In the developing countries, the discarded crab, shrimp and lobster shells usually be thrown into the garbage or in the ocean. In the developed countries, the relevant processing cost is expensive. These shells actually contains useful substance, such as protein, calcium carbonate, nitrogen and shell system (a kind of polymer that similar to cellulose). And the potential value of these shells to chemical industry has often been ignored. Nature, the International weekly journal of science said scientists should find a sustainable way to extract the shells of crustaceans, and the government and enterprises should invest the abundant and cheap renewable resource.
Scientists predicted, the value of per ton dried shrimp shell is about 100~120 dollars. It can be ground and used as animal feed additive, bait, manure and chitin production. Crustacean’s shell contains 20%~40% protein, 20%~50% calcium carbonate and 15%~40% chitin, but what these ingredients can be used to do?
Protein is an excellent animal feed, for example, the value of essential amino-acid in penaeus shrimp shell can be compared to soybean meal. At present, these proteins cannot be used because of the damage in manufacturing process. With the rapid development of animal husbandry, crustacean’s shell comes from Southeast Asia can be transformed into protein-rich animal feed.
Calcium carbonate is widely applied in pharmacy, agriculture, construction and paper industry, and it is mainly from marble and limestone. Although its source is rich, may contain heavy metals that is difficult to remove.
Professor in the Department of Chemical and Biomolecular Engineering, National University of Singapore said, it is destructive, wasteful and expensive that extracting chemicals from discarded shells. It requires separating out different ingredient, this process is called fractionation. Protein can be removed by sodium hydroxide solution, and calcium carbonate can be decomposed by hydrochloric acid but both are corrosive and hazardous solvents. In addition, in order to make chitosan, researcher should use 40% concentrated sodium hydroxide solution to process chitin. Using shrimp shell to make 1 kilogram chitosan needs more than 1 tonne of water.
Another option may be to design and use ionic liquid that can dissolve carbohydrate polymers and extract chitin. Chitin polymers produced in this way have long chains and a high molecular weight, and can be spun into fibres and films for wound dressings and water treatment. These progress requires more efforts from all parties, and strong support from policymakers, research institutes, governments, funders and public. Biological refining from shell waste will provide new business opportunity for Southeast Asia.
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