Science and engineering researchers cook up a solution to a big agricultural waste problem

Researchers from the Faculties of Science and Engineering are turning food waste into liquid gold.

It’s a project that holds the promise of solving a big problem. According to the Ontario government, food waste accounts for nearly 25 per cent of what’s dumped into municipal landfills, with field crops topping the list. As that waste decomposes, it releases methane – a greenhouse gas that contributes to climate change.

Hydrothermal carbonization is one way to redirect agricultural waste and put it to much better uses. It’s a thermochemical process that converts wet biomass and organic waste like fruits and vegetables into hydrochar, a carbon-rich solid fuel with high energy density. Hydrochar can be burned for heat or converted into solid, liquid or gas biofuels.

There’s just one problem with hydrothermal carbonization – it requires a whole lot of water. Right now, that process water’s being discarded. And it can’t just be poured down the drain – it needs to be treated and neutralized because it’s a concentrated, complex and acidic brew of organic and inorganic materials.

Shakirudeen Salaudeen, an assistant professor in the Department of Mechanical Engineering, wondered if the left-over process water could be made valuable and useful.  Salaudeen is a long-time champion of circular economies, where products and materials are regenerated, recycled, refurbished and remanufactured. “Figuring out what to do with process water is the missing link in creating a true circular biomass economy.”

Hydrochar is the focus for nearly all of the research being done around hydrothermal carbonization. Salaudeen wanted to give process water its due. He secured provincial funding from the Ministry of Agriculture, Food and Agribusiness and posted a job for a graduate student to join his research group and take on a process water-focused research project.

Nancy Boamah answered the call from halfway around the world. After graduating with a bachelor of science degree in chemical engineering from Kwame Nkrumah University of Science and Technology in Ghana, Boamah worked with EWB-KNUST on community-based sustainable engineering projects and the Ghana Atomic Energy Commission.

Like her supervisor, Boamah says she’s motivated by finding hidden value in things that are discarded. Utilizing process water could significantly reduce the operating costs of hydrothermal carbonization and open up new revenue streams for farmers and food producers.

She got to work making process water in Salaudeen’s lab in the Arthur Bourns Building, half a carrot at a time. A local farmer had donated bushels of blemished carrots that would’ve gone unsold and sent to landfill – up to half of all carrots are discarded because of aesthetic or sizing defects.

Carrots are composed almost entirely of water, making them ideal for Boamah’s research project. Her process water recipe calls for 30 grams of unpeeled carrot and 270 grams of deionized water that are run through a restaurant-grade blender and then poured into a pressure reactor. The reactor’s like an air-tight rice cooker, albeit one that retails for $50,000 and is deceptively heavy. A shot of nitrogen gets pumped in, the pressure reactor goes into a heating mantle and then cooks the carrots and water anywhere from 30 to 120 minutes at temperatures ranging from 180 to 280 degrees celsius. Different temperatures, pressures and reaction times change the composition of the process water.

What’s left when the cooking’s done is a slurry of solids and liquids that Boamah puts through a filter to separate the process water from the solid hydrochar. Without wasting a drop of the orange-tinted process water, she studies its physical and chemical properties and stores it vials that fill a a well-stocked fridge in the lab.

It’s chop, blend, cook, pour, filter, analyze and repeat. Boamah’s does this more than 100 times over the past year-and-a-half. “I could do this in my sleep.”  But she’s yet to start dreaming of carrots.

Along with recruiting Boamah, Salaudeen found two research collaborators but this time only needed to look across campus. He reached out to McMaster’s Biology Department and asked if any faculty were plant experts. This time, it was professor Robin Cameron who answered the call and enlisted the help of postdoctoral fellow Fathy El-Gebaly, who grew up on a family farm in Egypt where they grew wheat, corn and rice.

Cameron and El-Gebaly are studying how to enhance a plant’s resistance to viral infection. These infections – which disrupt physiological mechanisms such as respiration and photosynthesis – are responsible for more than 40 per cent of overall annual yield loss in crops. Many of the chemical pesticides that reduce the impact of pathogenic infections are harmful to human and environmental health and are either banned or being phased out.

So could process water, rich in plant compounds, be a non-toxic, eco-friendly alternative to pesticides? Cameron and El-Gebaly are now working with Boamah and Salaudeen to develop plant immunity-stimulating formulations using process water from the hydrothermally carbonized carrots.

The process water is being applied to the base of cucumber plants growing in the McMaster Learning and Discovery Greenhouse. McMaster is believed to be the only Canadian university with a campus greenhouse that mirrors the size and conditions found in commercial greenhouses where the majority of cucumbers are grown – it’s Canada’s second largest greenhouse crop next to tomatoes. Before McMaster built the new research and teaching greenhouse, Cameron couldn’t grown cucumber plants to their full size in her own lab – the experiments with process water would’ve been cut short.

Early results are promising. The plants are already more than three metres tall and producing cucumbers. There’s been a marked difference in the size of the plants’ root structure.

Just as Salaudeen suspected, process water can be safely utilized rather than discarded. It’s a small-scale research project with huge potential – greenhouse production of cucumbers alone reached nearly 290,000 metric tonnes in 2023, valued at $870 million. Boamah’s already committed to continuing her PhD studies at McMaster, working with Salaudeen to expand their hydrothermal carbonization research project. Studying the process water left over from carbonizing a blend of agri-food waste is one avenue they’ll be exploring.

El-Gebaly says the collaboration with Boamah and Salaudeen in the Faculty of Engineering represents research and McMaster at its best. “Progress cannot occur in isolation. Knowledge evolves over time and is continuously shaped by the contributions of others. As a researcher, I strongly agree with what Henry Ford once famously said – ‘coming together is a beginning, keeping together is progress, working together is success.”

To celebrate their successful research collaboration, the greenhouse cucumbers might soon be added to a salad, with Boamah and Salaudeen adding in some slightly blemished carrots.