Effect of ozonation on Spirulina platensis filaments by dynamic imaging particle analysis

Increasing interest in microalgal research calls for simple and automated tools to identify algal species' taxonomic level, examine their quality, monitor their growth, determine their size and shape, and enumerate them. We demonstrate the applicability of micro-flow imaging as an innovative tool to count algal cells and determine their shape and size, toward a future systematic species database, and biofuel applications. Ozonation was used to introduce changes in cell morphology such as cell oxidation, lysis and agglomeration, which were characterized by micro-flow imaging. Two ozone system configurations were used—batch and semi-batch—to oxidize four different Spirulina platensis samples, each presenting a different initial morphology correlated to culture growth stage, environmental conditions and hydration–dehydration of the cells. The ozone dose acted differently in each system: with the batch system (ozone dose of 5–15 mg L⁻¹), the dominant action was breakage of spirulina filaments into smaller ones; with the semi-batch system (ozone dose up to ∼510 mg L⁻¹), the dominant action was perforation of the cell walls and an increase in filament transparency (measured by mean intensity). The study also showed the influence of culture growth stage on ozonated spirulina count and shape analysis.