PRODUCTION OF CALCIUM OXIDE FROM WASTE OYSTER SHELLS FOR A VALUE-ADDED APPLICATION OF ANTIBACTERIASuree Tongwanichniyom, Thanit Pattamapitoon , Napimporn Sangvichien and Somkiat PhornphisutthimasAbstract The production of calcium oxide was investigated from waste oyster shells as a value-added application in inhibiting bacteria. Oyster shell powder was prepared in 4 forms: natural oyster shell powder (NOSP) and calcined in a programmable furnace for 2 hours at 700°C (OSP700), 800°C (OSP800) and 900°C (OSP900). All forms were analyzed for physical properties using thermogravimetric analysis, X-ray diffraction and Fourier transformed infrared spectrometry. The results indicated that the calcium carbonate of NOSP, OSP700 and OSP800 had a rhombohedral structure of calcite. On the other hand, the calcium carbonate structure of OSP900 changed to calcium oxide (CaO) and calcium hydroxide (Ca(OH)2 ). The findings were consistent with the Fourier-transformed infrared spectrometry results as they showed the peak of CâO stretching, indicating a calcite structure, whereas the characteristics of the Ca=O group and OâH stretching of the functional group indicated the structures of CaO and Ca(OH)2. OSP900 showed qualitative antibacterial activity by its inhibition zone on NA medium. Quantitatively, OSP900 had the highest antibacterial activity against Escherichia coli and Staphylococcus aureus at concentrations of 0.5% and 1.0% w/v, respectively, with significant differences for an exposure time of 30 minutes. In addition, OSP900 gave the best inhibition of E. coli in contaminated vegetables at a concentration of 0.5% w/v. The results of this study revealed the usefulness of OSP900 for further antibacterial applications in contaminated vegetables. |