Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA)
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TOPIC: Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA)

Re: Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA) 06 Apr 2014 17:30 #8124

  • KaiMikkel
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skdentel - when you state that, "...the only alternative for urban areas is incineration," I wonder why you don't mention the most widely utilized option in the US which is landfilling. Personally, I prefer the option of landfilling (the "best worst option") given that it provides a very meaningful financial incentive to rethink our dangerous sanitation system. Landfilling is expensive but it also provides a controlled environment which, for at least some period of time, is monitored. In stark contrast, applying Class A sludge to land faces zero restrictions on where and in what quantity it may be applied. We know, for instance, that this stuff is increasingly showing up in people's yards, in peoples' gardens and on children's athletic fields, etc.

Also, contrary to you statement, land application is very much rampant in Europe. The push to land apply this material is growing worldwide in response to its ever increasing volume (thanks to an exponentially growing population), the high cost of landfilling and due to rapidly shrinking space in landfills.

Finally, while I understand your point about limited resources, I am confused by your blanket unwillingness to adopt even the most rudimentary steps to ensure that something is safe before implementing it. Hasn't a blanket refusal to address the latter put us in the position that we currently find ourselves, namely at a point in time where rates of industrial disease are skyrocketing, hundreds of species are being rendered extinct every day and global temperatures are in chaos? Looking back in history, the mindset that has us rushing into rolling out "solutions" usually ends up producing a host of undesirable and unexpected results, which many times cancels out any real or perceived benefit. Don't we owe it to future generations to be a little more cautious than we currently are? I think they deserve it.

Re: Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA) 29 Apr 2014 13:16 #8368

  • JKMakowka
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Back on topic, at least somewhat:

Here in Uganda we have been brainstorming for a while to find a sustainable way to deal with fecal sludge from emptied pit latrines (or potentially also UDDTs) in a simple, but relatively safe way that can be scaled up in a decentralized fashion.

One of the ideas was to use these kind of breathable membranes to come up with an more safe and less odor problematic alternative to sludge drying beds that could be used in (peri-)urban settings.

The concept I have in mind are long black sacks (not unlike the plastic bag bio-digesters) made out of these breathable membranes that are fed with freshly emptied sludge from one side, while the somewhat dried and thus storage, dehumidification and solar-heat treated sludge can be removed on the other side then.
Given a long enough storage period and sufficient heating from the sun (maybe supported by running a heat-exchanger coil underneath the bags that is feed by standard solar water heaters) the result should be quite safe to handle in (non-food?) agriculture I assume.
I also guess that the smelly ammonia that probably can escape through the membrane is less of a problem given that the pit-latrine contents are already a bit older mostly.

The question really is if it can be made to smell only a little and if the treatment is sufficient without needing a lot of space and expensive foil/membrane.

It would be also interesting to see if non-permeable foil might work sufficiently well too, although the drying properties are definitely a plus of the breathable membrane.

I also wonder how UV stable the material is and if it might be necessary to do the heating completely through external heat exchangers instead, which I would like to avoid as those add to the cost.

Any thoughts on this are appreciated.
Krischan Makowka
“You never change things by fighting the existing reality. To change something, build a new model that makes the existing model obsolete” - Buckminster Fuller
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Re: Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA) 30 Apr 2014 09:19 #8386

  • muench
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The posting of Kris reminded me that I wanted to post some photos that I took of a sample of the breathable membrane that Steve Dentel brought with him to Delhi to the Toilet Fair in March.

Here is the photo, one can see the three layers of fabric (the photo was taken on a white table cloth). The teflon / PTFE / breathable membrane part is the thin white film in the middle - protected by the two other layers:

IMG_4467smaller.jpg


And two more photos attached below.

(and please let's not start that whole debate again whether this teflon/PTFE material is a problem for the environment, I think it has been discussed sufficiently above. If anyone wants to discuss it further in a more broader sense, please start a new thread on it. Here, let's rather focus on the research ideas, e.g. the ones that Kris posted above).

I saw that Steve Dentel's team got Phase 2 or follow-up funding from the BMGF - congratulations!!
Could you tell us more about it please, Steve?

I saw it here on Sanitation Updates:

sanitationupdates.wordpress.com/2014/04/...gs-for-pit-latrines/

A team at the University of Delaware has received US$ 250,000 in additional funding to continue its research on “breathable membrane” linings for pit latrines.

The breathable fabric helps to prevent groundwater pollution, while also protecting sanitation workers from exposure to pathogens. Heat from biodegradation of the feces or from the sun gradually expels water vapour, but prevents the escape of particulate or dissolved constituents.

Dentel is piloting the membrane technology in the slums of Kanpur, India, in collaboration with WaterAid. He wants to get them in place before the beginning of the rainy season in June. Since the membrane is reusable, the cost of using susch a sophisticated technology can be reduced.

At the same time, Dentel is working with UD engineering colleagues Daniel Cha and Paul Imhoff to apply the technology in wastewater treatment facilities in the USA and South Korea.


What exactly are the research objectives of this Phase 2? How much time do you have for it? What are these planned applications in the USA and South Korea?

Kind regards,
Elisabeth
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Dr. Elisabeth von Muench
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Last Edit: 06 May 2014 09:16 by muench.
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Re: Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA) 06 May 2014 04:14 #8477

  • skdentel
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@ Kai Mikkel Forlie,
You are incorrect that landfilling is the most common option in the U.S. - and I assume you are talking about wastewater sludges. The most common option is in fact application to soils (55%) with landfilling at 21% (Source: Dentel, S.K. Wastewater Sludge Global Overview: United States. In Wastewater Sludge: A Global Overview of the Current Status and Future Prospects, IWA Publishing,2011). And, of course, the U.S. as a country does not exemplify urban areas.

