Respirometry as a tool to quantify kinetic parameters of microalgal mixotrophic growth.

Modeling microalgal mixotrophy is challenging, as the regulation of algal metabolism is affected by many environmental factors. A reliable tool to simulate microalgal behavior in complex systems, such as wastewaters, may help in setting the proper values of operative variables, provided that model parameters have been properly evaluated. In this work, a new respirometric protocol is proposed to quickly obtain the half-saturation constant values for several nutrients. The protocol was first verified for autotrophic exploitation of ammonium and phosphorus (Monod kinetics), as well as of light intensity (Haldane model), further elaborated on specific light supply basis. It was then applied to measure the kinetic parameters of heterotrophic growth. The half-saturation constants for nitrogen and phosphorus resulted comparable with autotrophic ones. The dependence on acetate and dissolved oxygen concentration was assessed. Mixotrophy was modeled as the combination of autotrophic/heterotrophic reactions, implemented in AQUASIM, and validated on batch curves with/without bubbling, under nutrient limitation, and different light intensities. It was shown that the reliability of the proposed respirometric protocol is useful to measure kinetic parameters for nutrients, and therefore to perform bioprocess simulation.