Sol-Char Toilet: Using Concentrated Solar Energy to Treat Fecal Waste and Produce a Valuable Soil Amendment - biochar (Uni Colorado, USA)

  • kglinden
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Sol-Char Toilet: Using Concentrated Solar Energy to Treat Fecal Waste and Produce a Valuable Soil Amendment - biochar (Uni Colorado, USA)

We are a group from the University of Colorado in Boulder (Environmental Engineering and Chemical Engineering areas) who was recently funded as part of the Reinvent The Toilet Challenge. We are developing a solar-concentrator based technology to treat fecal waste. We have an engineering in developing communities program that many of the students/researchers working on this project have either gone through or recently graduated from. Check out our project description below and see more on our Facebook page, link below.


Sol-Char Toilet: Using Concentrated Solar Energy to Stabilize Fecal Waste and Produce a Valuable Soil Amendment (University of Colorado, Boulder, USA)

Project Description:
Last September, our team here at the University of Colorado, Boulder took on the BMGF challenge to reinvent the toilet with a novel approach that utilizes concentrated solar energy to safely and efficiently char fecal waste without the need for intensive pre-drying.

As a quick overview, our toilet – the Sol-Char Toilet – is a waterless, self-contained toilet that functions off-the-grid. Concentrated sunlight is delivered to fiber optic bundles located at the focus of parabolic concentrators (see Concept Sketch). The fiber optic cables are fed to the reaction compartment of the Sol-Char where the various individual cables are terminated at an outer or “solar” lid positioned over the waste collection container. The innovative transmission of concentrated solar power illuminates the inner collection container and disinfects the waste though conduction, convection, and radiation heat transfer. The reaction compartment comprises two or more containers that are alternated between “collection” and “reaction” modes via a simple carousel system that can be automated (powered with photovoltaic energy) or manually controlled. The reactor is designed to achieve high temperatures (300oC to 750oC) and produces a safe and useable product.

Research Goal:
Our goal during this phase 1 of research is to develop a functioning toilet prototype that will provide a scientific basis for utilizing concentrated solar energy to safely disinfect and transform human waste into valuable end products (such as char for agricultural soil application).

On-going research activities include:
• Solar collection and transmission optimization
• Reactor modeling and fabrication
• Char product evaluation and testing
o Hydrothermal carbonization (HTC) and dry pyrolysis chars will be compared
o Dry pyrolysis will also be evaluated with mixed waste and urine diversion to determine the best utilization of nutrients
o Adsorption studies will be conducted in the liquid and gas phase to determine if the char can be further enriched with NPK
• Means for odor control, gas utilization, and final product storage
• User interface and safety features
Our prototype development is underway and we are excited to further advance this technology. We welcome your feedback and comments!

Title of grant: Grant Number OPP1065047 – Solar Toilet
Lead organization: University of Colorado, Boulder
Contact: Karl Linden, Principal Investigator
Location of research: Current phase of research is being conducted in Boulder, CO
Start and end date: September 2012 to December 2013
Grant type: Reinvent the Toilet Challenge (RTTC), Round 2, Phase 1, grant value: $1,780,351 according to www.gatesfoundation.org/How-We-Work/Quic...s/2012/08/OPP1065047

Links and further readings:

Documents in SuSanA library: www.susana.org/en/resources/library/details/1759

• For more information you can link to a presentation and paper that was presented at the Faecal Sludge Management (FSM2) Conference in Durban, South Africa in October 2012 here:
www.susana.org/en/resources/library/details/1759

Video of the presentation by Scott Summers at the same conference:


• You can also like us on Facebook!: www.facebook.com/SolarBiochar






Karl G. Linden, Ph.D.
Helen and Huber Croft Professor of Environmental Engineering
Civil, Environmental, and Architectural Engineering
University of Colorado Boulder
428 UCB; 1111 Engineering Drive, ECOT 441
Boulder, CO 80309
Phone: (303) 492-4798, Fax: (303) 492-7317
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Web: ceae.colorado.edu/klinden/
Twitter: @waterprof
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  • JKMakowka
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Re: Sol-Char Toilet: Using Concentrated Solar Energy to Treat Fecal Waste and Produce a Valuable Soil Amendment (Colorado)

Nice idea for heat-transfer, but how realistic is it have an expensive sun following parabolic concentrator (as shown in the sketch) for such kind of toilet?

Heating up stuff to 300-750°C in one's toilet compartment also seems like a quite big fire hazard and maybe a bit of an overkill also (>60°C for some time is fine for killing pathogens).

