Guide for composting toilets

Composting toilets are not a recent invention. The need for alternative waterless toilet systems first arose from outbreaks of disease, such as the cholera epidemic in nineteenth-century London, which was traced back to the city’s contaminated wastewater and resulted in thousands of deaths. Despite these early challenges, the ‘water closet’ (WC) eventually became the standard, reaching even the most remote rural areas by the mid-20th century. However, the concept of the environmentally friendly toilet that conserves water persisted and gained notable supporters. For instance, the architect Friedensreich Hundertwasser built his own composting toilet in the 1970s and praised its benefits.

Today, composting toilets are experiencing a resurgence due to increased environmental awareness, permaculture, and the revival of the self-sufficiency movement. The following section will explain how composting toilets work, where they are currently used or applicable, and the benefits and drawbacks to consider.

The purpose of a composting toilet is evident from its name: it transforms human excretions into nutritious compost or humus, which is beneficial for the soil. This process helps close the natural cycle of food production, intake, and excretion. Composting toilets utilize various microorganisms, such as compost insects, worms, bacteria, algae, and fungi, to process urine and feces. Additionally, composting toilets operate entirely without water, eliminating the need for a connection to the sewage system. This makes them an environmentally friendly alternative to conventional toilets that conserve water.

If you think that a waterless operation inevitably leads to unpleasant odors, you’re mistaken! The use of litter helps to absorb and bind the liquids in the waste, and the exhaust system effectively manages and reduces odors.

The principle of a composting toilet is straightforward. As described, the excretions are collected and processed into compost, which is then returned to nature in a nutrient-rich state. However, the composting method can vary depending on the model. Some toilets perform only pre-composting, while others achieve complete composting, meaning a full conversion of the excretions into compost within the toilet itself.

The capacity of the collection container plays a crucial role in this process. Models with a capacity between 20 and 200 litres typically only collect and store the excretions until the container is full and the excretions have undergone a certain degree of pre-composting. To expedite the fermentation process and reduce the volume of the excretions, heaters or stirring units (either electric or manual) are often used. Once the container is full, it is emptied, and the waste is either added to a garden compost or taken to a central collection point where it is fully composted after a resting period.

In composting toilets with an integrated composter, the decomposition of collected excretions occurs directly and completely within a special bioreactor. Since the transformation of excretions into finished compost typically takes 24 months, the collection container usually needs a capacity of several hundred litres to accommodate the decomposition process.

Additionally, air supply in toilets with integrated composters must be carefully regulated. Oxygen is crucial for composting, but it also produces decomposition gases and heat that need to be managed. This is achieved through a ventilation system. Depending on the model, this system may use either an electrical exhaust air system, which increases electricity costs and requires a power connection, or a non-electric exhaust air system that relies on the chimney effect. The chimney effect utilizes ascending warm air from the composting process to direct gases outward.

Depending on their design, toilets with integrated composters may require additional electrical accessories, such as rotary vessels, heating rods, or stirring units, to facilitate the composting process. However, more advanced models can operate without electricity, further enhancing their environmental benefits.

For models with collection containers and those with integrated composters, using the toilet is similar to using a conventional toilet. The sitting position and the act of using the toilet remain unchanged. The main difference is the absence of a flush, as excess liquid can disrupt or prevent the composting process. Instead, litter is added to the excretions. While this may seem unusual at first, it offers both financial and environmental benefits: the waterless operation saves water and eliminates the need for complex wastewater treatment. Additionally, the cost of acquiring a composting toilet is offset within a short time.

The litter used helps with faster drying, odour retention, and minimization of the excretions. It also regulates moisture in the collection container, which benefits the composting process. However, since the excretions are collected in a single container, a substantial amount of litter is needed to bind the urine effectively. The amount of litter required is significantly higher than that used in alternative toilet systems, such as TROBOLO composting toilets. Suitable litter materials include bark mulch, sawdust, or similar cellulose-based materials, and even uncontaminated (toilet) paper can be safely used.

With the use of litter and an exhaust air system, odour formation is successfully minimized, making the composting toilet not only water- and energy-saving but also hygienic. Finally, the finished compost can be used as fertiliser for ornamental plant beds, effectively returning valuable nutrients to nature.

Despite the clever design of a composting toilet, it does require some accessories. Fortunately, these are minimal. Disposal and cleaning are nearly as straightforward as using the composting toilet itself. Let’s take a closer look at these three aspects.

The necessary accessories for a composting toilet are generally the same across different models. One indispensable component is the litter, which binds the moisture from excretions and helps prevent odours. Models with an electric exhaust system or other electrical devices, such as stirring units, also require the appropriate power connection.

The method of excretion disposal varies depending on the model. Composting toilets without built-in composters require an external composting facility where the collected waste, including litter, can be emptied. For the most efficient composting, a closed fast composter is recommended.

However, a traditional compost pile can also be used. In this case, the excretions should be left to rest for at least 24 months to ensure complete decomposition, though you can continue adding other organic waste from the garden and kitchen. To prevent rainwater from washing away the compost, covering it with a tarpaulin or similar material is advisable.

For models with an integrated composter, the finished compost can be removed directly from the toilet—after a resting period of at least two years—and used to fertilise ornamental plants, flowers, trees, and shrubs.

The cleaning process for a composting toilet differs only slightly from that of a conventional toilet. Due to its waterless operation, toilet brushes and cleaning agents are unnecessary. Externally, the cleaning requirements are similar to those of a standard toilet, as the appearance and usage of both are almost the same. Typically, cleaning is limited to wiping the seating surface with a damp cloth. As for the composter, no cleaning is required, since its primary function is to facilitate decomposition and fermentation.

Composting toilets are generally suitable for both indoor and outdoor use, though the model design ultimately determines the best location. Toilets with an integrated composter are less flexible in placement due to the large reactor volume, whereas models with smaller collection containers offer more versatility. If adequate space is available, composting toilets with larger reactors can also be used indoors. Their waterless operation makes them especially suitable for locations without a sewage system connection, such as allotments, golf courses, dog training grounds, nurseries, riding stables, as well as weekend or holiday homes. However, if a model requires electrical components like exhaust systems, stirring units, or heating rods, access to a power connection is essential.

The preceding explanations illustrate that the different models and versions of composting toilets offer far more than the possibility of implementing ecological and autonomous lifestyles. Rather, they are a cost-effective and, above all, hygienic alternative to the conventional toilet in the long run. In the following, we will conclusively compare the different benefits and disadvantages.

Benefits

• Waterless: no connection to the sewage system is requires
• Free of chemicals: no chemical additives are required for the decomposition of liquid and solid waste
• Hygienic: no compromises in terms of hygiene compared to conventional toilets
• Environmentally friendly disposal: thanks to the composting of excretions, the natural nutrient cycle of food production, intake and excretion is closed
• Odourless: litter and exhaust air reliably reduce odours
• Autonomy: the waterless functionality allows for an autonomous operation without a sewer connection and guarantees the greatest possible independence

Disadvantages

• Long composting intervals: it usually takes 24 months for the excretions to transform into usable compost soil
• Accessories: the more complex the model and the more direct the composting should be, the more accessories are required for the reactor
• Space consuming: models with integrated composter inevitably require a capacity of several hundred litres which effectively takes up a lot of space
• Electricity costs: models with an electric exhaust system, stirring unit and heating rods increase the cost balance – albeit slightly