Mollusc shells: nuisance waste or a sustainable biomaterial source?

Every year 7-plus million tonnes of mollusc shells are discarded by the seafood industry. Considered as unwanted waste, the vast majority of these shells are either thrown in landfills or dumped at sea. Not only is this an expensive and ecologically harmful practice, it is a colossal waste of potentially useful biomaterials.

Dr James Morris and a team of CACHE researchers from the Royal Belgian Institute of Natural Sciences are looking at environmentally and economically sustainable options for these shells.

One of the most exciting applications proposed by Dr Morris is the use of discarded shells to restore damaged oyster reefs and cultivate the growth of new oysters. The restoration of these reefs requires little money and effort, but can have huge ecological advantages.

"Healthy shellfish populations can have many benefits to the environment: cleaning the water, providing a complex structure for other organisms to call home and also acting as a coastal protection structure," explained Dr Morris.

Mollusc shells consist of over 95% calcium carbonate, which is used in many agricultural and engineering applications. Crushed shells can be spread on farmers' fields to control soil acidity or fed to egg-laying hens as a calcium supplement. Calcium carbonate is also a common ingredient in cement mix and has found additional use in effectively treating wastewater. Unfortunately, the vast majority of the world's calcium carbonate comes from ecologically harmful and unsustainable limestone mining.

"Re-using shell waste is a perfect example of a circular economy, particularly as shells are a valuable biomaterial. Not only does it improve the sustainability of the aquaculture industry moving forwards, but it can also provide secondary economic benefits to shellfish growers and processors as well," said Dr Morris.

By researching how mollusc shells can act as a secondary source of calcium carbonate, Dr Morris and his team hope to provide a more sustainable alternative to mined limestone. He hopes that his work will emphasise the economic value of recycling these discarded shells back into use.

"The proper disposal procedure for shell waste is in landfill, which costs a lot of money and can be a big burden for shellfish farmers and seafood producers," said Dr Morris. "Simply finding a use for shells to avoid taking them to a landfill already has economic value!"

Image: Artificial oyster reef in the Netherlands. Credit: Dr James Morris.