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

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

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

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 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

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 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.

Thanks, very interesting presentations.

Did I understand the "wetted surface area" slide correctly, that after a while a dry crust forms close to the membrane, that slows the drying of the more interior fecal sludge? And ideas how the sludge could be stirred before that happens?

I am also a bit dubious about the conclusions based on the "current progress" slide... volumes without measuring the actual water content can't really measure the effectiveness of the membrane because you only estimate what went in. And even if your assumption is correct, the actual reduction in water content seems not all that high, i.e. at the current size of the drum you would have to empty it every month without the membrane and maybe every 1.5 months with?

Hello everyone. My name is Shray Saxena and I have been working on this project for the past 2 years under the advisement of Dr. Steven Dentel, Dr. Paul Imhoff and Dr. Daniel Cha.
To summarize, in this project we use a breathable membrane for the dewatering of fecal sludge and containment of pathogens as the sludge dries due to the partial pressure difference between the inside and outside the membrane bags. This partial pressure difference is created due to the temperature difference or the humidity difference (wet sludge is 100% humid).
Recently, we started field trials of these membrane bags in Kanpur, India where we provided two toilets to 2 households in urban slum areas. These bags line the inside of a perforated 55-Gallon drum which will act as the storage for fecal matter from active toilet users. This perforated drum is housed on the roof of the house in a honeycombed wall chamber surrounding it. The toilet seat is housed in the superstructure above the drum and the connection is a funnel shaped sheet metal design. The toilet seat used is a locally made squatting type seat based on the SATO pan design. This particular design contains a counter-weighted trapdoor through which any solid or liquid passes through due to its weight. It has been shown that this SATO pan design reduces the amount of flush water used in a toilet. It should also be noted that all connections between the toilet seat and the drum is air tight and no odors are expected to escape back into the superstructure.
In addition, the drum is placed on a wheeled platform which makes the replacement of a fully sludge filled bag easy to maneuver. We also provide a replacement drum and membrane so that the toilet does not go out of commission once the active drum is full. This supplementary drum also provides a good amount of waiting period for the fully sludge filled drum before the replaced drum fills up, hence more drying time for the full drum. Each drum also has a seep hole in the bottom connected to a pipe which runs through the nearest drain, so that in case of leakages the users’ house is not contaminated.
Since, this is a pilot research study, we have limited the number of uses to 4 per day which includes 1 liter/use of wash water. We are regularly monitoring these toilets on a weekly basis through our collaborators WaterAid India and Shramik Bharti.
Currently, we see that one 55 Gallon drum gets full in approximately 50 days of regular usage under the winter conditions of Kanpur. We hope that in the summer months (June-July), the filling rate and drying rate will reach an equilibrium.
Please find attached two presentations:
1) Fecal Sludge Management 3 conference
2) Graduate Seminar at University of Delaware. Spring 2015.

This is not a conventional "flush" toilet. In India, a small amount of water is used for rinsing instead of paper, and this amount is included in our calculation of the required drying rate. So the "u-tube" being planned by WaterAid fill not have a large hold-up volume. Its purpose, of course, is odor control, so it is desirable but not essential.
The membrane we used is also defined as oleophobic, so I don't believe oil is penetrating into the membrane. There is some research suggesting that nonpolar functional groups on proteins are the culprits.

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You are planning to use a flush toilet with that (implied by the u-trap)? Wouldn't the bag fill up with water way too quickly?

Otherwise: anaerobic septic sludge really isn't the best substitute for fresh feces. My guess is that the higher oil and fat content of fresh feces is what is causing you trouble.

Elisabeth, thanks for the encouragement to update!
Yes, the "breathable membrane" has been promoted to Phase 2. We are very excited about this. Of course we have a lot of work to do!

To tell the truth, reviewers have been pretty skeptical of our work. It is hard to believe that the membrane does not clog when fecal sludge is right up against it. It has been surprising for us too.

We started out using anaerobically digested wastewater sludge as a very reproducible substitute. We also collected sludge from a camping site outhouse. In neither case was there a decrease in drying rate as drying occurred (except, of course, when the moisture is almost gone). Drying to completion, shaking out the dried material, and rinsing, we then repeated the experiment with the used fabric, up to five times, with no loss in drying rate. So the fabric acts like a non-stick surface, perfectly, and there was no sign of clogging.

More recently we have been using fecal sludge which we have to obtain from student volunteers (I'll skip the anecdotes here!). And it turns out that true fecal sludge is a bit stickier than the other sludges we were using (other researchers using soy paste and other substitutes should be alerted to this!). yes, the rate of moisture penetration through the membrane fabric does slow as drying progresses.

We were pretty dismayed by this, but repeated tests have now shown that (1) the rate is still pretty fast for the initial drying phase, which is the most important, and (2) the drying behavior does not deteriorate when the fabric is rinsed and re-used - it's pretty much the same as in previous cycles. So the news is not so bad after all.

So now, our research will now go in two directions. The first is a scientific inquiry into what's different about fecal sludge, using a variety of sophisticated analyses, so we can try to decrease its importance.

The second is more practical. Our calculations show that the membrane enclosure should be very suitable for certain applications, and the most obvious is where the fecal waste is contained above ground level so there can be plenty of surface area for drying. So picture this: the toilet, with u-trap, mounted onto a surplus 200-L drum with perforated walls. The fabric is made into a cylindrical, water-tight "bag" that fits into the drum and seals onto the u-trap at the top. We'll need a spacer between the bag and the drum for air flow and to protect the fabric from any sharp edges. Practically speaking, steps and rails, a privacy barrier, and so forth are needed too.

This is the working plan for our first generation model. It's obviously intended to be simple and low cost, while letting the fecal sludge lose water but keep everything else contained for later composting or other use. We're talking with apparel manufacturers about fabricating the bags to be water-tight, and we will be testing them with Wateraid in Kanpur and elsewhere. WaterAid suggests two drums, on roller wheels, so one can continue drying when the other is being used. Sounds good, although it doubles the cost.

While we learn how these units perform, we'll be working on designs for pit latrines and other systems. These are more challenging because we need ways for air to circulate around the fabric exterior to carry away the moisture. We've got some ideas on how this can be done. Phase 2 will be exciting!

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