Compost toilet specifics: the bins

Wendell Berry once said if you eat, you’re involved. He was talking about agriculture, but if you ask me, he really meant humanure. Getting your outputs sorted is a big and necessary task. For us, that meant designing and implementing a composting toilet system based on wheelie bins.

I thought I’d better give out the details of our compost toilet bin system, as we’re receiving many emails asking for the specifics of how the system fits together. It’s a simple design, but one that we’re very happy with. Here’s how the bins work:

The back of the toilet block showing chimney attached to each vent at the back of each bin. Click to enlarge.

The whole point of having these bins as our composting toilet system was to remove the need to handle the humanure until it had gone through its composting process and was safe to handle. We’re fine with handling open buckets of our own family’s sawdust-covered poo within a small humanure toilet system, but when we have a course here at Milkwood we can have up to 70 people on the farm each day. And though I value their presence (and their poo) I prefer not to process their collective contributions while they’re fresh, if i can avoid it.

So the bins are our solution. When one fills up, you roll it out, stand it aside in the sun, roll another empty in, lock it into place and continue on. No bucket handling, no processing. And a year later, each full bin has transformed into a rich, safe humus, ready to be added to the rootzone of our food forest trees. We label each full bin so we have a full inventory of when each lot of humanure will be ready to use.

The bins we’re using are normal 200 litre wheelie bins, used for household rubbish in Australia. We add a vent at the top of the back panel, a tap outlet at the bottom of the back panel, and a grate inside the bin. Each bin takes about 1 hour to prepare all up, and are best done as a batch. Once a bin is adapted, you’ve got it adapted for life, so it’s a worthy time investment.

The Grate

Each compost toilet bin has a home-made grate in them which sits about 5cm off the bottom of the bin. This grate provides a permeable barrier between the solids and woodchips coming into the bin, and the bottom of the bin reservoir. Any liquid (and there isn’t much, as the woodchips absorb most of it) moves through this grate and fills the bottom of the bin, and then drains out the bottom through the tap.

The grates were made by cutting a piece of galvanised steel mesh to size, and then adding a polyethylene surround (19mm low density irrigation pipe) to the mesh and wiring it on. A shadecloth cover is then tied to the grate to filter finer particles. The finished grate is wired to 4 bar chairs (the little plastic cones that support rebar while concrete is being poured), which raise it off the bottom of the bin. The completed grate can then be placed inside the bin, and can be removed easily when the humanure is used at the end of it’s composting cycle.

Milkwood interns Bel and Kade adding PE surrounds to the grates

Completed grate, shown upside down. Note detailed and professional shade-cloth attachment with crazy string

Grate in place in bin.

The Tap

The tap is very basic (tank flange – gate valve – snap on hose fitting) , and it’s construction is pretty obvious.  The only hard part is climbing into the bin to attach the flange. We place a screen of shadecloth over the inlet pipe, so solids don’t stop up the tap. The tap mechanism is very important as it prevents the bin from flooding with liquid. Flooding the bin would drastically increase it’s weight and will make the bin anaerobic, which stinks and looses lots of nitrogen.

When the bin is in use, the tap is then attached to a leachate hose (and turned on) which drains the liquids to a gravel-filled leachate pit (not dissimilar to the idea of a septic overflow, except there is much less liquid in this system).  We planted twisted willows on our leachate pit (which are thriving with the extra nutrient) to supply our rocket powered shower down the hill with stickwood and for carbon rich autumn leaves for our compost. Every output can be an input.

Once the bin is in processing mode (ie full, and sitting in the sun) the tap is closed. With the internal temperature of the bin getting up to 70ºc during processing, any liquid in the bottom will evaporate back into the bin’s contents.

inlet pipe wrapped and ready to take on all solids (and liquids)

taps and hose to take the liquids to the pit

The vent

The vent is at the top of the back panel of the bin. It’s a simple rainwater tank overflow screen riveted to gutter outlet (sourced from the local hardware), rivieted into a hole in the panel. The outside edge of this vent attaches to the chimney which draws air up and out of the bin. The suck is created by the heat generated by the morning sun hitting the black metal chimney and this additional airflow means that the toilet cubicle always smells pleasant, as any odours in the bin are being sucked away.

