CONVERSION OF RADIANT LIGHT ENERGY IN PHOTOBIOREACTORS

The conversion of radiant light energy into chemical affinity by micro organisms in photobioreactors is examined. The kinetics of entropy pro duction in the system is theoretically established from entropy and en ergy balances for the material and photonic phases in the reactor. A n egative chemical affinity term compensated for by a radiant energy ter m at a higher level of energy characterizes photosynthetic organisms. The local volumetric rate of radiant light energy absorbed, which appe ars in the dissipation function as an irreversible term, is calculated for monodimensional approximations providing analytical solutions and for general tridimensional equations requiring the solution of a new numerical algorithm. Solutions for the blue-green alga Spirulina plate nsis cultivated in photoreactors with different geometries and light e nergy inputs are compared. Thermodynamic efficiency of the photosynthe sis is calculated. The highest value of 15% found for low radiant ener gy absorption rates corresponds to a maximum quantum yield in the reac tor.