Lili Gao

Attached cultivation technology of microalgae for efficient biomass feedstock production

The potential of microalgae biofuel has not been realized because of low productivity and high costs associated with the current cultivation systems. In this paper, an attached cultivation method was introduced, in which microalgae cells grew on the surface of vertical artificial supporting material to form algal film. Multiple of the algal films were assembled in an array fashion to dilute solar irradiation to facilitate high photosynthetic efficiency. Results showed that a broad range of microalgae species can grow with this attached method. A biomass productivity of 50-80 g m(-2) d(-1) was obtained outdoors for Scenedesmus obliquus, corresponding to the photosynthetic efficiency of 5.2-8.3% (total solar radiation). This attached method also offers lots of possible advantages over traditional open ponds, such as on water saving, harvesting, contamination controlling and scale-up. The attached cultivation represents a promising technology for economically viable production of microalgae biofuels.

Subcritical co-solvents extraction of lipid from wet microalgae pastes of Nannochloropsis sp

In this paper subcritical co-solvents extraction (SCE) of algal lipid from wet pastes of Nannochloropsis sp. is examined. The influences of five operating parameters including the ratio between ethanol to hexane, the ratio of mixed solvents to algal biomass (dry weight), extraction temperature, pressure, and time were investigated. The determined optimum extraction conditions were 3:1 (hexane to ethanol ratio), 10:1 ratio (co-solvents to microalgae (dry weight) ratio), 90°C, 1.4 MPa, and 50 min, which could produce 88% recovery rate of the total lipids. In addition, electron micrographs of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were conducted to show that the algal cell presented shrunken, collapsed with some wrinkles and microholes after SCE extraction. The main composition of total lipids extracted under the optimum conditions was TAG which represented more than 80%. And the fatty acid profile of triglycerides revealed that C16:0 (35.67 ± 0.2%), C18:1 (26.84 ± 0.044%) and C16:1 (25.96 ± 0.011%) were dominant. Practical applications: The reported method could save energy consumption significantly through avoiding deep dewatering (for example drying). The composition of the extracted lipid is suitable for the production of high quality biodiesel.

Integration process of biodiesel production from filamentous oleaginous microalgae Tribonema minus.

Biodiesel production from microalgae has been receiving considerable attention. Past studies mainly relied on tiny sized single-cell oleaginous microalgal species, the biodiesel based on filamentous oleaginous microalgae was rarely reported. Thus, integrated process of biodiesel production from filamentous oleaginous microalgal strain Tribonema minus was studied in this work. The filamentous microalgae was cultivated for 21 days in 40 L glass panel, microalgae cells was harvested by DAF without any flocculants after the lipid content was 50.23%. After that, total lipid was extracted by subcritical ethanol from wet algal paste and 44.55% of crude lipid was triacylglycerols. Two-step catalytic conversion of pre-esterification and transesterification was adopted to convert the crude algal oil to biodiesel. The conversion rate of triacylglycerols reached 96.52% under the methanol to oil molar ratio of 12:1 during catalysis with 2% potassium hydroxide at 65°C for 30 min. The biodiesel product from T. minus conformed to Chinese National Standards.

Special biochemical responses to nitrogen deprivation of filamentous oleaginous microalgae Tribonema sp.

Both filamentous microalgae Tribonema and unicellular microalgae Nanochloropsis are promising feedstock for biodiesel production. Nitrogen starvation increased lipid content in Nannochloropsis but decreased that in Tribonema. In this study, biochemical responses of Tribonema under different levels of nitrogen (0N, 0.05N, 0.1N and 1N-BG11) were investigated. 1N-BG11 was sufficient during 15-day-cultivation, while the other levels were nitrogen limited. Cell growth was interrupted with 0N-BG11, but no differences in biomass among 0.05N, 0.1N and 1N-BG11. Both protein and lipid contents (% of dry weight) declined gradually inversely to the increment in carbohydrate contents under the decreasement of nitrogen levels. Both assays and TEM results showed that the cytoplasm in Tribonema contained no starch. Compared to nitrogen-replete condition, the TAG content (% of dry weight) decreased obviously under nitrogen starvation. Different levels of nitrogen did not cause fundamental shifts in fatty acid profiles in Tribonema.

Lipid accumulation and metabolic analysis based on transcriptome sequencing of filamentous oleaginous microalgae Tribonema minus at different growth phases

AbstractFilamentous oleaginous microalgae specie Tribonema minus is a promising feedstock for biodiesel production. However, the metabolic mechanism of lipid production in this filamentous microalgal specie remains unclear. Here, we compared the lipid accumulation of T. minus at different growth phases, and described the de novo transcriptome sequencing and assembly and identified important pathways and genes involved in TAG production. Total lipid increased by 2.5-fold and its TAG level in total lipid reached 81.1% at stationary phase. Using the genes involved in the lipid metabolism, the TAG biosynthesis pathways were generated. Moreover, results also demonstrated that, in addition to the observed overexpression of the fatty acid synthesis pathway, TAG production at stationary growth phase was bolstered by repression of the β-oxidation pathway, up-regulation of genes that funnels acetyl-CoA to lipid biosynthesis, especially gene encoding for phospholipid:diacylglycerol acyltransferase (PDAT) which funnels DAG to TAG biosynthesis.