In years gone past, tonnes of macadamia shells were discarded after the important kernel was extracted for consumption. Now, the shell of our native nut is a prized product that is recycled into some of the most unlikely products.
We know that macadamias are tough nuts to crack. The shells are notoriously hard and the delicious kernels are difficult to extract. Although farmers always knew the benefits of recycling their nutshells as mulch and compost for their trees, for many years this was where the use of the shells ended. In fact, millions of excess shells were sent to landfill each year.
However, as the industry strives to fight the war on waste, this is changing. The shell’s hardness actually makes it a valuable resource. From lifesaving medical treatment to renewable energy, the humble macadamia shell is finding a use in almost every walk of life. In fact, you may have been using macadamia nut shells without even knowing it!
Biochar is the result of burning macadamia shells at a high temperature in a special, low-oxygen environment. The resulting product called biochar, has to pass certain tests to confirm its carbon content and safety. It’s then used as a soil enhancer to both make soils more fertile and to store carbon in the soil so it’s not released as a greenhouse gas.
The process of making biochar can actually produce electricity! The biochar process creates oil and gas by-products that can be used as fuel for renewable energy plants. If the biochar is used to enhance soils and the process used to make it can produce renewable energy, this system is “carbon negative” and is an important weapon to limit climate change.
Activated charcoal made from macadamia shells is also used to make carbon filters for water and air purification. Such filters have both domestic and industrial applications so you might even have one in your home somewhere!
Currently, hospitals treat some poisonings (like paracetamol overdoses) by getting the patient to swallow charcoal made from coconut. In an exciting breakthrough in 2017, scientists discovered that finely crushed macadamia shells were more effective than traditional charcoal treatments. Doctors were particularly interested that the macadamia shells could be engineered to mop up specific toxins more effectively. This treatment may be in a hospital near you soon.
Particle board is notorious for absorbing moisture. But not if it’s made from macadamias! At the University of NSW researchers have made particle board from macadamia shells that is particularly suitable for high-moisture environments like kitchens, bathrooms and pool decks. They suggest that it might even be good for saunas because it smells so good!
The same properties that make macadamia shells such good biochar also suits them for making into high purity silicon carbide and silicon nitride nano-powders. These nano-compounds are used to make metal alloys and plastics more shock, heat and wear resistant. They may also have uses in electronics in the future.
Macadamias don’t just have utility, they also have beauty. Australian homewares designer Marc Harrison mills the shells into fine particles and melds them with a polymer to create a material reminiscent of 1930s bakelite in appearance. He moulds this into beautiful handcrafted bowls that reflect the shape of the cracked shells. Each item is hand finished by rubbing with macadamia oil. Truly beautiful!
Research continues into possible new and innovative applications for the resourceful and renewable macadamia nut.