Investigation of the Effects of Residual Flocculants on the Cultivation of Auxenochlorella Pyrenoidosa: Lipid Production and Transcriptomic Insights

Microalgae flocculation is an essential approach to replace the costly centrifugation method and lower the production cost of microalgae products. The chemical flocculation method features a short flocculation duration, high flocculation efficiency and low dosage, and has emerged as a research focus in recent years. In consideration of the requirement for a relatively high microalgal biomass concentration in actual production, the cultivation of microalgae typically involves initially achieving a substantial amount of microalgal biomass under optimized culture conditions, followed by the harvesting of these microalgal cells and subsequent cultivation under diverse circumstances, such as integrating the harvested biomass into wastewater for biological treatment or introducing the biomass into a nitrogen-deficient medium to increase lipid biosynthesis. Notably, after a considerable quantity of microalgal biomass is obtained in the first step, if chemical flocculants are employed in the harvesting operation, the residual chemical flocculants in the cell sediment are highly prone to permeate the subsequent culture medium and thereby influence microalgal cultivation. Nevertheless, this possibility has not been investigated in current research. In this study, the flocculant residue strongly affected the growth and lipid synthesis of A. pyrenoidosa in subsequent culture, and the latent mechanism was investigated via the transcriptome. These findings illuminate the considerable impact of flocculant residues on subsequent culture, which is conducive to a comprehensive assessment of the feasibility of the practical application of chemical flocculants in microalgae harvesting.