Abstract
Since the interspecific competition represents a critical issue for biodiesel production in open mass cultures of microalgae, laboratory studies aimed to select competitive species receive significant interest. In this work, a laboratory approach based on the method of multisizing cell counting was developed to monitor the competition course of single algal species grown in mixed cultures. Two marine microalgae, Dunaliella tertiolecta and Phaeodactylum tricornutum, were used to set-up an induced-contamination assay, with the aim to test their competitive capabilities. The evaluation of the oil production by dried biomass extraction was coupled to the growth assay to investigate the effect of competition on oil yield. The adopted experimental approach revealed effective as a method to selectively measure the algal growth of single species in mixed cultures, enabling to evaluate the competitive properties of Dunaliella outgrowing the contaminant species Phaeodactylum. At the end of the experiment the dominant species contributed more than 90% to the total biomass, while no loss of oil production was observed, the oil yield in the mixed being even higher than in the unialgal culture (3.15 vs. 2.28 mg). The outcomes of the induced competition suggest the use of Dunaliella as a competitive oil-producer species and especially support the potential of the experimental approach to be used for preliminary screening to drive species selection for open mass cultures.
Highlights
Microalgae biomass is currently considered the most promising alternative as oil source for biodiesel production [1] [2]
The adopted laboratory approach coupling the experimental design of induced competition with the instrumental multisizer-counting method proved effective showing high efficiency of Dunaliella, which exhibited competitive abilities to resist to the contamination of Phaeodactylum and to produce as high biomass in mixed as in unialgal culture condition
The oil production, which was not affected by the contamination event, supported the suitability of Dunaliella to be used in open mass-cultures for biodiesel production
Summary
Microalgae biomass is currently considered the most promising alternative as oil source for biodiesel production [1] [2]. For commercial oil production the algae should be cultured on a large scale at high productivity in open-pond systems, which can be economically feasible since mainly based on the natural solar energy [4]. Such cultivation systems, when supplied by natural sea-water, have the additional advantage to potentially decrease up to 90% water requirement. The use of brackish microalgae as feedstock allows increasing the inflow of fresh wastewater as nutrient source, providing the additional benefit of water treatment [5]
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