Growth response of Scenedesmus and Chlorella to elevated sulfate concentrations

This study examines the response of microalgae to elevated sulfate concentrations and pH variation in terms of growth rate and biochemical composition under simulated flue gas conditions. The observed response was species-dependent: Scenedesmus sp. tolerated higher sulfate levels than C. vulgaris, which showed chlorosis and growth decline at sulfate concentrations above 12 mM. Scenedesmus sp. exhibited higher sulfate tolerance by effectively regulating transporter activity and maintaining redox balance, thereby sustaining both growth and photosynthetic function. In contrast, C. vulgaris showed lower resilience to osmotic and oxidative stress, resulting in growth decline. Elevated sulfate induced toxicity and osmotic imbalance, thereby altering metabolic allocation. Maximum protein content occurred at 3 mM sulfate, while lipid content decreased with increasing sulfate concentration. Key fatty acid methyl esters (FAMEs) including linolelaidic acid methyl ester and cis-9-oleic acid methyl ester also decreased as sulfate levels increased. Moreover, microalgae prioritised protein synthesis over lipid storage to maintain metabolic stability and cellular resilience in a sulfate-rich environment. Overall, elevated sulfate negatively affected growth and lipid productivity, with clear interspecies variation in tolerance.