We’ve looked at cheap and cheerful home-made DIY compost toilets; waterless, sawdust toilets which are basically a bucket you need to empty yourself every few days. These systems work, speeding up the action and fertility of a conventional compost heap and providing an extremely environmentally friendly way of dealing with human waste. But, being of a ‘back to basics’ nature they really are not for everyone.
If you prefer a less hands on approach to the waterless toilet you can buy self contained compost toilets instead. These self contained systems are a very glamorous version of the bucket compost loo. Whereas a sawdust toilet merely stores your poo until it is added to a compost heap to break down, these self contained waterless toilets keep hold of the waste till it has decomposed completely. You do need to empty them, but rarely, and then you only ever remove a small amount of completely decomposed hummus which basically resembles a small tray of soil. A job even the most squeamish should be able to manage.
How Self Contained Compost Toilets Work
Lifting the lid on a self contained toilet should hold no surprises. Baffles usually hide the addition of the previous occupant, perhaps the biggest ‘put off’ for most people when confronted with a basic sawdust toilet. My particular favorite model actually has sensors in the seat which open the baffles when it feels the weight of a new occupant. That’s a much more sci-fi composting toilet than ours!
The addition of a chimney stack allows air to flow into the compost drum. This additional oxygen is crucial for the waste to compost aerobically.
The vent stack also allows water to evaporate from the human waste. This reduction of the liquid content completely changes the process. Evaporation reduces the bulk of waste material by up to 90%. So in simple terms the drum will take ten times as long to fill as my rustic sawdust toilet.
With most commercial self contained systems there is a fan incorporated into the vent stack to improve air circulation, removal of odours and evaporation. These fans can be run from the mains or battery power. If you’re off grid like us, double check the power consumption of the fan as they vary widely. You should be able to find one which is low enough wattage to run on the most basic of solar set ups. If you can put the vent pipe in with no bends, and a good roof clearance there are several models which will work well without a fan in operation.
At the base of the compost toilet is a reservoir for the water content of the waste. This then evaporates via the vent stack. However, the less power the fan uses the more chance there is of liquid building up and you may find you actually need to install an emergency overflow to cope with this, particularly if you use your self contained composting toilet on a continual basis.
The general idea with these self contained composting toilets is that the waste drops into a drum which you intermittently rotate. This keeps everything loose and ready to break down. Underneath the drum is a tray which collects the resulting hummus. You leave this hummus for at least a month before emptying. So you never go near any non-decomposed waste at all.
These self contained systems obviously have a limited capacity so it is crucial that the correct sized system is purchased. The cheapest models are really only suitable for occasional use. All sizes tend to come with the proviso that an overflow is fitted if there are likely to be significant numbers of extra people using the system. So for parties or weekend gatherings it might make sense to offer your male guests the use of a straw-bale in the yard for urinating.
Self contained compost toilets are odourless and very low maintenance. In homes they will need to be partially emptied every few months. Sawdust toilets on the other hand need to be completely emptied of fresh human waste every few days.
But, they are not as versatile as a more basic system. You really need to install the correct model for the volume of use you expect in the long term. Having to connect an overflow for excess liquid to run off might well be an installation process too far, when the whole concept is to have a self contained unit which can be sited anywhere.
For a more self sufficient future