How do Composting Toilets Work? Understanding the Process

Composting toilets are an innovative and environmentally-friendly alternative to traditional flush toilets. They aim to reduce water consumption and provide a sustainable method of waste disposal - converting human waste into nutrient-rich compost.

As concerns about water scarcity and environmental impact increase, it's crucial to understand how these systems work and why they are becoming more popular.

A composting toilet (sometimes referred to as an eco toilet) functions by breaking down waste matter through a natural process of aerobic decomposition.

This process involves the combined actions of bacteria, fungi, and other microorganisms, which convert the waste into compost over time.

By controlling factors such as temperature, moisture, and ventilation, composting toilets can effectively and safely manage waste without the need for large amounts of water.

The Green Loo Scandi-Pod (2-3 people part time) compact composting toilet system.

There are various types of composting toilets, each with their own design elements and methods to suit different needs and preferences.

Some systems incorporate additional features such as urine separating, which helps to reduce odours and speed up the composting process (although not always).

Despite the variations in design, the core concept of conserving water and promoting sustainable waste management remains the same across different models.

What is a Composting Toilet?

The best composting toilet depends on your needs. (RV, tiny home, 1 person or 4?)

A compost toilet is an environmentally friendly alternative to traditional flush toilets. It functions by breaking down human waste into harmless, nutrient-rich compost through a natural decomposition process.

Unlike conventional sewage systems, composting toilets do not require water or connection to a sewer line, making them ideal for off-grid living or areas with limited water resources.

The primary components of a composting toilet are the waste collection chamber, a ventilation system, and a finishing compartment or external composting bin.

Human waste, along with toilet paper, is deposited directly into the collection chamber, where it mixes with a bulking agent, such as raw pine wood shavings.

The bulking agent helps to balance the carbon-to-nitrogen ratio, creating ideal conditions for aerobic bacteria to thrive and break down the waste.

A composting toilet consists of recycled materials (hopefully!) and maybe a LED indicator like this RV Pod.

Note: The RV-Pod (above) diverts urine only because it is more often used for people ‘on the go’ that will dispose of the waste instead of using it for compost. 

The ventilation system plays a crucial role in maintaining air circulation and preventing odours. It draws fresh air into the chamber, promoting aerobic decomposition while venting excess moisture and gases, such as carbon dioxide and ammonia, to the outside environment.

Proper ventilation is vital to prevent the growth of harmful pathogens and unpleasant smells.

Once the waste has been thoroughly decomposed into compost, it can be removed from the finishing compartment or external composting bin. The resulting compost is rich in nutrients and can be used to fertilise plants and gardens.

However, it is essential to practice proper hygiene and follow local regulations regarding compost usage, as the potential presence of pathogens in human waste compost may pose health risks if not handled correctly.

In summary, composting toilets offer a sustainable and water-efficient solution for managing human waste. With proper maintenance and responsible disposal of compost, they can be an eco-friendly alternative to conventional flush toilets.

Functionality of Composting Toilets

Empty a composting toilet every few months using under-floor compost chamber (ex: Green Loo GL 90).

Collection Chamber

Composting toilets utilise a collection chamber to store and process human waste. Users deposit waste into the chamber by sitting on a standard toilet seat, often with a trap door or sliding mechanism preventing odours from escaping.

The collection chamber typically contains a mixture of carbon-rich materials such as sawdust, peat moss (non-renewable), or raw pine wood shavings (recommended).

This mixture plays a crucial role in absorbing moisture and promoting aerobic decomposition, which effectively breaks down the waste into compost material.

Aeration Process

Proper aeration is essential for the effective and odourless decomposition of waste in composting toilets. By keeping the chamber well-ventilated, oxygen-rich air can circulate throughout the system, promoting aerobic bacteria's growth.

These bacteria break down the organic matter in waste, converting it into a nutrient-rich, humus-like substance known as compost.

To aid in aeration, some composting toilets use mechanical mixing systems or manual cranks to regularly stir the waste and carbon-rich materials inside the chamber.

Moisture Evaporation

Moisture evaporation is another vital component of composting toilets' functionality. Excess liquid in the collection chamber can contribute to unpleasant odours and anaerobic decomposition, which is less efficient and produces foul-smelling byproducts.