This airflow also dries out the bin’s contents a little bit, which is great. And the mesh on the vent means no flies get into the bin from inside the chimney.

Vent from the outside. Simple but effective.

The back of the toilet block showing chimney attached to each vent at the back of each bin. Click to enlarge.

Other considerations

We’ve started adding rock dusts to the bucket of woodchips provided in the toilet cubicles. These will help incrementally re-mineralise our land over time, as the humanure gets used around Milkwood. The rock dusts also create a more interesting humus makeup for the microbiology which will move into the humanure in time.

After the bin has been removed for about a month we also throw a handful of worm castings (full of worms and worm eggs)  into the bin to increase the diversity of microbes and to start a population of worms breeding. High rise living for worms!!

We’ve hit on using metal plant tags, wired to each bin as it comes ‘out of service’, so we can track which bins are what ‘vintage’. We write the month and the year on the tag, so we know not to use that bin’s humanure for at least 1 year.

These compost toilets are proving a marvelous solution to all the bits we can’t feed to the chickens, or don’t want to add to a compost heap because of inquisitive dogs: chicken bones, dead rats, oversupplies of orange peel and so on. It’s good to have a nearby and useful place to put these things, rather than having to bury them and take them out of our active nutrient cycles.

We’re fairly sure we’ve calculated how many days it takes to fill a wheelie bin under normal usage: 150 person days – so one person with a normal digestion would take about 150 days to fill a single bin by themselves (and 6 people would take 25 days to fill a single bin, and so on). Using this rough guide we can now plan ahead for when we need to modify more bins. It will be good in the second year of this system, when we start to re-use the cleaned bins, but we ain’t there yet!

The back of the toilet block, with a neat array of bins - some full, some empty.

So that’s that. 5 months in and we’re still really happy with this compost toilet system for all sorts of reasons (though I’m sure there’s still room for improvement). If you are completely confused at this point, hop over to our description of our composting toilet system, or have a look at Jenkins’ Humanure website. You’ll get the gist.

You might also like to read:

19 Comments

  1. Posted April 18, 2011 at 9:45 pm | Permalink | Reply

    Thanks for sharing more info about your set-up :)

    I’m going to be doing something similar. Like this but crossed with the Ecowater Net-Drum set-up as per these two pdfs:

    http://files.uniteddiversity.com/Composting_and_Recycling/Compost_Toilets/Ecowaters_Net-Drum_Compost_Toilet_Plans.pdf

    http://files.uniteddiversity.com/Composting_and_Recycling/Compost_Toilets/Building_the_EcoWaters_Twin-Bin_with_Net_Composting_Toilet_System.pdf

    Loads more good composting toilet info at:

    http://files.uniteddiversity.com/Composting_and_Recycling/Compost_Toilets/

    Smiles,

    Josef.

  2. Posted October 31, 2011 at 11:52 am | Permalink | Reply

    Hi guys

    brilliant stuff because this is something I’m looking for a ‘how to’ kinda answer. My only thought is securing them re the weather – would NOT be a fun cleanup if they got blown over etc in wind/storm. I realise if you knew the storm was coming you’d take care of that but sometimes things are unpredictable and/or you’re not home…

    keen to see your thoughts on securing the wheelie bins. :)
    Kristy

    • Posted October 31, 2011 at 1:27 pm | Permalink | Reply

      Hi Kristy, once these bins are full they’re over 40kg in weight, so they’re at no real risk of blowing over…

  3. Posted May 19, 2012 at 12:33 pm | Permalink | Reply

    Hey guys, really love what you are doing here! What are your thoughts on the multiplication factor? You’ve figured out its takes one person approx 150 days to fill a bin, so 2.5 bins a year, then times say 100 peeps that about 250 bins of poo a year and so on. Is there a point where you just don’t need that much manure? I hope there isn’t but just wondering what you think :) Keep up the innovation, its the inspiration a lot of us are looking for.

