Could Wastewater Be A Triple Solution for Food Waste, Sustainable Proteins & Green Fuels?

Scientists have found a way to produce proteins by feeding yeast on upcycled wastewater from the food and pharma industries.

How would you like your wastewater-derived meat?

It may sound unappetising, but residual water from the food and pharmaceutical sectors could be a solution to our crippling food waste problem, while producing alternative proteins like meat and dairy analogues, as well as greener fuels.

Researchers from the Technical University of Denmark (DTU) tapped the salty residue from cheese produced by Danish dairy giant Arla to test a yeast strain called Debaryomyces hansenii. These microbes can thrive in highly saline environments, and the study found that they can be turned into valuable proteins to make meat analogues, dairy alternatives, pigments, and enzymes.

“There are businesses that create waste streams that are rich in nutrients, but also have a very high salt content, which is often a problem,” explains DTU Bioengineering assistant professor José Martinez.

“The salinity prevents utilisation of the nutrients while preventing businesses from discharging their waste streams as ordinary wastewater, which means they have to special treat, and this is costly. Why don’t we try to grow this type of yeast in these salty waste streams?” he explains.

Food waste meets pharma waste

In 2020, a study found that wastewater from raw cheese manufacturing – usually derived from the demineralisation of whey – was problematic, “posing severe environmental and public health problems” thanks to its acidic pH and the high amounts of phosphorus, total solids, oils and fats, and minerals involved.

Agriculture’s planetary impact is already massive – it accounts for a third of global greenhouse gas emissions. But a third of all food produced is either lost or wasted, which alone makes up 8-10% of emissions. So a solution that valorises a food industry sidestream that otherwise ends up harming the planet and our health has bags of potential.

Martinez has been researching yeast cells adapted to extreme conditions like high temperatures, low nutrient content, or high salinity for years. D. hansenii is adapted to aquatic environments, and can thrive in water up to six times as salty as seawater.

The experiment with Arla’s wastewater exceeded his expectations. The saline residue was also rich in lactose (a sugar), which the yeast cells easily metabolised. While more salt content meant more efficient growth, the yeast’s development wasn’t as efficient as it could be due to insufficient nitrogen levels.

To solve this bottleneck of the lactose-rich waste stream, Martinez met with Manuel Quirós, a cultivation specialist at Danish pharmaceutical giant Novo Nordisk. Quirós revealed that Novo Nordik had a salty residue of its own – linked to the manufacture of haemophiliacs – which was high in nitrogen.

“We simply mixed the two saline waste streams – the one with a high lactose content and the one with a high nitrogen content,” explains Martinez. “We used them as they were. We didn’t need to add fresh water, nor did we need to sterilize the fermentation tank, because the salt prevented the growth of other microorganisms. It was plug and play.”

His research team found that D. hansenii thrived in the mixture. To make the yeast a product of commercial interest, they used CRISPR technology to modify the strain into a protein as it grew.

CRISPR is a gene-editing technology that can cut the DNA of cells in specific places, allowing scientists and manufacturers to deactivate genes, insert new pieces of DNA into the genome, and change genes to get rid of mutations. It can help produce many different proteins and substances, and its potential has been explored by researchers using koji mould to make better-tasting meat analogues too.

A green fuel that’s actually sustainable?

Martinez initially settled on a fluorescent protein to be used as a model substance, enabling them to get a production target by measuring how strongly fluorescent the liquid was when the yeast cells were at work. The optimal mixture of the waste streams from Arla and Novo Nordisk was nearly twice as salty as seawater and contained 12g of sugar per litre.

According to the DTU, D. hansenii has been the target of “intense research” for decades. Previous studies have focused on finding the gene that makes the yeast cells salt-tolerant and trying to transfer it to plants so they can tolerate high salinity. This ended up being very complex, as salt tolerance is linked to several genes working in tandem.

Over the course of two years, Martinez and his colleagues worked to use the yeast cells themselves, leveraging their salt-tolerant attributes and modifying them to produce valuable ingredients. The use of CRISPR means this yeast and the food and pharma industry’s waste products can create a range of products.

But these aren’t limited to food. Martinez is part of a separate research collaboration exploring green fuels. Using this breakthrough, that effort could now include modifying D. hansenii to produce lipids (or fats) that can be converted into sustainable fuels.

Currently, many ‘sustainable’ fuels are built on palm or cereals. Palm oil is linked to mass tropical deforestation, while biofuels command 44% of the total cereal production in the US, which is a highly inefficient use of land and resources.

It’ll take at least a decade before Martinez’s research can be turned into commercial returns, since the lab-scale tests were only conducted on one to five litres of waste streams. The next challenge is to scale up to 10-30 litres, but Martinez expects hurdles in providing an efficient oxygen supply to the liquid. Expanding to thousands of litres will present obstacles as yet unknown.

For Novo Nordisk, though, the sustainability aspect is promising. The pharmaceutical company is already leaving a huge impression on the food industry through Ozempic and Wegovy, its GLP-1 agonist drugs. Across the US, one in eight Americans have tried such medications, and food companies big and small have been forced to innovate to cater to this demographic.

“Novo Nordisk wants to take full responsibility for our entire value chain,” explains Quirós. “Our strategy is called Circular for Zero. We have three focus areas: reducing the use of resources, reducing CO2 emissions, and minimising waste streams.”