Converting plastic to protein: US military-backed project employs pyrolysis to make food and fuel from waste

18 Oct 2022 --- Researchers at Michigan Tech University, US, have been awarded US$7.2 million to turn plastic waste into protein powder and lubricants. The study team landed the grant for its work on pyrolysis, a chemical method through which the US military wants to circularize its supply chains.

Awarded by the Defense Advanced Research Projects Agency (DARPA), the project will be a four-year cooperative agreement named BioPROTEIN (Biological Plastic Reuse by Olefin and Ester Transforming Engineered Isolates and Natural Consortia). 

“What we’re trying to do overall is to take plastic or mixed waste from military operations and make it into something useful for the military,” says Steve Techtmann, assistant professor of biological sciences at Michigan Tech. 

“Often, plastic is the hardest waste to deal with. Our project is trying to find ways to convert waste plastic into protein powder or nutritional supplements and lubricants. The general idea is that plastic is hard to break down using biology because it’s made up of a polymer and its units are stuck together.” 

“To break apart the polymer, some bacteria can do this, but it’s very slow. So, to convert plastic into food quickly, we need an alternative approach,” he asserts. 

Plastic waste to food and fuel 
The project will be broken into three phases. Firstly, the research team must show proof of concept that plastic waste can be transformed into protein powder and lubricant. This will entail designing and using a separation system to recover 2.5 grams of microbial protein powder. 

“There are systems for dealing with plastic where you recycle it. Michigan Tech made one where you take a plastic waste object and turn it into a new, valuable plastic product,” Techtmann says. “Our plan is to put plastic in and turn it into something entirely different on the other side of the box.”

“This research will allow us to take the plastic waste we’re generating in the world and turn it into something valuable: food and fuel.” 

The process of taking plastic waste and converting it into protein powder and lubricant. Image Credit: Steve Techtmann/Michigan Tech

The second phase will be to recover 100 grams of microbial protein powder from culture medium. In the final phase, the team will have made a “black box” that can function as a field operational unit and purify entire kilograms of protein powder. 

The goal is for the system to be self-sustaining for as long as 28 days, asserts Techtmann, and for it to fit on the back of a truck and use solar energy for power. The researchers want to develop a circular economy for plastics in the US military.

Additionally, the team will 3D print many of the system components and make these designs open source – making the system affordable in settings beyond the military, such as in disaster relief scenarios.

Breaking down bacteria 
The team’s pyrolysis process converts plastic into compounds that look like oil using heat and a reactor, which can deconstruct polymer chains. The oil-like compound is then fed to a community of oil-eating bacteria. 

The bacteria grow very fast on this oily diet, Techtmann explains, which produces more bacterial cells that are about 55% protein. It’s through this process that the team says it can convert plastic to protein very quickly. 

The researchers envision a final system wherein soldiers will throw their plastic waste into a container, which is taken into processing reactors to be broken down by heat and/or chemicals. Once broken down, the byproduct will be fed into a vat with the bacteria, which “chew on whatever flows there and grows.” The cells are then dried down into a powder. 

Ting Lu, a professor of bioengineering at the University of Illinois, is collaborating on the project and says he aims to engineer bacteria to upgrade the protein powder with maximum nutrition.

“By enriching specific amino acids and polyunsaturated fatty acids, we hope to increase the nutrient content of the powder and tailor it for military needs,” Lu says.

The team is also working with regulators such as the US Food and Drug Administration to ensure that product development is safe for human consumption. 

By Louis Gore-Langton