Energy innovation potential of oleaginous microalgae

Figures & data

Figure 1.  Diatom cells including lipid bodies (shown by arrows) in their cytoplasm.

Figure 2.  Hydrocarbon molecules produced by the chemical race B of Botryococcus braunii and Aurantiochytrium.

(A) C₃₀ botryococcene, (B) squalene and (C) main biosynthetic pathway of botryococcene and squalene. 1) Squalene synthase gene, BSS; 2) squalene synthase-like gene, SSL-1; 3) squalene synthase-like gene, SSL-2; 4) squalene synthase-like gene, SSL-3.

CoA: Coenzyme A.

Figure 3.  Oil-accumulating colony of Botryococcus braunii (race B).

(A) Differential interference contrast microscopy. (B) Fluorescence microscopy of Nile red-stained colony. Nonpolar lipids including botryococcene show bright yellow fluorescence. Red fluorescence is autofluorescence derived from chlorophylls in chloroplasts.

Figure 4.  Oil-accumulating cells of Aurantiochytrium sp. strain 18W-13a.

(A) Differential interference contrast microscopy. (B) Fluorescence microscopy of Nile red-stained cells. Yellow fluorescence indicates nonpolar lipids including squalene. Peripheral red fluorescence indicates phospholipids, the major component of the cell membrane.

Figure 5.  Cultures of Botryococcus.

(A) Laboratory-scale seed culture. (B) The 480-l-scale tube bioreactor system.

Figure 6.  World energy demand and oil supply potential of algal plants.

Traditional fuel includes oil, gas and coal. Traditional biofuels include oil and alcohol from rapeseeds, corn, palm oil and sugarcane.

Reproduced with permission from [76].

Table 1.  Oil-producing algae.

Algae	Oil content (% dry cell weight)	Biomass productivity (g/l/day)	Oil productivity (g/l/day)	Useful oil component
Botryococcus braunii	25–75 [6]	0.125 [85]	0.036 [85]	Hydrocarbon
Aurantiochytrium sp.	25 [36]	1.625 [36]	0.975 [36]	Hydrocarbon
Chlorella spp.	28–31 [6]	0.23 [86]	0.044 [86]	TAG
Dunaliella spp.	23 [6]	0.75 [87]	0.12 [87]	TAG
Nannochloropsis spp.	31–68 [6]	0.75 [88]	0.28 [88]	Fatty acid
Neochloris oleoabundans	35–54 [6]	0.40 [89]	0.13 [89]	TAG
Phaeodactylum tricornutum	20–30 [6]	0.24 [86]	0.044 [86]	TAG, fatty acid
Pseudochoricystis ellipsoidea	32 [90]	3.46 [90]	NA	TAG
Euglena gracilis	<31 [91]	NA	NA	Wax ester

NA: Not available; TAG: Triacylglycerol.

Table 2.  Biomass and lipid productivities of microalgae cultured in wastewaters.

