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My discussions with dry toilet designers and salesmen quickly become futile «dialogues of the deaf». Even when confronted with analytical facts, they hang on to their scientifically disproven (and even environmentally harmful) technical solutions.

I prefer to confront sanitation engineering academics who ultimately recognize the merit of my arguments. Scientists have a better mutual understanding, even if they are not on the same side. When such colleagues have exhausted their scientific arguments, they usually put forward the supreme argument, i.e. the application of law on matters of sanitation. In contrast, with those environmentalists who have not gone beyond conventional systems, discussions become futile as they are often emotionally based.

Dry Toilets and their Misconceptions

The first misconception is the idea of separating urine from faeces.

A Danish dry toilet designer who came to Brussels to give a conference asserted «animals that in nature do not necessarily defecate and urinate at the same time». It is therefore «natural» to separate both effluents. Such a justification lacks scientific backing.

It would be more honest to say that we separate the effluent for reasons of technical convenience: in order to space out the required manipulation of toilet effluent by the user. Urine, which is easy to store in a separate container, represents 90% of our excreta’s mass. Dried faeces take up little room. Once urine is evacuated from a toilet by simple draining, removal of the little solid matter remaining can wait a few months. Thanks to this trick, dry toilet use resembles that of a conventional WC. The occasional user practically sees no difference. New technologies also help: the toilet basin receives a silicone coating on which water doesn’t stick, and urine drains down without a trace. The toilet manufacturer’s purpose is attained: our excreta are evacuated out of our sight. We can continue to pretend that there is no problem.

Internal composting within a container under the toilet is always inspired by the desire to avoid having to handle our excreta, i.e. as less as possible. Unfortunately, it is impossible to provide the necessary aerobic conditions for good composting in a tank or pit. True composting must be done directly on the ground, in symbiosis with soil’s fauna. Anaerobic fermentation is inevitable in containers. It removes nitrogen and a good part of the carbon from the humus forming process, and it generates nitrate and ammonium pollution.

Regrettably, there is a high price to pay in financial, technical and environmental terms for such intellectual comfort.

Technically, storing urine separately automatically brings about emergence of odours, followed by complex and costly solutions to this. As we shall see about the biolitter toilet, or BLT, the key to odour control is directly linked to the mixing of urine, faeces and cellulose-containing litter. When you separate the two effluents, odours appear on both sides. To get rid of these, you need a forced ventilation system with piping, etc. A conventional dry toilet like the Clivus Multrum [2] occupies a room-sized volume in a home, and involves piercing of the floor, ceiling and roof for pipe work. During a power outage, the ventilation system stops, and: hello odours… and flies.

You must really want to have such a set-up which easily costs 5.000 € (plus the cost of the room it occupies in the house) and consumes about 100 to 200 € in electricity per year. If a bona fide user took the time to analyse the environmental impact of this toilet, he would go straight to the closest plumber to have a conventional WC installed along with a good treatment system.

The second misconception is to mistake dried faeces for humus.

Almost all off-the-shelf dry toilets on the market work on the same principle [3]. When you go through colourful catalogues of these, you will notice the discretion about where the urine goes after that. It is most disturbing to find what is none other than dried faeces presented as «compost». As soon as urine is removed from the faeces, composting of these solids becomes quite difficult. When the solids are mixed with peat moss for example, there is at best a sort of curing process by drying, but definitely no formation of humus.

Dry toilet designers and salesmen don’t have the exclusive «privilege» of misunderstanding the nature of humus. During discussions with sanitation engineering technicians, I am often stunned at the scope of their ignorance in pedology (study of soils), the knowledge of which is capital to the understanding of water treatment’s environmental impact. Just recently, one such technician could not understand my disapproval of sewage sludge valorization for agricultural purposes. He considered the sludge as organic matter identical to humus. Thus, he conceived that nitrogen removed from black water as contained in the sludge is spread on the ground as humus; and that in so doing, centralized wastewater treatment is a factor of farmland soil fertility. Even disregarding the heavy metal content of sewage sludge, it is easy to show that this reasoning is completely false. What is unfortunate is that well-intentioned ecologists and dry toilet representatives spread the same scientifically undefendable disinformation. The propagation of these ideas is a deterrent to the expansion of a generalized consciousness of such environmental waste.

The third misconception is to believe that stored urine can be harmlessly used in the garden.

Urine is collected in a tank where, thanks to ever-present enzymes [4], organic nitrogen is transformed into ammonium ions. This explains urine’s ammonia (NH₃) smell after a few hours in a chamber pot. Considering that about 80 % of our excreta’s organic nitrogen is contained in urine, it’s easy to understand its potential impact on a receiving milieu.

In fact, in form of ammonia, nitrogen can only oxidize when it ends up in nature. Thus are formed toxic nitrous ions (NO₂^-), which oxidize into nitrates (NO₃^-). Stored urine becomes a concentrate ammonium nitrate solution (= chemical fertilizer) containing also nitrite ions. Dry toilet manufacturers recommend using stored urine, diluted 8 times (or more) for plant irrigation.

By adding 8 times urine’s volume in water, one may ask what happened to the publicized water conservation to justify the initial purchase of the toilet. All the same, a greater problem lies what happens to the ammonia contained in the liquid, where percolation and oxidization set in. As ammonia, (NH₄⁺), nitrogen will infiltrate much easier and quicker [5] into the water table than if it was in nitrous (NO2-) form: that is a most insidious pollution. The ammonium ions present in the liquid, when spread on the soil, oxidize into nitrates. These have undeniable fertilizing qualities and act as a chemical fertilizer, but in a more harmful way, because they contain highly toxic nitrous ions (NO₂^-). To assert that stored and diluted urine can harmlessly be used in the garden can only be justified by total ignorance of physicochemical processes that take place in stored urine as well as those that partake in the soil.

