Growing Scenedesmus quadricauda in used culture media: is it viable?

Large-scale cultures of freshwater microalgae species demand high volumes of water used for culture media preparation. The recycling of culture media may help decrease cultivation costs, use valuable nutrients that may still remain in the medium after use and make it a green production system. This work investigated the effects of using culture media up to three times to grow Scenedesmus quadricauda. After a first use, culture media were either supplemented with nitrogen (N) and phosphorus (P) or with all nutrients of the medium composition. The effects of used culture media on the algae were verified through chlorophyll a concentrations, number of cells per coenobium, population density, growth rates, and biochemical composition (lipid classes, proteins, and carbohydrates). Cells were harvested through centrifugation before each culture medium use. The results showed that all nutrients should be added to the used medium at each new inoculation; protein/carbohydrate ratios were the best indicator of cell physiological status (higher in controls and lower in used media), and hydrocarbons accounted for 20 % of total lipids in controls and were produced under healthy conditions in S. quadricauda. According to the present results, at least three culture medium uses may be performed without affecting biomass yield, and it may be as promising as fresh medium for general biomass applications, such as biofuels production, but we do not recommend its reuse for fine biomass applications. Even though cells grew well in recycled media with all nutrients added, they were not as healthy as the ones in the control. (AU)