**2.2.5 Others (calcination, red tide, coagulation, fertilizer, etc.)**


### **2.3 Recycling limitation**

Recycling of waste oyster shells has much limitation in environmental engineering. First, the quantity of waste oyster shells is too much to be recycled in environmental engineering. Second, a plan to retreat the waste oyster shells contaminated after adsorption of heavy metals should be prepared above all. Third, recycling of waste oyster shells would require removal of impurities through proper processing and treatment through a calcination process, which decreases the economic feasibility. Fourth, the repeated use lowers the efficiency below commercial products.
