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The prospect of depletion of natural energy resources on the Earth forces researchers to seek and explore new and alternative energy sources. Biomass is a composite resource that can be used in many ways leading to diversity of products. Therefore, microalgal biomass offers great potential. The main aim of this study is to find the best physical method of microalgal biomass pretreatment that guarantees efficient lipid extraction. These studies identifies biochemical composition of microalgal biomass as source for biodisel production. The influence of drying at different temperatures and lyophilization was investigated. In addition, wet and untreated biomass was examined. Cell disruption (sonication and microwave) techniques were used to improve lipid extraction from wet biomass. Additionally, two different extraction methods were carried out to select the best method of crude oil extraction. The results of this study show that wet biomass after sonication is the most suitable for extraction. The fatty acid composition of microalgal biomass includes linoleic acid (C18:2), palmitic acid (C16:0), oleic acid (C18:1), linolenic acid (C18:3), and stearic acid (C18:0), which play a key role in biodiesel production.

In recent years, researchers have highlighted the role of low cost-efficient agro-industrial by-products used as supplements in algal culture media. The aim of the study was to identify and characterize the basic metabolic pathways in Tetradesmus obliquus cells induced by supplementation with beet molasses in photoheterotrophic and mixotrophic culture conditions. to assess the impact of the nutritional strategy in unicellular algae, growth curves were plotted and lipid, carbohydrate, and protein levels were determined. Fourier Transform Infrared Spectroscopy was applied to measure the Tetradesmus obliquus cell composition. Additionally, the C16-C18 fatty acid profile of Tetradesmus obliquus was determined by gas chromatograph/mass spectrometry. The switch from autotrophy to photoheterotrophy and mixotrophy contributes to shortening of the adaptation growth phase. The highest protein content was obtained in the mixotrophic growth. This study has demonstrated high content of 18:1, cisΔ 9 , 18:2, cisΔ 9,12 , ω6, and 18:3, cisΔ 9,12,15 , ω3 in photoheterotrophic and mixotrophic culture conditions. High levels of proteins and essential fatty acids make Tetradesmus obliquus cell biomass important for human and animals health. Microalgae are not only a source of many valuable bio-products e.g. proteins, carbohydrates, lipids, ω3 and ω6 fatty acids or pigments applied in many different commercial sectors but can be a simple and economical solution to wastewater treatment and waste management 1. Algal cells utilize effectively agricultural, industrial and municipal wastewaters, waste raw materials, and by-products from many branches of industry. Algae are capable of assimilating organic compounds and other ingredients for biomass production and synthesis of both basic and specific metabolites. Additionally, the use of wastewaters and waste materials make microalgal biomass and bio-product production environmentally friendly 2. A number of studies have described supplementation of the algal culture medium with agricultural waste such as dairy manure 3 , liquid waste produced in piggeries 4 , post-fermentation effluents and wastewater from fruit, vegetable or cultivated plant processing, i.e. residues of cane bagasse and pineapple peel 5 , cassava 6 , sweet sorghum 7 , or hydrolysate of Jerusalem artichoke tubers 8. Most algae are autotrophs; however, some species such as Auxenochlorella protothecoides 9 Parachlorella kessleri 10 and Tetradesmus obliquus can assimilate organic compounds. Cultivation modes based on organic carbon sources include heterotrophy, photoheterotrophy, and mixotrophy 11. Compared to the heterotrophic mode, the photoheterotrophic and mixotrophic cultivation systems have several advantages e.g. intensification of algal growth and synthesis of valuable metabolites, such as fatty acids 12. Green algae growing in photoheterotrophic and mixotrophic culture conditions are natural producers of polyunsaturated fatty acids 10,13. In terms of human nutrition, one of the most important PUFAs are essential fatty...

The aim of this study was to determine the suitability of beet molasses, an agro-industrial by-product, as an alternative culture medium component for photoheterotrophic and mixotrophic cultivation of Parachlorella kessleri. Application of beet molasses improved microalgal cell growth and modified the biochemical composition of P. kessleri biomass. During the addition of molasses to culture media with simultaneous aeration, the maximum biomass productivity, oil and protein productivity, and calorific value were 0.42 g L−1 day−1, 112.56 and 244.95 mg L−1 day−1, and 22.1 MJ kg−1, respectively. Under these conditions, the total content of polyunsaturated C16-C18 fatty acids decreased, which was suitable for application in biodiesel. Besides oils and carbohydrates, P. kessleri had an ability to synthesize significant amounts of proteins, especially during molasses utilization. This provides a possibility of a wide range of non-fuel applications of P. kessleri biomass.

Algal biomass is regarded as an alternative source for producing renewable fuels, given the chemical nature of storage products: lipids, starch, and proteins. Many factors affecting the production of microalgal biomass and lipid accumulation include the light and CO2 concentration, i.e. critical factors for determination of the biochemical composition of microalgal biomass. Our objective was to evaluate the effect of three different light/dark photoperiods (12/12 h, 16/8 h, 24/0 h) and the CO2 concentration (from air and 5% v/v CO2‐enriched air) on the growth rate, productivity, and changes in the biochemical composition of Chlorella protothecoides biomass. Continuous illumination stimulated growth under supplementation of air CO2. At 5% CO2, the maximum C. protothecoides growth rate was found under 16/8 light/dark cycles and longer duration of light yielded a decrease in the specific growth rate. The photoperiods and CO2 concentrations influenced the biomass productivity. Chlorella protothecoides produced biomass more efficiently at the 24/0 and 16/8 light/dark cycles under supplementation of air CO2 than at addition of 5% CO2. However, under the 12/12 light/dark cycle, biomass productivity was higher at 5% CO2. The light photoperiod greater than 16 h did not increase biomass productivity. These factors also influenced the content of lipids and carbohydrates. A maximal lipid content was observed for the 24‐h photoperiod for air CO2, whereas the addition of 5% CO2 affected lipid and carbohydrate production.