Edit: Somehow all those "reinvent the toilet" prototypes are seriously over-engineered.

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  • joeturner
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Re: Sol-Char Toilet: Using Concentrated Solar Energy to Treat Fecal Waste and Produce a Valuable Soil Amendment (Colorado)

JKMakowka wrote: Edit: Somehow all those "reinvent the toilet" prototypes are seriously over-engineered.

Absolutely.

I like the idea of biochar, but why do these things always have to use such complicated and expensive components?
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  • kglinden
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Re: Sol-Char Toilet: Using Concentrated Solar Energy to Treat Fecal Waste and Produce a Valuable Soil Amendment (Colorado)

Thanks Joe Turner and JK Makowka for checking out our post and ideas. The RTTC is really looking to push boundaries of technology - so we are moving forward interesting research on concentrated solar energy transmission. At the same time we are one of the only groups looking at human fecal waste (not synthetic) as a stock for biochar production - there are a lot of interesting findings here that we look forward to sharing on this forum and elsewhere. Check out our Facebook page for regular updates as well.

Once we understand the potential of the concentrated sunlight using state of the art components, we definitely need to re-engineer the system to make it practical and affordable. Being a research prototype, we are trying to make it the best we can using all our modern tools. So yes - solar tracking is one of those and is an important component for optimum efficiency.

Good point about tradeoffs in temperature. We can certainly achieve pasteurization/disinfection at much lower cost, and that is an option - but we are going to first demonstrate biochar potential, then we can scale back as we value engineer the system. It may mean just targeting killing pathogens. We will look for an economic argument for producing biochar (briquettes?, Ag amendment?, C sequester?) - much more interesting and usable than a bunch of sterile fecal sludge.......

Karl G. Linden, Ph.D.
Helen and Huber Croft Professor of Environmental Engineering
Civil, Environmental, and Architectural Engineering
University of Colorado Boulder
428 UCB; 1111 Engineering Drive, ECOT 441
Boulder, CO 80309
Phone: (303) 492-4798, Fax: (303) 492-7317
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Web: ceae.colorado.edu/klinden/
Twitter: @waterprof
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Re: Sol-Char Toilet: Using Concentrated Solar Energy to Treat Fecal Waste and Produce a Valuable Soil Amendment (Colorado)

I'm sorry to ask a stupid question, but why use solar at all? Couldn't sludge be charcoaled using simple technologies such as the rocket stove ?

It strikes me that the rocket stove is more likely to be affordable and scalable than a solar based system, given it can be built from available materials.
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  • richardpfisher
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Re: Sol-Char Toilet: Using Concentrated Solar Energy to Treat Fecal Waste and Produce a Valuable Soil Amendment (Colorado)

Hi Joe,

I'm one of the researchers on the CU-Boulder Reinvent The Toilet team. Thanks for your questions and comments.

The major thrust of using concentrated solar power, as opposed to a rocket stove or furnace/retort, is that there is extremely low energy input and no fuel source required to power the system (only moderately clear skies). There are substantial capital costs associated with our research prototype (tracker, parabolic mirrors, fiber optics) but only a low-amperage 12 VDC power is required to track the sun, which can be supplied by a small PV panel.

I hope that helps to answer your question.

Best,
Chip Fisher
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Re: Sol-Char Toilet: Using Concentrated Solar Energy to Treat Fecal Waste and Produce a Valuable Soil Amendment (Uni Colorado, USA)

Really cool. I agree with a few replies about the cost and technology access. But I work with numbers. How much cost of one ready-working of these units? and possible uses of this faecal-biochar: activated carbon filters, fuel, soil conditioner, any other? What price you think you can take of the bio-char efluents?
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Re: Sol-Char Toilet: Using Concentrated Solar Energy to Treat Fecal Waste and Produce a Valuable Soil Amendment (Uni Colorado, USA)

Hi RodrigoBIS,

Thanks for your comments and questions.

Unfortunately, I cannot quote a price on our prototype, mostly by the fact that it is a research unit to demonstrate our concept. There are too many caveats to determining that cost to enumerate in this forum.

As far as the possible uses to fecal biochar, all the applications you mentioned are certainly possible and fecal biochar's efficacy in each application depends on the feedstock properties (diet, water content, etc.) and processing conditions (temperature and heating rate of the reactor). The same can be said of any biomass feedstock used in pyrolysis to produce biochars. We're currently investigating the economic viability of all the above applications.

One of the more attractive applications for fecal biochar is its use as a solid fuel source. We've done studies in which we produced briquettes from biochar, processed at various reactor temperatures. It turns out that fecal biochars produced in the lower temperature range of pyrolysis have a higher heating value (HHV) greater than or equal to that of typical supermarket charcoal and greatly outperform the same biochar produced at much higher temperatures.

