Simple method for measuring the spectral absorption cross-section of microalgae

The spectral absorption cross-section of microalgae is an essential parameter in modeling the microalgae metabolism and growth kinetics as well as in estimating the productivity and efficiency of photobioreactors. This paper presents a simple experimental procedure for retrieving the average spectral absorption cross-section of concentrated microalgal suspensions. The method combines experimental measurements of the normal-hemispherical transmittance and reflectance of the suspensions in conventional cuvettes with an inverse method and analytical expressions obtained from the modified two-flux approximation accounting for absorption and multiple scattering. The method was validated with direct measurements of the scattering phase function and of the absorption and scattering cross-sections of freshwater microalgae Chlorella vulgaris. It was able to retrieve the absorption cross-section with acceptable accuracy. The latter was then used to estimate successfully the fluence rate using a simplified light transfer model, the local rate of photon absorption, and the biomass productivity in flat plate PBRs.