Fuel from yoghurt residues

Bacteria convert the wastewater of yoghurt production into valuable bio-oil

Yoghurt is not only delicious, it can also produce fuel from a waste product that is produced during production. © George Rudy / thinkstock
Read out

Valuable Waste Product: Researchers have developed a method that transforms sour whey into fuel for airplanes - with the help of bacteria. The microorganisms process the quark and yoghurt byproduct and convert it into a high carbon product in several steps. The result is a bio-oil that can be processed in a refinery.

Quark, Greek yogurt or cream cheese are popular foods. But every liter of milk that goes into the production of these products generates twice as much waste: so-called sour whey. In addition to lactose and fructose, it mainly contains lactic acid and, because of its high acidity, it can not be fed to animals in large quantities, nor can it be reused as otherwise. Therefore, the whey is usually disposed of or distributed on agricultural land.

But in the future, coveted products could emerge from this waste. Because scientists around Lars Angenent of the University of Tübingen and his colleagues have developed a method that makes the whey recyclable - without the use of additional chemicals. They succeeded thanks to tiny helpers: bacteria.

Bacteria as useful helpers

To make the sour whey recyclable, the researchers gave it to a bioreactor with different bacterial cultures - a so-called reactor microbiome: "This microbiome is an open culture in which bacteria can also settle from outside, similar to the microbiome in our gut. Sterilization of the bioreactor or waste water is therefore not necessary, "explains Angenent.

The micro-organisms convert the individual constituents of the whey in two steps at different temperatures: first, bacteria convert sugar into acid at 50 degrees Celsius as an intermediate - the same acid that is produced when milk turns sour. In a second tank, another transformation takes place at 30 degrees Celsius. "Certain bacteria are selected and the process is directed in such a way that more valuable organic substances with longer carbon chains are formed, " reports the biotechnologist. display

Sour whey becomes fuel

In the end, the mixture eventually contained products with six to nine carbons in a row - especially caproic and caprylic acids. The highlight: These substances can not only be used as animal feed and even serve to prevent diseases because of their antimicrobial properties.

They can also easily be converted into fuel, for example, for airplanes. Because of the high carbon content, the mixture from the bioreactor develops lige properties. According to the scientists, this oil can be easily separated, purified and then further processed in a refinery.

Sustainable circular economy

"So we produce bio-oil from bacterial production, " says Angenent. The innovative thing about it is that no other chemicals rich in carbon dioxide would have to be used for the process, and the wastewater alone would be sufficient. So far, the production of substances with long carbon chains has been achieved only by adding expensive chemicals.

The production of Bio- l is part of the development of a circular economy, which recycles all waste products into more valuable materials, as the team emphasizes. "A circular economy can only be truly sustainable if the energy comes from renewable sources and the carbon for chemicals comes from carbon dioxide and other carbonated wastes like sour whey, " concludes Angenent. Now we need to look at how other waters could be turned into useful chemicals as well. (Joule, 2017; doi: 10.1016 / j.joule.2017.11.008)

(Eberhard Karls University T bingen / Cell Press, 28.12.2017 - DAL)