to the waste stream. Just like any manure, when properly handled, that black gold is fantastic for soil and plants. The keys to closing your personal nutrient loop—keeping poop out of the waste stream and returning the resources to your soil—include careful handling and composting, along with lots of time.


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The easiest way to close your poop loop is to install a commercial composting toilet, such as those made by Clivus Multrum, Sun-Mar, Composting Toilet Systems, Advanced Composting Systems, Sancor Industries, and Naturum. Unlike the primitive units I worked with in the early 1980s, some of these companies offer systems that flush like a standard toilet; facilitate the separation of liquids from solids (excess liquids were the bane of early systems); and operate with very little assistance. Parents of little ones can green kids' elimination, too, by choosing compostable diaper liners such as gDiapers inserts. Menstrual fluid and organic cotton pads/tampons are also completely compostable, along with other solid human waste. Composting toilets turn poop and other organic matter into semi-finished compost, though most studies agree that the compost they create may still contain disease-causing organisms.

Most people either compost the composting toilet's end product further using fresh organic matter to create a hot pile (the heat kills nasty stuff); treating it with earthworms (which has been shown to be especially effective, see below); burying it in a wild area where it won't be disturbed; or storing it for an extra year in closed containers to allow the bad organisms to die off completely. Once finished, many users still limit use of the finished compost to nonfood plant beds in the garden, just to be on the safe side. 

The next advance in composting toilets may well be Source Separating Vermicomposting units, as recent research at the University of British Columbia showed that they reliably produce a more finished and much "cleaner" end product than standard composting toilets do. I was not able to locate a commercial U.S. source of a separating/urine diverting vermicomposting toilet unit, though there are said to be commercial units in Europe and it appears you can, or at least could, buy one called a Dowmus if you live in Australia. If you want to take on the challenge, I'd suggest typing "vermicomposting toilet" into the search engine of your choice.


Related: How to Have the Most Organic Poop

Commercial options aside, it's quite possible to design and operate a composting system that will safely and effectively deal with the special challenges involved in composting poop.

Isn't this the same as sewage sludge, otherwise known as biosolids—which most organic researchers say isn't such a good idea to spread on farms or gardens? Yes and no. Biosolids are the solids left over after the treatment of everything that gets flushed and dumped down the drain, including not only human waste, but also toxic cleaning products, industrial chemicals, and in some cases, the petrochemical and heavy metal residues washed off roadways when it rains. Yuck. Makes plain old poop sound downright attractive, doesn't it?

Not quite ready to take up sustainable elimination yourself? Well, if you have pets you can start by composting their waste. Yes, I know pet poop is on the list of compost-pile no-no's, but that is due to the possibility of on-board disease-causing organisms that could infect humans and not the compostability of the material. Composting pet waste is perhaps even more important than composting human waste because so much of what pets eliminate ends up in landfills, where it can contaminate groundwater, rather than in sewage-treatment facilities. 

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The U.S. Department of Agriculture recommends composting as a good way to deal with large amounts of dog waste, and dog parks and pet owners are looking into ways they can compost it. To compost dog waste at home, simply set up a dedicated, covered bin for it in an out-of-the-way area where it will be able to remain undisturbed for a year. If you are willing to wait that long for all of your compost, you can add your kitchen and garden waste directly into that bin. Otherwise, keep those separate.


Add dog droppings as available, covering each addition with an equal amount of a dry, high-carbon material like sawdust, shredded dry leaves, or shredded paper, and then treat that bin as you would any other compost pile. Once it's full, start a new bin for fresh waste and let the first one slowly compost and age for at least a year. If you need the bin, shovel the partially composted material into a different covered container to age. 

There are special, long handled-tools designed for scooping poop, which are great for use in your own yard. For off-site adventures, you may want to carry compostable (not just "biodegradable," which may not be particularly compostable in home bin conditions) poop bags. With compostable bags, you can transport deposits home and drop them right into the bin. Remember to wash your hands/gloves and tools when working with fresh or partially composted pet waste to reduce the chances of your picking up something nasty.

Related: How To Compost

The straight poop on cat poop: Cat poop has a truly terrifying reputation, but if you know the facts, you can safely compost cat droppings (or the entire contents of the litter box if you use a plant-based litter such as Swheat Scoop or Yesterday's News). What's the deal? Cats are the only animal known to excrete toxoplasma eggs (oocytes) in their poop. Humans can catch toxoplasmosis from handling feline poop, and the disease can be quite serious for developing babies and for people with immune challenges. The good news is that putting cat poop a good hot compost pile (175 degrees Fahrenheit—rare for home composting) or composting/aging it for a total of 18 months will kill the vast majority of oocytes it might contain.

Vermicomposting doesn't appear to be an effective way to shorten the composting time for cat poop, as earthworms can serve as hosts for toxoplasma, as well. For that reason, it's a bad idea to opt for a worm-based system for dealing with cat waste. Feel free to compost cat droppings or cat litter (the plant-based kinds only) as you would dog waste in a traditional compost bin; just plan on storing it for an extra 6 months to age, for a total composting/aging time of 18 months.

This article originally appeared on Rodale Wellness.