Every year I hit Toronto's Cottage Life Show to see the latest in technology for living in the woods, and every year there is another composting toilet idea. Trying to deal with human waste without simply flushing it away is a continuing challenge for designers; you can call it compost but it is still poop. Smell is also a big issue; when I had an Incinolet incinerating toilet, the pall of poop smoke could hang around the cabin for hours. With our current Envirolet composter, there is no odor most of the time (at the beginning of the season it can smell of cooking urine for a while) but we have to live with the constant drone of the fan.
Finnish composting toilet manufacturer Biolan has another idea I had not seen before: Freeze the stuff. The Icelett has a refrigeration unit that chills the poop down to -15 degrees Celsius (5 degrees Fahrenheit) which kills any biological activity and smell. It needs no vent pipe or drain; just plug it in. It won't be warm and toasty to sit on like most composters, but the manufacturer claims: " Thanks to the heat lock formed by the condensing air, the Icelett is pleasant to sit on, and the seat does not feel cold."
There are a couple of issues; the unit uses 1.44 kWh/day, which isn't much but is more than other composting toilets. (Many designs have heaters in them to increase the rate of composting and to vaporize urine, and this is comparable). It's not for hot climates; they write that for normal usage the ambient room temperature should not be higher that 25 °C. (77F). I suspect that it will smell a bit until the stuff freezes, and when you empty it, you are dealing with straight poop, and have to then put it into a composter.
To be honest, I have always been a bit dubious about Biolan composting toilets, since they have no heaters and no mechanical ventilation. I described them a few years ago and wondered:
According to the distributor, adding a peat moss and sawdust mixture after each use and sealing it up tight generates enough heat and biological action to do the job and evaporate most of the liquid. The literature says that it can serve a family for a year without emptying. Most of the other composting toilets we know of have mechanisms to aerate the poop and electric fans to keep the air moving; this has none of that. Can something so simple work and be odorless as the manufacturer claims?
I am more convinced about their Naturum model. It is a urine separating toilet; most of the smell actually comes from urine, and most of the work done by heaters in conventional composting toilets is to evaporate it. The poop also composts much more quickly when it is separated. They also have an optional fan and even have instructions for connection through a heat recovery ventilator. More at Biolan
There are two distinct paths in the composting toilet world, simplicity like the Biolan, which requires some work, perhaps a bit of smell and definitely getting used to a different experience, or the high tech world of the Envirolet VF, where one has an almost conventional toilet connected to a vacuum pump and macerator, which then pumps into a composter. More water, more electricity, more equipment and you still have to get your hands dirty and empty the composter. I think there is a compromise somewhere in the middle.