Posted on 10/13/2013 4:49:24 AM PDT by Wonder Warthog
A novel device that uses only sunlight and wastewater to produce hydrogen gas could provide a sustainable energy source while improving the efficiency of wastewater treatment.
A research team led by Yat Li, assoc. prof. of chemistry at the Univ. of California, Santa Cruz, developed the solar-microbial device and reported their results in ACS Nano. The hybrid device combines a microbial fuel cell (MFC) and a type of solar cell called a photoelectrochemical cell (PEC). In the MFC component, bacteria degrade organic matter in the wastewater, generating electricity in the process. The biologically generated electricity is delivered to the PEC component to assist the solar-powered splitting of water (electrolysis) that generates hydrogen and oxygen.
Either a PEC or MFC device can be used alone to produce hydrogen gas. Both, however, require a small additional voltage (an "external bias") to overcome the thermodynamic energy barrier for proton reduction into hydrogen gas. The need to incorporate an additional electric power element adds significantly to the cost and complication of these types of energy conversion devices, especially at large scales. In comparison, Li's hybrid solar-microbial device is self-driven and self-sustained, because the combined energy from the organic matter (harvested by the MFC) and sunlight (captured by the PEC) is sufficient to drive electrolysis of water.
In effect, the MFC component can be regarded as a self-sustained "bio-battery" that provides extra voltage and energy to the PEC for hydrogen gas generation. "The only energy sources are wastewater and sunlight," Li said. "The successful demonstration of such a self-biased, sustainable microbial device for hydrogen generation could provide a new solution that can simultaneously address the need for wastewater treatment and the increasing demand for clean energy."
Microbial fuel cells rely on unusual bacteria, known as electrogenic bacteria, which are able to generate electricity by transferring metabolically generated electrons across their cell membranes to an external electrode. Li's group collaborated with researchers at Lawrence Livermore National Laboratory (LLNL) who have been studying electrogenic bacteria and working to enhance MFC performance. Initial proof-of-concept tests of the solar-microbial (PEC-MFC) device used a well-studied strain of electrogenic bacteria grown in the laboratory on artificial growth medium. Subsequent tests used untreated municipal wastewater from the Livermore Water Reclamation Plant. The wastewater contained both rich organic nutrients and a diverse mix of microbes that feed on those nutrients, including naturally occurring strains of electrogenic bacteria.
When fed with wastewater and illuminated in a solar simulator, the PEC-MFC device showed continuous production of hydrogen gas at an average rate of 0.05 m3/day, according to LLNL researcher and co-author Fang Qian. At the same time, the turbid black wastewater became clearer. The soluble chemical oxygen demand—a measure of the amount of organic compounds in water, widely used as a water quality test—declined by 67% over 48 hours.
The researchers also noted that hydrogen generation declined over time as the bacteria used up the organic matter in the wastewater. Replenishment of the wastewater in each feeding cycle led to complete restoration of electric current generation and hydrogen gas production.
Qian said the researchers are optimistic about the commercial potential for their invention. Currently they are planning to scale up the small laboratory device to make a larger 40-L prototype continuously fed with municipal wastewater. If results from the 40-L prototype are promising, they will test the device on site at the wastewater treatment plant.
"The MFC will be integrated with the existing pipelines of the plant for continuous wastewater feeding, and the PEC will be set up outdoors to receive natural solar illumination," Qian said.
"Fortunately, the Golden State is blessed with abundant sunlight that can be used for the field test," Li added.
Too bad those thousands of politcians and White Hut occupants couldn’t be fed into a machine that will propel our vehicles.
Wonder what boondoggle will evolve from this discovery?
“Wonder what boondoggle will evolve from this discovery?”
Certainly it must be a strategy of “clean energy” scientists to put out press releases that create over-excitement and fawning press coverage, all with the ultimate goal of securing more government grant money. My guess is that most of these ideas are completely impractical or unworkable when scaled up.
It's for the children and the Earth Mother, so you better get in line and do it right or else.
Sounds like a self-sustainable power/waste disposal system for cities. Anything to get us to local control of energy would be a good thing. Therefore this invention will go the way of the Doe Doe bird.
———an average rate of 0.05 m3/day———
Hmmmm......
I suppose they will institute “crap credits”.
True. But it would be so much more satisfying to burn the bureaucrats and politicians directly, even though that energy supply wouldn't last as long.
I’d like a tank of sewage and a bright sunny day please!
Often true. As Sturgeon's Law puts it "90% of everything is crap". But you've gotta do the research to find the 10% that are good ideas.
I suppose they will institute “crap credits”.
LOL! Why not? They’ll come up with any bogus notion to tax.
Any community above a certain size already has that. It's called "a sewer system". And those work just fine with "household toilets". But treating the wastes from those systems is not free.
Waste treatment costs cities and towns a LOT. If the waste treatment part has even reasonable efficiency, it can offset (or maybe even eliminate) those costs, and put out energy at the same time.
Not unreasonable for the small lab cell they tested (pic is at original article link). Next step is to test the scaling laws of the system with their forty liter prototype.
Its called a sewage treatment plant.
What do they plan to do with the hydrogen?
I would guess that they would probably use it in a fuel cell to generate electricity. It is, after all, the perfect fuel for such cells. Just making the wastewater plant "energy self supporting" would be a major plus in the budget of pretty much any city of size. If the overall process turns out not to produce "sludge" or even reduces the amount of same that has to be disposed of as solid waste would be another significant plus.
I think the correct way to look at this is as a way to make wastewater treatment much more efficient/less costly, not as a major energy producer.
It won’t work.
They will try to use genetically modified microorganisms.
No No GMO!
IMHO, if this process goes farther than a lab curiosity,, it will main be because it is used as a pretty bauble attract varieties of grant funds.
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