Sludge-powered bacteria generate more electricity, faster


Research News


Changing the surface chemistry of electrodes leads to the preferential growth of a novel electroactive bacterium that could support improved energy-neutral wastewater treatment.

To grow, electroactive bacteria break down organic compounds by transferring electrons to solid-state substrates outside their cells. Scientists have utilized this process to drive devices, such as microbial electrochemical systems, where the bacteria grow as a film on an electrode, breaking down the organic compounds in wastewater and transferring the resultant electrons to the electrode.

Scientists are now looking for ways to improve this process so it produces hydrogen gas at a negatively charged cathode electrode, which can then be converted to electricity to power wastewater treatment plants. This needs electroactive bacteria that efficiently transfer electrons to a positively charged anode electrode that do not use hydrogen for their growth.

Krishna Katuri, a research scientist in the lab of Pascal Saikaly, and colleagues have now found a novel electroactive bacterium, called Desulfuromonas acetexigens, that preferentially grows when the surface chemistry of the anode is changed in a specific way. The bacterium produces a higher current density than the most important current-producing bacterium, Geobacter sulfurreducens, and in a shorter time.

“We consider this a breakthrough discovery in the field,” says Katuri.

In tweaking the surface chemistry, the researchers modified graphite electrodes to produce amino, carboxyl and hydroxide groups on their surface. When sludge and acetate, an organic compound used as feed, were placed in a glass chamber together with the electrode, bacteria quickly grew on the electrode’s surface. Analyses revealed that D. acetexigens preferentially grew quickly on the modified electrodes, while G. sulfurreducens grew on conventionally used unmodified electrodes tested as controls.

Further analyses showed that D. acetexigens generated a current density of around 9 amperes per square meter within 20 hours of the process starting, compared with only 5 amperes per square meter in 72 hours by G. sulfurreducens.

Also, D. acetexigens does not use hydrogen as feed. This means that a microbial electrochemical reactor treating wastewater could combine the electrons and protons produced by this bacterium to generate hydrogen gas at the cathode.

“We next plan to study how D. acetexigens transfer electrons and to learn how to maximize their activity at the anode,” says Saikaly. “We’re also fabricating a pilot-scale microbial electrolysis cell reactor to treat domestic wastewater with this bacterium while recovering hydrogen gas as energy. Solar panels will be integrated into the pilot reactor with the aim of using solar and hydrogen energy to achieve energy-neutral or even possibly energy-positive wastewater treatment.”


From EurekAlert!

18 thoughts on “Sludge-powered bacteria generate more electricity, faster

  1. Interesting, but.
    “panels will be integrated into the pilot reactor with the aim of using solar and hydrogen energy to achieve energy-neutral or even possibly energy-positive wastewater treatment.”
    Adding energy from suunlight does not make the treatment process energy neutral any more than adding a coal fired boiler would.

  2. What?
    Which electrode, Why. To what end?

    What is this ‘acetate’. Surely its a high energy substance in its own right so how do you gain anything feeding it to bacteria in a septic tank. A septic tank bristling with ‘carefully’ modified electrodes.
    Please me I’ve lost the plot and not them

    OK. So then it does ‘do’ something (make hydrogen) which is then used to power the ‘process’
    But that’s no good, solar panels are needed. Do folks have to stop pooping after sunset?

    Surely to goodness, the business of treating “wastewater” (in The Grand Scheme of Things, is there actually such stuff?) is to kill/inactivate harmful bacteria *and* remove chemical/metallic poisons.

    *Ideally* without destroying the organic content – which. suitably detoxified, can/will/SHOULD be put back into the soil/dirt of the fields from which the ‘organic waste’ (again, No Such Thing) came from

    Or have they devised an quite bizarre/pointless/expensive way of burning organic material in the Sure & Certain Knowledge they will Save The World.

    They could *NOT* be more wrong

    • Acetate is the basic source of energy we use from breaking fatty acids down into two carbon chunks, which then go through the citric acid cycle in the mitochondria. It would very likely not be that abundant in sludge.

  3. energy from coal is “free” ,except for the infrastructure..
    energy from solar is “free” ,except for the infrastructure..

  4. I might not be understanding the full potential of this new discovery, and so the first thing i thought of was if a nuclear reactor is used as the energy source instead of solar panels, then it might also be possible to simultaneously turn lead into gold as a bonus.
    Just leave the lead in the nuclear reactor for a long period of time, and it will convert lead into gold via neutron capture and beta decay. two reactors = win, win!

  5. D. acetexigens generated a current density of around 9 amperes per square meter within 20 hours of the process starting

    How much energy is this representing, assuming P still equal voltage times current?

    How much hydrogen is produced per square meter?
    If not very much, it may be more useful to continue producing hydrogen from fossil fuel.

    However, part of it sounds interesting, although current treatment plant seem to work well already.

  6. “Changing the surface chemistry of electrodes …”
    Using couple of electric eels for electrodes might improve efficiency even more /sarc

  7. biofilms of bacteria growing on your graphite electrodes sounds more like a problem than anyway to generate more low density power.

    • Electric eel is basically a capacitor, parallel = more current, series = higher voltage. Out of water either way the shock can be much more painful.
      Bob, if you are inclined to do a test please send the data.

    • If you live anywhere in vicinity of a old fashioned AM radio transmitter mast, just stick the headphones jack end into a fresh potato and ‘voila’ you can listen to radio with a minimum carbon (hydrate) footprint.

  8. It seems a ridiculously complex and probably inefficient alternative to anaerobic digestion producing methane. Which competent water treatment organisations have been doing for decades.

  9. Of course, you could just dewater the sludge, burn it in a fluidized bed incinerator, and then use a heat recovery steam generator to make the electricity. But that won’t get you government grant money.

  10. It’s always “we need more study.”

    Wake me up when someone’s actually deploying a useful technology. I’ve been reading about bio-this and bacteria-that for 20 years now, with little change in actual technology.

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