Cellular response in fresh water microalgae to polluting compounds of flue gas when used as carbon source

Attention has lately been given to the use of microalgae as provider of valuable biomass or as production organism. To be able to use algae in industrial production, especially of biofuels, the cultivation procedures need to be improved in terms of efficiency and minimization of production costs. To reach these goals understanding of both process conditions as well as biological response to such conditions is needed for optimization of algal cultivation. Carbon dioxide, the carbon source during phototrophic growth, should be provided at high levels to result in the high biomass concentrations needed for a feasible production. Suitable high-level sources of CO2 are flue gases from industrial activities, which when used for algal cultivation will be a way of carbon capture reducing CO2 emissions. However, flue gases contain additional components that may affect cellular activity negatively. The aim of this research is to understand the physiological behavior of microalgae in industrial conditions to be able to optimize cellular performance. This initial project was launched to provide basic information about response of several types of microalgae that could grow in fresh water conditions to the main gaseous pollutants in flue gas, NO and SO2. This knowledge would guide the selection for a deeper characterization of effect-response relations and control of metabolism in algae in response to industrial conditions. Ten strains of fresh water species and one marine were selected based on reported fast growth and interesting composition such as high levels of lipids. The algae were screened for growth and cellular composition in cultivations with fresh water mineral medium. Artificially produced flue gas, mimicking effluents of pulp mills, consisting of 15% CO2 with 100 ppm NO and 10 ppm SO2 included for the last period of the cultivations was bubbled into the cultures. All strains tested were able to grow and two Scenedesmus strains, an isolated strain from a nearby lake, Chorella protothecoides and Chlamydomonas reinhardtii exhibited the highest specific growth rates. The highest levels of cellular macromolecules were found in Chlorella emersonii (45% carbohydrates), Nannochloropsis salina and the local isolate (65% proteins), and Botrycoccus braunii (57% lipids). It can be concluded that all strains tested were able to grow in cultures with flue gas as carbon source, also the marine species Nannochloropsis salina, and that the gaseous components decrease pH which needs to be monitored carefully to avoid that large drops in pH inhibit algal growth