Purple bacteria can help harvest the green fuel from wastewater

Bacteria can use organic molecules and gaseous nitrogen (instead of carbon dioxide and water) to provide carbon, electrons and nitrogen for photosynthesis. (Image: Photo file)

Scientists have discovered that a purple bacterium – which stores the energy of light – can help recover the hydrogen fuel contained in the wastewater and recover the carbon from any type of organic waste. Organic compounds in domestic and industrial wastewater are an important potential source of energy, bioplastics and even protein for animal feed. However, in the absence of an efficient extraction method, treatment plants reject them as contaminants. A study, published in the journal Frontiers in Energy Research, is the first to show that supplying electric current to purple phototrophic bacteria can recover nearly 100% of the carbon from any type of organic waste, while generating more energy. hydrogen for the production of electricity.

"Carbon emissions are one of the biggest problems in today's wastewater treatment plants," said Daniel Puyol of King Juan Carlos University, Spain. "Our light-based biorefinery process could provide a way to harvest green energy from wastewater, with a zero carbon footprint," said Puyol.

Purple phototrophic bacteria capture the energy of sunlight using a variety of pigments that give them orange, red or brown hues, as well as purple.

GOOD DEALS

"Purple phototrophic bacteria are an ideal tool for recovering organic waste resources, thanks to their extremely diverse metabolism," Puyol said.

Bacteria can use organic molecules and gaseous nitrogen (instead of carbon dioxide and water) to provide carbon, electrons and nitrogen for photosynthesis. This means that they grow faster than alternative phototrophic bacteria and algae and that they can generate hydrogen, protein or a biodegradable type of polyester as a byproduct of metabolism. . The predominant metabolic product depends on the environmental conditions of the bacteria, such as light intensity, temperature and the types of organic substances and nutrients available.

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"Our group manipulates these conditions to adapt the metabolism of purple bacteria to different applications, depending on the source of organic waste and the demands of the market," said Abraham Esteve-Nunez of the University of Alcalá in Spain. "But what is unique in our approach is the use of an external electrical current to optimize the production of purple bacteria," he said.

The researchers analyzed the optimal conditions to maximize hydrogen production by a mixture of species of purple phototrophic bacteria. They also tested the effect of a negative current, that is, electrons provided by metal electrodes in the growth medium, on the metabolic behavior of the bacteria. The first key finding was that the nutrient mix at the origin of the highest hydrogen production rate also minimized CO2 production.

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"This demonstrates that purple bacteria can be used to recover valuable biofuel from organic materials commonly found in wastewater – malic acid and sodium glutamate – with a low carbon footprint," Esteve said. Nunez.

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