Construction of a Novel Bio-reactor System With Semiconductor-Photocatalysts

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The semiconductor powders such as Tio_2, and Pt-impregnated Tio_2, under irradiation with a light, cause the excitation of electrons from valence to conduction bands and assist the photocatalytic oxidation and reduction of less reactive chemical species. In the present work, we obtained several findings by conducting the experimental studies in order to construct a bioreactor system with photocatalysts as follows :1. The regeneration of the coenzyme NAD (nicotinamide-adenine dinucleotide) with the enzyme (alcohol dehydrogenase) was examined by its photoreduction in Tio_2 suspensions. The enzymeimmobilized TiO_2 had both the activities of photochemical oxidation and enzymatic reduction of NAD. Itwas possible to achieve the cyclic reaction with NAD regeneration by this catalyst.2. Effective absorption coefficients of light were evaluated from the observed profile of light intensity in a square column with gas-liquid-solid dispersion containing TiO_2 particles. Quantum efficiencies were obtained from the measured photooxidation rates of NADH(reduced form of NAD) in a small annular photoreactor. In an annular reactor (10cm o. d., 4.6cm i. d.) and height (=1m) with gas-liquid-solid dispersion, photooxidation rates of NADH were measured and experimental results agreed well with those calculated from the model using the effective absorption coefficient.