Although organic compounds in domestic waste water and industrial waste water can be used as an energy source, no effective extraction method is available to exploit their potential. But now researchers may have found a cost-effective solution that can change waste water into electricity.
Dr. Daniel Puyol from King Juan Carlos University in Spain is one of the co-authors of the research.
"One of the most important problems of the current water treatment plants is the high CO2 emissions," Dr. Puyol. "Our light-based biorefinery process could be a means to harvest green energy from waste water without carbon footprint."
The study is the first to show that purple phototrophic bacteria, when simply supplied with electric power, can recover nearly 100 percent carbon from any type of organic waste while generating hydrogen gas for electricity production.
Purple phototrophic bacteria catch energy from sunlight using a variety of pigments, which turns them shadows of orange, red, brown, or purple. However, scientists are most interested in the versatility of their metabolism.
"Purple phototrophic bacteria make an ideal tool for medium recovery of organic waste, thanks to their very diverse metabolism," said Dr. Puyol.
The bacteria can use organic molecules and nitrogen gas instead of carbon dioxide and water, to supply the carbon, electrons and nitrogen needed for photosynthesis. This means that they can generate hydrogen gas, proteins or a biodegradable polyester as by-products of the metabolism.
The research team analyzed the best conditions for maximizing hydrogen production through a mixture of purple phototrophic bacterial species. They also tested the effect of a negative flow on the metabolic behavior of the bacteria.
First, the experts discovered that the nutrient mix with the highest hydrogen production also minimized the production of CO2.
"This shows that purple bacteria can be used to recover valuable biofuels from organic compounds found mostly in wastewater – malic acid and sodium glutamate – with a low carbon footprint," said Professor Abraham Esteve-Núñez, lead researcher.
The researchers also discovered that purple bacteria are able to use electrons from a negative electrode or "cathode" to capture carbon dioxide by photosynthesis.
"Recordings from our bio-electrical system showed a clear interaction between the purple bacteria and the electrodes: negative polarization of the electrode caused a detectable electron consumption, in combination with a reduction in the production of carbon dioxide."
"This indicates that the purple bacteria used electrons from the cathode to capture more carbon from organic compounds via photosynthesis, so less is released as CO2."
The collection of surplus CO2 produced by purple bacteria would be useful for reducing carbon emissions, or for refining biogas from organic waste for use as fuel. According to Dr. Puyol, however, is still the main objective of the research.
"One of the original aims of the research was to increase bio hydrogen production by donating electrons from the cathode to the metabolism of purple bacteria, but it seems that the PPB bacteria prefer to use these electrons to fix CO2 instead. of H2. "
"Recently, we have obtained funding to pursue this goal with further research, and we will work on this in the coming years." Stay tuned for more metabolic alignment. "
The study is published in the journal Limits in energy research.
By Chrissy Sexton, Earth.com Staff Writer