Dear Shrikant,

Just for your information: The Evapotranspiration Toilet is being used in Northern Brazil, e.g. in the State of Ceará. Links: (clip on how to build it), www.setelombas.com.br/2010/10/bacia-de-evapotranspiracao-bet/ and agriculturainfoco.blogspot.com.br/2012/0...camente-correta.html (description + pictures, in portuguese - use google translate).

José Carlos de Araújo, professor in engineering at the Federal University of Ceará in Fortaleza, has experience with the system, having built about 70 Evapotranspiration Toilets in 5 different locations. You can contact him This email address is being protected from spambots. You need JavaScript enabled to view it. Some of his statements from an interview we did earlier this year:

Construction time: 1 – 2 days.

Costs: BRL 700 (about USD 220) for small BET of 3m3. Excavation by owner, construction (e.g. ferrocement is cheaper than bricks or blocks) with local masons.

Area required: about 40m2 for 6 persons and 80l/person/day

Cleaning: in Ceará not before 7 years (= age of the oldest one built; up to now, they have regularly inspected built examples over the last years, none to be emptied yet); if sludge must be emptied, it should be already mineralized and could be used as fertilizer without health risks.

Maintenance problems: none up to now, but users have been sensitized not to throw hard objects into the toilet (100DN pipes used).

Grey water: usually only black water, but possible, requires adjustment of the dimension.

Infiltration rainfall: has not been a problem yet, but should probably be evaluated better in a very humid climate zone.

Some challenges: (1) convince people who are not used to "tanks" without emptying, build up confidence that the system works; (2) hydrical stress/drought: banana plants may need additional water; (3) rocky ground: can to be built above ground (probably more expensive).

I hope that you find the answers to your questions. My personal opinion: excellent system, economic, easy to build - no need for highly skilled workers or contractors, avoids the emptying problem, e.g. in rural areas without or with very expensive services.

Regards, Marco, www.ecopsis.com (Switzerland and Brazil)

Dear Elisabeth,

Much appreciated.

Rajiv

Dear Rajiv,

Thanks for pointing this out. In my role as moderator, I have now moved the previous posts on this toilet type into this new thread by Nitya. I think it makes sense to keep it all together in one thread.

Regards,
Elisabeth

Thanks Nitya.

The evapotranspiration toilet being built by Marta and Pawan seemed interesting. The data that you have put together with Marta and Pawan, in the attachment makes the storyline more robust and the technology an interesting option for places with high water table...well up to a point

Shrikant Navrekar and others had a brief discussion about this last month. See www.forum.susana.org/106-user-interface-...spiration-technology

I was wondering if you or others at the forum could take a shot at bringing your two discussions together.

Thanks, once again

Rajiv

Dear all,

On the occasion of World Toilet Day, I am sharing a variant on the leach pit toilet, The Evapotranspiration Toilet (EVT).

Marta Vanduzer-Snow and Pawan Singh have developed and installed this in rural Uttar Pradesh. They have tested and used it for over three years. I thank them for sharing their model and experience.

The Evapotranspiration Toilet (EVT) is an on-site sanitation system for the chemical and biological treatment and reuse of human excreta and household blackwater. It has been developed and popularized over the last two to three decades by permaculture practitioners in different countries, especially the U.S. and Brazil. It is a natural, zero discharge system, digesting, absorbing, and releasing all of the human excreta. Best of all it uses old tyres and has a simple construction. It is an innovation and improvement on the conventional leach pit toilet. EVTs can be used in high water-table areas as the leachates move upwards rather than downwards or sideways into the aquifer.

EVTs have an impermeable, underground substructure filled with layers of materials, decreasing in size with each rising, successive layer. Together the substructure layers use the anaerobic digestion, capillary action, evaporation, and transpiration processes to filter, release and absorb the waste matter. Anaerobic digestion converts a portion of the human excreta into biogas, exiting out the pipes. The digested matter travels up and out the tank through capillary action. The nutrients leave the system by incorporating into the plants’ biomass through mineralization and absorption by the plants’ roots, while evapotranspiration removes the liquid, either transpiring through the plants or evaporating at the surface from the soil.

The total cost to construct one unit is ₹ 10,639 including the tank and superstructure. If used properly, one unit can last a lifetime for a family of five. The superstructure has a pour-flush porcelain squatting platform, a regular ceramic pan with attached footrest, set into a brick and concrete base. It is attached to a water trap that creates a water seal and odor barrier.

The full story is in the attachment. Please contact Marta (This email address is being protected from spambots. You need JavaScript enabled to view it.) and Pawan for more information.



Regards
Nitya

Hi Shrikant,

this is a very interesting solution and one that has got me thinking. The first thoughts that come to mind is that it will have a limited life... eventually the solids will build up in the rubble layer sufficiently to block the inlet. Might be quite some time though...

Next, I have an issue with bananas and other large-leaf plants being able to cope with anoxic water. The level will rise until there is an equilibrium between inflow and evapo-transpiration. This means potentially a high water table with nutrient-rich water but no oxygen. Such plants don't generally like that at all.

However, if the system is proven, then maybe my concerns are invalid. This is like a leach field that also acts as the biodigester... I don't have an issue with the cost for rubble, sand and gravel, these would be required for a leach field anyway. But can the gas be harvested? If so, that would be extraordinary. Also, shame that the solids can't be extracted as a soil amendment... flush and forget.

I'm not sure how you would get the rubble into the bottom of the pit and on top of a liner without piercing the liner. Perhaps that is why it is successful so far, there are holes in the bottom for drainage...

cheers
Dean

Dear Shrikant,

It is interesting to see new systems, but this one makes no sense to me. Just the investment in the digging, the plastic liner, the gravel and the sand seem impractical and too expensive. Also the pipes to the surface would emit terrible odors. Why does the drawing mention biogas, when there is no mechanism to capture it? Have any of these been done? What results have been received? How many users can supposedly send their sewage to one of these? How long does one of these supposedly last?

If there is room for this, why not make some beautiful, inexpensive ArborLoos?
en.wikipedia.org/wiki/Arborloo
These could be made with translucent polycarbonate sheets, which would be strong and lightweight, to be moved to new holes when they fill and the same banana plants and fruit trees can be planted there. No one would have to manipulate excrement, only dig new holes in the soil. Just an idea.

Best wishes,
Chris Canaday

Hello everyone !

Recently I came across a design of toilet being tried out in Uttar Pradesh, India which is supposed to be based on Evapotranspiration technology. As per my knowledge this technology is basically suggested for the secondary treatment of septic tank effluent. However the toilet under reference has a design where the fresh excreta are directed into the evapotranspiration system.

Has anyone worked on such toilets ? or does anyone have any technical information in favor or against such technology ?

I would like to have my doubts cleared on following points

1. Whether this technology can be applied to fresh excreta
2. The system comprises of
a. a pit lined with polythene
b. a series of used tyres which is claimed to serve as the anaerobic chamber (the tires are not glued to each other)
c. two vent pipes protruding upto 2 ft above ground level
3. It is claimed that
a. the anaerobic digestion takes place in the tire section
b. there is no sludge formation but everything gets either evaporated or transpired through plants (banana) growing above the toilet bed / tank
c. there is neither any out-coming effluent from the system nor any leaching takes place in surrounding soil

Shall be thankful to have information on the above points
Or would like to have a discussion on this topic