Insight into the effect of carbon composition on microalgae cultivation using acidogenic fermentation liquid: Growth kinetics, biochemical composition synthesis, and physiological characteristics

Abstract

The cultivation of microalgae using acidogenic fermentation liquid shows great potential due to the ample presence of volatile fatty acids (VFAs) as organic carbon (OC) sources. However, the availability of inorganic carbon (IC) sources in the fermentation liquid might be insufficient to support microalgal photosynthesis, thereby limiting the application of this approach. This study aimed to address this limitation by introducing NaHCO3 as additional inorganic carbon sources into the fermentation liquid. The effects of different VFAs and organic carbon to inorganic carbon ratios (OC/IC) on the growth kinetics, biochemical composition synthesis, and physiological characteristics of microalgae were investigated. Results showed that C. pyrenoidosa cultivated in acetic acid with an OC:IC ratio of 3:1 exhibited the highest values for the specific growth rate (0.245 d−1) and maximum biomass productivity (0.254 g·L−1·d−1). Furthermore, acetic acid was more beneficial than other VFAs in promoting microalgal photosynthesis and contributing to lipid accumulation. The highest lipid content of C. pyrenoidosa (39.9 %) was obtained with acetic acid at the OC/IC ratio of 3:1, and the highest percentage of polyunsaturated fatty acids (74.6 %) was obtained with acetic acid in the 100 % OC group. The flow cytometry results indicated that at OC/IC ratio of 3:1, the proportion of normal cells in different organic acids groups higher than other OC/IC ratios. Acetic acid was beneficial for maintaining normal cell morphology, and IC sources could increase microalgal cell sizes and reduce cell mortality. This study deepens the understanding of microalgae cultivation using fermentation liquid and provides theoretical insights for the application of this approach.