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Current Affairs

Purple bacteria may help in harvesting green fuel from wastewater

Date: 23 April 2020 Tags: Energy


 Purple bacteria, which store energy from light, can help harvest hydrogen fuel from sewage, and recover carbon from any type of organic waste.



Organic compounds in household sewage and industrial wastewater are a rich potential source of energy, bioplastics and even proteins for animal feed -- but with no efficient extraction method, treatment plants discard them as contaminants.



  • The study is the first to show that supplying electric current to purple phototrophic bacteria can recover nearly 100 per cent of carbon from any type of organic waste, while generating hydrogen gas for electricity production.

  • Purple phototrophic bacteria are extremely versatile thanks to their complex metabolic system that involves major carbon, nitrogen, sulphur, phosphorus and iron pathways, catalysed by various enzymes, he says.

  • They absorb infrared energy through their photosystem, which is composed of carotenoids and bacteriochlorophylls. This means that they can be used to extract valuable products, such as biofuels like biohydrogen, bioplastics like PHA and even single-cell proteins, from waste sources.

  • Purple phototrophic bacteria capture energy from sunlight using a variety of pigments, which turn them shades of orange, red or brown -- as well as purple.

  • Purple phototrophic bacteria make an ideal tool for resource recovery from organic waste, thanks to their highly diverse metabolism.

  • The 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 alternative phototrophic bacteria and algae, and can generate hydrogen gas, proteins or a type of biodegradable polyester as byproducts of metabolism.

  • The researchers analysed the optimum conditions for maximising hydrogen production by a mixture of purple phototrophic bacteria species.

  • They also tested the effect of a negative current -- The first key finding was that the nutrient blend that fed the highest rate of hydrogen production also minimised the production of CO2.

  • This demonstrates that purple bacteria can be used to recover valuable biofuel from organics typically found in wastewater -- malic acid and sodium glutamate -- with a low carbon footprint, that is, electrons supplied by metal electrodes in the growth medium -- on the metabolic behaviour of the bacteria.