Towards a better tinyhouse

Inventing to freedom?

Toilet solutions for a tinyhouse roundup and roundaround.

with one comment

Yes, I just made up that word. It means speculation and stuff around existing solutions, in addition to existing ones.

Anyway, I’ve been following the “alternative toilets” thread on the tinyhouse forum, and a few days ago I read the Humanure Handbook (his term for human piss & crap is “humanure”). Interesting book, for sure, but I don’t agree with everything he says. He mentions a book, Compost Engineering, that sounds interesting, too, and I think I would have to read more about this before attempting homebrew improvements – or rather adaptation to a tinyhouse context – of the composting process.

But I was thinking of more general improvements:

1. Place whatever composter there is outside the habitable area, so if it does malfunction it is easier to clean up, while the receptacle is obviously better inside. To do this without water, you could use a Teflon toilet bowl and tube, to transfer the humanure outside. In a previous post, I posted a link to a site selling teflon sheet that could be used to make this. Teflon’s pretty amazing stuff, I wonder how well this would work. I wonder if you could figure out a “dry flush” mechanism, which prevented any humanure from sticking to any visible area of the toilet bowl automatically, that might be more acceptable to a lot of people, and non-stick materials would certainly help. I tried to find out more about Nasa’s air-flush toilet, but no dice.

2. Decide what you want (see below). If we can complete the nutrient cycle, that’s great, but if you just wanted disposal, an idea that occurs to me is that you could dry the piss and crap by evaporation, as an “air head” or “nature’s head” does (BTW, it is clear from the info in the humanure handbook, mainly because of the temperature and size of the storage chamber, that no meaningful decomposition is actually occurring in these toilets, rather they are just drying the material, i.e. they are, rather, desiccating toilets, and only the crap, not the piss), then pasteurize it, and it would be perfectly safe to put in the municipal garbage. You can get odor proof bags, made with foil-plastic laminate material, though as stated in the marketing material of these toilets, it does not smell when dry.

Or maybe you could find a gardener that would be happy to take it, but that seems like a hurdle. Crap takes up quite a small amount of space when dried – a human outputs about only 60 grams of solids per day in feces, and the rest of the crap is water.

Disposing of the (sterilized) urine on a lawn also seems like a very simple solution. The problem is that it might require a large lawn area for full time use. Would have to check that, If you have a drip or subsurface greywater system anyway, just increase the size, and, it could be perfect.

Bizarrely, the author of the humanure handbook does not mention pasteurization even once in the whole book . Yet from the data he gives about temperature-time treatments required to kill pathogens, it is clear that this would not be hard at all. I suggest the (dedicated) use of a kitchen appliance of some sort. A slow cooker might be good. I noticed you can get temp-resistant plastic slow cooker liners, basically plastic bags, you could line the storage chamber of the Nature’s head (or more practically a homebrew version for a fraction the cost) with a bag, then every month or two, you just tie it shut with a twist tie, and put it in the slow cooker for 10 minutes, and it is microbiologically safe. They are made to reliably reach the necessary temperatures, because they have to for food safety.

In all fairness, doing this on a large scale might not be a good idea, because some units would malfunction, some people would be too lazy to do the pasteurizaton step, etc, but you could certainly make a unit that performed the operations automatically, and refused to release the material until it had been pasteurized. In the Dymaxion house, a futuristic house by Buckminster Fuller, this approach of putting the humanure in the garbage rather than mixing it with water, was used, but I don’t know if they dried or even pasteurized it.

3. A water content sensor. One of the problems with dry composting is that it can only be done within a narrow water content range. You can get inexpensive sensors made to measure the water content of soil, so you might use one of these to measure the water content of the compost pile without user intervention, and water the pile if needed.

There are a lot of different toilet options out there for toilets of all sorts , looking something up on wikipedia, and following the links gives a view of some of the options. I think it’s fair to say we are talking about several different functions these toilets provide:

1. Waste disposal to avoid transmissible diseases.
2. Keeping the smell and mess down, or at least somewhere else from the habitable area.
3. Completing the nutrient cycle.
4. Preventing environmental pollution (undesirable release of nutrients, chemicals, and bacteria in the wrong place).
5. Prevent contraction of non-transmissible diseases like an e-coli infection.

