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[Display omitted] • Chlorella sp. ABC-001 showed the best growth and lipid yield with flue gas 10% CO 2. • Chlorella sp. ABC-001 was unaffected by NO but SO 2 severely inhibited cell growth. • Galdieria sulphuraria was adopted to remove SO 2 and enhance CO 2 and NO removal. • SO 2 removal is attributed to ionic interactions as well as assimilation by cells. • The dual-strain system showed stable growth under simulated flue gas supply. This study aims to propose a biological system that allows for direct utilization of flue gas for carbon dioxide capture and utilization by microalgae. The strain Chlorella sp. ABC-001 is employed for its high growth rate as well as lipid and carbohydrate content. Toxicity tests showed that cell growth was unaffected by NO, but the presence of SO 2 showed critical damage on cell growth. Hence, an extremophile alga, Galdieria sulphuraria 5587.1 was applied to build a dual-strain cultivation system to mitigate the effect of SO 2 toxicity and increase CO 2 capture efficiency. All SO 2 was removed by Galdieria culture and the system exhibited stable growth from a simulated flue gas stream containing CO 2 , NO and SO 2. Combined CO 2 biofixation rate of 793 mg/L/d and lipid productivity of 113 mg/L/d was achieved. The results showed that this new cultivation system is a promising alternative for reducing CO 2 emissions from power plants. [ABSTRACT FROM AUTHOR]

The commercial production of microalgae-derived docosahexaenoic acid (DHA) has been expanding due to several advantages of algal over fish oil produced DHA. While the DHA production technology from microalgae is already economically competitive, alternatives to pure glucose and yeast extract still need to be explored to reduce the costs and increase the profits further. In the present study, orange peel waste (OPW) and various nitrogen sources were investigated as alternative nutrient sources for the economic cultivation of Aurantiochytrium sp. KRS101. The utilization of orange peel extract (OPE) supplemented with NaNO 3 showed a higher DHA yield than that supplemented with NH 4 Cl or urea, and pH 5.5 was found to be the optimum initial condition for Aurantiochytrium sp. KRS101. OPE optimized with supplemental NaNO 3 (1.2 g/L) resulted in a DHA yield of 0.63 g/L, which was 2.5 fold greater than the yield obtained using a conventional basal medium containing a similar amount of total nitrogen and 67% greater total carbon sources. This result implied not only that the conventional use of glucose and yeast extract have lower efficiency levels during nutrient metabolism but also that the types of carbon and nutrient sources have a significant effect on the DHA yield. The addition of supplemental glucose further enhanced the biomass, fatty acid methyl esters (FAME), and DHA yields, which unveiled the high C:N ratio requirement of Aurantiochytrium sp. KRS101. These results suggest that the development and optimization of microalgae fermentation using OPE and NaNO 3 is a possible route for the economical production of DHA and for the additional utilization of food waste. [ABSTRACT FROM AUTHOR]

The microalgae-based biorefinement process has attracted much attention from academic and industrial researchers attracted to its biofuel, food and nutraceutical applications. In this paper, recent developments in cell-disruption and lipid-extraction methods, focusing on four biotechnologically important microalgal species (namely, Chlamydomonas , Haematococcus , Chlorella , and Nannochloropsis spp.), are reviewed. The structural diversity and rigidity of microalgal cell walls complicate the development of efficient downstream processing methods for cell-disruption and subsequent recovery of intracellular lipid and pigment components. Various mechanical, chemical and biological cell-disruption methods are discussed in detail and compared based on microalgal species and status (wet/dried), scale, energy consumption, efficiency, solvent extraction, and synergistic combinations. The challenges and prospects of the downstream processes for the future development of eco-friendly and economical microalgal biorefineries also are outlined herein. [ABSTRACT FROM AUTHOR]