To address this issue, composting toilets use ventilation systems and evaporation techniques to reduce moisture content in the chamber.

For instance, some systems have fans to promote air circulation, while others utilise a separate chamber for urine diversion, filtering the liquid waste for evaporative purposes.

As a result, maintaining the appropriate moisture levels within the composting toilet ensures efficient and odour-free waste processing.

Benefits of Composting Toilets

A self contained composting toilet from Nature Loo showing interior compartment.

Compost toilets offer several advantages that make them an attractive option for many people. These benefits include reduced ecological impact, water conservation, and efficient waste management.

Environmental Impact

Composting toilets have a significantly lower environmental impact than traditional toilets. They help to prevent the pollution of water sources by reducing the amount of sewage that enters rivers, lakes, and oceans.

By keeping human waste contained, they also help limit the spread of harmful pathogens and reduce the chances of contaminating local ecosystems.

In addition, the compost produced from these toilets can be used as a nutrient-rich fertiliser for plants, reducing the need for chemical fertilisers and promoting sustainable agriculture practices.

Water Conservation

One of the significant advantages of composting toilets is their ability to conserve water. Traditional toilets use large amounts of water for flushing, which can put a strain on local water supplies, particularly in areas prone to drought or with limited access to freshwater.

In contrast, composting toilets do not require any water for flushing, making them an ideal solution for conserving water resources. This is particularly important as concerns about water scarcity and the need for sustainable water management practices continue to grow.

Waste Management

Composting toilets are a practical and efficient means of managing human waste. They work by breaking down solid waste and toilet paper into compost through aerobic decomposition, reducing its overall volume and potentially converting it to a useful end-product.

This waste reduction means that the need for complex sewage systems and water treatment plants is minimised, leading to less infrastructure and maintenance costs.

Additionally, composting toilets help to reduce the reliance on environmentally damaging methods of waste disposal, such as landfills and sewage dumping, which can contribute to water pollution and other problems.

By opting for a composting toilet, users are actively choosing a more sustainable and responsible waste management method.

Types of Composting Toilets

Some toilets separate solid and liquid waste although GreenLoo advocate against urine diversion (above: Green Loo Oz-e-Pod).

Quick Note: The Oz-e-Pod (above) is not urine diverting. Green Loo has suggested not using urine diversion (compost needs moist, so removing urine is detrimental).

Self-Contained Units (Pods)

Self-contained composting toilets are designed to have all components in one unit, often making them suitable for small spaces (like tony homes!) where no under floor space is required. They typically consist of a toilet seat, drum, or box where waste is collected and composted.

These toilets require regular maintenance, such as turning a handle to aerate the compost or adding bulking agent to facilitate the composting process. The finished compost can be removed and used in the garden, following the manufacturer's guidelines for safe handling.

Some advantages of self-contained units include:

  • Easy installation
  • Minimal plumbing requirements
  • Flexibility in usage locations

Central Units with external compartment

Central composting toilet systems consist of a separate toilet fixture connected to a central composting container, which is typically located outside the living space, such as in a basement or a separate compartment.

The waste is either transported using gravity, a vacuum, or a small pump to the composting container. Over time, the waste breaks down into usable compost, which can be removed and used in non-edible landscaping applications.

Central units offer more capacity and can accommodate multiple fixtures, such as a toilet and urinal. These systems are beneficial for larger households or facilities with higher usage demands.

Key features of central composting toilets include:

  • Ability to support multiple fixtures
  • Larger capacity for waste processing
  • Separate composting container for odour control and ease of maintenance

Both types of composting toilets serve their unique purpose and cater to different requirements.

While self-contained units are ideal for RVs, tiny homes and smaller usage, central units provide an effective long-term solution for bigger households and facilities.

Maintenance and Usage

The EcoLet Separera can be used as an RV composting toilet and/or for tiny homes, boats, caravans etc.

Composting toilets require regular maintenance to ensure proper functioning and odour control. In this section, we will discuss the use of composting additives, waste removal, and other important aspects of maintaining a composting toilet.

