Supplementary material
Light emitting diodes (LEDs) applied to microalgal production
Peter S.C. Schulze1,2, Luísa A. Barreira1, Hugo G.C. Pereira1, José A. Perales2 and João C.S. Varela1,*
1 - Centre of Marine Sciences, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
2 - Centro Andaluz de Ciencia y Tecnología Marinas, University of Cadiz, Campus Universitario de Puerto Real, Cádiz, Spain
•Corresponding author: Varela, J.C.S. ().
Table S1 Impacts of light quality in microalgal growth parameters and preferred growth wavelengths (λmax) of several algae classified according to Keeling [S1] and percentage of diminished biomass production under alternative wavelengths (λmin).
Microalga / λmax (nm) / λmin (nm) / % less at λmin / Outcome / Refs.Cyanobacteria
Synechocystis sp. PCC 6803 / 612
620
660 / 535
470 / n.i. / LEDs peaking at 612, 620 and 660 nm showed better growth than green (535 nm) and blue (470 nm) LEDs. / [S2]
Arthrospira platensis / [620–
645] / [460–
475] / 75 / Arthrospira platensis (syn. Spirulina platensis) grown under red light showed higher growth rates. / [S3]
Arthrospira platensis / 630 / 470 / 80 / Red LED light was considered to be the most effective light source for photoautotrophic cultivation compared to blue, green, yellow and white LEDs. Red LEDs gave rise to the highest growth rates and biomass production at light intensities of 300-3000 µmol m−2 s−1 as compared to blue LEDs. Green LEDs obtained higher biomass production than blue LEDs. / [S4]
Chlorophytes
Acutodesmus obliquus CNW-N / 660 470 / s / - / Acutodesmus obliquus (syn. Scenedesmus obliquus) showed always lower biomass production under blue (470 nm) LEDs as compared to red, green and white (daylight) LEDs. Furthermore, A. obliquus FSP-3 grown under FLs showed higher biomass production than under white (daylight) LEDs. / [S5]
Acutodesmus obliquus FSP-3 / 660
470 / s / -
Botryococcus braunii Bot-144 / 660 / 470a / 21 / Carbon fixation was highest under blue light. Red LED more effective regarding the supplied optical energy. Shapes of aggregates changed between blue and red LEDs. / [S6]
Chlorella kasseri / 660 / 470 / 18 / Red LEDs produced highest number of cells with highest weight, blue LEDs led to increased cell size. / [S7]
Table S1 (Continued).
Microalga / λmax (nm) / λmin (nm) / % less at λmin / Outcome / Refs. /Chlorella sp. / 660 / 460 / 7 / White LED light resulted in slightly more biomass than blue or red LED light alone. Mixed LED light (red : blue; 1:9, 3:7, 5:5, 7:3, 9:1) showed always higher biomass production than white, red or blue light alone, whereas a ratio of 5:5 showed highest, 32% more, biomass production than red light alone. / [S8] /
Chlorella pyrenoidosa / 660 / n.i. / - / No need for additional blue light. Photosynthesis only slightly affected by flashing LEDs (5ns on-cycle, 45ns off-cycle). / [S9] /
Chlorella sp. / 660 / 460 / 37 / Red LEDs most effective in nutrient removal from agriculture digestates and growth as compared to white, yellow (590 nm) and blue LEDs, in decreasing order. / [S10] /
Chlorella sp. / [650–680] / [440–470] / 21 / Mixotrophic culture of Chlorella sp. and Saccharomyces cerevisiae; Biomass productivity was highest under red followed by blue and green LEDs. / [S11] /
Chlorella sp. FC-21 / 660 / 450 / 27 / Red light was found to be the most suitable light source (2.5 times higher specific growth rate than FL). Mixed LEDs of red and blue (3:1) or additional white LED (1:1:1) did not increase the growth rate (no CO2 supplementation). / [S12] /
Chlorella vulgaris / n.i. / n.i. / - / Blue LEDs (420-450 nm) showed higher biomass production than FLs. / [S13] /
Chlorella vulgaris / 660 / 450 / 39 / Similar biomass production under red, white and yellow (590 nm) LEDs as well as blue and purple (410 nm). Green light showed lowest biomass production (65% less than the red LEDs). / [S14] /
Chlorella vulgaris / 625
660 / 470 / 56 / Red light is most efficient for nutrient removal. Blue light resulted in a 56% decrease of the growth rate and final biomass production. / [S8,S15] /
Table S1 (Continued).
