Kinetic study of a new photosynthesis bioreactor design using TiO2 particles combined with enzymes

A new photo-bioreactor for an electron transfer system using a photocatalyst combined with enzymes is proposed by the use of a ceramic membrane separating photocatalysis from biocatalysis to allow highly selective production of enzymes that is promoted by photocatalysis without denaturation of the enzyme due to direct light irradiation. In this work, an electron transfer system which combines TiO2 photocatalyst particles with two enzymes was studied with formate dehydrogenase (FDH) as a catalyst of CO2 fixation. Methyl viologen (MV), NAD and diaphorase (DAH) were used to mediate electron transfer from TiO2 to FDH. The kinetic study of MV+ production by TiO2 particles revealed that MV+ production follows a reaction scheme consisting of MV+ generation with Langmuir-Hinshelwood expression and an independent first-order decay of MV+ in a homogeneous reaction. The performance of the total photo-bioreactor with a ceramic membrane, which separates enzymes from TiO2 to protect them from direct UV irradiation, was successfully demonstrated. Using batch operations, the total performance of the system was examined. Concentrations both of MV and NADH affected the rate of CO2 fixation: the total reaction kinetics was discussed to optimize the total performance. The kinetic parameters of the so-called ping-pong reaction of DAH were determined experimentally and the coupled reaction with TiO2-MV+-DAH-NADH-FDH-CO2 was discussed quantitatively with an assumption of a steady-state.