Here’s an interview with Joe Jenkins, author of The Humanure Handbook, a guide to compost toilets. Composting toilets are a potentially very good idea – they could save enormous amounts of water, energy, and money everywhere, address problems caused by aging and inadequate wastewater infrastructure in developed countries, and bring life-saving basic sanitation to billions who don’t have it now.

There are commercial composting toilet systems available – you can see some in Chapter 6 of Jenkins’s book. I don’t know why they have not caught on more widely. Maybe it’s a case like the QWERTY keyboard where the design that caught on is not the best one available, but simply an adequate design that got implemented at scale first, and is now hard to displace. Or maybe the designs are too expensive and/or just not good enough to overcome the incredible power of social taboos about human waste, which are not to be taken lightly. If this is the case, the technology may be stuck in a chicken and egg problem where it is not quite good enough to be adopted on a larger scale, and it is not going to be improved unless and until it is subjected to a larger marketplace. People are not going to take a risk on it as long as they are content with the flush toilet system they already have. That said, it really would not be rocket science to come up with better designs. It would just have to be taken seriously as a research and development project and have some real resources thrown at it, the kind of resources we routinely throw at weapons, chemicals, drugs and electronics.

Let’s assume we get to a better, cheaper composting design that everyone will want in their house – what then? The composting toilets people are using now need a carbon source such as sawdust to balance out the nitrogen in the feces. That is fine on a small scale, but on a large scale we would now need a system to produce and distribute sawdust or something similar to billions of people. That sounds like a sustainability problem. A possible solution there would be to build the carbon source into packaging of consumer products – instead of all the plastic wrap we use now, make consumer packaging out of some sort of carbonaceous waste (corn stalks, switchgrass?). When people unwrap things they would just throw it into the toilet.

The next problem is what to do with the compost. Compost is great stuff that gardeners love. But not everybody is a gardener, and now you have done this on a large scale. You have to collect the stuff and get it to gardens, parks or farm fields where it can be used. So now you are back to a system of trucks or pipes to do this – not much different from what we do now, except you have moved the treatment step from the central wastewater plant to individual homes.

A biogas system is a possible alternative technology. Instead of the aerobic composting system, you would put your bodily waste, carbonaceous packing material, and food waste (the same ingredients from your aerobic system) in a sealed reactor with the right microbes to break it down to methane. The solids remaining should be less than with the aerobic system although you still have to deal with them. You can use the methane for anything you use natural gas for now – heating, hot water, or electricity which you can either use or sell back to the grid. An intriguing possibility is to feed it into a fuel cell rather than burning it. Whereas both aerobic composting and combustion will liberate the carbon from the carbon source back into the atmosphere (if the carbon source is plant-based, it will be the same carbon absorbed from the atmosphere when the plants were grown), an ideal fuel cell (which may not have been invented yet) theoretically will produce only electricity, clean water, and elemental carbon. So in theory, the carbon is sequestered. You still need to pick it up and do something with it. Since I’m daydreaming, we’ll use some kind of biotechnology to turn it into cement.