I apologize for not being able to answer your question about price tag of our prototype, so to speak, more specifically at this time but I hope I was able to address your other questions.

Thanks again,
-Chip Fisher
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Re: Sol-Char Toilet: Using Concentrated Solar Energy to Treat Fecal Waste and Produce a Valuable Soil Amendment (Uni Colorado, USA)

Dear all

To all those who are interested in this discussion on the Sol-Char Toilet: here is your chance to interact with Richard (Chip) Fisher and Ryan Mahoney live during the upcoming webinar hosted by SEI on Tuesday (26 Nov.) at 16:30 Sweden time.
During this webinar, you will get the chance to see a live presentation of the project and recent achievement and ask questions. Other participants are Alison Parker (Cranfield University, (Nano Membrane Toilet) and Jeroen Ensink (London School of Hygiene and Tropical Medicine, New concepts for on-site sanitation based on bio-additives and pit design).
Attendance at this webinar is open!
(If you miss the event live, you can view the recording on Youtube a few days later)
See here for more information: fhttp://forum.susana.org/forum/categories/139-general-information-and-announcements/5624-sanitation-expert-chats-bmgf-grantees-stockholm-environment-institute-invitation-for-4th-webinar-on-tuesday-26-november#6427 or contact: This email address is being protected from spambots. You need JavaScript enabled to view it.

Best regards
Dorothee

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Re: Sol-Char Toilet: Using Concentrated Solar Energy to Treat Fecal Waste and Produce a Valuable Soil Amendment (Uni Colorado, USA)

Dear all,

I am writing this post to provide people who don't have access to Youtube videos with a quick overview of what Chip and Ryan presented during the fourth webinar that SEI organised on 26 November (see Arno's post about it here: forum.susana.org/forum/categories/139-ge...mit=12&start=12#6564 ).

Chip and Ryan shared the presentation. Their presentation starts exactly here in the Youtube video:


Sol-Char Toilet: Using Concentrated Solar Energy to Stabilize Fecal Waste and Produce a Valuable Soil Amendment (University of Colorado, Boulder, USA)
By Richard (Chip) Fisher and Ryan Mahoney


The powerpoint slides that they used (please note that the Appendix contains several additional slides):

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Two of the slides as a visual input:







Notes that I took from Chip’s presentation (Chip is the leader of the “reactor team”):
  1. They are using concentrated solar power and fibre-optics cables to transmit colar energy to pyrolise and disinfect excreta and to produce something useful (biochar).
  2. The fibre optics cables transmit the solar energy (which is concentrated with the parabolic dishes) to a pyrolysis reactor.
  3. The prototype reactor is sitting right now at the parking lot outside and should be working well because it is a bright sunny day. (follow-up question: can you share photos of your prototype reactor? And what would happen in practice on a cloudy day? No more disinfection possible on cloudy days?)
  4. They are testing the fibre optics in their first generation prototype which they will take to the fair in Delhi in March.
  5. There are two reactors which are located on a caroussel. One serves as the collection vessel; when full it is rotated to the second position where heat is added to the reactor via the fibre optics cables.
  6. Fibre optics can effectively transmit solar energy from the focal point in the parabolic dishes to the reactor. 8 parabolic dishes are used as solar concentrators (follow-up question: you realise that these parabolic dishes look a bit flimsy and could easily be damaged in practice if installed at a household level?).
  7. They are concentrating the solar energy 2000 times (= 2000 suns). Theoretical maximum value: 5000 times.
  8. 500-1000 W delivered in power.
Notes that I took from Ryan’s presentation (Ryan is the leader of the “biochar team”):
  1. The toilet works with urine diversion. The urine is circulated around the reactor to take advantage of the waste heat for disinfection (follow-up question: which pathogens in urine are you looking to kill? Normally urine is sterile?).
  2. There is a dumping mechanism to dump out the content of the reactor after pyrolysis.
  3. The prototype is designed to process 2 kg of faeces and 4 kg of urine in 4 hours.
  4. All the energy comes from solar energy, no additional energy required.
  5. They have tested the energy contents of the biochar produced. At 300 °C reactor temperature, the biochar is competitive in terms of heating value compared to other energy sources like char coal (at reactor temperature of 750°C, the energy content of the faecal biochar is reduced). Follow-up question: is that not to be expected? Why even try it at 750 °C?
  6. They are investigating the properties of the biochar when it is used as a soil amendment (see powerpoint slides for details)
  7. They are working on improving the solar tracking accuracy.
  8. They have a problem with generating too much energy, too much solar flux (follow-up question: does that mean the reactor is getting too hot? How do you deal with this problem?).
Questions from the audience:

(1)
Question by Daniel Yeh:
"What is the power density?"

