As we learned in the previous post on greywater, blackwater—that is, wastewater from toilets—contains far more contaminants than greywater (from other domestic sources), and is correspondingly more hazardous, and more expensive to treat.
And untreated sewage is a big health problem in many places around the world. But is all this sewage really necessary?
Normal flush toilets add human waste to clean fresh water, before flushing the mixture away into the sewers. In essence, this means turning two valuable resources into an environmental problem. It’s a broken system.
We can close this broken cycle and eliminate sewage at its source, by composting human waste on site using a dry composting toilet.
The simplest type of dry composting toilet is known as the Humanure toilet. It consists of a bucket with a seat, which can easily be home-made, to which sawdust or a similar cover material is added after every use.
When the bucket is full, it gets emptied into a compost pile, where it breaks down into compost that can be used on the garden—though it’s always best to avoid contact with vegetables that will be eaten raw, in case some pathogens remain.
Another type of composting toilet has two composting chambers each with its own seat. One chamber is in use while the other is composting down. Again, sawdust is added after each use, but the chambers only get emptied about once or twice a year.
There is also a wide range of commercially available composting toilets, from small ones that fit in a tiny house or a camper van,
to high-end, free-standing composting toilets that come with every convenience, like these ones near Ben Nevis in Scotland.
Some composting toilets separate urine from feces, others don’t—there’s no single right answer. The range of possible designs is endless, but the principle remains the same: dealing with human waste safely on site by making it into valuable compost.