Hello Krischan, Thank you for your questions.

The dry crust formation is an indication of absence of free water. The sludge crust will hence, not be a problem until the very end of the drying cycle. I would also point out that continuous stirring will definitely help in removing the deposits which do settle down due to sedimentation. But in a field situation such deposits will offer resistance to the drying rates and hence lab results should provide a good substitute for the same.

For your second concern about the actual reduction in water content, I agree that an increase in 0.5 months is not much over an impermeable container. For this particular reason we have replacement drums which will allow the fully filled sludge drums to dry for 1.5 + 0.5 = 2 months. That, given certain hot and dry climates could be a sustainable model for these Eco-Vapor toilets.
I hope this helps.

And here you can see the video from Shray's presentation in Hanoi (I had the pleasure of chairing it; managed to slip in a reminder of the discussion forum to the audience at the start ):



Or go to time 17m26 s here:



The question and answer session starts at 27:28.

Hello All,

I just wanted to update about the field application of the breathable membrane toilets. We have a total of two toilets in two households in Kanpur, India which are in active use. We are still learning about the effect of different weather conditions on the membrane drying rates (drying time).
A good summary of the field work till date has been documented by our collaborators, WaterAid India, here -

www.wateraid.org/news/news/the-ecovapour...ation-in-indias-slum

Please feel free to revert any questions/concerns about the toilets and its technology on this post. I will be happy to answer them.

Thanks,
Shray Saxena

My condolences go out to the family of Prof. Dentel. I was already wondering why his account was removed.

On topic: have there been further trials if increasing the aeration around the membrane, or a different membrane arrangement that does not allow a big 'clump' of feces (with a low volume to surface area ratio) to form?
The idea is very good, but it's a pity that the current data seems to not show such a great increase in drying rates.

Hello JKMakowka,

Thank you for your question.
We currently have a ventilation pipe for the toilets to reduce odors from spreading inside the house. We 'guess' that it increases the drying rates however small that may be. Further laboratory testing is under way to quantify this amount.
Our next phase of testing is a change in design from a large 55-gallon drum to a smaller 10.5 gallon drum size. This allows for a higher volume to surface area ratio. But as shown in my presentation that Elisabeth has posted, the drying rate is dependent a lot more on the ambient temperature and humidity conditions.
The drying rates are slow for a over-populated nation of washers but it should work well for drier and hotter climates where water stress is an issue.

Thanks,
Shray Saxena

An update on this research project was recently published here:
iwaponline.com/washdev/article/11/3/505/...hable-laminate-lined

Field demonstration of breathable laminate-lined container-based toilets in Kanpur, India Shray Saxena; Puneet K. Srivastava; Steven K. Dentel; Paul T. Imhoff; Daniel K. ChaJournal of Water, Sanitation and Hygiene for Development (2021) 11 (3): 505–514. doi.org/10.2166/washdev.2021.011

Abstract

Drying of fecal sludge (FS) enclosed in a breathable, hydrophobic membrane laminate was investigated in 208 and 40 L container-based toilet (CBS) systems referred to as Eco-Vapor toilets (EVTs). EVTs were constructed and pilot tested in four households in urban slums of Kanpur, India over a period of 2 years. The average moisture losses of 0.8 and 0.9 kg/day were observed in laminate-lined 208 L drums for Year 1 tests, and this in situ drying decreases disposal frequency by 8 days compared with CBS that do not allow FS drying. In Year 2, smaller EVTs with 40 L laminate-lined drums and waste segregation increased replacement time over conventional CBS by 45%, as opposed to the 19% increase observed in Year 1 tests. Despite its limitations, the stagnant film model using meteorological data predicted the mass-loss rate within 52 and 28% error for the 208 and 40 L drums, respectively.

HIGHLIGHTS

Eco-Vapor toilets (EVTs) use breathable laminate-lined drums to store and dry fecal sludge.
Drying rates of 40 L containers were higher than those of 208 L drums.
In situ drying in the 40 L EVT extended the replacement time by 45%.
The stagnant film model predicted mass-loss rates within 28% error for the 40 L EVT.

(When I saw Steven Dentel as a co-author for a moment I thought my memory had failed me. He died in 2015. So I am a bit confused now. Perhaps his son with the same name? Or just to honour his legacy.)

Kind regards,
Elisabeth

Hi Elisabeth,

This work was Dr. Steve's brainchild. Hence, we added him as a co-author. It is to honor his legacy. 

As an update - we are also continuing the work with laminate-lined pit latrines and we're funded recently under the Humanitarian Grand Challenge. We hope to publish soon.

Thanks,
Shray