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

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.

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.......

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?

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.

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