LONDON: A purple bacterium – which stores energy from the light – can help to extract hydrogen from waste water and recycle coal from all types of organic waste, researchers have found.
Organic compounds in household wastewater and industrial wastewater are a rich potential source of energy, bioplastics and even proteins for animal feed – but with no effective extraction method, treatment plants discard them as pollutants.
A study, published in the magazine Frontiers in Energy Research, is the first to show that the supply of electric power to purple photophilic bacteria can recover almost 100 percent of carbon from all types of organic waste while producing hydrogen for electricity production.
"One of the most important problems with current treatment plants is high CO2 emissions," said Daniel Puyol of King Juan Carlos University in Spain.
"Our light-based biorefinery could provide a way to harvest green energy from wastewater, without carbon footprint," said Puyol.
Purple photoprophic bacteria capture energy from sunlight with different pigments, making them shades of orange, red or brown – as well as purple.
"Purple photoprophic bacteria are an ideal tool for recycling from organic waste, due to their varied metabolism," said Puyol.
Bacteria can use organic molecules and nitrogen – instead of carbon dioxide and water – to provide carbon, electrons and nitrogen for photosynthesis.
This means that they grow faster than alternative photoprophic bacteria and algae, and can generate hydrogen gas, proteins or a type of biodegradable polyester as byproducts of metabolism.
What metabolic product that dominates depends on the bacterial environmental conditions – such as light intensity, temperature and the types of organic and nutrients available.
"Our group manipulates these conditions to set the metabolism of purple bacteria to different applications, depending on organic waste and market requirements," said Abraham Esteve-Nunez of Alcala University in Spain.
"But what is unique about our approach is the use of an external electric current to optimize the production of purple bacteria," he said.
The researchers analyzed the optimal conditions for maximizing hydrogen production through a mixture of purple photrophobic bacteria.
They also tested the effect of a negative current – that is, electrons supplied by metal electrodes in the growth medium – on the metabolic behavior of the bacterium.
The first key hardness was 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 Esteve-Nunez. (ORGAN)