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Algal technology has potential to combat the global energy crisis, malnutrition, and production of several value added products useful for the mankind. The cost effective cultivation system is the basis to realize this goal. Microalgal production in raceway ponds seems to be most promising, especially in the large scale. Several environmental (location of the cultivation system, rainfall, solar radiation, etc.), engineering (pond depth, CO 2 delivery system, methods of mixing, power consumption, etc.), and biological (light, pH, oxygen accumulation, salinity, Algal predators etc.) parameters affect the biomass productivity in the open pond system. Vertical mixing is an important criteria influencing the algal growth compared to axial mixing as it determines the frequency by which cell will travel from bottom (dark zone) to surface (light zone) of the open pond. Therefore, different research works on the various designs of raceway ponds were mostly focused towards enhancing the vertical mixing (e.g. Design of bend and surface geometry, engineering flow field, etc.) and CO 2 residence time (e.g. Closed, sump, airlift driven raceway ponds etc.). The present study summarizes the current state of knowledge for the biomass production in raceway ponds. [ABSTRACT FROM AUTHOR]

In this work, the effects of several factors, such as temperature, reaction time, and solvent and acid quantity on in situ transesterification yield of wet Nannochloropsis salina were investigated. Under equivalent total solvent volume to biomass ratio, pure alcohol showed higher yield compared to alcohol–chloroform solvent. For esterifying 200 mg of wet cells, 2 ml of methanol and 1 ml of ethanol was sufficient to complete in situ transesterification. Under temperatures of 105 °C or higher, 2.5% and 5% concentrations of sulfuric acid was able to successfully convert more than 90% of lipid within 30 min when methanol and ethanol was used as solvents respectively. Also, it was verified that the optimal condition found in small-scale experiments is applicable to larger scale using 2 L scale reactor as well. [ABSTRACT FROM AUTHOR]

An interest in biodiesel as an alternative fuel for diesel engines has been increasing because of the issue of petroleum depletion and environmental concerns related to massive carbon dioxide emissions. Researchers are strongly driven to pursue the next generation of vegetable oil-based biodiesel. Oleaginous microalgae are considered to be a promising alternative oil source. To commercialize microalgal biodiesel, cost reductions in oil extraction and downstream biodiesel conversion are stressed. Herein, starting from an investigation of oil extraction from wet microalgae, a review is conducted of transesterification using enzymes, homogeneous and heterogeneous catalysts, and yield enhancement by ultrasound, microwave, and supercritical process. In particular, there is a focus on direct transesterification as a simple and energy efficient process that omits a separate oil extraction step and utilizes wet microalgal biomass; however, it is still necessary to consider issues such as the purification of microalgal oils and upgrading of biodiesel properties. [ABSTRACT FROM AUTHOR]

Mass cultivation of microalgae is necessary to achieve economically feasible production of microalgal biodiesel, but the high cost of nutrients is a major limitation. In this study, orange peel extract (OPE) was used as an inorganic and organic nutrient source for the cultivation of Chlorella vulgaris OW-01. Chemical composition analysis of the OPE indicated that it contains sufficient nutrients for mixotrophic cultivation of C. vulgaris OW-01. Analysis of biomass and FAME production showed that microalgae grown in OPE medium produced 3.4-times more biomass and 4.5-times more fatty acid methyl esters (FAMEs) than cells cultured in glucose-supplemented BG 11 medium (BG-G). These results suggest that growth of microalgae in an OPE-supplemented medium increases lipid production and that OPE has potential for use in the mass cultivation of microalgae. [ABSTRACT FROM AUTHOR]

Microalgal cultivation has been limited by the efficiency and costs associated with providing light energy, the most expensive and essential element needed for microalgal growth to a culture, particularly to cultures grown in a photo bioreactor (PBR). This study examined the economic benefits of using flashing illumination conditions in the context of microalgal cultivation. Chlamydomonas reinhardtii was cultivated under various conditions, including various inoculum sizes, light intensities, and durations of the light and dark periods. Our results showed that the highest microalgal growth efficiencies could be obtained using a large inoculum size under high intensity illumination accompanied by a 1:1 ratio of light and dark periods. The duration of the flashing light period was further optimized; permitting light energy savings of 62.5% of the light energy expended under continuous illumination conditions without reducing the biomass or lipid productivity. This study provides a more economical approach to cultivating C. reinhardtii via optimized flashing illumination without sacrificing microalgal growth or lipid content. [ABSTRACT FROM AUTHOR]

The synthesis of aminoclays with Mg2+ or Fe3+, placed in metal centers by sol–gel reaction with 3-aminopropyltriethoxysilane (APTES) as a precursor, is demonstrated, producing –(CH2)3NH2 organo-functional pendants which are covalent-bonding onto cationic metals. The protonated amine groups in aqueous solution lead the efficient sedimentation (harvesting) of microalgae biomass within approximately 5 min and 120 min for fresh and marine species, respectively. To our surprise, the aminoclays did not depend on microalgae species or media for microalgae harvesting. In particular, the harvesting efficiency (%) of microalgae was not decreased in a wide pH region. The harvesting mechanism can be explained by the sweep flocculation of microalgae, which is confirmed by measurement of zeta potential of aminoclay in aqueous solution where aminoclay shows a positively charged surface in a wide pH region. In order to reduce the cost of aminoclays and to make the harvesting procedures simple, the membrane process using aminoclay-coated cotton filter is introduced for the treatment of 1 L-scale microalgae stocks. It is successfully performed with three recycles using the same aminoclay-coated cotton filter after removing the harvested microalgae biomass. Conclusively, the aminoclay-based microalgae harvesting systems are a promising means of reducing the cost of downstream processes in microalgae-based biorefinery. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, spent yeast from a brewery was used as the growth substrate for the docosahexaenoic acid (DHA)-rich microalga, Aurantiochytrium sp. KRS101. A significant biomass yield (6.69g/l/d) was obtained using only spent yeast as the growth substrate, with simple stirring as pretreatment. Maximization of nutrient utilization through the use of stepwise cultivation increased the yield to 31.8g/l of biomass. DHA constituted 38.2% (w/w) of the total fatty acids, and the highest DHA productivity was observed when the C/N ratio was 20:1 (w/w). Spent yeast thus served as a good growth substrate for the production of DHA. Economic assessment revealed that stepwise cultivation using spent yeast as either the sole growth substrate or as a nutrient source could substantially reduce the production cost of microalgal DHA. [Copyright &y& Elsevier]