Abstract
The purpose of this work is to define optimal growth conditions to maximise biomass for batch culture of the cyanobacterium Arthrospira maxima and the microalgae Chlorella vulgaris, Isochrysis galbana and Nannochloropsis gaditana. Thus, we study the effect of three variables on cell growth: i.e., inoculum:culture medium volume ratio (5:45, 10:40, 15:35 and 20:30 mL:mL), light:dark photoperiod (8:16, 12:12 and 16:8 h) and type of culture medium, including both synthetic media (Guillard’s F/2 and Walne’s) and wastewaters. The results showed that the initial inoculum:culture medium volume ratio, within the range 5:45 to 20:30, did not affect the amount of biomass at the end of the growth (14 days), whereas high (18 h) or low (6 h) number of hours of daily light was important for cell growth. The contribution of nutrients from different culture media could increase the growth rate of the different species. A. maxima was favoured in seawater enriched with Guillard’s F/2 as well as C. vulgaris and N. gaditana, but in freshwater medium. I. galbana had the greatest growth in the marine environment enriched with Walne’s media. Nitrogen was the limiting nutrient for growth at the end of the exponential phase of growth for C. vulgaris and N. gaditana, while iron was for A. maxima and I. galbana. The growth in different synthetic culture media also determines the biochemical composition of each of the microalgae. All species demonstrated their capability to grow in effluents from a wastewater treatment plant and they efficiently consume nitrogen, especially the three microalga species.
Highlights
Microalgae, such as cyanobacteria and eukaryotic algae, are photoautotrophic microorganisms that use inexpensive and widely available natural resources, such as CO2, H2 O and inorganic salts, to transform radiant energy into valuable products contained in the biomass
For A. maxima, the results showed that MC1 was the best culture medium
All microalgae and cyanobacterium studied were able to grow in wastewaters (Table 1) maintaining the inoculum:culture medium ratio of 5:45 and a light photoperiod of 12:12, obtaining similar biomass production in the three non-sterilised wastewater samples (AD1, AD2 and AD3) (Figure 7)
Summary
Microalgae, such as cyanobacteria and eukaryotic algae, are photoautotrophic microorganisms that use inexpensive and widely available natural resources, such as CO2 , H2 O and inorganic salts, to transform radiant energy into valuable products contained in the biomass. These photosynthetic microorganisms are among the most promising new sources of energy, since they are renewable and neutral with respect to CO2 emissions. 70,000 of which more than 40,000 have been published [1] Because of this enormous number of species, we selected four different microorganisms with different compositions and behaviour in this work.
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