RADIATIVE TRANSPORT AND HYDRODYNAMIC MODELING OF MICROALGAE PHOTOSYNTHESIS IN BIO-FLOW REACTORS

摘要

A simplified two-phase flow PCH (physicochemical hydrodynamics) model is developed for modelling and simulation of microalgae growth in bio-flow reactor. The model considers carbon balance through coupled gas-phase and liquid-phase transport equations. The transport model accounts for interfacial transport of CO_2 from gas bubble/slug to liquid, and microalgae photosynthesis reactions. A simplified photosynthesis reaction is adopted in the model, which assumes a pseudo-first order reaction for glucose pathway. The reaction rate is calculated assuming that it is proportional to the solar absorption rate by microalgae in the liquid. The reaction model also includes a simplified photoinhibition sub-model which assumes that the rate of photoinhibition is proportional to the square-root of solar irradiation reaching the algae cell. The Beer-Lambert law is used to calculate the radiative transfer of solar flux in seeded microalgae liquid flow. Analytical solution was obtained for single-channel bio-flow reactor. Decrease of the CO_2 concentration in gas bubble/slug and in liquid flow is assumed to be the result of the microalgae growth in bio-flow reactor. Two efficiency parameters are defined: CO_2 conversion efficiency and photosynthesis efficiency. The conversion efficiency is calculated based on the decrease of CO_2 between the bio-flow reactor inlet and exit. The photosynthesis efficiency is based upon the heating value of microalgae yield versus solar irradiation. The rate of microalgae yield is calculated by multiplying the mass stoichiometric coefficient of photosynthesis reaction to CO_2 consumption rate. Model analysis provided some insight of the microalgae formation in bio-flow reactor as interpreted from the PCH-coupled photosynthesis model that includes a dimensionless number as a potential scaling parameter for gas-phase only CO_2 supply operation; photosynthesis efficiency increases with increasing CO_2 molar concentration (i.e., number of moles per unit volume) at the reactor inlet for both gas-phase and liquid-phase only CO_2 supply; an optimal irradiation flux for maximum photosynthesis efficiency - a factor to consider should artificial light source be used for harvesting algae.