A composting toilet is a toilet that uses no water to flush. For most of us, that conjures up visions of smelly pit toilets encountered on camping holidays. But modern composting toilets have come a long way in recent years. They are now sophisticated systems that will break down your waste and turn it, as their name suggests, into compost. A properly maintained composting toilet won’t smell – in fact it can even leave your toilet or bathroom smelling better than a conventional toilet.

How they work

Composting toilets work by providing a suitable environment for aerobic decomposition – the same process that breaks down organic waste in a garden compost bin, or animal droppings in the wild.  At a glance, a composting toilet looks like a pit toilet, with a seat and a chamber below. Instead of flushing you simply close the lid after use. Extraction vents generate a gentle flow of air through the chamber that helps to aerate waste, extract the moisture and expel odours. Some brands of composting toilet have fans and/or heaters to dry the waste more quickly. Some use worms in the composting chamber to help break down matter.
As the water is extracted, the remaining matter gradually breaks down to produce compost.
It can take from six months to up to three years for the waste to be fully composted. The compost is then removed and can be dug into your garden as fertiliser. People are often surprised how little composted material is left after the water content has been extracted.
Composting toilets also produce a small amount of liquid, which is normally drained off into the soil or into a tray where it can evaporate.

The composting process can be helped by throwing in a handful of dry leaves or sawdust, either daily or each time the toilet is used. This ensures a good carbon-nitrogen mix, which helps aerate the pile and prevents compacting. You can keep a bowl of sawdust beside the toilet and throw in a scoop after using the toilet.  

Types of composting toilet

Composting toilets can be divided into two types: batch systems and continual processing systems.  Batch systems consist of two or more chambers in the collection unit below the pedestal. When one chamber is full, it is rotated or removed to continue composting, while another chamber fits beneath the toilet.

Continual processing systems consist of a single chamber, with the waste gradually moving down as it composts over a period of six months to a year. The processed compost is then removed from the bottom.

Batch systems take up a bit more space than continual composting systems as you need space for two or more collection chambers. Manufacturers or retailers can recommend a suitable model for the amount of use it will get (depending on the number of people using it, whether it is for a main home or a weekender, and so on), and the space you have available.

Smell

Most people’s first reaction when they hear about composting toilets is to assume that they smell. In fact the opposite can be true. A composting toilet’s constant extraction system will remove odours from your bathroom or toilet even when you are not using the toilet. That can leave your bathroom smelling better than a conventional toilet.  If a composting toilet does smell, it indicates it has not been installed or operated correctly.

Environmental benefits

Composting toilets offer important environmental benefits:

1. They don’t need water: a composting toilet can reduce your indoor water use by about a third.

2. They create compost: this returns nutrients to the soil and means you don’t need to use chemical fertilisers

3. They process waste on-site: this reduces the need for sewage systems and reduces the amount of sewage that gets pumped out into waterways and oceans.

Other benefits

1. A composting toilet can eliminate the need for a sewage system on remote properties.

2. It is possible to compost other organic matter, such as food scraps, in a composting toilet.

Installing a composting toilet

Composting toilets require some space underneath the toilet for the composting chambers.  You can either install them on a raised platform with a pedestal, or you can install the toilet like a conventional toilet, with a pit sunk into the floor beneath.  Composting toilets work best when kept warm so are best located in a warm part of your home.

Health regulations

Composting toilets are well-established in Australia and most councils can advise you on the health regulations governing their installation. Manufacturers and suppliers of composting toilets will also be able to advise you on health regulations.  The processed compost ought to be safe to use as fertiliser in your garden, although to be on the safe side it is best not to use it on vegetables.