Shells are more than pretty collectables or what remains after a nice mussel meal. The microscopic structures that make molluscs so unique can form the inspiration for better building materials, while shell waste from aquaculture may provide ecologically – and economically – viable solutions for human-created problems.
Humankind has always used shells produced by molluscs for varying purposes, from ornaments to cutting tools, and until the previous century, even as a way of payment. Even today, shells could be of great value, but we use them too little. That is the conclusion of a research project by some of our scientists, published in a special edition of the science journal Marine Genomics.
The durability and sturdiness of a shell, for example, is something builders can only admire. By researching which microstructures make shells so strong, but at the same time so light, we can develop new sustainable biomaterials. This sort of ‘biomimetic’ applications could prove to be extremely useful for areas like the construction industry.
“Biomimicry is based on the principle that biology has been evolving for hundreds of millions of years, while we have only been building for a couple of thousand years. As such, there is still a lot we can learn from biology,” says researcher James Morris.
Specifically, new design strategies have been inspired from the so-called ‘molluscan nacreaous layer’, in which mineral platelets are arranged like brickwork, in single layers. This microstructure has been shown to be extremely strong, and while scientists have been able to imitate it, industrial applications are not yet on the agenda.
What Shell Waste?
Molluscs account for 23 percent of global aquaculture production, which equates for around 15 million tonnes of biomass each year. The shells of these organisms take up about 60 percent of the product in weight.
“Aquaculture produces a lot of shell waste”, says Morris. “At this moment, the majority of shells end up in landfill, but as incredible structures, they have potential applications that could be more useful, if only we didn’t view them as a waste product.”
The most often named use of shells is their incorporation in building materials. A study published in 2012 tested mortar mixed with ground shell waste, and found it to be an eco-friendly alternative to cement. “But that application is not in large-scale practice yet.”
Water Treatment, Biodiesel and Bone Tissue Regeneration
A use of the shell waste that is in practice, albeit on a limited scale, is acid soil mitigation, mostly in Spain. Farmers use crushed shells to bring down the acidity of their land. In some places in the US, on the other hand, dead oyster shells are used to form reefs for shoreline protection through wave attenuation. Similar artificial oyster reefs are being tested in the Netherlands.
Other purposes for shell waste could be as absorbents in water treatment and CO2 capture techniques as well as catalysts in biodiesel production. The calcium carbonate derived from shells can even promote bone regeneration in surgical procedures.
The biomimetic applications based on shell structure, as well as alternative uses for shell waste, remain unrealised on a commercial level. The researchers are confident, however, that the idea of sustainability is spreading in the public conscience. As a result, there should be a shift in mind-set: away from considering mollusc shells as a waste product and towards considering them as a valuable resource and a bio-mineral that we have more to learn from.