To resume, spreading human urine in the garden resembles that of spreading liquid pig manure on farmland. All the truer when you consider that dried faeces also end up there. Normally, spreading urine is subject to the same regulations as that of industrially produced liquid manure. The quantity of nitrogen (N) spread as liquid manure cannot exceed 200 kg per year per hectare. Thus, when spreading urine and faeces, one person’s annual 10 kg nitrogen production, requires a garden of at least 500 m² (or over 5300 ft²). A family of four will require a garden of 2000 m² (a half acre). Below this surface area, standards would be exceeded, but it is highly probable that even above this, there will be pollution. 

The fourth misconception is to believe that the main advantage of dry toilets is water conservation.

We have seen that water savings are less important when you have to dilute urine for its reuse in the garden. This entails another, graver misconception: the belief that the main purpose of a dry toilet is to avoid water pollution. In a way, this may be true, but take note that urine spread in the garden pollutes our underground water reserves more than does conventional sewage treatment. In a similar sense, another misconception would be the belief that a proper sewage treatment repairs the damage done by flushable WC’s. This is without doubt the most serious mistake. Persons with good intentions and who are motivated to protect the environment are deceived into believing in purification systems using plants. We must insist that there is no good method of purifying black water. A tragic and irreversible waste is committed the moment excreta are discharged into water [6].

The fundamental problem

After having read the above analysis, the reader can rightly ask what to do if both WC’s and current dry toilets on the market are equally harmful.

To answer this question, we must:

• revise our relationship with our own excreta;
• understand the basic laws that rule how all ecosystems work;
• focus on techniques that integrate these new parameters.

To start, we most consider a fundamental rule:

Fundamental Rule

Each kilogram of plant and animal biomass that is not returned to the earth, jointly and simultaneously, to renew the process of soil formation, weakens the ecosystem’s production capacity and becomes a pollution threat to water and air. As a result, the great natural cycles that are nitrogen, phosphorus, carbon and water will always be disrupted.

What is «plant or animal biomass»?

Plant Biomass	Animal Biomass
Wood, dead leaves, straw, stems, leaf stalks, grape stalks, etc.	Animal carcasses, animal and human dejecta.
Rich in carbon, poor in nitrogen.	Rich in nitrogen, poor in carbon.
High carbon/nitrogen ratio (C/N) : up to 300.	Low carbon/nitrogen ratio (C/N) : around 7.
If these two types of biomass are not combined simultaneously in the process of soil formation, there cannot be sustainable water management, nor sustainable food production practices.
Conversely: if we mobilize all available biomass and return it to the earth to renew the process of soil formation, global water and food shortages would be resolved within two generations, without massive capitalization.

When examining the prime cause for worldwide water shortages, we discover fundamental wrong decisions relative to biomass management. Under pretext of «energy valorization» or «water purification», the ongoing massive destruction of biomass is progressively unbalancing the biosphere towards a point of rupture. Even a substantial part of the greenhouse effect is due to incorrect biomass management.

Human fecal biomass is far from a «negligible quantity». The nitrogen contained in humanity’s dejecta represents an equivalent mass of 40% of worldwide agricultural nitrogen use (data published in 2000; actually this %-age is superior). In the animal world (large terrestrial animals, not including insects), human biomass is in second place, after cattle and before pigs. When considering sustainable management of the biosphere, massive destruction of human dejecta that is justified by reason of water purification is a kind of collective suicide. In this sense, the actual principle of black water treatment, whatever the system used, is incompatible to the concept of sustainable development [7] .

You can better understand this notion when reading the chapter on the importance of humus at the start of the Water purification using plants page.

To comply with the above «fundamental law», it is necessary to find a technical solution, which will renew and perpetuate the humus formation cycle by returning our dejecta to the biosphere, jointly and concurrently with plant biomass. The biolitter toilet (BLT) is one of the possible solutions to this requirement.

What must we revise in our relationship with our own excreta?

To resume, we must admit once and for all that human dejecta are not waste to be eliminated, but are an integral part of the ecosystem that makes us thrive. Our food comes from the earth, and our dejecta must return to the earth, but through a process that we had better understand to avoid committing mistakes beyond repair.

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[2] …that I would easily call «Clivus Monstrum».

[3] Dry toilets in which urine and faeces are not separated are better, but that is not enough. For good dry toilet design, you must understand soil formation processes.

[4] The enzyme is called urease. It is capable of hydrolyzing urea into ammonia and carbon dioxide.

[5] …due to the small scale of ammonium (NH₄⁺) ions.

[6] This assertion is particularly true of intensive pig raising over slatted floors. The nuisance (smell and nitrate pollution) generated by spreading liquid pig manure on farmland is due to the transformation of the manure’s organic nitrogen into ammonia during initial storage. This is the same phenomenon that occurs in most dry toilets, when storing urine in a separate tank.

[7] One of the first flushable WC’s was built in England at the end of the 18^th century by a plumber, Thomas Capper. Initially, it was a set-up reserved for the rich. Its environmental impact was therefore limited. Those who were subjugated by hygienist ideas viewed the WC as the ultimate solution to urban sanitation problems. They could not foresee the environmental disaster provoked by its generalized use. We now know of credible alternative solutions that would solve housing sanitation problems without our rivers becoming open-air sewers. The WC must therefore be considered as an accident in human history, an error that there is still time to correct. What is most bothersome is that many sanitation engineers persist in their hygienist mentality, with 19^th century techniques.

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