    • Posted May 19, 2012 at 4:31 pm | Permalink | Reply

      Well I’m not sure you could ever have *too* much nutrient of that type in a poorly favored area like ours… but i suppose in theory. We’re forever waiting for the next bin to be ready because we’ve got so many areas we want to use the manure to establish plantings, so no probs yet! :)

  4. Posted September 15, 2012 at 11:42 pm | Permalink | Reply

    Amazing setup, well organized, engineered, and built. I’m going to start a similar system today, but I have one main question: Is the fluid drain at the bottom 100% necessary? I can imagine it will be a bit heavier with the fluid, but I have these thoughts: 1. I want to make the system somewhat portable, so having to build a leachate pit wouldn’t be ideal. 2. I would like to keep the humanure completely contained in the composting process, and 3. Everything in my neck of the woods is frozen for 5 months of the year so it wouldn’t drain whatsoever anyway in the winter, and might actually crack with ice forming and melting. Any thoughts on these issues as I go into this building process?

  5. Posted October 25, 2012 at 10:19 pm | Permalink | Reply

    “Is there a point where you just don’t need that much manure?”

    Most soil that grows plants is happy with as much compost you can give it, but I guess there is a limit eventually, or in urban spaces without much growing land at all. If you can’t use it in your immediate land, you might want to sneak it out and dump it in a friendly forest or something (after it’s safely decomposed, of course)? We humans put ourselves at the top of a huge food chain, using more and more of the world’s productive land every year to feed ourselves. We need to keep the nutrients we use in the biosphere, not waste them underground or turn them into pollutants. Organic agriculture can feed the world only if we keep all of our food nutrients in the production cycle; otherwise, logically, we’ll need to keep adding artificial fertilisers. If you can’t return it to the farm, at least return it to some other grateful plants in the biosphere.

    I’m waiting to hear your followup of how the bins were when you emptied them a year later, because there seems to be a risk of them going anaerobic in there or slowing down their decomposition for any reason, and you won’t know it until you go to empty them. The humanure handbook emphasises that the frequent emptying of the bucket onto the compost heap and layering it with fluffy carbon materials like weed stalks is essential to Jenkins’s tried and true, fail proof anaerobic composting success.

    • Posted October 26, 2012 at 9:08 am | Permalink | Reply

      In our situation, i can’t see us even not needing manure for tree plantings – but ask me again in 20 yrs :) – re emptying the bins, we’ve now done many rounds of emptying – after 9 months, you’re basically left with a woody compost of sorts. We’re now emptying the bins after 9 months into our humanure hacienda for an extra stage of composting action that is in contact with microbes and worms etc, after which it’s worm-rich humus and ready to be useful planting medium for tree pantings. It’s all working well…

  6. Posted April 28, 2013 at 7:15 am | Permalink | Reply

    hello
    Are you sure that it takes only one person to fill a wheelie bin in 150 days?
    That seems like a lot. We are trying to find a system which works and this looks great and thanks for an excellent detailed explanation.

    • Posted April 28, 2013 at 7:39 am | Permalink | Reply

      Yeah we’re pretty sure, it’s hard to be exact but we based it on how long it took us all to fill one, then multiplied that time by the number of people to get how long it would take a single person to fill one?

      Also the fact that its black in there adds hugely to the timeframe because people don’t chuck in masses of sawdust to cover their poo, b/c they can’t really see it… In a small bucket system it’s the other way around… The evidence is too close and people (our guests, anyway) tend to add far more sawdust that they need to b/c they want it to look like a windswept beach after they’ve left it… Funny but there you go

  7. Skye
    Posted August 18, 2013 at 5:36 pm | Permalink | Reply

    Thanks so much for your awesome detailed build instructions and photos!! About to attach one of these to my little bush hut. Just wondering how you keep the flies from entering the bin (and poo) through the open lid? I cant figure out a way to make it fly-tight myself… or dont you bother? Any fly issues? Appreciate any advice!!

    • Posted January 14, 2014 at 11:04 am | Permalink | Reply

      We do our best to screen the toilet building, keep the door closed and the lid closed.

      The vent pipes at the back of the building keep the air flowing in through the toilet seat and out through the vent. This means the smells emanate from the top of the vent pipe rather than the toilet seat so that the flies are attracted to the top of the vent pipe rather than the toilet. You could make this more effective by adding a small extractor fan.

  8. nokomis
    Posted January 14, 2014 at 5:06 am | Permalink | Reply

    We want to try this in a cool, shady location (Seattle, US northwest). My concerns:

    1. Without your hot sun, how to reach temperatures where the microbes can start their work (mesophilic at 21C / 70F — thermophilic at 40C / 104F)

    2. Heavy rainfall most of the year here; we can’t drain leachate to a trench as you do, because the rain runoff would wash it downhill to neighbors.

