How Composting Toilets Work

Waterless composting toilets are a modern, stylish alternative to the standard flushing toilet. They are odourless, simple to install and very easy to maintain.

Instead of flushing waste away, compost toilets work to Water Saving Toiletsave water by breaking down waste without any water or septic tank connection.

  • All waste is captured by the toilet system, where it is broken down by microbes that naturally occur in organic material.
  • Usually a handful of sawdust is added to the system after each toilet use to help manage moisture levels within the system. Excess liquid is drained away to keep an optimum moisture level within the system while the ventilation shaft ensures adequate fresh air is circulating to keep the composting microbes happy and remove odours.
  • Once the system reaches capacity, it is emptied and the process starts again. The composting process creates a soil like substance called humus. Humus is a great soil conditioner and a natural fertiliser for plants. It can be added to the garden once the composting process is complete

Managing the Composting Process

maintaining moistureMaintaining an Optimum Moisture Level

Understanding the importance of moisture in a compost pile is key to understanding how composting toilets work.

Below a 40% moisture level, organic matter starts to become dehydrated and the composting process slows down. Above 60%, not enough oxygen is available for the microbes breaking down the waste, and the compost becomes anaerobic (no oxygen) and can start to smell.

To maintain the right balance, composting toilets separate liquids from solids, keeping the moisture content at an optimum level of 50%. A false or mesh floor within the chamber is often used to do this. Liquid drains away through the floor and then into an absorption trench in the ground. Liquid can also evaporate through the ventilation system.

A handful or two of sawdust is added to the system after every use to absorb excess moisture and aid the composting process.

Thermophiles and MesophilesCompost Temperature

Like the moisture level, the temperature of the compost is also important to the fast breakdown of organic matter. Naturally occurring microorganisms that live in the compost generate heat while eating and multiplying.

There are two types of microorganisms that live in compost: Mesophilic organisms, who like to live in temperatures up to 40°C, and thermophilic organisms, who thrive in temperatures from 41 to 80°C. Thermophilic organisms are the most efficient of the two types of microbes. This is why composting toilets are designed to trap heat within the system.

Keeping compost temperature high is also very important for health reasons. Many pathogens, or disease-causing bacteria, die at temperatures greater than 55°C, so it’s smart to keep the compost nice and warm at all times.

When the composting toilet is full, the chamber is sealed and often placed in the sun. Again, this keeps the thermophilic microbes working hard by keeping the temperature high. In colder climates and in winter, the compost can be insulated and kept inside a shed or other outdoor storage area to maintain a high temperature until it is ready to be used.


Diagram of a composting toiletVentilation and Oxygen Supply

The final ingredient for healthy compost is ventilation.

Thermophilic microbes need oxygen to break down waste efficiently – in fact, they need several cubic metres of oxygen every day to stay active. Unlike septic tanks, which work anaerobically and can develop unpleasant smells, composting toilets stay odour free because they have adequate ventilation allowing the microbes to breathe. The ventilation further ensures any odour is quickly removed from the compost.

Wally's Microbe MixCompost Microbe Booster

Adding a good quality microbe mix booster such as Water Wally’s Microbe Mix  to your toilet (mixed with a bulking agent) once a week is a great way to keep your toilet working well in times of heavy use, cold weather or when someone is using broad-spectrum antibiotics.

By topping up the levels of microbes regularly, you can ensure a healthy toilet and a fuss free composting process.