Influence of flue gas mimicking effluents of paper mills on growth and cellular composition of fresh water species of microalgae

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. One important factor is to reach as high biomass concentrations as possible e.g. by using high levels of carbon dioxide provided by flue gas. The aim of this project was to study the influence of flue gas simulated to mimic effluents of pulp mills on growth and cellular composition of microalgae. 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 in cultivations with fresh water mineral medium and artificially produced flue gas bubbled into the cultures consisting of 15% CO2 with 100 ppm NO and 10 ppm SO2 included for the last period of the cultivations. 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% of carbohydrates), Nannochloropsis salina and the local isolate (65% of proteins), and Botrycoccus braunii (57% of 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.