Microalga / λmax (nm) / λmin (nm) / % less at λmin / Outcome / Refs. /Chlorella vulgaris / 430 / 625 / 70 / LEDs peaking at 625 nm not suitable to grow C. vulgaris. Mixing blue and red LEDs increased biomass production but was still 17% less than sole blue LED lights. / [S16] /
Dunaliella salina / 660 / n.i. / - / 25% blue photons with 75% red photons resulted in higher growth rate than only red light. / [S17] /
Haematococcus pluvialis / 470
421 / 625 / 3
15 / LEDs with emission peaks at 380, 421, 470 and 625 nm had higher volumetric productivity than FLs. Blue light induced cell growth arrest. / [S18] /
Haematococcus pluvialis / 470 / 625a / 45 / Blue LEDs, compared to red, green and white, evoked increases in cell size and growth kinetics. Blue light caused suppression of cell growth. White light less efficient than blue light. / [S19] /
Scenedesmus sp. / 670
450 / s / - / White light irradiated algae had a 45% higher production rate than those under single blue or red LEDs. When red light was mixed with blue light (almost regardless to the mixing ratios), production rates were 50 % higher than only under white light. / [S20] /
Mychonastes homosphaera / 660 / n.i. / - / Mychonastes homosphaera (syn. Chlorella minutissima) produced 8% less biomass under red and white LEDs compared to FLs. / [S21] /
Tetraselmis
suecica F&M-M33 / 624 / 470 / 50 / Biomass productivity equal between cool white LEDs and red LEDs as well as between green and blue LEDs, respectively. Approximately 75% more cells when grown under red light compared to those under white, blue and green LEDs. Furthermore, cells under red light were more motile and smaller. / [S22] /
Table S1 (Continued).
SAR: Stramenopiles /
Nannochloropsis
oceanica CY2 / 475
630 / s / - / N. oceanica CY2 showed similar biomass production under blue, red, yellow (~590 nm) and white LEDs thus was slightly higher under FLs. / [S23] /
Nannochloropsis sp. / 470 / 680 / 26 / Cells exposed to green LEDs (550 nm) showed higher growth rates than those under red LED light. / [S24] /
Phaeodactylum tricornutum / blue, ? / red,
? / 22 / Blue LED light results in NPQ and has higher photoprotective potential. Evidence found that diatoms need blue light to acclimatize to high light intensities. / [S25] /
Skeletonema costatum / 456 / 656a / 9 / With increasing spectrum absorption coefficientb among different LED light sources, growth rate increased and saturation of light quantity decreased. Cell numbers between green and red LED light were similar. / [S26] /
Achnanthes sp. / 450 / 650a / 44 / Blue LED light was more efficient in terms of net photosynthesis rates than FLs, yellow and red LEDs in all diatoms, especially for Nitzschia sp. Nitzschia sp. showed removal of dissolved inorganic nitrogen, dissolved inorganic phosphorus, acid volatile sulphide from growth medium in decreasing order as follows: blue LEDs > FLs > red LEDs > yellow LEDs. Blue light yielded highest chlorophyll content in Nitzschia sp. / [S27] /
Amphora sp. / 450 / 650a / 35 /
Navicula sp. / 450 / 650a / 33 /
Nitzschia sp. / 450 / 650a / 47 /
SAR: Alveolata /
Alexandrium
tamarense / 450 / 650a / 39 / Cells showed highest growth rate under blue LED light, followed by FL, red- and yellow LED light in decreasing order. / [S27] /
Table S1 (Continued).
Microalga / λmax (nm) / λmin (nm) / % less at λmin / Outcome / Refs. /Hacrobia: Haptophytes /
Isochrysis galbana / 460 / 660 / 80 / Blue light (470nm) was considered to be more economical than FLs. A mix of red and blue LEDs gave same optical density than fluorescent or sole blue light. / [S28] /
Isochrysis galbana / red,
? / blue,? / 32 / Flashed blue light provided highest biomass production compared to continuous FL as well as flashed red or white LEDs. Cell weight was not affected by light quality / [S29] /
Isochrysis sp. / n.i. / n.i. / - / Broad band blue light source obtained higher photosynthesis rate than white light. Cell concentration was similar between both light sources. / [S30] /
Abbreviations: a: growth rates; b: Spectrum absorption coefficient reveals the quantum efficiency of photosynthetic effective photons absorbed by microalgae. It also reflects the efficiency of a light source to promote growth of microalgae; FAME: fatty acid methyl esters; FLs: fluorescent lamps; n.i.: not investigated s: similar biomass production; SAR: Stramenopiles-Alveolata-Rhizaria megagroup.
