Finding ways to make use of every part of our food sources is an ancient idea that’s getting a second look from Canadian researchers in such fields as chemical engineering and biotechnology.
Their aim is to develop new processes to turn crop waste such as corn stalks, switch grass and sugar cane residue into alternative fuels, hydrogen and other useful gases. The focus is on crop waste, rather than the edible parts of crops, because scientists realize the need to preserve food sources.
While the goal is to release energy from such waste, the processes used to do this can be quite different. Franco Berruti, a professor of chemical engineering and director of the Institute for Chemicals and Fuels from Alternative Resources at the University of Western Ontario, has developed a thermo-chemical conversion technique that exposes cereal-crop residue, called stover, to high temperatures in the absence of oxygen. This produces “thermal cracking,” where molecules shatter and become fragments.
Whereas biological processes to break down crop waste can take days, this thermal conversion takes seconds – 10 tons of biomass can be processed each day. The chemical reaction produces energy-rich bio-oil as well as by-products such as bio-char (ash-like leftovers), carbon, and light gases like methane or ethane.
“You cannot take the bio-oil and put it in the tank of your car,” says Dr. Berruti. “It’s the equivalent of crude oil, [but] a renewable crude oil.”
With an eye to commercialization, Dr. Berruti and his colleague Cedric Briens have developed a portable machine to carry out the faster conversion process. “We would like to see this become a business and revenue opportunity for farmers,” he says of the machine, which fits on a trailer that can be pulled by a light truck. The unit could be taken from farm to farm during harvesting season to convert the leftover organic materials.
He’s already received substantial interest from manufacturers for the technology and expects to have a prototype ready by the fall. A spin-off company called Agri-Therm will take the product to market.
University of Windsor professor Jerald Lalman is taking a different tack, aiming to increase the amount of biomass turned into energy using a biological approach. Dr. Lalman, who holds the Canada Research Chair in Environmental Biotechnology in the department of civil and environmental engineering, is experimenting with steam explosion and dilute acid hydrolysis to extract valuable sugars from crops. The sugars are then fed to a fermentation system made of micro-organisms sourced from local waste treatment facilities.
But where the microorganisms would naturally convert the sugars to methane, Dr. Lalman has devised a way to “trick” them to turning the waste sugars into more valuable hydrogen. He sees a market for his biological process among car manufacturers that are experimenting with hydrogen-fuelled cars.
Both researchers are sensitive to the political issues in this field, beyond the food-vs.-fuel debate. For one, there is a need to define crop “waste”: some materials can add value simply by being ploughed back into the ground to improve soil conditions. So products that don’t decompose quickly, such as rice or flax stover, are the most promising for converting into energy.
Dr. Berutti and other scientists are also turning their attention to extracting energy from other waste products such as wastewater-treatment sludge or coffee grounds.
Given the interrelated needs to dispose of crop waste in an environmentally sensitive way and to explore alternative fuel sources, the field is open to solutions from many departments. “I would like to see the development of multiple technologies,” says Dr. Berruti, “and the contribution of all disciplines in a coordinated way.