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Arthrospira platensis, a well-known cyanobacterium, is widely applied not only in human and animal nutrition but also in cosmetics for its high amounts of active products. The biochemical composition plays a key role in the application performance of the Arthrospira biomass. The present study aimed to evaluate the growth and biochemical composition characteristics of A. platensis, cultured with a nitrogen-free and seawater-supplemented medium in an outdoor raceway pond in winter. The results showed that the biomass yield could achieve 222.42 g m−2, and the carbohydrate content increased by 247% at the end of the culture period (26 d), compared with that of the starter culture. The daily and annual areal productivities were 3.96 g m−2 d−1 and 14.44 ton ha−1 yr−1 for biomass and 2.88 g m−2 d−1 and 10.53 ton ha−1 yr−1 for carbohydrates, respectively. On the contrary, a profound reduction was observed in protein, lipid, and pigment contents. Glucose, the main monosaccharide in the A. platensis biomass, increased from 77.81% to 93.75% of total monosaccharides. Based on these results, large-scale production of carbohydrate-rich A. platensis biomass was achieved via a low-cost culture, involving simultaneous nitrogen deficiency and supplementary seawater in winter.

Mass cultivation of photosynthetic microalgae combined with mitigation of carbon dioxide (CO 2 ) emissions from industrial off-gases to produce lipids as a biodiesel feedstock can help environmental sustainability. However, traditional open microalgae mass cultivation systems that use sunlight are typically no more than 30 cm deep due to light attenuation and self-shading by the mircroalgae and, therefore, have low CO 2 uptake efficiency due to their shallow depth. To address this issue, a non-energy consuming light guide was employed to diffuse light deep into a top-lit, 120 cm deep open gas-lift cultivation system. This gas-lift system has been already shown to increase areal biomass productivity by 60%. Without any increase in supplied light energy, the light guide enhanced light penetration into the bioreactor and resulted in further increases in biomass and lipid productivities per unit area of 33% and 16%, respectively. The factors influencing light and CO 2 absorption rates were investigated with a Plackett-Burman experimental design. Mathematical models for predicting biomass and lipid production as well as optimal bioreactor configurations for maximizing lipid production and minimizing production costs were then determined by applying response surface methodology. The optimum configuration of operational parameters identified by the optimization function was then verified in the gas-lift bioreactor equipped with the light guide and resulted in areal biomass productivity of 34.4 g dw /m 2 day and areal lipid production of 223.9 g Lipid /m 2 . [ABSTRACT FROM AUTHOR]

The effect of biomass concentration on areal productivity and photosynthetic efficiency of Nannochloropsis sp. CCAP211/78 was studied in three outdoor pilot-scale photobioreactors: an open raceway pond (OPR), a horizontal tubular (HT) photobioreactor and a vertically stacked horizontal tubular (VT) photobioreactor. The reactors were operated continuously as turbidostat at different biomass concentrations. For all systems highest areal productivities were obtained on days with a high light intensity, while the highest photosynthetic efficiencies were obtained on days with a low light intensity. Ground areal biomass concentration exceeding 51 g m − 2 had a negative effect on the areal productivity and photosynthetic efficiency. No significant effect of biomass concentration on the productivity was found for the HT at ground areal biomass concentration lower than 51 g m − 2 . Also for the VT, no significant effect of biomass concentration was found with the exception of the highest biomass concentration of 2.0 g L − 1 (68 g m − 2 ) resulting in decreased productivity. For the open raceway pond the highest biomass concentration (0.5 g L − 1 or 94 g m − 2 ) resulted in significantly lower areal productivity, compared to the lower biomass concentration (0.25 g L 47 g m − 2 ). Highest areal productivities were obtained for OPR and VT, most likely due to more efficient light interception. In this study we observed that night biomass loss was coupled to net growth. At lower biomass concentrations and concomitant higher growth rates the specific biomass loss rate was higher. Microalgal specific light absorption coefficient was correlated to biomass concentration; higher biomass concentrations resulted in higher specific absorption coefficients, resulting in a steeper light gradient in the microalgal cultures. [ABSTRACT FROM AUTHOR]

