Antibacterial Properties of Scallop Shell Derived Calcium Hydroxide Powders

Globally increased bivalve aquaculture production results in a vast amount of by-product discharges such as scallop shells. Utilization of these wastes to produce new products such as antibacterial agents can cooperate to reduce environmental problems and provide a high value-added product at a lower cost. In this study, scallop shells are heat-treated at 800°, 900°, 1000°, and 1100°C for 4 hours at atmospheric conditions. X-ray diffraction analysis revealed that calcium carbonate is the only inorganic phase in the powdered scallop shells. Ten weeks after the thermal treatment of the scallop shells, the calcium hydroxide phase was the only crystalline phase determined by X-ray diffraction analysis for the samples calcined at 1000° and 1100°C. At lower calcination temperatures, calcium carbonate and calcium hydroxide phases were co-existing in the samples. Scanning electron microscopy investigations depicted that using scallop shells as a starting material to synthesize nanometer-sized calcium hydroxide is achieved. It was determined that applied calcination temperature has a significant effect on the particle size of the obtained calcium hydroxide phase. Antimicrobial activity of calcined and uncalcined shell powders were tested against Escherichia coli and Staphylococcus aureus. No antibacterial activity was detected for the uncalcined scallop shell powders. However strong antibacterial activity was determined for the powders after subjection to calcination. Calcination of scallop shells is an environmentally friendly, readily applied, and low- cost approach to achieve nanometer-size calcium hydroxide that can be used as an inorganic antibacterial material in various composite systems.