Evaluation of various techniques for microalgal biomass quantification

• Biomass quantification of microalgae using new techniques.
• Dynamic ranges of measurements higher than 20 g l-1 by dielectric permittivity and ODNIR sensors.
• Oxygen production rate is a good proxy of microalgae concentration in DCW lower than 1 g l-1.
• Fourier equation enhanced the image analysis for estimation of microalgae concentration up to 6 g l-1.

Biomass concentration is one of the most important parameters in the biotechnology processes. Its measurement relies on the physical, chemical or biological properties of the cells. Several techniques were applied in this work to measure the cell concentration of four microalgae: Botryococcussp., Botryococcusbraunii, Chlorella vulgaris, and Ettlia sp. The experiments were performed using samples taken from a chemostat for each strain to provide microalgal cell suspensions in a stable physiological state and concentration. The dry cell weight (DCW) was used as the reference method for the evaluation of other methods. The two commercial sensors used to determine optical density and dielectric permittivity showed a broad effective measurement range up to more than 20 g l−1. A Red–Green–Blue model analysis of microalgal digital images in combination with Fourier equation significantly extended the measurements range up to 6 g l−1. Cell count using a flow cytometer showed a broad range of linearity to DCW in washed samples, but other counting methods using hemocytometer and microscopic automated count were limited. Finally, the oxygen production rate, representing the photosynthetic activity, showed a linear regression with DCW at cell concentrations lower than 1 g l−1.