Table S2 Comparison between LEDs and fluorescent lamps (FLs) largely based on data from ref. [S31,S32].
LEDs / Fluorescent lampsLED type / Value / FL type / Value
PCE (%)a / Blue (InGaN) / ~50 / Cool white T8 / 30
Red (AlGaInP) / ~40
Green (InGaN) / ~17b
Amber (AlGaInP) / ~8b
Cool white pc-LEDs / ~30
Lifetime (h)c / Standard LEDs / ~25,000-50,000; up to 100,000
(at T ≤ 70°C) / Standard FLs / ~12,000-20,000
Long lifetime FLs / ~50,000
Emission range(nm) / Single colour LEDs / FWHM: ~20 / Coloured and white FLs / 400–700
White LEDs
(pc-LEDs) / 400–700
Cost of
single illuminant
(€/Winput)d / SMD 5050 LED strips (60LEDs/m) / ≥0.5-1.6e / FL T8 lamps
(58 W) / ~0.1-0.3f
Cost of Complete
Systems
(€/Winput)c / High Power LED module / ~4-6g / FL T8 lamps
(58 W) / ~0.7-2h
Pros / Quick response (ns scale), allowing the flashing of LEDs at high frequencies; Tailored light design easy applicable. / Well established in microalgal production.
Cons / When heated up, efficiency and lifetime decreases drastically: AlGaInP-chips are more sensitive than InGaN to temperature. Cooling of LEDs is recommended if a high PPFD is achieved using high power LEDs or a high stock density;
Limited market for single colour LED lamps in photosynthetic efficient wavelengths (i.e. 430 nm and 660 nm). / FLs containing mercury, as being highly detrimental to the environment and difficult to recycle;
Electrodes can burn out, causing complete failure of the lamp.
a. Power conversion efficiency (PCE) only reveals the efficiency of an illuminant (glossary box); thus, the overall system efficiency (OSE) should also be considered, as it takes into account electrical drivers, reflectors, or rather every obstacle and electrical resistance between the input power source and the irradiated object (i.e. a photobioreactor) [S33]. FLs can have a much lower OSE than LEDs, considering that they release photons in all directions and reflectors are needed, absorbing optical energy, when light is required in only one direction. LEDs have already reflectors incorporated, where losses have already been considered in the PCE.
b. To increase the efficiency and thermal stability of LEDs, some LED manufactures are producing more efficient InGaN chips with a phosphor cover, converting the emitted blue photons into light within the green and amber wavelength ranges (i.e. Luxeon ® Rebel Phosphor-Converted (PC) Amber LED; http://philipslumileds.com) [S34,S35].
c. LED lifetimes may exceed the lifetimes of power converter. Many power converters have a lifetime of 30.000-50.0000 h (source: Osram constant current LED power supplies, http://osram.com).
d. Light sources are typically compared using Kilolumen (a measure of light intensity perceived by the human eye). Hence, as this comparison is unsuitable for photosynthetically purposes, the prices are given taking into account the input wattage of an illuminant. Suppliers are only examples; other suppliers might offer cheaper and more sustainable products.
e. e.g. http://okledlights.com; http://rs-online.com.
f. It depends on the supplier; http://rs-online.com.
g. e.g. Philips (green power LED production modules).
References:
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S3 Chen, H.-B. et al. (2010) Modeling on chlorophyll a and phycocyanin production by Spirulina platensis under various light-emitting diodes. Biochem. Eng. J. 53, 52-56
S4 Wang, C.-Y. et al. (2007) Effects of using light-emitting diodes on the cultivation of Spirulina platensis. Biochem. Eng. J. 37, 21-25
S5 Ho, S.-H. et al. (2014) Enhancing lutein productivity of an indigenous microalga Scenedesmus obliquus FSP-3 using light-related strategies. Bioresource Technol. 152, 275-282
S6 Baba, M. et al. (2012) Wavelength specificity of growth, photosynthesis, and hydrocarbon production in the oil-producing green alga Botryococcus braunii. Bioresource Technol. 109, 266-270
S7 Koc, C. et al. (2013) Use of red and blue Light-emitting diodes (LED) and fluorescent lamps to grow microalgae in a photobioreactor. Israel J. Aquacult. 65. IJA_65.2013.797
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