In 2012, the global aquaculture industry produced over 15 million tonnes of molluscs. As populations continue to swell across the world, coastal countries have begun to wade into the vast ocean landscape with ambitions to forge aquaculture empires that serve as a sustainable food source.
But, if we are to become truly sustainable we first need to reassess waste production, says Dr James Morris from the Royal Belgian Institute of Natural Sciences. The seafood industry produces 7 million tonnes of mollusc shells each year and a large proportion ends up in landfills or dumped at sea. At the dawn of a global aquaculture boom, Morris and a team of CACHE researchers are in pursuit of circular economy, transforming the industries ‘waste’ into a bountiful biomaterial with universal benefits.
“Shells are an incredible and beautiful biomaterial. But, as the aquaculture industry is focussed on food production, shells are considered a nuisance waste rather than a potential secondary resource,” says Morris.
The shell makes up around 30 – 70% of the live weight of the animal, so are a significant part of the production. In 2012 alone, around 6 - 8 million tonnes of shells were produced as a by-product of global aquaculture activities. While there are many examples of this biomaterial being used in a variety of applications, the majority are discarded.
“The main barrier to shells being used rather than dumped is simply introducing the idea to those producing the shells in aquaculture, and to relevant companies that could find a use for the calcium carbonate – that makes up ~99 % of the shells. My role has been researching how shells can be reused, and then linking relevant industries together with shell producers in similar regions to see if mutually beneficial partnerships can be made,” explains Morris.
“Improving sustainability in mollusc aquaculture, in general, is important to me because I believe it is an environmentally friendly food source that will play an increasingly important role in our diets in the future as the human population grows. Shell reuse is part of this step towards improved sustainability.”
In recent years there has been a push in all industries to improve recycling and reuse of materials - the circular economy. In aquaculture, shell re-use can be an example of this.
The Potential of the Circular Economy
Historically, mollusc shells were deeply ingrained within human culture and society has used them as tools, currency, and jewellery. Likewise, science has long known about the incredible attributes of mollusc shells, and material scientists are still unable to match such attributes when attempting to mimic their structure. “You can still find shells as a jewellery item; however, these are not usually a by-product of aquaculture and tend to be from more exotic groups. I think as technology has advanced we have looked away from natural materials as solutions. But, now, there is a growing interest in the field of biomimicry, which has come back to the idea that we can still learn and gain a lot from nature and natural materials, such as shells.”
Morris and his researchers at the CACHE network are exploring the potential for the valorisation of shells from the aquaculture industry, both from an economic and environmental standpoint. CACHE is a €3.6M Marie Curie Initial Training Network (ITN) funded by the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework programme FP7/2007-2013. It brings together ten partners from six different European countries and includes three SMEs and a shellfish consultancy.
From using ground shells in bone and tissue re-engineering procedures to large-scale carbon sequestration techniques, there is enormous potential for this biomaterial currently considered by industry was 'waste'. For conservation, one of the most exciting applications is the use of discarded shells to restore damaged oyster reefs and cultivate the growth of new oysters. Morris explains, “This is a particularly interesting application. Oysters need a hard surface for their young to settle on before they grow into adult oysters and prefer to settle on other oyster shells. However, in many areas climate change, disease, and overfishing have meant that shells are no longer present and young oysters have nowhere to settle. Using shells from aquaculture to form artificial reefs can promote the next generation of oysters. The restoration of these reefs requires relatively little money and effort but can have huge ecological advantages.”
Established oyster populations can have many positive impacts on the local environment including cleaning the water, and providing a structure that other marine animals can call home. If done correctly, this application is relatively simple, cheap, and can provide significant environmental incentives.
For agricultural and engineering applications, mollusc shells consist of over 95% calcium carbonate. When crushed and spread over farmland, the shells can control soil acidity on fields or be 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.
“Shells are already used as a liming agent in some parts of Europe - Northern Spain particularly - to treat acid soils. But more commonly, mined limestone is used. Obviously, waste shells are a more sustainable solution than limestone from mining if shells are produced close to the areas that require soil treatment. Other applications can include the use of shells in wastewater treatment facilities as a filter layer. Wastewater treatment is necessary for all urban areas, so the potential for shell incorporation is large and not confined to regions.”
Morris believes that reusing shell waste is a perfect example of a circular economy, especially since 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. "The proper disposal procedure for shell waste is in a landfill, which costs a lot of money and can be a big burden for shellfish farmers and seafood producers. Simply finding a use for shells to avoid taking them to a landfill already has economic value! But, I think the major barrier to getting this message across is simply knowledge exchange between the aquaculture industry, other calcium carbonate-using industries, and science. Getting these groups together and discuss reuse ideas is the first and most important step.”
The mollusc and seaweed aquaculture has a chance to continue its growth sustainably. If the industry can find new ways to achieve this through technology, research, and collaboration, aquaculture could become an important part of the global future food security solution as human population continues to grow.
“I’m passionate about advocating and promoting sustainable practices in mollusc aquaculture, and I'm interested in the new technologies that are allowing production to expand - moving the farms away from the coastline into offshore areas as well as mixing different types of aquaculture together. This helps to form simplified ecosystems as farms, rather than monocultures - this is called integrated multi-trophic aquaculture,” said Morris, “Aquaculture is still a growing industry. There are many challenges ahead for it to continue growing, but I think that many in the industry understand that – if we are to avoid the same issues seen in other food production sectors - starting from a sustainable base is the best way to grow the industry and not face problems in the future.”
By: Kira Coley, UK Correspondent
