How Does a Composting Toilet Work?

It was finally my turn.

After standing under the blazing sun in the September heat, I opened the door to the port-a-potty. A blast of the most putrid, horrid smell hit me like a ton of bricks.

And that experience is exactly what crossed my mind the first time I heard about a composting toilet. I mean, surely these things must stink up your home/boat/RV/wherever else they get used, right? As it turns out, they don’t. Modern composting toilets are actually highly efficient at breaking down waste and doing so without releasing that ton of bricks.

Important Features of a Composting Toilet

How does a composting toilet work? While there are a wide variety of composting toilets on the market, they all work in a similar fashion. They are made up of a toilet seat, a composting bin, a ventilation fan, a way to turn the compost and an access door to remove finished compost.

Many also have a system of separating urine, which is important for two reasons. One, urine actually has a strong scent and is the main reason port-a-potties smell so bad. Two, a key part of the composting process is removing all the excess moisture. If urine was not separated, the composting process would take much, much longer.

Another feature some composting toilets have is a heater. This is particularly important in areas where the temperature drops. Heat is a fundamental component of the composting process. When it gets too cold, the material stops breaking down and your compost bin simply becomes a storage container until it warms back up.

How Composting Toilets Break Down Waste

Composting toilets function basically the same way as your backyard compost bin. Aerobic bacteria breaks down the material into usable soil. In order to do this, the composting bin at the base of the toilet needs to create the right environment for this bacteria to work its magic.

As mentioned above, heat is absolutely essential, along with some moisture and the right amount of oxygen. You also need to add the aerobic bacteria to the bin to get things started.

The aerobic bacteria is added via a composting medium. This can be dirt, peat moss or coco coir. Most composting toilet users recommend avoiding dirt since this can lead to bugs in your bin, which is something you definitely do not want (if bugs do become a problem, you can use diatomaceous earth to get rid of them). Between peat moss and coco coir, I’d recommend the latter since it’s a bit more environmentally friendly.

Once the composting medium has been added to the bin, your composting toilet is ready to use. After the toilet has been used a few times, it’s time to start rotating the agitator. The agitator is typically a stainless steel mixer inside the bin that rotates when you turn the handle on the outside of the toilet.

Most composting toilets will need the agitator rotated every few days or about twice a week. This helps the compost break down quicker by exposing it to oxygen and moving around that aerobic bacteria.

The amount of time that passes before the compost is ready to be removed varies from toilet to toilet. Some composting toilets won’t actually finish the composting process because their bins are too small. This is a common issue on boats where there isn’t space for a larger compost bin.

Illustration: Shutterstock

On composting toilets with larger bins, it may take months to a few years before the composting bin needs to be emptied. Larger composting toilets will often have separate bins, one for new waste that is just beginning the composting process and a separate bin for compost that is completed. The compost moves from one bin to the other via agitators and screens.

Once completed, this compost can be used around trees or other plants in your yard.

While a composting toilet may seem like a huge inconvenience to you, it can drastically reduce your water usage and you’ll know exactly what’s happening to all the waste you produce. If you’re interested in using a composting toilet in your home, be sure to check your city/county building code, as many have specific requirements.

Read More:
Solar Composting Toilets Highlight Green Changes to NYC Park
Composting Toilets: Why We Should Give a Crap
Streets Made from Toilets: Gross or Green?

By Brian Brassaw

Brian formerly managed the Earth911 Recycling Search and shared green living tips and tricks on Earth911’s Instagram, Pinterest and Twitter accounts. Brian also shares DIY projects on Little Pilots Lounge.