More Hot Poop on Composting Toilets

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In 2005 I visited the Cottage Life Show in Toronto and wrote The Hot Poop on Alternative Toilets, looking the various toilets on the market. Since then I have become convinced that these toilets have a much bigger future. We can't continue using drinking water to flush away our waste, and we can't afford to keep wasting our waste; at some point soon these are going to be coming into our homes and offices. Don't laugh; already, if you want to build to the Living Building Challenge standard, they are pretty much the only way to go. That's why they are in the new Bullitt Center.

So what has changed in the last eight years? Disappointingly, not very much.

The fundamental aim of the composting toilet designers is to deal with our inhibitions about poop. We have grown up with a flush-and-forget system where we don't see the stuff, we don't have to deal with it, we send the problem somewhere else. Most of the attention is going to making the composting toilet experience as close to this as possible, sometimes by really elaborate means.

The Biolan Keeps It Simple

Biolan Composting toilet

Biolan/ Lloyd Alter/CC BY 2.0

Then there is the Biolan. This Finnish design is really nothing but a big insulated barrel with no moving parts, no fans, nothing. It works when there is enough poop and compost bulking material in it so that the microorganisms generate enough heat to start turning it into compost. When it is full, you empty it with a shovel and a wheelbarrow. Excess liquid is collected in a plastic jug, although once composting really gets going it is mostly evaporated by heat generated. Simple, basic, cheap and works on the same principle as almost every other toilet in this post: Poop + bulking agent (usually peat moss and sawdust) + heat + time = compost.

But telling people that they are going to be sitting on a barrel of poop is, I think, a hard sell.

The Sun-Mar Uses a Drum


Sun-Mar Self-contained Unit/ Lloyd Alter/CC BY 2.0

Where in the Biolet the stuff just sits there, The Sun-Mar system has a rotating drum that breaks everything up and exposes it to more air, promoting aerobic decomposition. It feels a lot less like sitting on a pile of waste when it is all mixed up in the drum, somehow more high-tech when you add the bit of muscle.


Lloyd Alter/CC BY 2.0

Excess moisture falls to the bottom; between the electric fan that sucks air down (eliminating smells) and the heating element under the bottom, most of the liquid waste is evaporated. I know many people who are very happy with this system; I have used one in the home of Laurence Grant, who has had it inside his bathroom for seventeen years. More at Sun-Mar

The Envirolet Eliminates the Step


Envirolet / Lloyd Alter/CC BY 2.0

Note the sign next to this Envirolet toilet: "no step-up: Envirolet is easier to use at 3AM." This is a dig at that step in front of the Sun-Mar toilet shown above, where you need to step up to clear the drum and the collection tray under. When Andy Thomson was going to put a Sun-Mar in the Sustain Minihome, he was going to chop a hole in the floor to drop it down to conventional toilet height.

You don't have to do that with an Envirolet; it doesn't have a drum, it doesn't have much of anything but a stainless steel rack. Envirolet says you don't want to crank the compost and mix it up; it cools down the compost, kills the aerobic reaction and is the wrong approach to composting. They design a wide box to allow lots of air circulation around the pile, and have a rake to knock the top of the pile off and spread it around a bit when it gets too high.

There is a handle on the side that opens a trap door once you are sitting down, so you don't have to look at the contents. Don't forget to turn that handle, like my mom did on my Envirolet. You then have a mess.

The unit has no drain, and a heating element helps the fan evaporate the liquid. When I bought mine, I was dubious about whether such a simple system could work, but it does, although I learned to control the amount of toilet paper that goes into it.

The Mulltoa Is Highly Automated


Multoa/ Lloyd Alter/CC BY 2.0

The Swedish designers of the Mulltoa (sold in the USA as the Biolet) have tried to make it as much like a conventional toilet as possible and for a self-contained unit, do a pretty good job of automating the process. Sitting down on the toilet activates the trap doors; closing the seat activates the" the stainless steel mixing mechanism that efficiently breaks down paper and distributes moisture into the compost material in the upper chamber." It now comes with LED indicators that tell you when it is time to empty the unit, and when it needs the thermostat turned up to evaporate the excess moisture.

IMG 2261 from Lloyd Alter on Vimeo.

