Dry bath, how not to waste water and help the environment


In the context of a family home we can save considerable amounts of water and at the same time avoid the production of sewage, using toilets that run without water.

There is a wide variety of designs and proposals on "dry" or "composting" bathrooms, all have in common, that a conventional toilet bowl is not used, that depending on the type, consume between 3 and 20 liters of water in each use.

The different proposals for toilets that work without water, we can divide them into two groups: Those that act by dehydration and those that compost the excrements.

dry bath

Dry sanitary systems based on dehydration

Something becomes dehydrated if all the water it contains is removed. In a dry bath the content that falls in the treatment chamber is dehydrated; This is achieved with heat, ventilation and the addition of drying material.

You have to reduce the humidity of the content to less than 25% as fast as possible, since at this level the elimination of pathogens is accelerated, there are no bad odors or reproduction of flies.

The use of a specially designed toilet bowl, which deflects urine and stores it in a separate container, facilitates dehydration of the stool.

Urine contains most of the nutrients and is generally free of pathogens, so it can be used directly as a fertilizer, that is, without further processing.

In general, it is more difficult to dehydrate excrement mixed with urine, although in extremely dry climates dehydration is facilitated.

Features of the dry dehydration toilet

dry baths

A special urine separating cup is used. There are both home and industrial models. They have a urine deposit in the front of the cup. From this collector, urine flows through a hose to an absorption well below or next to the toilet. It can be used as fertilizer in vegetables (mix 1 part of urine with a proportion of 5 to 8 parts of water).

Ashes and lime are used to help dehydrate and neutralize odors.

Due to the strictly dry handling, little organic matter is produced, for this reason the chambers can be of a smaller size than in the composting toilet.

The toilet paper is stored in a separate container and subsequently burned.

It is necessary to try to have enough ventilation in the solid deposit boxes, for example with a 4-inch chimney, which rises directly without elbows or deviations up to 1 meter upwards from the roof of the house. The odors of the urine separating cup can be controlled by adding a little water inside the collector after each use.

The organic matter that is obtained is harvested annually. It does not present any kind of smell. In addition, the presence of lime and ash will have dried and compacted the earth a little. For this reason it is recommended to mix it with topsoil and sand before using it as fertilizer for fruit trees. Do not use this type of fertilizer in vegetables.

The deposit of these dry ecological baths is usually built with double chamber, which alternates in its use. Each of them has an approximate volume of 60 cubic centimeters and they go roundabout so when one is filled it is left closed so that the process ends, while the other one is filling up.

The dry toilet with solar dryer

dry ecological baths

This dry toilet is a variation of the first model. Humidity is the most important risk factor in a sanitary system based on dehydration, but adding a solar heater to the process chamber reduces that risk.

This concept was developed in Mexico and systems have been installed for example in the Sierra Gorda de Querétaro.

The dry solar wc are used in the same way as normal dry toilets, where there are drawers with prefabricated fiberglass solar dryers.

The material in the treatment chamber is human excreta and ash, and / or a mixture of earth and lime in a ratio of 5: 1.

The urine is channeled to an absorption well located near the toilet or processed as fertilizer. The used toilet paper is placed in a box or bag that is placed near the cup to be burned periodically. It is also built as a double chamber system.

Dry sanitary systems based on decomposition (ecological composting toilets)

Composting is an aerobic biological process subject to controlled conditions in which bacteria, earthworms, fungi and other organisms decompose organic substances to produce humus.

In a dry composting toilet, human excreta and other organic materials are deposited, for example vegetable remains, straw, peat, sawdust and coconut shells.

It is a treatment chamber where soil microorganisms are responsible for decomposing solids, as happens in a natural environment with all organic materials.

To achieve optimal conditions for compost, you must control the temperature, air circulation, provide some moisture, and ensure a good combination of materials.

The humus that is produced in the process is an excellent soil conditioner, free of human pathogens, but this depends on achieving the right conditions and that the material is stored for the necessary time in the chamber.