Wastewaters	Microalgae	Nutrient removal from wastewater			Biomass yield (g/l)	Biomass productivity (mg/l/day)	Lipid content (% biomass)	Lipid productivity (mg/l/day)	Ref.
		Nitrogen	Phosphorus	Other nutrient
Municipal wastewater
Concentrated municipal wastewater	Chlorella kessleri Chlorella protothecoides	ND ND	ND ND	ND ND	2.01 1.31	402 262	ND ND	ND ND	[46]
Secondary urban wastewater	Botryococcus braunii	ND	ND	ND	ND	345.6^†	17.85 (TL) 1.91 (HC)	6.17^† (TL) 6.60^† (HC)	[47]
Secondary domestic wastewater	B. braunii	NO3^2- 79.63%	PO4^3-100%	ND	0.48 (after 14 days) 1.88 (over 14 days)	34.3^‡	36.14 (TL)	12.4^‡ (TL)	[49]
Concentrated municipal wastewater	Five strains of Chlorella sp., Heynigia sp., Hindakia sp., Micractinium sp. and Scenedesmus sp.	ND	ND	TOC 82.27–96.18%^§	ND	231.4–275.0	28.30–33.53 (TL)	74.5–77.8 (TL)	[48]
Concentrated municipal wastewater	Auxenochlorella protothecoides	TN 90.60% NH4^+-N 100%	TP 98.48%	COD 79.10%	1.12 (first stage) 1.16 (second stage)	ND ND	28.90 (TL) 33.22 (TL)	ND ND	[50]
Agricultural wastewater
Secondary piggery wastewater	B. braunii	NO3^--N 80% (620 mg/l )	ND	ND	8.5	708.3	ND	79.2^¶ (HC)	[51]
Pretreated piggery wastewater	Chlorella vulgaris	TN 10–54 mg/l NH4^+-N 6– 42 mg/l NO3^--N 0.2–19 mg/l NO2^--N 2–16 mg/l	TP 4.8–12.5 mg/l	COD 17–67 mg/l	0.2–1.14	6.67–38.0	28 (TL) 3–43 (TFA)	ND	[52]
Primary piggery wastewater	Chlorella pyrenoidosa	TN 54.7–74.6% NH4^+-N 91.2–95.1%	TP 31.0–77.7%	COD 36.5–57.6%	ND	ND	ND	6.3 (TL)	[54]
Anaerobic digested dairy manure	Chlorella sp.	TN 75.7–82.5% NH4^+-N 100%	TP 62.5–74.7%	COD 27.4–38.4%	1.47–1.71	70.0–81.4^#	9.00–13.7 (TFA)	6.7–11.1^†† (TFA)	[53]
Industrial wastewater
Carpet mill wastewater	B. braunii Chlorella saccharophila Dunaliella tertiolecta Pleurocystis carterae Consortium	ND ND ND ND NO3^--N 99.7–99.8%	ND ND ND ND PO4^3--P 96.6–99.1%	ND ND ND ND ND	ND ND ND ND ND	34 23 28 33 39	13.20 (TL) 18.10 (TL) 15.20 (TL) 12.00 (TL) 12.00 (TL)	4.5^‡‡ (TL) 4.2^‡‡ (TL) 4.3^‡‡ (TL) 4.0^‡‡ (TL) 4.7^‡‡ (TL)	[56]
Soybean processing wastewater	C. pyrenoidosa	TN 88.8% NH4^+-N 89.1%	TP 70.3%	SCOD 77.8%	ND	640	37 (TL)	400 (TL)	[57]
Shochu distillery wastewater	Schizochytrium sp.	TN 67%	ND	COD 35% Crude protein 67% Total free amino acid 87%	ND	ND	25.8 (TFA)	850^§§ (DHA)	[58]
Soybean curd wastewater	B. braunii	ND	ND	ND	2.92	73	23.84 (HC)	17.4^¶¶(HC)	[44]

^†Estimated from biomass value of 14.4 mg/dm^-3/h.

^‡Estimated from biomass value of 0.48 g/l after 14 days.

^§Values from all selected 17 strains.

^¶Estimated from biomass value of 0.95 g/l after 12 days.

^#Estimated from biomass values of 1.47 and 1.71 g/l after 21 days, respectively.

^††Estimated from biomass values of 0.141 and 0.233 g/l after 21 days, respectively.

^‡‡Estimated from biomass productivity and lipid content value.

^§§Estimated from biomass value of 3.4 g/l after 4 days.

^¶¶Estimated from biomass value of 696.3 mg/l after 40 days.

COD: Chemical oxygen demand; DHA: Docosahexaenoic acid; HC: Hydrocarbon; ND: Not determined; SCOD: Soluble chemical oxygen demand; TFA: Total fatty acid; TL: Total lipid; TN: Total nitrogen; TOC: Total organic carbon; TP: Total phosphorus.

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