One complaint about the Mulltoa has been that since sitting on the toilet opens the trap doors, it was hard for men to use to pee; some would sit, others would use their knee to hold it down. They've fixed that; now when you lift the toilet seat, the trap doors open.

There is a lot of tech in this toilet; mixer motors, sensors, lights. It's priced accordingly. More at Eco-Ethic

The Sun-Mar Centrex Separates the Processes


Centrex by Sun-Mar/ Lloyd Alter/CC BY 2.0

There are many people who simply cannot get used to the idea of composting toilets, that they are basically sitting on top of a pile of poop. The manufacturers get this and have been developing systems to address this. Sun-Mar offers the Centrex, a large-capacity design where they separate their drum from the toilet, which is raised above the unit. A marine-style valve toilet is installed above, so that for the user, it is flush-and-forget.

But it is not flush and forget for the owner/operator; I had one of these and had a lot of trouble with it. There is no limit to the amount of water that goes into it and in my family, they used a lot of it. The water has to go somewhere, and needs its own approved management system. I found that I was never getting really good compost, just soggy poop. (Sun-Mar says I was using the wrong bulking agents). Perhaps with a better installation and a family that wasn't so heavy on the footpedal it would have worked better.

Sun-mar Centrex

Lloyd Alter/CC BY 2.0

Sun-Mar also offers a dry version, where a dry toilet sits a distance above the drum and the poop drops through a 10" diameter pipe. Really, if you have the room, this is a better idea than the wet unit.

Envirolet Uses Suction and Limits Water


Envirolet/ Lloyd Alter/CC BY 1.0

Envirolet is taking a different approach to the flush-and-forget problem. They hook a vacuum toilet up to to a pump and macerator that just sucks it out of the bowl, using very little water, just enough to clean the bowl, really. It's all then pumped into the composter. It still needs maintenance; they are talking about automating the supply of bulking agent to the composter but haven't yet. It seems to solve the problem of too much water but is expensive, starting at $3700. This is a lot of money and a lot of technology to serve essentially one purpose: to make it feel like a regular toilet. But I am really beginning to wonder if the problem isn't the toilet, it's the people.

Envirolet dry

Envirolet dry/CC BY 2.0

Really, this is doing the same thing: a dry toilet well above the composter. So much less stuff if you can just get over the squeamishness of the idea that what comes out of your body isn't zipped away.

The Separett Separates the Urine


Separett / Lloyd Alter/CC BY 2.0

Except for the Biolan barrel, all the composters we have shown have heating elements to evaporate liquid, primarily urine. The Separett is different; it is a urine separating toilet. The urine is collected in a jug and diluted and sprayed around your garden; urine is sterile and is full of phosphorus so this makes perfect sense.


Lloyd Alter/CC BY 2.0

Inside, it is nothing more than a bucket lined with a bag. The bucket is rotated a bit when you sit on the seat so that it fills evenly, and since there is no urine, powerful fans dry the poop and suck away the smell. You then switch the buckets and either add some soil and let the bucket of poop sit for six months to kill all the pathogens, or dump it into another composter.

While I think urine separation is a great idea, I am not sure if I am ready to deal with a bucket of plain, unmixed poop. But in Sweden, thousands have. More at Separett and previously in TreeHugger.

Finding the Right Balance of Features

There are so many conflicting stories, so many contradictions. Some say you don't want to disturb the compost; others want to churn it. All say that it is a reaction that generates heat, but they run fans to evaporate moisture and take away smells. Water is the enemy of composting, yet the manufacturers keep making more elaborate and expensive ways of using it to simulate that flush-and-forget feeling.


Biolan Naturum/Promo image

Before going to the Cottage Life show I spent some time online studying the Biolan Naturum; I thought it might be the most interesting compromise of competing interests. It separates the urine so that there is less moisture to deal with; it is insulated and warmed inside by the composting action; it has a crazy rotating mechanism that moves the poop out of sight. It seemed like this might address all the issues. But the Biolan representative told me that they hardly sell any of them and didn't have enough room in the booth to show it.


Biolan Naturum/Screen capture

It's a shame, because there is a real need for a plausible alternative to the water flush toilet for the home, and while I have suggested before that we are getting close, we are not there yet.

See all our stories tagged Composting Toilets.