Beer Byproduct Used in Marmite Can Also Recycle Electronic Waste

Every year, more than 50 million tons of electronic devices are thrown out or discarded, becoming what is known as e-waste. Around 17% of this waste is formally collected for recycling, where the devices are broken down and any valuable parts are salvaged.

While it is possible to extract valuable metals – such as aluminum, zinc and copper – from this waste stream, proper recycling has been limited by recovery methods that can’t easily separate the different types of metal ions.

Now, scientists have developed a new method that uses spent brewer’s yeast – the same brewing industry byproduct that is used to make Marmite – to selectively reclaim metals from e-waste. Details of the new method are published in Frontiers in Bioengineering and Biotechnology.

Reduce, reuse, recycle

The first step in salvaging metals from electronic scrap is usually hydrometallurgy – a process where a series of acids are applied to the waste material to leach out the metals, forming a polymetallic solution that can be refined later. But this refinement process is tricky.

“The challenge is that some metals have similar properties leading to co-precipitation or simultaneous sorption,” said study author Dr. Klemens Kremser, a postdoctoral research fellow at the University of Natural Resources and Life Science (BOKU), Vienna.

Chemical precipitation is the most common processing method for metal recovery. However, it is generally considered unsuitable for large-scale processing as it produces a high amount of contaminated sludge as a byproduct. The use of biochar – a biosorbent similar to activated carbon – has also attracted attention, but concerns over removing powdered biochar from wastewater have hampered things.

“Brewer’s yeast, on the other hand, is a cheap byproduct from beer brewing considered as well investigated and safe,” Kremser said. This brewer’s yeast is the same material that is used to make the yeast extract for Marmite, Vegemite and other yeasty spreads.

Recycling with yeast

Kremser and his colleagues obtained 20 liters of spent brewer’s yeast from a local brewing company for use in their experiments. After separating the biomass from other brewing residues and drying thoroughly, the yeast was ready for action.

“Yeast cells are covered with surface active groups which can change their nature by [the] changing of the pH,” Kremser explained. “Depending on their nature, they have a different charge, allowing the sorption of metal ions. By changing the pH, some metals can be bound preferably, allowing [for] selective binding at different pH values.”

The researchers prepared a simulated polymetallic solution using solutions of copper, zinc and nickel, measuring the total metal content using inductively coupled plasma mass spectrometry (ICP-MS). They then tested how the yeast performed as a selective biosorbent when it was mixed into the test metal solutions and the pH and temperature were adjusted. The yeast was also tested against a real polymetallic waste stream.

At optimal pH and temperatures, the researchers were able to recover more than 50% of the aluminum, 40% of the copper and more than 70% of the zinc included in the test metal solutions. The yeast also captured more than 50% of the copper and 90% of the zinc from the real polymetallic waste sample tested.

Love it or hate it?

The research team found that adjusting the temperature of the process had relatively little impact on metal recovery rates, except for in the case of zinc, where warmer temperatures (up to 50 °C) improved recovery by around 7%.

In any case, acid treatment was able to remove the metal bound to the surface of the yeast, while leaving the yeast intact enough to be recycled and re-used. In this study, the same batch of yeast was used up to five times without any significant impact on its metal recovery capabilities.

This is a good sign that the process could be suited to larger sustainable scale-ups, but the researchers say that more work still has to be done before this technique can be launched at the industrial scale.

“The limitation for now is the scale,” Kremser explained. “The study was performed in small volumes [at] laboratory scale. Future studies will have to investigate the applicability of this method in larger and industrial scale.”

It shouldn’t be a problem in terms of securing enough yeast though, as Kresmer points out: “People will continue drinking beer, so there should be enough starting material available!”

But the researchers are still interested in examining other potential limitations that might come into play when dealing with large volumes of highly varied electronic waste.

“Other metals which can be present in polymetallic solutions might interfere with the biosorption process,” Kresmer explained. “We will further investigate the effect of even more complex metal solutions to test [for] potential interference[s].”

Dr. Klemens Kremser was speaking to Alexander Beadle, Science Writer for Technology Networks.

Reference: Sieber A, Jelic LR, Kremser K, Guebitz GM. Spent brewer’s yeast as a selective biosorbent for metal recovery from polymetallic waste streams. Front Bioeng Biotechnol. 2024;12. doi: 10.3389/fbioe.2024.1345112

About the interviewee:
Dipl.-Ing. Dr. Klemens Kremser is a postdoctoral research fellow at the University of Natural Resources and Life Science, Vienna, Austria. His research at the Institute of Environmental Biotechnology focuses on the development and investigation of bio-based processes for the recycling of different waste materials.