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Building a better composting toilet

Building the humanure haciendaThis week, I've written about cool composting toilets like the Clivus Multrum (easy to use but not as safe) and Joseph Jenkins' thermophilic composting system (more time-consuming but producing vegetable-garden-safe compost).  Today, I'd like to mention two systems that seem to combine the best of both worlds.

The first system isn't one I've actually seen online, but it seems to be an obvious upgrade to Jenkins' Humanure Hacienda for those of us who don't mind cold butts.  Why not simply make a platform above each composting bin and deposit your waste directly?  Presumably, the slatted bin sides and the addition of straw or hay and food scraps would still prompt the pile to heat up, and there'd be no need to handle poop.

Wheelie bin composting toiletA design that's already been tried out is Milkwood's rollie bin composting toilet.  This Australian farm brings in a lot of students and interns, so the proprietors didn't feel comfortable handling strangers' waste.  Instead, they built a raised outhouse that dropped humanure into a rolling trashcan.  When the first can filled up, it could simply be rolled out of the way to compost in the sun for a year while a new can took its place.

What kind of interesting composting toilet have you come up with?  I'm very curious to hear from anyone who's designed a thermophilic humanure composting system that's not based on Jenkins' design.

The Weekend Homesteader starts your journey with projects that are basic but also useful.



This post is part of our The Humanure Handbook lunchtime series.  Read all of the entries:




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Using the bins is an interesting idea! Not only does it eliminate the need to run around with fresh crap, but these bins are watertight. So they won't leach fluids into the environment.

But there may be a couple of downsides.

  • It is hard to believe that the composting process would get enough oxygen in these bins, since the walls of these bins don't let anything in.
  • The material might get too wet, because very little water will evaporate from these bins when they're closed. You might end up with a stinky swamp in a plastic box.
  • This size bins would be very heavy when full.
  • Using a bin prevents worms and other critters from helping with the composting process.
Comment by Roland_Smith Fri Sep 14 12:54:23 2012
Roland --- I agree with you on all of the potential downsides. I wish Milkwood had been using them longer! As it is, I'm leaning toward the other system primarily for the reason of aeration. (And because I want to keep using our bins to haul in biomass. :-) )
Comment by anna Fri Sep 14 13:08:11 2012
I have to wonder if all the fuss necessary to turn human solid waste into something usable is worth it. Human manure is 90% E.coli, not a particularly good source of any nutrient. As we mentioned earlier, herbivore manure provides via its cellulosic fiber content a valuable componet to the soil texture, not provided by the human type...Most of the nitrogen in animal waste is contained in the urine. That's probably worth dealing with. Just bury the solids and forget 'em?
Comment by doc Fri Sep 14 17:00:53 2012

Doc --- "Human manure is 90% E. coli." I find that very hard to believe. Where did you get that figure?

The trouble with just disposing of humanure by burying it, as we've found, is that if you don't go ahead and mix in the carbon materials, it ends up smelling and attracting flies. If you're going to use up all that carbon, it seems like you want to then put the product to use in the garden!

Comment by anna Fri Sep 14 18:27:09 2012

Estimates are that human feces is 66-85% by weight of water, 3-5% dietary fiber and 55% bacteria (which are also mostly water). See Latrine literature review.

But according to wikipedia, only 0,1% of our gut flora are E.coli or related. The aforementioned report states that only 7% of bacterial RNA collected from fecal samples belongs to earobic bacteria (which includes E.coli, Enterococci and Lactobacilli).

Anna, this reports also investigates pit latrines. I think it presents good evidence that they are not quite optimal. One might say an endorsement for thermophilic aerobic compostation from another angle.

Comment by Roland_Smith Sat Sep 15 04:20:39 2012

Roland --- I knew I could count on you for some hard data! I see where Doc's numbers come from now --- it sounds like bacteria in general may be the majority of the dry weight of humanure.

By the way, I think I just won Mark over to the thermophilic humanure composting idea! I offered that he could put anything at all I'd been vetoing on the list in exchange. (Sounds a bit like the kind of deal you don't want to make in a fairy tale.... :-) )

Comment by anna Sat Sep 15 08:30:55 2012

From what I've read so far, thermophilic composting is way better than a pit latrine. Both from an environmental and a health harzard standpoint.

As long as you add enough fluffy carbon-rich material to aerate the pile properly and cover it up against flies. Finding or making that material sounds like the biggest challenge.

Comment by Roland_Smith Sun Sep 16 04:23:15 2012
Roland --- I think we've found a sawdust source, which is part of why Mark gave it the go-ahead. A local sawmill charges $15 per pickup truck load --- we'll try to get some this week if it doesn't rain too hard.
Comment by anna Sun Sep 16 13:59:05 2012
By "burying it" I meant to discard it and not use it. It's just not a particularly good fertilizer. A healthy human GI tract absorbs most nutrients very efficiently from our food and the effluent is mostly the excess population of our normal gut flora. Grazers & browsers can't absorb all the cellulose they ingest, so their manure has more desirable qualities as a soil supplement. If you have to add cellulose to humanure, you're essentially "manufacturing" grazer manure.
Comment by doc Mon Sep 17 19:53:21 2012
Doc --- I understand what you meant, but in order to bury humanure, you either have to dig a hole every time you want to use the bathroom (very annoying), or you need to cover your poop with something high in carbon so it doesn't cause a problem until it's covered. So you end up right back at the using-up-carbon problem.
Comment by anna Tue Sep 18 09:54:57 2012