BACKGROUND: Biochemical oxidation reactions require oxygen to be supplied by dispersed bubbles. Drawbacks of the gas-liquid system are enzyme denaturation and low oxygen utilization efficiency. Therefore, oxygen production through the decomposition of H 2 O 2 is useful for controlled oxygen transfer in bioreactors.
RESULTS:Catalase-containing liposomes (CALs) were prepared in 50 mmol L -1 Tris/0.1 mol L -1 NaCl buffer (pH 7.4) and the kinetic model was developed for the oxygen production by CAL-catalyzed decomposition of 1.0 mmol L -1 H 2 O 2 . Applying the model to the observed time course of oxygen produced gave overall resistance in the reaction based on the pseudo-steadystate assumption inside liposomes for H 2 O 2 and oxygen. The reaction resistance was estimated with the liposomal catalase concentration e t,in and the kinetic parameters of free enzyme reaction. At e t,in = 0.59 μmol L -1 , the CAL reaction proceeded under reaction control, while at e t,in = 5.05 μmol L -1 , the H 2 O 2 transfer resistance was involved. For the latter case, the permeability coefficient P P of H 2 O 2 through the liposome membrane was determined as 1.06 × 10 -6 m s -1 at 25 • C. The model predicted the H 2 O 2 concentration inside liposomes with different e t,in values. Furthermore, the oxygen concentration in the CAL dispersions was reasonably simulated. The oxygen production rate could be altered based on temperature (10-55 • C) and the fractional volume of CALs. CONCLUSION: The CAL-catalyzed oxygen production was controlled based on the e t,in and P P values, which determine the relative importance of the reaction and H 2 O 2 transfer resistances. The CAL would be applied to oxidation reactions instead of gas-liquid systems.
Reverse electrodialysis (RED) power generation using seawater (SW) and river water is expected to be a promising environmentally friendly power generation system. Experiments with large RED stacks are needed for the practical application of RED power generation, but only a few experimental results exist because of the need for large facilities and a large area of ion-exchange membranes (IEMs). In this study, to predict the power output of a large RED stack, the power generation performances of a lab-scale RED stack (40 membrane pairs and 7040 cm2 total effective membrane area) with several IEMs were evaluated. The results were converted to the power output of a pilot-scale RED stack (299 membrane pairs and 179.4 m2 total effective membrane area) via the reference IEMs. The use of low-area-resistance IEMs resulted in lower internal resistance and higher power density. The power density was 2.3 times higher than that of the reference IEMs when natural SW was used. The net power output was expected to be approximately 230 W with a pilot-scale RED stack using low-area-resistance IEMs and natural SW. This value is one of the indicators of the output of a large RED stack and is a target to be exceeded with further improvements in the RED system.
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