To maintain optimal conditions, sufficient oxygen must circulate in the accumulated material. The compost chamber must have 50 to 60% humidity, a carbon / nitrogen ratio (C: N) of 15: 1 to 30: 1 must be reached, and the temperature must be above 15ºC.

A great diversity of organisms contributes to the decomposition of feces and other materials in the sanitary composting. They vary in size, ranging from viruses, bacteria, fungi and algae to worms and insects.

All of them play an important role in mixing, aerating and decomposing the content of the material stacked in the treatment chamber: its activity is positive and must be maintained. You can even place earthworms in the sanitary: if the environment favors it, multiply, make holes in the compost material and consume odors and organic matter, transforming them into enriched organic soil.

In general, there is no separation of urine, and an eventual excess of nitrogen is balanced by the use of high-carbon materials (sawdust, ground straw, etc.). Nor does it have to separate the toilet paper, since it is organic material and can be added without problems.

The toilet "clivus" or "clivus multrum"

It has been more than fifty years since composting toilets were introduced in weekend homes in Sweden. To date, a wide variety of models that are used in different parts of the world have appeared.

dry toilet

This type of toilet has become quite popular in various parts of the world like Mexico because of the inclusion of design in the book The barefoot architect, something like a guide when it comes to Bioconstruction. It is available for download in our library next to micho more materials on the subject.

It is a compost toilet with a chamber where urine, feces and part of the household's organic waste are processed.

It consists of a compost chamber with an inclined floor or floor, air ducts and, at the lower end, a storage area. A pipe connects the dry toilet bowl of the pedestal with the receptacle and generally has a special duct for kitchen waste. There is a permanent air circulation thanks to the natural current that originates in the air passages of the compost chamber. The air exits through a vent, sometimes implemented as a fairly complex system of interconnected PVC pipes. To the clivus multrum not only the faeces arrive, but also the paper

Commercial dry toilets

dry wc

There are many dry wc models on the market. There are those who compost in the same sanitary and others who compost in different receiving cavities that change shape and volume according to our needs and whose mission is to receive or accumulate, ferment and allow a comfortable and harmless withdrawal of the result.

There is no design limit in the supply of industrial dry toilets either. There are those that consist of a simple composting drum with the cup or seat, and when the bag is filled simply pulls, to the complex systems with rotary reception containers, temperature detectors, aeration systems and electronic control.

These models usually carry aeration systems and even solar collectors, which facilitate the fermentation and drying of organic matter.

In addition, practically all models use the use of microorganisms that collaborate and accelerate the decomposition process of organic matter, also reducing its volume considerably and making an important step of composting within the toilets themselves.

Remember that almost 90% of our excrement is water, so the remaining 10% becomes clean and dry organic fertilizer.

dry toilet

Almost all manufacturers of dry organic baths are from the United States, Australia, Canada and northern Europe. But the good thing is that they are already distributed all over the world, even in Spain.

It is very important, also, the work done by these dry toilets to reduce the risk of disease transmission that does occur with its discharge to natural channels, as microorganisms also break down bacteria, fungi, pathogenic organisms, and so on.

In summary, the advantages of dry wc over conventional sanitation can be specified that:

  • They do not use water. It is only necessary for occasional cleaning.
  • They do not pollute the soil or groundwater.
  • They can be integrated into any existing home, including a block of flats.
  • They are cheap, because they can self-build.
  • They are hygienic and innocuous.
  • They do not produce bad odors if they are well designed.
  • They do not depend on centralized services.
  • They suppose a great saving in canalizations and purification stations.
  • They provide resources, such as fertilizers and fertilizers.
  • They allow populations with few resources to access safe sanitation that keeps their waterways clean.

The materials consulted by ecocosas.com for this article on dry toilets:

The website Tierramor.org

Barefoot architect's manual by Van Lengen Johan (available at our library).

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