Weed to gold: How scientists are helping solve the medicinal cannabis industry’s waste problem

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A team led by the University of Auckland’s Associate Professor Saeid Baroutian are investigating sustainable solutions for the medicinal cannabis industry’s waste. Photo / Chris Loufte

It’s one of New Zealand’s fastest-growing industries, but producing medicinal cannabis happens to come with a rather unique challenge: what to do with unused material.

That’s just a problem a team of University of Auckland scientists are working to solve, in a new programme aiming to transform its waste into valuable resources.

The process behind the project, also involving South Island-based producer Greenlab and Crown-owned Callaghan Innovation, involves destroying active cannabinoids from the waste and then turning the material into solid or liquid fertiliser that can be used to help grow new cannabis plants.

“It’s a perfect example of bringing the circular economy to the medicinal cannabis sector,” said lead researcher Associate Professor Saeid Baroutian, of the university’s Circular Innovations (CIRCUIT) Research Centre.

“Instead of the current linear ‘take-make-dispose’ system, our technology will connect productivity for the sector with environmental, social, legal and cultural acceptability.

“That is a big step towards true sustainability.”

With a forecasted value of nearly NZD$80 billion by 2026, medicinal cannabis is one of the fastest growing industries around the world.

In New Zealand, it has the potential to generate exports comparable to kiwifruit in value.

But with this growth comes the challenge of managing medicinal cannabis waste, which includes unused plant matter, cultivation trimmings, discarded extraction chemicals and trashed testing samples.

There’s currently no specific infrastructure available to deal with cannabis waste and most, as happens overseas, ends up in landfills.

“This adds to the more than one million tonnes of organic waste already disposed of each year in New Zealand landfills,” Baroutian said.

“The problem here is not only the release of methane, a greenhouse gas more potent than carbon dioxide and a major contributor to global warming.

“Sending organic waste to landfills also means valuable resources are lost and cannot be effectively reused in the economy.”

With our local industry still getting established, there’s no public data available yet on the amount of waste being produced – but in Canada, it’s estimated that more than 150 million tonnes of it is generated every year.

For commercial medicinal cannabis operations, waste management was unique and complex, Baroutian said.

“The plant has unique qualities and, as an illegal drug outside of its medicinal use, there are strict Government controls over waste handling,” he said.

“Cultivators must record every gram of discarded material by tagging, tracking and tracing the waste from origin to final disposal.”

“This means that in addition to separating hazardous from non-hazardous waste, techniques used must render all waste beyond recognition and account meticulously for every scrap so producers can maintain their licence.”

The process worked by mixing cannabis waste with water and then heating it to high temperatures, causing a chemical reaction breaking the waste down into simpler and safer substances.

All cannabinoids such as THC and CBD - the psychoactive compounds in cannabis – were destroyed during this process.

Under high temperature and pressure, the material in cannabis plants went through a chemical transformation process converting the wet plant waste into a dark, crumbly and dry substance that looked like charcoal.

This solid product was called “hydrochar”, but, unlike charcoal or coal, wasn’t harmful to the environment.

Being carbon and nutrient-rich, it could be added to soil to improve fertility and water retention for better cannabis plant growth.

The liquid product from the process was also rich in solubilised carbon and valuable nutrients like nitrogen, phosphorus, and potassium, which could be recovered and used as a biofertiliser to help cannabis plants grow healthier and faster.

The next step was to develop a solution for its widespread use.

Current methods for cannabis waste disposal include biological treatment, which involved breaking down the waste into simpler compounds using bacteria and other microorganisms, or incineration, but both options came with challenges.

Incineration, while effective, happened to be banned under New Zealand’s air quality regulations, due to the formation of toxic gases and particulate matter.

“Composting and anaerobic digestion of cannabis waste can only occur at an approved facility with suitable systems to control odours from the process and deal with the leachate and digestate,” said Dr Rupinder Brar, Greenlab’s director of cultivation & resource recovery.

“Although this is an approved method of disposal, there is no scientific evidence on the fate of cannabinoids in the composting or anaerobic digestion process.”

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