Semi-continuous algal cultivation was completed in outdoor flat-panel photobioreactors (panels) and open raceway ponds (raceways) from February 17 to May 7, 2015 for side-by-side comparison of areal productivities at the Arizona Center for Algae Technology and Innovation in Mesa, AZ, USA. Experiments used two strains of Scenedesmus acutus (strains LB 0414 and LB 0424) to assess productivity, areal density, nutrient removal, and harvest volume across cultivation systems and algal strains. Panels showed an average biomass productivity of 19.0 ± 0.6 g m day compared to 6.62 ± 2.3 g m day for raceways. Photosynthetic efficiency ranged between 1.32 and 2.24 % for panels and between 0.30 and 0.68 % for raceways. Panels showed an average nitrogen consumption rate of 38.4 ± 8.6 mg N L day. Cultivation in raceways showed a consumption rate of 3.8 ± 2.5 and 7.1 ± 4.2 mg N L day for February/March and April/May, respectively, due to increase in biomass productivity. Excess nutrients were required to prevent a decrease in productivity. Daily biomass harvest volumes between 18 and 36 % from panels did not affect culture productivity, but density decreased with increased harvest volume. High cultivation temperatures above 30 °C caused strain LB 0414 to lyse and crash. Strain LB 0424 did not show any difference in biomass productivity when peak temperatures reached 34, 38, or 42 °C, but showed decreased productivity when the peak temperature during cultivation was 30 °C. Using algal strains with different temperature tolerances can generate increased annual biomass productivity. [ABSTRACT FROM AUTHOR]

Lipid accumulation is critical in the production of biodiesel from microalgae. However, little work has been done on the assessment of lipid accumulation during nitrogen stress in large research-scale outdoor raceways during different seasons; most values for lipid accumulation are assumptions based on work completed in laboratory settings or outdoor photobioreactors. This study focused on the use of raceway ponds operated in batch cultivation mode with an area of 30.37 m to determine the impacts of nitrate-nitrogen concentration and cultivation depth on the ability of Scenedesmus acutus strain LB 0414 to accumulate lipids. A concentration of less than 60 mg N-NO L was required for removal of nitrogen in the cultivation medium within 8 days to stimulate lipid accumulation and increase lipid productivity. When nitrate concentrations were increased to prevent nitrogen depletion, lipid productivity decreased, which demonstrates that stressing is needed to induce lipid accumulation for increased lipid productivity. Additionally, decreasing cultivation depth below 9 cm, compared to raceways operated at a depth of 20-24 cm, increased lipid productivity by 62 % in December 2014 and 38 % in February 2015. More desirable environmental conditions, mainly increased sunlight and temperature, in February, increased biodiesel productivity for all raceways and account for the decrease in productivity differences. This research highlights increased lipid productivity found by reducing cultivation depth and nitrogen concentrations in outdoor raceways and provides insight into the optimal conditions for large-scale biodiesel production. [ABSTRACT FROM AUTHOR]

