While there are organic compounds in household wastewater and industrial wastewater that can be used as an energy source, there has been no effective recovery method to exploit their potential. But now researchers can have identified a cost-effective solution that can make wastewater into electricity.
Dr. Daniel Puyol of King Juan Carlos University in Spain is one of the co-authors of the study.
"One of the most important problems with current sewage treatment plants is high CO2 emissions," says Dr. Puyol. "Our light-based biorefinery process can provide a way to harvest green energy from wastewater, without carbon footprint."
The study is the first to show that when it is simply delivered with an electric current, phototrophic bacteria can recover almost 100 percent of carbon from all types of organic waste while producing hydrogen for electricity production.
Purple photoprophic bacteria capture energy from sunlight with different pigments, making them shades of orange, red, brown or purple. Researchers, however, are most interested in the diversity of their metabolism.
"Purple photoprophic bacteria are an ideal tool for recycling from organic waste, due to their varied metabolism," says Dr. Puyol.
Bacteria can use organic molecules and nitrogen, rather than carbon dioxide and water, to provide carbon, electrons and nitrogen needed for photosynthesis. This means that they can generate hydrogen, proteins or a type of biodegradable polyester as byproducts of metabolism.
The research group analyzed the best conditions for maximizing hydrogen production through a mixture of purple photophilic bacteria. They also tested the effect of a negative current on the bacterial metabolic behavior.
First, experts discovered that the nutrient mixture that gave the highest hydrogen production level also minimized the production of CO2.
"This shows that purple bacteria can be used to recycle valuable biofuel from organic substances commonly found in wastewater – malic acid and sodium glutamate – with low carbon pressure," says co-author Abraham Esteve-Núñez.
The researchers also found that purple bacteria can use electrons from a negative electrode or "cathode" to capture carbon dioxide through photosynthesis.
"Records from our bioelectrochemical system showed a clear interaction between the purple bacteria and the electrodes: negative polarization of the electrode caused a detectable consumption of electrons in connection with a reduction of carbon dioxide production."
"This indicates that the purple bacteria used electrons from the cathode to capture more carbon from organic compounds through photosynthesis, so less released as CO2."
Capturing excess CO2 produced by purple bacteria would be useful for reducing carbon dioxide emissions, or for refining biogas from organic waste for use as fuel. According to Doctor Puyol, however, the main objectives of the research are still.
"One of the original purposes of the study was to increase biohydrogen production by donating electrons from the cathode to purple bacterial metabolism. However, it appears that PPB bacteria prefer to use these electrons to fix CO2 instead of creating H2."
"We have recently received funding to drive this goal with further research and will work for this in the following years. Get ready for more metabolic tuning."
The study is published in the journal Frontiers in Energy Research.
By Chrissy Sexton, Earth.com Staff Writer
Original article can be found by clicking here