Repurposing Shells

Artificial oyster reef in the Netherlands is pictured. Image credit: Dr. James MorrisResearchers from the Royal Belgian Institute of Natural Sciences are investigating different uses for the 7 million tonnes of mollusk shell waste discarded by the seafood industry each year.

Currently clogging landfills or being disposed of in the sea, Dr. James Morris and his team of researchers believe the discarded shells can used for other environmental purposes.

"Mollusk shells are viewed by the aquaculture and seafood industries as 'nuisance waste' and largely disposed of in landfills," says Dr Morris. "Not only is this an expensive and ecologically harmful practice, it is a colossal waste of potentially useful biomaterials."

One of the proposed applications for the discarded shells is to use them to help restore damaged oyster reefs and to promote the growth of new oysters. Apart from the ecological impact, the process would cost very little and would require almost no effort. "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," explains Dr. Morris.

Consisting of over 95 percent of calcium carbonate (popular in agricultural and engineering applications), crushed mollusk shells could also be used to control soil acidity on farms and as a calcium supplement for egg-laying hens. It is also an important ingredient in cement mix and has proven effective in wastewater treatment applications. However, most of the world’s calcium carbonate comes from harmful and unsustainable limestone mining.

"Reusing 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," says Dr. Morris.

Researching how mollusk shells can act as another source of calcium carbonate, the research team hopes to provide a more sustainable alternative to mined limestone, while emphasizing the financial impact repurposing the biomaterial would have.

"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," says Dr. Morris, "simply finding a use for shells to avoid taking them to a landfill already has economic value!"