PREPARATION AND APPLICATION OF ZnO/MULLITE FOR THE INACTIVATION OF ESCHERICHIA COLI AND SALMONELLA ENTERICA IN WATER

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Department of Engineering

ABSTRACT
Several procedures are commonly used for water disinfection from bacteria. Unfortunately each procedure has its shortcomings. The most important shortcoming is the formation of disinfection by-products. Photodegradation of microorganisms using photocatalysts (such as ZnO) could be a good alternative. However, ZnO is a wide band gap (3.2 eV) semiconductor, and demands UV irradiations for excitation. In order make the synthesized ZnO active under visible light for the photo excitation, the ZnO must be supported. In this work, ZnO semiconductor particles, supported with mullite in varied proportion was developed (10%- ZnO/mullite, 20%-ZnO/mullite, 30%-ZnO/mullite, 40%-ZnO/mullite and 50%-ZnO/mullite) and synthesized by impregnation method followed by calcination at 1200 0C. Different concentrations (0.5g/L, 1g/L, 1.5g/L and 2g/L) of the synthesized photocatalyst were used to disinfect water and also toreduce the COD level under visible light irradiation. Between 90%-98% inactivation of E.coli and S.enterica and 64% COD reductionwas achieved in 90 minutes respectively under visible light irradiation. The 1g/L and 30%-ZnO/mullite photocatalyst gave the best bacteria inactivation of 98% while the 1g/L and 50%-ZnO/mullite photocatalyst gave the highest percentage COD reduction of 64. Control experiments that were carried out showed 35% inactivation and 14% COD reduction under visible light irradiation. The synthesized photocatalyst were characterized using UV-Visible absorption spectrophotometry, X– ray diffraction (XRD), Specific surface area analysis, pH of point of zero charge (pHPZC) analyses and Scanning electron microscopy (SEM) techniques.The kinetics of the degradation of methylene blue (MB) carried out under visible light irradiation using the synthesized photocatalyst, gave a degradation percentages of 82 for the unsupported ZnO and 68 for the 50%-ZnO/mullite.