# Shell Waste Management and Utilization: Mitigating Organic Pollution and Enhancing Sustainability
###### Abstract  
Every year, close to 8 million tons of waste crab, shrimp and lobster shells are produced globally, as well as 10 million tons of waste oyster, clam, scallop and mussel shells. The disposed shells are frequently dumped at sea or sent to landfill, where they modify soils, waters and marine ecosystems. Waste shells are a major by-product, which should become a new raw material to be used to the best of their potential. There are a number of applications for waste shells in many fields, such as agriculture, medicine, chemical production, construction, environmental protection, cosmetic industry, food and feed industry, and a plethora of other (often niche) applications, which are being developed by the day. This review provides a broad picture of crustacean and mollusc shell waste management and reutilization possibilities, reviewing well established, current, and potential strategies, particularly from the standpoint of sustainability challenges and energy demand. crustacean shells; mollusc shells; valorization; waste bioeconomy; repurposing +
Footnote †: journal: Applied  
Shells should therefore be disposed of in relation to geographical distances between their source and processing facilities, considering the cost-effectiveness of transport, fossil fuels, and potential applications [11]. Shells are composed mainly of chemically stable calcium carbonate (CaCO\({}_{3}\)) (Table 1). The decomposition of shells is impossible without any treatment. Their thermal decomposition requires high temperatures of over 1000 \({}^{\circ}\)C, resulting in high-energy consumption and the frequent emission of greenhouse gases [12]. The disposal and handling of waste shells can thus become a major operational and financial burden. People have traditionally always given value to shells, which is a practice to retain from environmental, economic, and social standpoints. As far as we know from archeological findings of durable remains, shells have a long history of recognition as a valuable resource. They were used already in Paleolithic times [13; 14; 15], as tools or ornaments. In many cultures, shells and shell beads have been used for money [16; 17], even to date [18] demonstrating how standards determine value and illustrating the forms of social authority that constitute worth. In modern times, some mollusc species are in high demand due to the aesthetic value of their shells. It is estimated that at least 5000 mollusc species are marketed for ornamental purposes, mostly gastropods, the trade which has not been thoroughly documented nor quantified [19; 20]. Additionally, several million tropical gastropods are exported each year in the scope of the marine ornamental trade to become clean-up animals in tropical aquaria in their life-span, after which the issue of their shells is vague [21]. Communities try to contribute to resolving the issue of sustainable use of existing mollusc shell waste and numerous projects are launched worldwide to sensitize the local population on their reuse as decorative and useful items. However, those practices are just a drop in the sea until the valorization of shells and the unlocking of markets for new products thereof becomes the prime consideration of the industry (Figure 1). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Shell Type** & **CaCO\({}_{3}\)** & **Na\({}_{2}\)O** & **SO\({}_{3}\)** & **MgO** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **SO\({}_{4}\)** & **Other** \\ \hline River oyster & 96 & 1 & 0.7 & 0.7 & 0.3 & 0.4 & - & 1.8 \\ Sea oyster & 92 & 1 & 0.7 & 0.7 & 4 & 0.4 & - & 1.2 \\ Clam & 97 & 0.4 & 0.4 & 0.1 & 0.8 & 0.1 & 0.1 & 1.1 \\ Green mussel & 96 & 0.4 & 0.4 & - & 0.8 & 0.1 & 0.1 & 2.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition (%) of various raw bivalve shells. Adapted from [PERSON] et al. [7]. Their habitat location and shell type determine their exact chemical composition. When calcined (pyrolysed), shell chemical composition modifies, as calcium carbonate (CaCO\({}_{3}\)) converses into lime (CaO).