These bacteria convert wastewater into clean energy

The purple phototrophic bacteria, which can store light energy, when they are supplied with an electric current they can recover about 100% of the carbon from any type of organic waste, while generating hydrogen gas for use as fuel.

Organic compounds in domestic wastewater and industrial wastewater are a rich potential source of energy, bioplastics and even proteins for animal feed, but without an efficient extraction method, treatment plants discard them as contaminants.

Purple Phototrophic Bacteria

Published in Frontiers in Energy Research, the present study is the first to demonstrate that purple phototrophic bacteria, which can store energy from light, when supplied with an electric current can recover about 100% of the carbon from any type of organic waste, while generating hydrogen gas for the production of electricity.

These bacteria capture the energy of sunlight through a variety of pigments, which give them an orange, red or brown, as well as purple. But it's the versatility of your metabolism, not its color, what makes them so interesting for scientists.

The predominant metabolic product depends on the environmental conditions of the bacteria, such as the intensity of light, temperature and the types of organic substances and nutrients available. The use of an external electric current to optimize the production of purple bacteria, a concept known as "bioelectrochemical system", works because the various metabolic pathways in purple bacteria are connected by a common currency: electrons. For example, an electron supply is required to capture the energy of light, while converting nitrogen to ammonia releases excess electrons, which must dissipate. By optimizing the flow of electrons within bacteria, an electric current, provided through positive and negative electrodes, such as in a battery, can delimit these processes and maximize the speed of synthesis.

According to the authors, this is the first reported use of mixed cultures of purple bacteria in a bioelectrochemical system, and the first demonstration of any phototrophic change metabolism due to interaction with a cathode. Capturing the excess CO2 produced by purple bacteria could be useful not only to reduce carbon emissions, but also to refine biogas from organic waste for use as fuel.