Open cultivation systems are the most economic option for microalgal biomass production but their harvesting cost, bacterial invasion, and water usage are still deterring large-scale applications. Therefore, in this study, low-cost techniques for harvesting, bacterial disinfection, and medium recycling were sequentially implemented for Ettlia sp. For harvesting, the employed auto-flocculation harvested 96% of algae but was not able to remove bacteria that invaded during cultivation. For this reason, hydrodynamic treatment was applied as a bacterial disinfection method for medium recycling, and treated up to 100% of the bacteria in the supernatant. Afterward, the supernatant was replenished with nutrients and reused to grow microalgae. In medium-recycled cultivation, auto-flocculation recycled (AR) medium showed the highest final biomass concentration of 3.84 g L−1, while the centrifugation recycled (CR) medium and the fresh medium (FM) resulted in 3.78 and 3.67 g L−1, respectively. In addition, the lipid content of the AR group was highly increased to 20.4%, resulting in the highest lipid productivity of 0.11 g L−1 d−1. Moreover, an analysis of fatty acid methyl ester compositions confirmed that 76.6% of lipid from the AR group were mainly composed of C16-C18, which are suitable for biodiesel. Consequently, the results showed that the implementation of low-cost techniques not only reduced process costs and water usage but also enhances both the biomass and lipid productivities of the species. [Display omitted] • Low-cost harvesting, bacteria control, and medium recycling were combined. • Auto-flocculation harvested microalgae but left bacteria in the supernatant. • Hydrodynamic cavitation disinfected bacteria with low-energy consumption. • Biomass productivity of auto-flocculation recycled medium was slightly increased. • Auto-flocculation recycled medium resulted in 1.6-fold higher lipid productivity. [ABSTRACT FROM AUTHOR]

• Hydrolyzed H. tuberosus replaced fructose in heterotrophic Ettlia sp. cultivation. • Hydrolysates of algal residue replaced yeast extract as N source. • Sequential hydrolysis was developed to utilize C and N sources simultaneously. • Lipid productivity was enhanced with sequential hydrolysates medium. Heterotrophic cultivation of microalgae results in substantial productivity but requires significant nutrient input. Alternative sources of major nutrients such as C and N should be carefully selected to make heterotrophic production of microalgal biomass feasible. In this study, Helianthus tuberosus and lipid-extracted algae (LEA) were hydrolyzed with sulfuric acid to grow Ettlia sp. YC001. Hydrolysis of H. tuberosus with 0.3 N of sulfuric acid resulted in fructose yield of 0.51 g g−1 and glucose yield of 0.14 g g−1 at 80 °C in 1 h. Proteolysis of algal residue with 2 N of sulfuric acid resulted in amino acid yield of 0.38 g g−1 at 110 °C in 24 h. To simplify the production of hydrolysates, the hydrolysis conditions were combined to establish a tailored sequential hydrolysis process. Then, simultaneous neutralization and salt removal of the hydrolysates were done with barium hydroxide. Consequently, cultivation of Ettlia sp. with the diluted sequential hydrolysate of H. tuberosus and LEA successfully achieved 5.90 g L−1 d−1 of biomass productivity and 1.42 g L−1 d−1 of lipid productivity with Ettlia sp. [ABSTRACT FROM AUTHOR]

• Rapid induction of lipids in Chlorella by mild electric treatment (31 mA and 4 h). • 2.1-fold improvement of triacylglycerol (TAG) content relative to the control. • Promotion of biosynthesis of polyunsaturated linoleic and linolenic acids. • Electric lipid stimulation through transformation and de novo biosynthesis. In this work, a new stress-based method for rapid induction of triacylglycerol (TAG) and total and polyunsaturated fatty acid accumulations in Chlorella sp. by mild electric stimulation is presented. When a cathodic current of 31 mA (voltage: 4 V) was applied to the algal cells for 4 h, the TAG content of the electro-treated cells was sharply increased to a level 2.1 times that of the untreated control. The contents of the polyunsaturated linoleic (C18:2n6) and linolenic (C18:3n3) acids in the electro-treated cells were also 36 and 57% higher than those in the untreated cells, respectively. Cyclic voltammetry and various biochemical analyses indicate that TAG and fatty acid formations are electro-stimulated via de novo fatty acid biosynthesis and metabolic transformation in the Chlorella cells. [ABSTRACT FROM AUTHOR]