Background: Microalgae are a potential source of sustainable commodities of fuels, chemicals and food and feed additives. The current high production costs, as a result of the low areal productivities, limit the application of microalgae in industry. A first step is determining how the different production system designs relate to each other under identical climate conditions. The productivity and photosynthetic efficiency of Nannochloropsis sp. CCAP 211/78 cultivated in four different outdoor continuously operated pilot-scale photobioreactors under the same climatological conditions were compared. The optimal dilution rate was determined for each photobioreactor by operation of the different photobioreactors at different dilution rates. Results: In vertical photobioreactors, higher areal productivities and photosynthetic efficiencies, 19-24 g m-2 day-1 and 2.4-4.2 %, respectively, were found in comparison to the horizontal systems; 12-15 g m-2 day-1 and 1.5-1.8 %. The higher ground areal productivity in the vertical systems could be explained by light dilution in combination with a higher light capture. In the raceway pond low productivities were obtained, due to the long optical path in this system. Areal productivities in all systems increased with increasing photon flux densities up to a photon flux density of 30 mol m-2 day-1. Photosynthetic efficiencies remained constant in all systems with increasing photon flux densities. The highest photosynthetic efficiencies obtained were; 4.2 % for the vertical tubular photobioreactor, 3.8 % for the flat panel reactor, 1.8 % for the horizontal tubular reactor, and 1.5 % for the open raceway pond. Conclusions: Vertical photobioreactors resulted in higher areal productivities than horizontal photobioreactors because of the lower incident photon flux densities on the reactor surface. The flat panel photobioreactor resulted, among the vertical photobioreactors studied, in the highest average photosynthetic efficiency, areal and volumetric productivities due to the short optical path. Photobioreactor light interception should be further optimized to maximize ground areal productivity and photosynthetic efficiency. [ABSTRACT FROM AUTHOR]

Arthrospira platensis, a well-known cyanobacterium, is widely applied not only in human and animal nutrition but also in cosmetics for its high amounts of active products. The biochemical composition plays a key role in the application performance of the Arthrospira biomass. The present study aimed to evaluate the growth and biochemical composition characteristics of A. platensis, cultured with a nitrogen-free and seawater-supplemented medium in an outdoor raceway pond in winter. The results showed that the biomass yield could achieve 222.42 g m−2, and the carbohydrate content increased by 247% at the end of the culture period (26 d), compared with that of the starter culture. The daily and annual areal productivities were 3.96 g m−2 d−1 and 14.44 ton ha−1 yr−1 for biomass and 2.88 g m−2 d−1 and 10.53 ton ha−1 yr−1 for carbohydrates, respectively. On the contrary, a profound reduction was observed in protein, lipid, and pigment contents. Glucose, the main monosaccharide in the A. platensis biomass, increased from 77.81% to 93.75% of total monosaccharides. Based on these results, large-scale production of carbohydrate-rich A. platensis biomass was achieved via a low-cost culture, involving simultaneous nitrogen deficiency and supplementary seawater in winter. [ABSTRACT FROM AUTHOR]

This work concerns an attempt to develop large scalecultivation of Porphyridium sp. outdoors. Theimpact on cell growth and production of solublesulphated polysaccharides of light-path length (LP)was studied in flat plate glass reactors outdoors. TheLP of the plate reactors ranged from 1.3–30 cm,corresponding to culture volumes of 3–72 L. The sidewalls of all reactors were covered, ensuring similarilluminated surfaces for all reactors. Maximal daytemperature was maintained at 26 ±1 °C.Growth conditions of pH (7.5), stirring (withcompressed air) and mineral nutrients, were optimal.Maximal volumetric concentration of the soluble sulfated polysaccharide (1.32 g L-1) was obtained in winter with the smallest light-pathreactor (1.3 cm ) at a cell density of 1.37 ×1011cells L-1. Under these conditions, theviscosity of the culture medium was also highest,being inversely proportional to the culture'slight-path. Highest areal concentration of solublepolysaccharides (60 g m-2) and areal cell density(3.01 × 1012m-2) was recorded in the 20 cmLP reactor, progressively lower values being obtainedas the light path became shorter. A similar patternwas obtained for the areal productivity ofpolysaccharides, the highest being 4.15 g m-2day-1 (considering the total illuminated reactorsurface), produced in the 20-cm LP reactor.The main sugar composition (i.e. xylose, galactose andglucose) of the sulfated polysaccharides was similarin all reactors. As viscosity increased with timeduring culture growth, there was a substantial declinein bacterial population. Cultivation throughout mostof the year provided good evidence that a light pathlength of 20 cm in flat plate reactors under theseconditions is optimal for maximal areal solublepolysaccharide production of Porphyridium sp. [ABSTRACT FROM AUTHOR]