You are also incorrect about the situation in Europe. Even in the five countries with the largest sludge production, agricultural use is less than half (45%), and in the other countries that allow land application, it is typically used for only 10-15% of all sludges. Nor is there a "rampant" trend to increase these numbers over time(source: G. Mininni and S. Dentel, State of sewage sludge management and legislation on agricultural use in EU member states and in the United States" 1st Intl. IWA Conf. on Holistic Sludge Management,May 2013, Västerås, Sweden).

Your reference to a "blanket unwillingness" is also incorrect. I *have* done an in-depth literature search and, as I have indicated in my previous posts, although the membrane is refractory, there is no evidence of toxicity or environmental harm from its use. To repeat research of this nature when it has already been performed would not be an appropriate use of Gates Foundation funding.
_________________________________________________
Steven K. Dentel, Ph.D., P.E., DEE
Professor, Dept. Civil & Environmental Engineering
University of Delaware, Newark DE 19716 USA
Tel: 302-831-8120 Fax: 302-831-3640
ce.udel.edu/~dentel/
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Last Edit: 06 May 2014 09:15 by muench.

Re: Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA) 06 May 2014 04:25 #8478

  • skdentel
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Krischan,
Thanks for the question!
Your suggestion makes sense: the interior heat would increase the vapor pressure and drive off more vapor through the membrane. We also know that some air can penetrate from the exterior into the contents. However, this air entry will not be fast enough to maintain an aerobic interior, so the waste decomposition will be anaerobic and therefore generate organic sulfur and organic amine odorants. They're likely to penetrate the membrane, but we do not yet know the extent. There are also hydrophobic membranes that will not allow odor penetration, but this is at the expense of drying rate.
This is an interesting direction for further work. Because fecal wastes are predominantly water, the ability to release water content should be valuable in terms of volume reduction and waste stabilization.
_________________________________________________
Steven K. Dentel, Ph.D., P.E., DEE
Professor, Dept. Civil & Environmental Engineering
University of Delaware, Newark DE 19716 USA
Tel: 302-831-8120 Fax: 302-831-3640
ce.udel.edu/~dentel/
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Re: Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA) 06 May 2014 07:31 #8482

  • JKMakowka
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skdentel wrote:
Krischan,
Thanks for the question!
Your suggestion makes sense: the interior heat would increase the vapor pressure and drive off more vapor through the membrane. We also know that some air can penetrate from the exterior into the contents. However, this air entry will not be fast enough to maintain an aerobic interior, so the waste decomposition will be anaerobic and therefore generate organic sulfur and organic amine odorants. They're likely to penetrate the membrane, but we do not yet know the extent. There are also hydrophobic membranes that will not allow odor penetration, but this is at the expense of drying rate.
This is an interesting direction for further work. Because fecal wastes are predominantly water, the ability to release water content should be valuable in terms of volume reduction and waste stabilization.


Hmm, you are right, and potentially releasing quite a bit of methane into the atmosphere is probably not that wise either.
I am guessing that just increasing the surface to volume ration to keep in aerobic is probably not going to be cost efficient...

Unrelated to that:
I forgot to mention that the bottom should be probably water permeable to allow draining also, even though that would require some sort of treatment plant for the percolate.

If the drying/dewatering rate is too fast one might also run into trouble with the movement of the sludge through the "bag"... as always the devil lies in the details :-/
Krischan Makowka
“You never change things by fighting the existing reality. To change something, build a new model that makes the existing model obsolete” - Buckminster Fuller

Re: Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA) 09 May 2014 04:15 #8530

  • skdentel
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Krischan,
The breathable membrane fabric could be used on the bottom as well, and no treatment should be needed, because none of the sludge constituents get through the fabric. Only water vapor and other gases.
The fabric facing upward would need to be UV-resistant; some fabrics are available of this type.
_________________________________________________
Steven K. Dentel, Ph.D., P.E., DEE
Professor, Dept. Civil & Environmental Engineering
University of Delaware, Newark DE 19716 USA
Tel: 302-831-8120 Fax: 302-831-3640
ce.udel.edu/~dentel/
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Re: Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA) 09 May 2014 04:56 #8531

  • skdentel
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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!
_________________________________________________
Steven K. Dentel, Ph.D., P.E., DEE
Professor, Dept. Civil & Environmental Engineering
University of Delaware, Newark DE 19716 USA
Tel: 302-831-8120 Fax: 302-831-3640
ce.udel.edu/~dentel/
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Re: Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA) 09 May 2014 06:29 #8532

  • JKMakowka
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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.
Krischan Makowka
“You never change things by fighting the existing reality. To change something, build a new model that makes the existing model obsolete” - Buckminster Fuller

Re: Breathable membrane enclosures for fecal sludge stabilization (University of Delaware, USA) 09 May 2014 12:56 #8545

  • skdentel
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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.
_________________________________________________
Steven K. Dentel, Ph.D., P.E., DEE
Professor, Dept. Civil & Environmental Engineering
University of Delaware, Newark DE 19716 USA
Tel: 302-831-8120 Fax: 302-831-3640
ce.udel.edu/~dentel/
_________________________________________________
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