Answer by Chip:

"At the concentrator side it is 2000 kW/m2, i.e. where we are getting the light down to our focal point. We are transmitting 500 W through the 8 fibres. The reactor has an outer diameter of 4 inch (= 10 cm). This means it is 30 kW/m2 at the reactor side." My follow-up question: is this a lot? What are we comparing this against? Why did you ask, Daniel, did you have a certain value in mind?

(2)
Question by Luiza Campos:
"Is this toilet for a household or for a community level installation?"

Answer by Ryan:
"We have not yet decided where we will do the field trials. It is in principle designed for the household level (our prototype is for a household). But it could also be for shared toilets in the future; a larger scale would probably increase the efficiency of the process."

If anyone has further questions or comments, then please put them here by replying to this post.
Thank you again to Chip and Ryan for giving this presentation!

Regards,
Elisabeth

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(Funded via GIZ short term consultancy contract)

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  • richardpfisher
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Re: Webinar 4 Write-up with Q&A

Hi Elisabeth,

I am providing answers to your follow-up questions below.

Chip's Presentation:

Your question under point 3:
There are some photos attached below. In the case of cloudy days, the current prototype will not disinfect waste. For a phase II prototype (if we get the chance to make one!), we would incorporate electric heaters or higher storage capacity to account for days/weeks of no-sun. These changes would involve a new reactor design and reconfiguration of the system.












Your question under point 6:
I wouldn't describe the concentrators as flimsy, they're machined from solid 25mm aluminum blocks. The reflective surface, however, is easier to damage - it's basically a polymer that we can adhere to the aluminum dish. The film is more robust against environmental damage than one might think - it's a reflective film that's used in the US desert southwest for concentrated solar power to electricity plants (think sand and dust storms). For the sake of time, we made the concentrators out of solid aluminum but if we ever sold a toilet with our CSP and reactor system, the concentrators would be made of an entirely different material that doesn't shine and scream, "I'm super expensive, please steal me and sell me." Most likely fiberglass or something similar.


Ryan's Presentation:

Your question under point 1:
The pathogens in urine which we have evaluated are E. Coli and MS2 phage (a surrogate organism for viruses). It is true that healthy urine is sterile, however there is evidence that in urine diversion scenarios, there can be significant fecal contamination of urine.

Your question under point 5:
The better heating value from lower-temperature biochar is not necessarily expected, but due to the relatively high concentration of ash in this feedstock the energy density does infact decrease. With some feedstocks, the higher temperature actually further concentrates the energy because the bonds which are formed arrange themselves in a more energy dense way (thus the MJ/kg HHV will increase). However, because the ash content of feces is relatively high (~5%) this non-combustible portion becomes a larger fraction of the total post-charring (~15% at 300C, 50% at 750C). The end use of the char we generate is still undetermined (could be agricultural or fuel), but in the case of implementing biochar as a soil amendment, the porosity and aromaticity (portion of graphite-like domains in the char) tends to increase with temperature. Increased porosity and aromaticity improve a char's adsorption capacity (water, cations, etc) and recalcitrance in the soil, respectively. So depending on the end-users needs, we would either go to a relatively low or high temperature.

Your question under point 8:
What we meant was that we're "baking" the waste too quickly and creating a burning the bread, so to speak. At power levels comparable to what we've measured here in Boulder, we've observed a semi-solid synthetic feces charge into the reactor to have a hard char crust (20-30mm thick in places) with a gooey, non-charred region in the center after 4 hours on-sun. So we're thinking of ways to dial-back the power at the reactor and slow-down the heating process so that we get an evenly dried and evenly charred product from each batch reaction.


To address your follow-up to Daniel Yeh's question:

The short answer: yes, it's a lot compared to electrical heaters or other similar-sized (diameter = 80mm) power delivery modes. Please take those numbers with a grain of salt, it was not a detailed estimate by any means. We don't know the exact area of the illuminated portions of the reactor yet, but will be able to give a better estimate of the power density soon.

Let me know if you have any other follow-up questions.

-- Chip Fisher 303.746.2549
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  • rahulingle
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Re: World's first solar-powered toilet set for India launch

World's first solar-powered toilet set for India launch

Attractive interface design though not clear how one would use it.

Best regards,

Rahul Ingle
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