One of the biggest contributors to the climate crisis is our throw-away society.
From household waste and single-use plastics to byproducts from food production, we burn fossil fuels and spend money to truck our “garbage” to landfills and processing facilities, where some of it releases greenhouse gasses or pollutants into the environment as it breaks down.
The circular economy represents an alternative to this culture of disposability, a system in which materials are reused or regenerated as much as possible.
Tapping into this idea, Carleton University researchers Abid Hussain and Eugene Fletcher are developing new technologies for converting various types of waste into biofuel and valuable chemicals — and demonstrating a pathway to a more sustainable future.
Biogas for Electricity, Heat or Fuel
Hussain, a professor in Carleton’s Department of Civil and Environmental Engineering, led waste-to-energy and climate change mitigation projects at prominent institutions such as the United Nations and Asian Development Bank before coming to the university.
In his main laboratory on campus, a collection of custom-designed bioreactors — with components such as vessels, gauges, sensors and heating or cooling systems — display the range of research that he and his talented graduate students are doing.
In one anaerobic (or oxygen-less) digestor, microorganisms help break down conventional green bin waste and generate biogas. Typically, the gases released from this process would be about 55 per cent methane. But by introducing a special set of microorganisms and zapping the material with electrons, Hussain has increased the methane concentration to about 80 per cent — a viable product that could be used to generate electricity, heat buildings or fuel vehicles.
In collaboration with a small company in the Northwest Territories, Hussain is also experimenting with operating this digestor at lower temperatures, which could be a boon in northern communities where waste decomposes slowly and the cost of supplying propane for fuel is extremely high.
“Instead of sending food waste to the landfill, where it not only releases greenhouse gases but also attracts wildlife, we could use it to produce renewable energy,” he says.
“That would help both budgets and sustainable waste management practices.”
Green bin waste is only part of Hussain’s research program. In another type of reactor — a fermenter — he is looking to derive useful chemicals from the remnants of corn that has been used to produce ethanol.
“You can optimize the design of a reactor and the conditions inside the reactor to channel towards a particular chemical,” he explains.
Corn leftovers can be used to make acetic acid and butyric acid, for example, which are used in pharmaceutical manufacturing, as solvents and as building blocks for biodiesel, perfume and other cosmetics.
“It’s more than just lab work,” says Hussain, who is partnering with his industrial collaborators to develop these technologies at a pilot scale.
“The insights we’re gaining are intended for real-world application.”
Tackling Plastic Pollution
Carleton biology researcher Eugene Fletcher is also aiming to produce biofuel from waste, and he’s tackling plastic pollution at the same time.
Less than 10 per cent of the four million tonnes of plastic thrown out every year in Canada is recycled.
Fletcher’s solution involves “editing” the genes of yeast, a single-cell fungus that’s best known for its ability to convert sugars into carbon dioxide and ethanol, a key step for making both beer and bread.
By introducing new DNA through heat shocking yeast, he essentially gives it new instructions, so it recognizes plastic compounds as a source of carbon and converts this “food” into ethanol.
“Some bacteria can break down plastics naturally, but they require very stringent and expensive growth conditions and cannot easily be scaled up to an industrial level. Yeasts are easy to grow and engineer.”
Fletcher acquires yeasts from suppliers, similar to how a baker or brewer would, and grows them in his lab in glass tubes containing vitamins, minerals and sugar. The yeasts are then heated to 42°C, which opens up their pores, allowing them to absorb the new instructions he designed.
Like Hussain, he is also working with byproducts from the dairy industry and with plant waste, reengineering yeast so it converts these sugars into propionic acid, which is used as a preservative in animal feed and to make some cosmetics.
“When you break down corn husks or wheat bran or even forestry waste, the basic structure of their building blocks is like that of some plastics,” Fletcher says. “It doesn’t matter that one grows naturally and one’s plastic — at a chemical level they are similar. And all of this can be transformed into biofuels or other valuable products.
“The big picture is that we’re trying to help solve a major societal problem. But we’re also developing new tools and learning new science.”
