How Does A Composting Toilet Work

How Does A Composting Toilet Work -
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How Does A Composting Toilet Work

You may have heard about composting toilets before, and what their benefits and uses are. They save water and electricity, they are easy to use, and eco-friendly too. It’s actually quite ingenious, but how does a composting toilet work?

What is a Composting Toilet?

A composting toilet is a special kind of toilet, which instead of flushing solid waste down the pipes into a local or municipal sewer system, keeps the waste onboard and allows it to compost.

The basic function of a composting toilet is that the waste passes down into a holding tank or chamber, where oxygen and bacteria cause it to break down quickly. In other words, with a composting toilet, you can turn human waste into compost that can then be used to fertilize a garden.

The Basic Features and Functions

Composting toilets are actually quite simple and straightforward, and there is not all that much that needs to be said here in terms of their function. That said, there are a few key features and functions of the composting toilet, which make it what it is. Let’s take a look at the main features and how they work to effectively compost your waste.

Liquid Waste Separation

Many composting toilets will come with a special urine separator. The reason for this is because liquid waste, your urine, is not going to compost, and therefore needs to be taken care of separately. Some composting toilets will separate the urine using some method, and it is then stored in a separate holding tank which needs to be emptied when it starts to fill up.

Although, some composting toilets do not come with this feature and store the liquid waste in the same area as the solid waste, in which case it is the process of evaporation that takes care of the liquid waste.

Some composting toilets even feature a separate urine evaporation chamber just for this. Moreover, some composting toilets feature a drain or overflow valve system which can be used to drain the urine into a drain, sewer system, or even just into a hole in the ground.

Self-Contained vs. Central Units

Another thing which you need to know about composting toilets is that there is a difference in terms of waste storage. So, the basic principle here is of course that your solid waste goes into a holding tank, otherwise known as the composting chamber, where it then breaks down into compost which you can use for fertilizing your garden or lawn. However, there is a difference in terms of where that compost tank is placed.

First off, you have self-contained composting toilets, which feature the holding or composting tank right below the toilet bowl. These are very easy to install and empty; they don’t take up much space, and they tend to be very cost-effective.

On the other hand, there are central units, which feature the toilet in a bathroom which then requires some sort of drain or plumbing which carries the waste from the toilet bowl into a separate composting or holding tank in another location, usually in a room below or beside the bathroom.

The Composting Process

The next thing you need to know about has to do with the composting process itself. The liquid waste has been separated from the solid waste, and the solid waste has made its way into a holding tank or composting chamber, but what happens in these chambers? Human waste decomposes pretty quickly, but it still takes some time.

In most high-quality composting toilets you will find some sort of crank handle agitator, which is used to stir the waste around, introducing more oxygen, which aids in the decomposition, into the mix. The more oxygen present, the faster the waste will decompose. Anaerobic bacteria feed on the waste, mainly compounds in the waste, and through this bacterial breakdown process, these bacteria turn human waste into compost.

Another thing to keep in mind is that some composting toilets have this all happen in one tank. However, there are higher-quality models which then send the composted waste into a second or third chamber, which lets the compost dry, so it is ready for use.

Venting Features

The other thing that can come in handy with composting toilets is the venting feature. Not all composting toilets come with air venting features. Some simply send the waste down into the holding tank where it sits until it is fully composted. The agitators help add air to the mixture, but in all reality, for this process to work effectively, better venting is required.

This is why many composting toilets come with venting hoses and electric air fans to help push air out. More than anything, this helps to prevent the buildup of foul odors and noxious gasses associated with human waste.

Not all composting toilets feature this, but it is definitely a great addition if you have a few extra bucks to spend. It really helps cut down on gases and smells that nobody wants to deal with.


So there you have the basic functions and features of a composting toilet. More or less, if you have a high-quality model, the liquid and solid waste will be separated, with the liquid waste being stored in an evaporation tank, a holding tank, or being drained off in some manner. 

The solid waste enters the composting tank, where oxygen and bacteria break the waste down until it is usable compost. It really doesn’t get much easier or more eco-friendly than that!

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