    We’d appreciate any thoughts that anyone has on this. nokomis at sonic net.

    • Posted January 14, 2014 at 10:10 am | Permalink | Reply

      Hi Nokomis,

      1. Although thermophilic composting would be great to achieve, our system ensures that human pathogens are rendered innocuous by using TIME. Its the fact that the material is kept in the bins for at least 9 months that makes it safe. Once the 9 months are up we tip the bins into a great big pile to homogenise and enliven with soil microorganisms. I don’t think it matters that your material does not “compost” in the bin, as long as it in not disturbed or at least 9 months, to break the human pathogen life cycle.

      2. Our leachate trench is more than 60cm deep & completely underground. It’s covered by 20cm of heavy clay soil. The only liquid that goes into the absorption trench is urine (contaminated with fecal matter), and rainwater can’t really enter it.

      If you are contemplating building one of these and it seems too hard, consider an easier option may be just to harvest and re-use your urine only, it contains %80 of the nutrients and is generally pathogen free & much easier to deal with.

      Cheers
      Nick

  9. Shady Seattle
    Posted January 31, 2014 at 1:14 am | Permalink | Reply

    Our purpose is to dispose of feces on site (and all urine together with it, no diverting). For leachate, an absorbtion trench like yours is not possible for us. So – to put it briefly – if we managed to dry out the liquid from the leachate, leaving only dry crystals/residue, would that dry residue still be considered dangerous?

    • Posted January 31, 2014 at 5:48 am | Permalink | Reply

      We do this with our lovable loo system and it works brilliantly, so if yr talking domestic scale, look at that design? http://milkwood.net/2012/08/17/building-a-jenkins-style-lovable-loo/

      If you’re talking community scale, you either need to accept you’ll be emptying buckets 3 times a day (we did that for a few years, not a huge problem, tho tasking the job to volunteers didnt go so well), or figure out a ‘deep litter’ system for wheelie bins or whatever that deals with the extra liquid load?

  10. Mick
    Posted June 26, 2014 at 7:39 pm | Permalink | Reply

    Can you please post some photos of what it looks like inside.
    i.e how you attach a seat to the bin without gaps.

8 Trackbacks

  1. By Wholistic » Blog Archive » Composting Toilet on April 18, 2011 at 7:55 pm

    [...] http://milkwood.net/2011/04/18/compost-toilet-specifics-the-bins/ [...]

  2. By Wheelie Bin Compost Loos | Compost Toilets on May 4, 2011 at 9:14 pm

    [...] Milkwood Permaculture, Australia. Wendell Berry once said if you eat, you’re involved. He was talking about agriculture, but if you ask me, he really meant humanure. Getting your outputs sorted is a big and necessary task. For us, that meant designing and implementing a composting toilet system based on wheelie bins. [...]

  3. [...] Compost toilet specifics: the wheelie bins Share this:MoreEmailDiggPrintLike this:LikeBe the first to like this post. This entry was written by milkwoodkirsten, posted on October 28, 2011 at 6:00 am, filed under farm and tagged cob, interns, rocket mass heater, rocket-stove. Bookmark the permalink. Follow any comments here with the RSS feed for this post. Post a comment or leave a trackback: Trackback URL. « Funky Urban Permaculture Designs by VEG [...]

  4. [...] Compost toilet specifics: the wheelie bins [...]

  5. [...] (designed to transporting wheelie bins of rubbish I imagine) would be a much better idea for our wheelie bin humanure toilets than our current plan that involves winches and skids to crank wheelie bins up onto the [...]

  6. [...] their cycle back through the system yet again, as all things do when you have systems like our wheelie bin compost toilet system or our lovable loo over at the tiny [...]

  7. […] a layer of rust.  You can also use reinforcing mesh supports  instead of the pipe sections as in this post on the Milkwood Permaculture site (though this gives a smaller space under the mass). This unit goes into the bottom of the barrel […]

  8. By Environmental Education | dantaresearspools on October 10, 2013 at 10:12 pm

    […] http://milkwood.net/2011/04/18/compost-toilet-specifics-the-bins/ […]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 10,614 other followers