What was it all about?

Many horticultural industries produce large amounts of waste requiring disposal that increases costs for producers. This project explored novel techniques to convert waste from horticultural industries into valuable products to improve profitability. These processes were developed to proof of concept stage during the work.

The first stage of the work used a variety of horticultural wastes including macadamia nut shells to produce metal nanoparticles. Gold and silver nanoparticles have antimicrobial properties and are increasingly being used in biomedical and pharmaceutical applications. The process using horticultural waste has advantages over current technologies for producing gold and silver nanoparticles because it doesn’t require the use of harmful chemicals and solvents. The research team trialled the technique on a variety of horticultural crop wastes as well as native plants. The team confirmed the antimicrobial properties of the nanoparticles that they produced.

To further assist Australia’s macadamia nut industry to make good use of waste, a second process was developed that uses the shells to produce activated carbons. High quality activated carbons are needed in a variety of applications in medicine, pharmaceuticals and the mining industry, including for extracting gold from cyanide slurries. Demand for the highly porous and adsorbing activated carbons is high.

Work done so far suggests that further mechanical property enhancement would be needed for development of activated carbon for the mining and industrial sectors, but since all activated carbons used in the gold mining sector are currently imported, with a significant ongoing replacement cost to the industry, the technique holds great promise.

Macadamia nut shells were also used in a third application. Activated carbon based on macadamia nut shells can hold agri-chemicals making it an ideal delivery mechanism on-farm. The team showed that liquid fertiliser can be combined with the activated carbon for slow release, preventing run-off and seepage. Applying fertiliser in this way could improve crop production, deliver phosphates and trace elements more efficiently and protect water sources. It could also improve targeting and uptake of existing pesticides. The team demonstrated that the particles work as a powder and as water sprays. The next step in developing this technology is plant and soil studies.