Development of an estimation tool for monitoring growth and starch storage in microalgae cultures based on gas balance analysis

Abstract

Extensive research has been conducted on using microalgae biomass as a feedstock for biofuel production. Despite this, effective and accessible monitoring tools are still needed to track key energetic molecules, such as carbohydrates and lipids, to enhance and optimize the production of enriched biomass. This study presents the development and assessment of a three-compartment stoichiometric model designed as a monitoring tool for on-line estimation of growth kinetics and carbon reserve accumulation, primarily in the form of starch and, at later stages, triglycerides (TAGs). The proposed method leverages the indirect measurement of the net oxygen production rate and stoichiometric relationships governing the metabolic transitions within the bioprocess. It considers three key biomass components – catalytic biomass/cell structural components, starch, and TAGs – which accumulate sequentially over time during batch cultures under nitrogen-limiting conditions. The metabolic shift during nitrogen deprivation was modeled using well-defined kinetic terms. Model parameters were identified from two progressively nitrogen-starved batch cultures of Chlamydomonas reinhardtii and evaluated on an independent batch culture. While the model successfully captures key trends in nitrogen uptake, biomass formation, and carbon reserve accumulation (primarily as starch), its applicability to larger-scale systems with more complex environmental conditions remains to be further investigated. Nonetheless, this approach provides a promising foundation for real-time monitoring and bioprocess control strategies in microalgal cultivation.