If traditional Western industry were a diagram, it would be a straight line. Resource extraction leads to production, distribution, consumption and finally disposal. Saied Baroutian is working to bend that line into a circle.

Baroutian, an associate professor of chemical and materials engineering, heads the Waste and Resource Recovery Research Group (WaRe3) at Waipapa Taumata Rau, University of Auckland.

He also leads the Master of Engineering Studies programme in Sustainable Resource Recovery, which gets students working closely with industry to solve real-world problems – often leading to jobs for the students.

Fundamentally, Baroutian’s research involves using high-tech processes in the service of principles that would have been familiar to his great-grandparents: minimizing waste, reusing what can be reused and turning things that aren’t useful into things that are.

Sargassum is a type of algae that normally provides a haven for creatures such as turtles, fish and eels. Since 2011, however, for reasons not entirely understood, unprecedented quantities of sargassum have been invading Atlantic and Caribbean coastlines.

Massive carpets of sargassum as much as a metre thick piled up on Caribbean beaches, driving away tourists. It got tangled in fishing nets and boat motors. It smothered coral reefs and killed sea creatures. One young man named Terrell Thompson saw how sargassum affected his native country of Barbados. He turned to Baroutian for help in solving the problem.

Baroutian, Thompson’s PhD supervisor, identified two possible solutions. One was using microorganisms. Certain strains of microbes and fungi can digest organic waste and transform it into useful products. Baroutian had been working on this with materials such as food waste and sewage sludge. Seaweed, however, was a challenge because its physical structure and chemical composition made it difficult for the microorganisms to digest.

A major problem in the linear economy is that valuable compounds such as metals and minerals end up being disposed of along with low-value waste because they’re too hard to separate. Baroutian is working to change that.

Separation processes often involve organic solvents such as hexane, acetone and methanol. These solvents, however, are expensive, toxic and flammable, making storing large quantities a health and safety risk. 

Unlike organic solvents, supercritical and subcritical fluids are cheap, non-toxic, non-flammable and easily reusable. They’re highly specific, dissolving only the desired compound. They also work much faster than organic solvents.

So, what are supercritical and subcritical fluids and why aren’t they in wider use? To explain, let’s look at a familiar concept.

Everyone knows there are three states of matter: solid, liquid and gas, right? However, in-between states can exist.

For example, water boils at 100⁰C and turns into vapour under normal circumstances. But under high pressure, water can remain in liquid form above that temperature. This very hot liquid water is called subcritical, and it’s an excellent solvent.

At temperatures above 374⁰C, water becomes neither liquid nor gas but something with the high diffusion rate of a gas but the ability to dissolve substances like a liquid. This substance is called supercritical, and it too is an efficient and specific solvent at specific temperatures.

Baroutian is also using supercritical and subcritical water in a project he’s undertaking in collaboration with a Ngāti Porou community of the Whareponga Valley in Ruatōria, East Cape. 

The community has a stand of native forest containing plenty of kānuka. Like its better-known cousin mānuka, kānuka is a tree native to Aotearoa New Zealand. Baroutian has been working with the community to produce high-value products other than honey from the resources it has.

Māori have long used kānuka for its medicinal properties. Baroutian is working with the community to extract bioactive antioxidants and flavours from the leaves using supercritical and subcritical water. The resulting “kānuka juice” is rich in antioxidants, he says.

Another technique, called fast pyrolysis, can produce liquid smoke flavouring. The technique involves burning kānuka wood in the absence of oxygen and collecting the vapours. The lightest vapours become liquid smoke, which has not only a unique flavour profile but strong antibacterial properties. 

With the support from Return on Science, an investment committee operated by UniServices, and in partnership with the Māori landowners, Baroutian and Business School lecturer Kiri Dell (Ngāti Porou) have formed a company called Kauruki, which means smoke or haze, to market the liquid smoke.

Despite all Baroutian’s research into recovering materials and producing high-value products, there is inevitably some waste that is of no value or that is highly toxic. It’s typically sent to landfills, where it can result in environmental contamination.

Baroutian says there’s a better way.

In some countries, hazardous waste is incinerated at high temperatures, but this can result in the formation of toxic compounds such as dioxins and in particulate matter that contributes to smog.

Hydrothermal technology involves breaking down waste with hot, pressurized water and oxygen or nitrogen gas.

At high temperatures and pressures, oxygen can be diffused into the water to produce oxidation – that is, burning.

However, it occurs at a far lower temperature than in an incinerator, 200 to 300⁰C compared to the 1000⁰C or higher used in hazardous waste incinerators.