Analysis of the growth of microalgae in batch and semi-batch photobioreactors

Global warming induced by increasing concentrations of greenhouse gases in the atmosphere has become today an important environmental concern. A worldwide problem has become the depletion of petrochemical fuels and the continuous rise in oil prize that call us to make a global effort in order to find alternative energetic sources. A gradual replacement of fossil fuels by renewable energy sources (i.e. biofuels) is needed. In this scenario the use of microalgae can be seen as a possible solution to the problem of global warming since this group of fast-growing unicellular organisms shows several advantages (widespread availability, absent competition with agricultural land, utilization of cheap and abundant nutrient sources, high oil and biomass yields, high quality of the byproducts, generation of biomass for biofuel production with concomitant CO2 sequestration and suitability for wastewater treatments and other industrial plants) which make them one of the most promising and attractive renewable sources for a fully sustainable and lowcarbon economy portfolio. Despite this growing interest, the current microalgae-based technology is still not widespread since it is affected by technical and economic constraints that hinder its full scale-up. Therefore, great R&D efforts are currently undertaken to produce biodiesel at competitive costs and with the required quality starting from microalgae feedstock. In particular given the potential benefits of microalgae, their cultivation should be studied and optimized to make them competitive as fuel producing systems in the global market. Coherently to the scenario above reported, this work is focused on the investigation of two microalgae strains, Nannochloris eucaryotum and Chorella vulgaris. In particular, growth kinetics of these strains are investigated by taking into consideration the effect of medium composition and gas concentration using batch and fed-batch photobioreactors. The aim of this characterization is thus to gain useful information for the cultivation of microalgae in order to optimize the viable production of biofuels and high value-added products at the industrial scale by means of a process which uses flue gases as CO2.