Posted: November 14, 2018 7:16:38 PM
A purple bacteria -which stores light energy- can help collect hydrogen fuel from wastewater and recover carbon from any type of organic waste, scientists have discovered. Organic compounds in wastewater and industrial wastewater are a rich potential source of energy, bioplastics and even proteins for animal feed, but without an efficient method of extraction, treatment plants discard as contaminants. A study, published in the journal Frontiers in Energy Research, is the first to demonstrate that the supply of electric current to purple phototrophic bacteria can recover almost 100% carbon of any type of organic waste, while generating hydrogen gas for the production of electricity
"One of the most important problems of current wastewater treatment plants is the high carbon emission," said Daniel Puyol, from the King Juan Carlos University of Spain. "Our light-based biorefinance process could provide a means to collect green energy from wastewater, with a zero carbon footprint," said Puyol.
Purple phototrophic bacteria capture the energy of sunlight using a variety of pigments, which make them orange, red or brown, as well as red.
"Purple phototrophic bacteria are an ideal tool for recovering resources from organic waste, thanks to its very diverse metabolism," said Puyol.
Bacteria can use organic molecules and nitrogen gas – instead of carbon dioxide and water – to provide carbon, electrons, and nitrogen for photosynthesis. This means that they grow faster than phototrophic bacteria and alternative algae and can generate hydrogen, proteins or a type of biodegradable polyester as byproducts of metabolism. What predominates the metabolic product depends on the environmental conditions of the bacteria, such as the intensity of light, the temperature and the types of organisms and nutrients available.
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"Our group manipulates these conditions to adjust the metabolism of purple bacteria to different applications, depending on the source of organic waste and market requirements," said Abraham Esteve-Nunez of the University of Alcalá in Spain. "But what is unique about our vision is the use of an external electrical current to optimize the productive production of purple bacteria," he said.
The researchers analyzed the optimum conditions to maximize hydrogen production through a mixture of purple phototrophic bacterial species. They also tested the effect of a negative current, that is, the electrons provided by metal electrodes in the middle of growth, on the metabolic behavior of bacteria. The first key finding was that the nutrient mix that fueled the highest rate of hydrogen production also minimized CO2 production.
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"This shows that purple bacteria can be used to recover valuable biofuels from organic compounds found in wastewater – malic acid and sodium glutamate – with a low carbon footprint," said Esteve-Nunez.
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