There is increasing demand for essential fatty acids (EFAs) from non-fish sources such as microalgae, which are considered a renewable and sustainable biomass. The open raceway system (ORS) is an affordable system for microalgae biomass cultivation for industrial applications. However, seasonal variations in weather can affect biomass productivity and the quality of microalgal biomass. The aim of this study was to determine the feasibility of year-round Tetraselmis sp. cultivation in a semi-ORS in Korea for biomass and bioactive lipid production. To maximize biomass productivity of Tetraselmis sp., f medium was selected because it resulted in a significantly higher biomass productivity (1.64 ± 0.03 g/L) and lower omega-6/omega-3 ratio (0.52/1) under laboratory conditions than f/2 medium (0.70/1). Then, we used climatic data-based building information modeling technology to construct a pilot plant of six semi-ORSs for controlling culture conditions, each with a culture volume of 40,000 L. Over 1 year, there were no significant variations in monthly biomass productivity, fatty acid composition, or the omega-6/omega-3 ratio; however, the lipid content correlated significantly with photosynthetic photon flux density. During year-round cultivation from November 2014 to October 2017, areal productivity was gradually increased by increasing medium salinity and injecting CO2 gas into the culture medium. Productivity peaked at 44.01 g/m2/d in October 2017. Throughout the trials, there were no significant differences in average lipid content, which was 14.88 ± 1.26%, 14.73 ± 2.44%, 12.81 ± 2.82%, and 13.63 ± 3.42% in 2014, 2015, 2016, and 2017, respectively. Our results demonstrated that high biomass productivity and constant lipid content can be sustainably maintained under Korean climate conditions. [ABSTRACT FROM AUTHOR]

Microalgae provide a powerful solar driven biotechnology platform for the production of the increasing quantity of food, fuel, high value products, fine chemicals and clean water required to supply our expanding global population. Light capture fuels all photosynthetically driven microalgae processes and consequently, maximizing light capture efficiency at minimal cost is central to process design. Raceway-style and paddle wheel operated open ponds, also known as high rate ponds (HRP 0), are widely used, easy to operate and offer low-cost evaporative cooling compared to energy intensive closed systems. Here, the concept of delivering light from the surface into greater depths of the algae solution was tested at pilot-scale, by fitting a standard HRP 0 with light transmitting guides designed to allow the capture of sunlight between ~10:00 am and ~3:00 pm to improve light distribution throughout the depth of the solution (HRP+). This prototype (HRP+) was analyzed to compare light distribution and biomass production efficiency against two control systems in two separate experiments such as: 1) a standard High Rate Pond (HRP 0), and 2) a standard HRP 0 fitted with no light transmitting dummy guides (HRP-) to maintain comparable fluid dynamics system characteristics. Under semi-continuous cultivation, HRP+ showed a significantly improved light distribution within the culture compared to the HRP- when operated at moderate to high densities. An increased proportion of the culture in the HRP+ was kept within the desired optimal photosynthetic zones while dark zones (unfit for photosynthesis and causing biomass loss) were drastically reduced compared to the HRP-. The HRP+ system exhibited a 3.9-fold higher maximum areal productivity of 49.2 ± 8.3 g·m−2·d−1 compared to HRP- (March–April 2018). Overall, this study establishes proof-of-concept of the functionality of light guides to improve light distribution and productivities in microalgae cultivation systems compared to the control systems run at the same incident light levels. • The light guides improve light distribution along the high rate pond cross-section. • The light guides increase the photon conversion efficiency and yield of the system. • At high culture densities, light guides reduce dark zones and respiration loss. • Light guides can increase photosynthetic zone without altering photo-inhibitory zone. • Using light guides lowers operational footprint and harvesting costs. [ABSTRACT FROM AUTHOR]