Dry toilets for domestic urban/rural use, occidental context
This tutorial is based on the dry toilets by Yves Desarzens, Maisons Nomades. They're non-flush toilets belonging to the composting toilets type.
Watch the tutorial video here
This dry toilets model was conceived for a domestic/family use in urban or rural area provided that there is a composting dedicated area.
In the case of an urban area, depending on the scale and context of the group housing, some problems such as the access to the composting area and the transportation of the toilets to this area could occur.
The consumption of water an the classic toilets model in the household
Classic pour-flush toilets represent 20% of the drinking water consumption of a household, almost 150€/y for a 4 members family. It's the second most consuming item after the shower (40%). The water used for the flush is drinking water (except in rare cases where rainwater is used), as son as it touches the excrement, this water becomes foul water contaminated and therefore unusable for any other uses.
Excrement: trash or resources ?
In average, a human products 50 Liters of solid excrement and 500 Liters of urine every year. in France, a person turns "30 Liters of drinking water into foul water" every day.
In solid excrement, we find minerals including nitrogen (1,1 lbs/pop/y), phosphorus (0,4 lbs/pop/y) and potassium (0,7 lbs/pop/y) but also pathogens such as bacteria, viruses and parasites and sometimes products such as antibiotics depending on the user's health.
In urine, we find minerals including nitrogen (8,9 lbs/pop/y), phosphorus (0,7 lbs/pop/y) and potassium (1,8 lbs/pop/y) and very rarely pathogens too.
These matters, casually considered as trash are flowed through the pipes with the foul water. Then followed by a long process of sewage treatment in water treatment plants found in the city suburbs. These process produce at the same time sewage sludge of which the waste-to-energy conversion is complex.
In the case where we consider the process in a cyclic way like for the animal manure, it's possible to see human excrement as a "resource". By respecting the hygiene requirements, human excrement can easily be composted and turned into pathogens-free humus which doesn't have anything to do with excrement anymore. For the antibiotics (besides significant use), the researches show that there's no durable effect on the composting. It's important to notice that animal manure already used contains at the start the same contaminants including antibiotics.
It's important to not separate the urine from the solid and carbon matter: the cellulose in the the carbon matter prevents the transformation of the urea, rich in nitrogen, ammonium ions (responsible for the stinky smell in urinals for example). This effect also has another very important and positive consequence: if the urine was released in the nature without cellulose addition, the ammonium ions would turn into nitrite ions and cause a faster degradation of the humus, the opposite of the expected effect. This problematic is encountered in some contexts where the large-scale urine recovery was thought for fertilizers creation.
Excrement: a resource thanks to dry toilets
There's plenty of dry toilets models. Here, the proposed model is a bio-litter toilet. It's the easiest model which doesn't need ventilation. This model is constituted of a stainless steel bucket which collects the dejection (urine and excrement), the toilet paper as well as the vegetable carbon matter. Whether it's in the sale room where they're installed or in the composting area, very few smells are emitted (actually the same amount emitted from classic water toilets).
1) A rich contribution of vegetable dry matter rich in carbon (straw, dead leaf, sawdust) 30 times more important than the excrement contribution, rich in nitrogen.
2) A good ventilation of the compost in order that the aerobic organisms which need oxygen are able to achieve correctly their decomposing work. The shreds participate in creating a well ventilated compost.
What type of user comfort for the dry toilets?
"+": the bio-litter toilets don't release any smell and don't make any unwanted noises unlike classic toilets.
"-": The bio-litter toilets require to regularly empty the bucket in the compost (twice a week for a 4 members family).
"Summary"The use of the bio-litter toilets allows to reduce 20% of the water consuming in the household, therefore the bill too. It also allows the creation of usable humus for the garden. All of this for the same or even better comfort compared to classic toilets.
1) Every measure in this tutorial are only for the stainless steel bucket below and for wood of a thickness of 1,2 in. It will be very simple to adapt the measure depending on the equipment of everyone.
2) It isn't recommended to use any other materials than stainless steel for the bucket. The other materials such as galvanized steel or plastic don't react well with urine through time. Furthermore, you have to make sure the bucket can support the weight of anybody. That's why stainless steel is recommended.
1) This wedge allows the support of the dry toilet on the wall of the room where it'll be installed.
2) It also allows to have the required width in order to lift the different toilet lids.
Remarque: Ce pilier sert à reprendre l'effort lorsqu'un usager s'assied.
Remarque: Cette cale sert à centrer le seau vis à vis des abattants.
Remarque: Cette cale sert à transmettre la masse de l'usager au pilier.
Remarque: Percer un trou de diamètre suffisant pour insérer la lame de la scie sauteuse pour l'intérieur de la couronne.
Remarque: Ce plat sert par la suite à la fixation de la charnière.
Remarque: Cette pièce permet l'appui de l'abattant sur le seau inox en prenant en compte l'épaisseur de l'anse du seau.
Remarque: Cette bavette protège des projections d'urines.
Remarque: Selon le matériau du mur, il peut être nécessaire de réaliser un pré-perçage et d'installer une cheville pour accueillir la vis.
Remarque: en cas de cours d'eau à proximité, il est recommandé d'établir la zone de compost au moins à 60m du cours d'eau, si possible en aval, afin d'éviter toute contamination lors de la phase de compostage.
1) Il est important de respecter les règles d'hygiènes basiques lors du vidage.
2) Il est possible de prévoir une zone de nettoyage à proximité de la zone de compostage avec le matériel nécessaire (robinet, gants, brosse dédiée, savon, desinfectant)
Remarque: Les clés d'un bon compost sont le rapport de 30 entre l'apport de la matière carbonée (broyats, feuilles, etc) et la matière azotée (excréments) ainsi qu'une bonne aération du compost. Celle-ci est permise par les trous entre les lattes du composteur et l’espace créé par la matière carbonée.
Le site eautarcie détaille le compostage de déjection humaine.