These are not always connected that closely. Obviously it would be great to have all 5, but a compromise on some if you have to isn’t the end of the world. Traditional municipal systems are great at 1,2 and 5, but mostly fail at 3 and 4, and are ridiculously expensive, and social problems may prevent them from being used (regulations and stuff would fall in this category). A desiccating-pasteurizing toilet seems like it would be pretty cheap and safe. Commercial composting toilets actually look a lot less impressive to me now that I know more about them – because, despite what the manufacturer’s claim, they are not so safe after all from a microbiological standpoint. (And, according to reviews they don’t work very well for disposal either.) As far as I can tell they do not (could not) achieve the high temperatures needed to kill all pathogens in the timeframe in which they work (storing material for 3 to 6 months). It does help a fair bit, though.

In a tinyhouse, you also want to do it without:
1. Suffering from misunderstandings from bad neighbors.
2. Costing too much, including power consumption if off grid.
3. Needing a whole lot of maintenance.
4. Taking up much space.

So it seems like a thermophilic composter would be a lot better. But, like I said, I think I would have to read more to really make any decisions or try to design something.

Stepping outside the box for a second, you have to ask yourself why, exactly, people prefer flush toilets over dry. I assume it is because they flush the humanure completely away, and it is covered immediately while the toilet is being used, preventing any smell, and there is no exposed pile of other people’s crap below, which you are granted the privilege of gazing upon, and which kinda seems like it might splash up somehow or something (whether or not it actually could).

In Japan the toilets they have do not cover the crap, and this shows in the odor around the bathrooms, but by sucking air into the toilet bowl, smell could be prevented. It seems like it is just the possibility of stuff sticking to the bowl, really, and the pile of crap exposed below. And then there is the engineering problem of getting dry material from one point to another, which seems to be the only other point in favor of flush toilets, because fluids are easy to move around. Still, society already has municipal disposal, recycling, and in some cities even compost collection, so after you get over any fecophobia, as long as humanure is reliably pasteurized, and the process is semi automated, I think dry toilet collection could indeed catch on, if the right toilet mechanism were developed… I think the sticking point is the dry flush mechanism. A roots blower like mechanism made of non stick stuff, and maybe rinsed with just a very small amount of clean water, maybe? Or maybe 2 telfon bowls, one in use while the other is automatically emptied and cleaned. Edit on 2010/11/01: Maybe it would be better not to have a flush mechanism at all. Just a nonstick tube, twisted so you don’t see the pile of stuff below. Humanure slides away immediately after being deposited. No moving parts. Negative air pressure is used to prevent any escape of smell. If the Tube was flexible and you didn’t want to have the airflow associated with this approach to preventing smell form entering the habitable area, you might add a moving part that squeezes the tube shut. That way there are no hinges, seams or whatever, exposed to the humanure. You still need the urine separation ability, apparently the most common approach is to use a front receptacle, and a rear receptacle. Another approach that occurs to me is to try to use the adhesive properties of the water, the effect which is so annoying when trying to pour a beer, causing the water to run preferentially along the side of the bottle. I.e. You have a single tube, with mixed solids and liquids coming down, then at the output of the tube have a rounded piece of glass (or other hydrophilic material) of the right shape, which gets the water sticking to it, then guides the water away to s separate chamber. One problem with this is that you get fecal contamination of the urine, which in some circumstances could be bad. One pro is that the urine rinses the transfer tube, but if it was a good nonstick material this might be unneeded anyway. It could also be used in tandem with the 2-receptacle approach, attached to the dry-matter output tube, just in case water is inadvertently dumped into the dry-only receptacle, it still separates most of the water, and puts it in the right container.

Anyway, other options, some from the thread, some of which might not be very practical, seem to include

1. Anaerobic digester. While reading up for the greywater MBR, I read some about these. Basically they only make sense if you need the methane for running an internal combustion engine, cooking, or a lot of water is already mixed with the waste material. The amount of methane you get per person of waste will not be near enough to do your cooking anyway. If you only want the heat, it would make more sense to burn the waste directly, you would get more energy out, and it is a much more compact system. Anaerobic digesters take quite a bit of space. They also require management sometimes, and the right input of nutrients.
2. Nature’s head and Air head, like I said, these seem to be basically desiccating toilets, and they don’t even deal with the piss, except to store it.
3. Sawdust toilet, see the Humanure handbook for details, the problem with this is that it seems to entail a big compost pile, and yet more chores.
4. Biolet, sun-mar, clivus multrum, etc, there are a dozen commercial composting toilet, and they are are ridiculously expensive, and most seem to get bad reviews.
5. Incinerating toilets seem to get bad reviews, and require a lot of energy. Also expensive.
6. So-called PETT, but this doesn’t seem practical for a tinyhouse.


Written by gregor

October 16, 2010 at 05:55

Posted in Uncategorized

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  1. […] previously posted after reading the book, here and about a dehydrate-pasteurize toilet that could be used with the humanure approach with a much […]

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