Researchers turn food waste into energy, use process water to grow food

Researchers from the faculties of Engineering and Science are teaming up to convert agricultural food waste into energy-dense solid fuel, then use the water left over from the process as an eco-friendly pesticide and fertilizer.

By Jay Robb, Faculty of Science March 20, 2026

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Robin Cameron

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Shakirudeen Salaudeen

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Researchers from the faculties of Science and Engineering have found a way to take a good environmental solution and make it even better.

Food and other organic material accounts for a third of Ontario’s waste stream, and 60 per cent of that waste winds up in municipal landfills. As that waste decomposes, it releases methane — a greenhouse gas that contributes to climate change.

One way to redirect more of this waste from landfills and put it to much better use is through hydrothermal carbonization. The process 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.

After it’s used, that water can’t just be dumped down the drain — it needs to be treated and neutralized because it’s a concentrated, complex and acidic brew of organic and inorganic materials. Right now, it gets discarded.

Shakirudeen Salaudeen, an assistant professor in the Department of Mechanical Engineering, wondered if there was value in the discarded water and a way to turn it into liquid gold.

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.”

He secured provincial funding from Ontario’s 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 degree in chemical engineering from Kwame Nkrumah University of Science and Technology in Ghana, Boamah worked with the university’s chapter of Engineers Without Borders on community-based sustainable engineering projects and the Ghana Atomic Energy Commission.

Like Salaudeen, Boamah is motivated by finding hidden value in things that are discarded. Using process water could significantly reduce the operating costs of hydrothermal carbonization and open up new revenue streams for farmers and food producers.

A recipe for clean energy

A local farmer donated a bushel of blemished carrots that would’ve gone unsold, and Boamah got to work making process water in Salaudeen’s lab in the Arthur Bourns Building, half a carrot at a time.

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, 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 cooks the carrots and water anywhere from 30 to 120 minutes at temperatures between 180 and 280 degrees Celsius.

Different temperatures, pressures and reaction times change the composition of the process water.

Boamah filters the resulting slurry 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 in the lab fridge.

It’s chop, blend, cook, pour, filter, analyze and repeat. Boamah did this more than 100 times over the past year-and-a-half. “I could do this in my sleep.”

Water-based solution

Salaudeen also reached out to McMaster’s Biology Department for plant experts. This time, professor Robin Cameron 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. The campus greenhouse mirrors the size and conditions found in commercial greenhouses where the majority of cucumbers are grown — Canada’s second largest greenhouse crop, next to tomatoes.

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.

A study in collaboration

Boamah will continue her PhD studies at McMaster, working with Salaudeen to expand their hydrothermal carbonization research project, including studying the process water left over.

El-Gebaly says the collaboration with Boamah and Salaudeen 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.