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.
“My guess is that most of these ideas are completely impractical or unworkable when scaled up.”
But, you have to give the Chinese guy some credit for understanding energy inputs and outputs - unlike the idiots in the government pushing ethanol...
“LOL! Why not? They’ll come up with any bogus notion to tax.”
We already pay a tax here for schools every time we take a crap, a school tax - it’s for the children of course...
Yep, you nailed on several important points. First, solids are going to be produced and disposed of as with current technology. Wouldn’t surprise me if if this used an old fashioned stabilization pond type bioreactor, which takes a lot of area and very likely to require tertiary treatment that would tilt the economics the wrong direction.
It’s perfectly scaled for cat boxes!!
“Doe Doe bird”
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That’s a new one on me, is the male of the species called a Buck Buck bird?
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.Ludicrous.
LOL. Could be. I wasn’t sure how to spell it. It’s a very old expression. Dodo Bird? Sort of like Snipes.
At this point, there is no data to decide one way or the other. If it turns out NOT to generate solids, IMO, this would be a major plus.
"Wouldn’t surprise me if if this used an old fashioned stabilization pond type bioreactor, which takes a lot of area and very likely to require tertiary treatment that would tilt the economics the wrong direction."
For this test reactor, they used two beakers. A wee bit early to talk about ponds and such.
Which part?? I kind of thought that the idea of combining the two approaches to overcome a disadvantage each has as a stand-alone technology was good innovative thinking.
The DoDo bird "was" quite real. A not-very-bright flightless bird native to a small island (Mauritius) in the Indian Ocean. They had no fear of humans, and were killed off by hungry sailors.
Rather than using the photovoltaics to directly generate electricity for the grid (via DC to AC conversion of course), they’re using it to make the digestion process “self-sustaining” — then turn methane into electricity in a fuel cell in order to produce hydrogen. Pelion on Ossa.
Thank you for the Natn’l Geographic presentation. I knew that......of course I knew that....didn’t I? LOL
It isn't methane they're converting, but the larger and more obdurate molecules (note the statement "dark wastewater becomes clearer"). Methane isn't "dark".
So they're using energy from the photovoltaics and energy from the hydrocarbons to get more total energy than either can get when run as a standalone process, while simultaneously cleaning the water. This still sounds like a "good thing" to me.
As to "why hydrogen" instead of direct electricity?? I dunno. I kind of wondered that myself. It may have to do with what their "electrogenic bacteria" are capable of.
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