Abstract
Biomass of microalgae and the components contained in their cells can be used for the production of heat, electricity, and biofuels. The aim of the presented study was to determine the optimal conditions that will be the most favorable for the production of large amounts of microalgae biomass intended for energy purposes. The study analyzed the effect of the type of lighting, the time of lighting culture, and the pH of the culture medium on the growth of Chlorella vulgaris biomass. The experiment was carried out in vertical tube photobioreactors in three photoperiods: 12/12, 18/6, and 24/0 h (light/dark). Two types of lighting were used in the work: high-pressure sodium light and light-emitting diode. The increase in biomass was determined by the gravimetric method, by the spectrophotometric method on the basis of chlorophyll a contained in the microalgae cells. The number of microalgae cells was also determined with the use of a hemocytometer. The optimal conditions for the production of biomass were recorded at a neutral pH, illuminating the cultures for 18 h a day. The obtained results were 546 ± 7.88 mg·L−1 dry weight under sodium lighting and 543 ± 1.92 mg·L−1 dry weight under light-emitting diode, with maximum biomass productivity of 27.08 ± 7.80 and 25.00 ± 5.1 mg·L−1∙d−1, respectively. The maximum content of chlorophyll a in cells was determined in the 12/12 h cycle and pH 6 (136 ± 14.13 mg∙m−3) under light-emitting diode and 18/6 h, pH 7 (135 ± 6.17 mg∙m−3) under sodium light, with maximum productivity of 26.34 ± 2.01 mg·m−3∙d−1 (light-emitting diode) and 24.21 ± 8.89 mg·m−3∙d−1 (sodium light). The largest number of microalgae cells (2.1 × 106) was obtained at pH 7 and photoperiod of 18/6 h under sodium light, and 12/12 h under light-emitting diode. Based on the results, it can be concluded that the determination of the optimal parameters for the growth and development of microalgae determines the production of their biomass, and such research should be carried out before starting the large-scale production process. In quantifying the biomass during cultivation, it is advantageous to use direct measurement methods.
Highlights
Microalgae are among the most widespread organisms
The most popular of them are the determination of dry matter [23], measurement of optical density, determination of chlorophyll content using a spectrophotometer, and a method based on counting cells using a counting chamber [24]
Based on the statistical analysis of the test results, it was found that the photoperiod used, and the pH of the culture medium had a significant effect on the amount of biomass and the content of chlorophyll a in microalgae cells of the C. vulgaris species
Summary
Microalgae are among the most widespread organisms. According to Guiry [1], it is estimated that there are up to 1 million species of algae on Earth. We meet them in the entire biosphere, but above all in fresh, salt, and saline waters. A characteristic feature of algae is the presence of chlorophyll [2,3], which enables photosynthesis to be carried out in each individual cell [4]. The efficiency of this process and the related biomass production is much higher compared to land plants [5]. Microalgae biomass has been widely used in various industries: pharmaceutical, food, animal feed, water purification, and biofuel production [6,7,8]. The biomass yield and the biochemical composition of microalgae depend on environmental and physiological factors such as culture temperature, pH, lighting intensity and type, availability of nutrients, and carbon dioxide [11]
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