As mentioned earlier, household-generated wastewater is a mixture of grey, dark, and blackwater. The disposal of blackwater, as potentially the most harmful part of wastewater for human health, and the environment is strongly controlled by legislative measures and as a result – most demanding.
One way to solve these problems at locations without municipal services (water/sewer systems), it to eliminate the sources of blackwater. It can be done by replacing traditional water-flushed toilets with composting or incinerating ones. For sure, they may somehow decrease the comfort of traditional toilets, but as we all know – no pain, no gain. And to make it clear, there is no pain, it’s rather an extra time required for periodical maintenance/service efforts.
Composting toilet makes the direct use of microorganisms to decompose human waste. It is pretty much the same biological process as the one happening on a garden composting site, but this time carried out “onsite” in the special cassette located under the toilet. Warm temperatures, humidity (little water), and continuous oxygenation – it’s all that is necessary for this aerobic biological process to keep going. Some extra “additives” like sawdust, peat moss, coconut husk fiber (known as coir). … can help to start-up and facilitate the composting process. The final product is a dry, odorless material looking like garden humus. However, in contrast to traditional garden compost, due to potentially higher content of pathogens and limited retention time in the toilet’s cassette, such “compost” cannot be directly used in gardening.
Indoor model: Nature’s Head® Composting Toilet with Standard Handle. Source: TomTur.com
Note that indoor composting toilets need an external hand crank to stir the solid waste and peat moss after each use. It is an important oxygenation step sustaining the odorless, aerobic decomposition process.
For an average family (2+2), the typical composting toilet’s cassette will have to be emptied at about 3 weeks intervals. Usually, it must then go through the 2nd (much-longer) stage of composting (this time outdoor) to achieve the full decomposition and elimination of pathogens.
Concept of an outdoor composting toilet. Source: “Composting Toilets (Dry and Wet)”, WaterNSW (Australia).
Usually, outdoor composting toilets do not need extensive maintenance. A much larger capacity combined with the natural oxygenation process makes them almost self-sustainable. However, an outdoor location has its own price, especially experienced in colder climate zones as well as during rainy seasons and nights…
Practical implementation – composting toilet on an ecological farm. Photograph: Predrag Milos/Alamy; Source: “The no-flush movement: the unexpected rise of the composting toilet”, Guardian (UK)
Gardening-grade humus from the composting toilet. Source: Sustainable Sanitation Alliance (SuSanA) – Wikipedia, Photo by Wolfgang Berger, Hamburg)
A modified version of a classic composting toilet is a Urine-Diverting Dry Toilet. By diverting urine to the separate cassette (tank), the moisture level in the cassette is more consistent creating a better “composting environment” for human waste. Unfortunately, in the end, you get not only useful compost-grade humus but also further “care-demanding” urine!
Composting toilets are best for homes with gardens as the end-product can be disposed of on your property (providing relevant local laws are respected). This will be the case of most off-grid houses including container-based ones.
In general, composting toilets do not use any water, that’s why they are called Dry Toilets. Note that portable composting toilets are often used by the RV industry to minimize the use of freshwater, eliminate the need for blackwater tank, and “not-much-enjoyable” waste disposal process.
Another version of dry toilets is an Incinerating Toilet. In such a toilet, the human waste is burned at high temperatures in an incinerator, instead of being biologically decomposed. The incinerator chamber is integrated with the toilet’s bowl in a compact (and frankly “stylish”) design.
Incinerating toilet “Cinderella” (Norway). Source: “The Hot Poop on the Cinderella Incinerating Toilet” by Lloyd Alter (TreeHuggger).
Cinderella: combustion chamber. Source: “The Hot Poop on the Cinderella Incinerating Toilet” by Lloyd Alter (Tree Hugger)
Compared to the biological decomposition of the waste in composting toilets where the whole process takes days if not weeks, burning the waste starts at the touch of a button and is almost instant. From the user’s point of view, there is no difference compared to the “button-activated” water-flush in traditional toilets. OK, there is one – each time, you will have to insert some sort of “coffee-type-filter” into the bowl to keep it clean (there is no water to flush the bowl after use!).
The end-product is a small amount of pure (and harmless) ash (according to the manufacturer – a volume equivalent to about one teacup per week for the family of 4!). It can be disposed of in garbage areas but also used as a fertilizer in the garden.
Incinerating toilets are much less service-demanding compared to composting ones. Unfortunately, they have their own limitations which are high initial cost and the need for energy for the operation (about 1 to 2 kW of electrical power for each “event”). This may be a real problem at off-grid locations.