Composting Additives

Composting toilets employ different types of microorganisms to break down waste into a nutrient-rich compost. These microorganisms require a proper balance of carbon and nitrogen-rich materials, moisture, and oxygen to thrive.

As a result, it may be helpful to add specific composting additives to facilitate the composting process:

  • Sawdust or peat moss*: These carbon-rich materials help to balance the nitrogen content of the waste and control odour.
  • Baking soda: Sprinkling baking soda into the toilet can help neutralise acidity and control odours.
  • Compost starter: Adding commercially available compost starters introduces beneficial microorganisms and enzymes that accelerate decomposition.

It is essential to follow the specific recommendations for the composting toilet model in use, as each system may have unique requirements for optimal performance.

* Sawdust is not recommended as it tends to be too fine. If using sawdust, the waste pile will compact and run a risk of becoming anaerobic. Peat moss is a non-renewable source. Instead, use raw pine wood shavings or hemp shavings (easy to find at produce stores).

Astronauts need to go to the toilet too!

Waste Removal

Periodic waste removal is necessary to prevent the composting chamber from reaching capacity. The frequency of waste removal depends on the size and type of the composting system as well as the number of users.

Generally, waste removal is required every six months to three years. Below are some essential points to consider during the waste removal process:

  • Identify the removal schedule: Consult the user manual or manufacturer guidelines for the recommended waste removal frequency for your particular composting toilet system.
  • Wear protective gear: When handling compost, always wear gloves, a mask, and protective eyewear to protect against possible pathogens.
  • Clean the chamber: Empty the compost chamber according to the specific process outlined in the user manual. This may involve removing a tray or accessing a separate compartment to retrieve the compost material.
  • Monitor the compost: Ensure that the compost is dark, crumbly, and earthy-smelling, indicating completion of the decomposition process. If the compost appears to be too wet, consider adding more bulking material like raw pine wood shavings or hemp shavings to improve aeration and maintain proper moisture balance.
  • Use or dispose of the compost: Finished compost can be used in gardens as a soil amendment or disposed of at a designated composting facility.

Source images used on this page:

Common Misconceptions

Many people have misconceptions about composting toilets, often stemming from lack of knowledge or negative experiences. One common belief is that composting toilets are unsanitary and produce foul odours.

In fact, properly maintained composting toilets are remarkably clean and odour-free, as they rely on the natural decomposition process to break down waste.

Another misconception is that composting toilets require constant attention and difficult maintenance. While they do demand some care, this is generally minimal and straightforward.

Composting toilets typically need to be emptied and cleaned at regular intervals, and users must ensure that the ratio of carbon-rich material is properly balanced with waste.

Thirdly, some people assume that composting toilets are only suitable for off-grid or rural environments. However, they can also be a viable option for urban areas, particularly where water conservation or reducing sewage waste is a priority.

In addition, there are composting toilet models specially designed for temporary use at events or construction sites.

A fourth misconception is that composting toilets pose a risk to human health due to the presence of pathogens. While it is true that raw human waste contains pathogens, the composting process effectively destroys harmful microorganisms when done correctly.

You need to work out where your (giant) compost pile is going to live!

Proper composting generates high temperatures, which kill pathogens, and the final compost product is safe for use in gardens or landscaping.

Lastly, some individuals believe that all composting toilets are expensive and only available to a select few. This is not the case, as there are various models on the market at different price points, ranging from basic and affordable to more advanced and costly systems.

In conclusion, clearing up these common misconceptions can help demonstrate the benefits and practicality of composting toilets. By understanding the facts, more people may consider using these eco-friendly alternatives to traditional 'everyday' toilets.

Frequently Asked Questions

How does a composting toilet work?

A composting toilet is like a special toilet that helps turn poo and pee into dirt that can be used to help plants grow. It does this by separating the pee and poo and using natural processes to break them down into dirt. Some of these special toilets use electricity or air to help speed up the process, while others just use natural bacteria and air. This helps the environment by reducing the amount of waste that needs to be treated in other ways.

Can a composting toilet system stink up your house?

Modern composting toilet systems are designed to minimize odours through the use of ventilation and sealing mechanisms, and when used properly, they do not create unpleasant smells.

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