For centuries, humans have obtained fuel from the strangest of sources: the remains of organisms that lived millions of years ago, seawater, decaying biomass and now, from cow's milk ... or more accurately, salty whey, a by-product produced during the manufacture of cheddar and similar cheeses.
Whey itself is the liquid left behind after milk proteins and fats are separated to form cheese curds. It is mostly water but still contains lactose, proteins, minerals, and other useful components that make regular whey valuable enough to process into everything from protein powders (the elixir of gym bros) to food ingredients. Fantastic stuff.
The issue is with its cousin, salty whey. During the production of cheeses such as cheddar, producers add salt to the curd before pressing. Some of that salt dissolves into the additional whey expelled from the curd, creating a particularly salty stream that is considerably harder to process or dispose of.
Salty whey can contain around 4% to 10% salt, roughly 15 to 20 times as much as conventional sweet whey.
This high salt content complicates conventional whey processing, while the combination of salt and a large amount of organic material also makes simply dumping the stuff a bad idea. Discharging untreated whey can deplete oxygen in waterways and damage aquatic ecosystems. Similarly, applying salty whey to land can affect crops and soil health. As a result, the material is classified as waste, and there is quite a lot of it.
Around 95,000 tonnes of salty whey are produced in the UK each year, according to Scotland's Heriot-Watt University. Individual dairy producers can generate tens of thousands of liters every week, and managing all that waste liquid is expensive. Despite these issues, salty whey still has one redeeming quality. It contains a particularly useful ingredient: sugar.
This is what British biotech firm Take Root Bio and researchers at Heriot-Watt's International Centre for Brewing and Distilling are going after. Working with support from the Industrial Biotechnology Innovation Center (IBioIC), the team developed a biological process that uses the sugars remaining in salty whey to produce bioethanol, ethanol produced from biological material rather than fossil feedstocks.
In conventional bioethanol production, microorganisms ferment sugars and convert them into ethanol, which can then be recovered and used as a fuel or as an ingredient in other industrial products. Until now, the salt content has made it difficult to replicate this process in salty whey. The team says it has successfully converted salty whey into bioethanol using a bio-based process. The process also produces a second residual stream that the team believes could potentially be recovered and reused.
Unfortunately for those who enjoy seeing exactly how the sausage, or in this case the cheese waste fuel, gets made, this is about as far as the team has gone publicly with the technical details. The researchers have not disclosed the microorganism used, the salt concentration in the feedstock, whether the whey undergoes any pretreatment or desalination, the fermentation conditions, or how much ethanol they produced from a given quantity of whey. They also have not disclosed what is in the second residual stream or what it might eventually be used for.
That said, if the proprietary process can be made economical at larger scales, then it's fantastic news for dairy producers. Instead of paying simply to manage or dispose of thousands of liters of salty whey, some of that material could become the feedstock for a useful fuel.
“We've always been interested in what happens when you stop looking at something as waste and start asking what else it could become,” said Kirk Siderman-Wolter, founder of Take Root Bio. The company has its roots in biosphere engineering, and previously worked on systems for growing and recycling food in space. It is now applying the same closed-loop thinking to food production on Earth.
Heriot-Watt brings an equally relevant background. The university has researched and taught brewing and distilling since 1903. Researchers there also work on waste valorization, the science of finding useful products hiding inside industrial by-products.
“This project gave us the opportunity to explore whether bio-based solutions could help unlock some of the value in salty whey while reducing the pressures associated with disposal,” said Dr. Shiwen Zhuang, a fermentation specialist at Heriot-Watt University.
Take Root Bio is exploring mobile production units that could be installed closer to dairies to avoid transporting huge volumes of salty whey to centralized processing facilities. Considering how much of the feedstock is water, the distance it has to travel can significantly impact the economics of the process.
The collaboration is also looking beyond cheese. Take Root Bio and Heriot-Watt are investigating whether similar techniques could be applied to other food and agricultural by-products, including waste from fruit and vegetable processing.
The researchers are even looking at the gases produced during fermentation. The company says future systems could potentially capture gases such as methane and hydrogen and feed them into other food-production processes.
Source: Heriot-Watt University
