BY KATIE - MYGREENPOD, 26 Dec '17

Microbes help turn Greek yoghurt waste into jet fuel and antibiotics for livestock

Consumers across the world enjoy Greek yoghurt for its taste, texture and protein-packed punch. Reaching that perfect formula, however, generates large volumes of food waste in the form of liquid whey.

Now researchers in the United States and Germany have found a way to use bacteria to turn the leftover sugars and acids from Greek yoghurt into molecules that could be used in biofuels or safe feedstock additives.

‘The agricultural market might seem smaller, but it has a very large carbon footprint, and turning acid whey into a feedstock that animals can eat is an important example of the closed cycles that we need in a sustainable society. The fuel market, of course, operates at a lower price, but its demand is virtually unlimited.’

LARS ANGENENT
Senior author, environmental engineer and microbiologist at Cornell University (United States) and the University of Tübingen (Germany)

How it works

Waste whey from Greek yogurt production is mostly made of the familiar milk sugar lactose, the fruit sugar building block fructose and the fermentation product lactic acid.

The researchers used bacteria to turn this mixture into an extract containing two more useful compounds: caproic acid (n-hexanoic acid) and caprylic acid (n-octanoic acid).

Both of these compounds are ‘green antimicrobials’ that can be fed to livestock in lieu of antibiotics. Or, with energy needs in mind, further processing could stitch the six-, seven-, and eight-carbon backbones of the obtained molecules into the chains of up to 14 needed to qualify as ‘drop-in’ biofuels for jet fuel. Both options have economic and social allure.

Scaling up

Traditionally, suppressing oxygen while feeding biodegradable waste to microbes results in the production of methane-rich gas through anaerobic digestion.

Instead, the researchers strung together two ‘open-culture’ reactors – the first tuned for heat-loving microbes fond of temperatures of 50°C, the second set at a more welcoming 30°C mark.

After seeding each reactor with a previously studied microbiome, and opening the setup to the acid whey and its own rich assortment of bacteria (such as common gut microbiota from the Lactobacillus family), caproic acid, caprylic acid, and other minor products could be continually extracted over a period of several months.

The next challenge will be to see what happens when the twin bioreactor system is boosted to pilot plant capacity.

‘There is much more that can be done to optimize the extraction process and to scale up in an economical way. We can also learn more about the nature of the microbiomes and the biology involved and start investigating whether this technology can be translated to other waste streams.’

LARS ANGENENT
Senior author, environmental engineer and microbiologist at Cornell University (United States) and the University of Tübingen (Germany)