A large amount of marine organic residue is generated and wasted from scallop shell processing manufacture. Because the waste product of scallop, especially the mid-gut gland contains a large quantity of heavy metals such as cadmium and copper, it cannot be effectively used. Now, a large part of these wastes are treated in landfills. However, in recent, the landfill treatment runs into trouble because of an environmental pollution and a decrease in proposed landfill ground. Consequently, the development of a new treatment method of the scallop waste is really required. In order to recycle the organic residue of scallop mid-gut gland, a new technology has been developed for removing the harmful cadmium and using as fish meal and fertilizer.
This treatment consists of a cadmium leaching process from the mid-gut gland in a sulfuric acid solution and a cadmium electro-deposition process. This new treatment technology corresponding to hydrometallurgical process can remove more than 95% of cadmium from the mid-gut gland. At first, influences of various factors on cadmium removal efficiency such as acid concentration, electrolytic voltage, anode materials and so on, were examined to decide the most suitable conditions of an electrochemical treatment method by using a small scale plant test.
And secondarily, a demonstration plant to enable one batch treatment of about 100kg/day was designed on the basis of the results of a fundamental experiment, and a prototype plant was built. Finally, a demonstration test was conducted.
The dried and crushed wastes products of scallop after the removal of cadmium were reused as a feed and fertilizer materials, and in the year 2000, two recycle plants of the scallop waste on the basis of this development research were constructed at Oshamanbe-cho and Sawara-cho in Hokkaido, and now under operating.