Composting Toilets for Highly Seasonal Use

August 24th, 2011 by KTU | Filed under 3. Finished Pavilion, Montana Sleeping Pavilion.

Warning: if you are not an extreme tree hugger and/or really don’t need a toilet without a septic system, you should skip this post.

I’ve spent a fair bit of time over the last two years researching composting toilet systems. I’ve discussed them with friends and have done some experiments at my cabin in Vermont. I’ve also had almost 10 years of experience with a commercial system (Envirolet) at my Vermont cabin.

Commercial composting systems are really set up for steady demand by a few people. Our use pattern is very different. We hit the system very hard for about four weeks a year and then it sits idle for the other 48 weeks.

Furthermore, most commercially available composting systems benefit substantially from electric heaters built into them. These use a fair bit of energy. My system in Vermont is not powered and it does not work very well, by which I mean the waste takes at least a year to decompose. I’ve concluded that we wouldn’t be happy with the performance of a conventional composting system at the Montana sleeping pavilion.

Instead, I’ve installed a “Lovable Loo” which I’m using in an unusual way…anaerobic composting instead of aerobic composting.

The Lovable Loo is basically a housing for a 5-gallon plastic bucket with a toilet seat on it. After each use, the user scoops a generous amount of saw dust or peat moss over the waste in the bucket. (We use peat moss because it’s easy to buy at the home center.) This essentially eliminates odors and provides a more attractive appearance than the alternative. When the bucket is full, the lid to the box is lifted, and the bucket lifted out and replaced with a new one. There are thousands of these systems in use and they are apparently used very successfully even in conditioned indoor spaces.

Lovable Loo installed in the "amenity hut"

Nearly all Lovable Loo users adopt an aerobic composting system. Basically they have a wire/wood bin on their lot somewhere and they empty the bins of waste into the bin to compost. If the mix of organic material, water, and air is maintained appropriately, these compost piles are efficient and fast at decomposing the waste. Aerobic composting does not smell, as the product of decomposition is largely C02, an odorless gas. The temperatures of composting are high enough that dangerous microbes are killed. However, this would not work on our site. First, I’m not wild about disturbing the landscape with a sizable composting bin. Second, I am also worried about maintaining the right conditions for composting when unattended.

Instead we are trying anaerobic composting, which is composting in a sealed chamber without oxygen. (Basically there are two kinds of bacteria…aerobic and anaerobic. We’re using the anaerobic bacteria.) Here’s how it works. Each bucket of waste is capped tightly with the standard bucket lids (which are extremely secure…darn near impossible to get off without a tool). We mark the bucket with the date using a Sharpie. We then simply let the contents decompose anaerobically for at least one season. (It might take two, but that remains to be determined…report in Summer 2012) Once decomposed, the contents (which should be essentially soil and water) can be returned to the land. I punched a small hole in the lid (1/16″ diameter) to prevent any internal pressure from the build up of biogas (mostly methane). Incidentally, the holding tank of a septic system is basically an anaerobic composter…waste settles to the bottom and decomposes anaerobically. This is also how most sewage treatment plants work.

The Lovable Loo system is relatively inexpensive, does not require any permanent fixtures in the hut, and thus can be abandoned at low cost if we don’t like it. However, if it works, it scales nicely to fewer/more people and is a pretty reliable low-fuss solution. Details on the Lovable Loo here. I also found the Humanure Handbook, written by the hippies who created the Lovable Loo, strangely interesting.

In our first season, which comprised an average of three users for four weeks (12 person-weeks) we filled five buckets. We adopted a protocol in which male users (and willing females) eliminated liquid wastes the way the other large mammals on our island do…this minimizes the volume of waste the system has to handle. After the first season, I can attest that we had no odors and the use experience was quite good, even for kids and city slickers. This has been a very good solution for our use case. I’m hopeful that the latency required for composting is less than one year, in which case we’ll have only five or so buckets digesting at any one time. If it takes two years, we’ll have ten, which would be manageable. (Incidentally, the optimal moisture level for anaerobic composting is very high…essentially you want to fill the bucket with as much water as it will hold before sealing.) More a year from now…

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11 Responses to “Composting Toilets for Highly Seasonal Use”

  1. Bob says:

    hi, I was wondering how the anaerobic composting of your waste has worked out? Also I was wondering if you had found filling the bucket to the top with water was really necessary.
    Thanks.

  2. KTU says:

    It worked out very well. I need to post some results from this past year. After one year, the waste pretty much looked like wet, black dirt. I emptied it onto the ground a distance from the bunk house and it seems that it will quickly be absorbed into the ecosystem. I have not tried any controlled experiments to see how much water is required. I do believe the contents of the bucket have to be quite wet for anaerobic composting to work, but I’m not sure just how wet. Since there isn’t really any cost to me in filling the bucket with water, I’m not inclined to test my luck with that variable.

  3. cabinguy says:

    Hey,

    I know it has been a while but I really like this idea. It is perfect for my tiny 144sqft cabin that will be used by two ppl (me and my wife) once every other weekend or so. I am not sure if you used this method indoors or not?

    I would like to use this indoors (in the bathroom of course. Any issues with that from your experience?

  4. KTU says:

    Should be fine indoors. Our “shed” is perfectly pleasant — just mild odor of peat.

  5. Mindy says:

    Intriguing. My only concern is with your use of the peat moss, which is a non-renewable resource. It might be more sound to use an alternative, such as sawdust, or grass clippings.

  6. Shon says:

    Hello,
    Just curious… Does anything else go in the bucket besides human waste, peat moss/sawdust and water? What about toilet paper in particular?
    Thanks

  7. KTU says:

    Yes, TP composts just fine.

  8. Shari says:

    Just wondering how many bags of peat moss did you use in a 2 week period for how many people?

  9. KTU says:

    Hi Shari,

    I think one of those dried/compressed bales from the garden center gets us through a season. For us, that is probably 4 weeks continuous use by 4-6 people. Saw dust also works well from what I understand.

    Best,

    Karl

  10. Bonnie Jones says:

    Greetings,
    Thanks for the great info. Can you give an update on how the anaerobic composting is going and whether a year seems like enough time?

  11. baubilt says:

    We’re about four years into use of the composting system. So far it is is working very well. One year seems to be about right for adequate composting. (Of course the time will depend on ambient temperature, so colder climates may require more time and warmer climates less time.) The bucket definitely needs to be adequately hydrated — the only less-than-ideal results have been for buckets not filled with water before sealing.

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