Bio-processing of algal bio-refinery: a review on current advances and future perspectives

Figures & data

Figure 1. Bio-fuel production from microalgae biomass.

Table 1. Application of thermochemical conversion on microalgal feedstock.

Thermochemical conversion technology	Microalgae species	Process conditions	Results	Ref
Slow pyrolysis	Chlorella protothecoides	1 g of sample, 5.5 ml stainless steel autoclave, 200-600°C, 5–120 min	Maximum oil yield of 52% at 500°C and 5 mins of operation time	[124]
	Nannochloropsis sp. after lipid extraction	1 g of sample, HZSM-5/sample (0/1-1/1), 300-500°C, 10°C/min for 2h, nitrogen at 30ml/min	Maximum oil yield of 31.1% at 400°C. Higher heating value of 32.2 MJ/kg and lower oxygen content compared to direct pyrolysis.	[125]
	Defatted & raw Scenedesmus sp. and Spirulina	100 g of sample, 450°C at 50°C/min, 2 h, nitrogen as carrier gas at 100ml/min	Higher heating value in range of 35.2–36.7 MJ/kg observed. Bio-oil yield in the range of 24-31%	[126]
	Tetraselmus chui	2.4 g of sample, maximum temperature of 500°C, 20 min with 10°C/min, helium carrier gas at 50ml/min in fixed bed infrared pyrolysis oven	The bio-oil obtained contains various alkanes, alkenes, aldehydes, amines, fatty acids and phenols. The bio-oil and bio-char exhibited high heating value of 28 MJ/kg and 14.5 MJ/kg.	[127]
	Tetraselmus chui, Chlorella vulgaris, Chaetocerous muelleri, Dunaliella tertiolera	100 mg of sample, max temperature of 750°C, 10°C/min, helium carrier gas at 50 ml/min	Maximum bio-oil yield for Tetraselmus chui of 43% at 500°C	[128]
Fast pyrolysis	Chlorella protothecoides	200 g of sample, 4g/min, 400-600°C, nitrogen carrier gas at 0.4m^3/h, vapor residence time of 2-3s in fluid bed reactor	Maximum bio-oil yield of 57.9% at 450°C. High heating value of 41 MJ/kg at low density and viscosity of 0.92 kg/l and 0.02 Pa.s with low oxygen content.	[129]
	Chlorella protothecoides and Microcystis aeruginosa	200 g of sample, 4g/min, 500°C, nitrogen carrier gas at 0.4m^3/h, vapor residence time of 2-3s in fluid bed reactor	High heating value of 29 MJ/kg of bio-oil which is 1.4 times compared to heating value of wood	[130]
Microwave-assisted pyrolysis	Chlorella spp.	30 g of sample, 6 g solid char as catalyst, 500-1250W (462-627°C), 20 mins, nitrogen carrier gas at 500 ml/min	Maximum bio-oil yield of 28.6% at 750W. The high heating value of bio-oil was 30.7 MJ/kg.	[131]
	Chlorella vulgaris	30 g of sample, 750-2250W, 5% activated carbon catalyst, nitrogen carrier gas at 300 ml/min	Maximum bio-oil yield of 35.83 wt% and bio-gas yield of 52.37% obtained at 1500W and 2250W, respectively. The activated carbon catalyst enhanced the yield.	[132]
Hydrothermal liquefaction	Chlorella vulgaris, Nannochloropsis oculata, Porphyridium cruentum and Spirulina	3 g of sample, 75 ml reactor, 27 ml of distilled water,1M Na2CO3 or 1M formic acid, 350°C for 1h	The high heating value ranged from 22.8 to 37.1 MJ/kg with bio-oil yields in range of 25-40%.	[133]
	Dunaliella tertiolecta	7 g of sample, 100 ml stainless steel autoclave with magnetic stirrer, 70 ml distilled water, 0-10% Na2CO3 as catalyst, 280-380°C, 10–90 mins of operation time	Maximum bio-oil yield of 25.8% at 360°C, 50min and 5% Na2CO3. High heating value of 30.74 MJ/kg	[134]
	Nannochloropsis sp.	4.27g of microalgae paste (79% water content), 200-500°C, 60 min in 35 ml stainless-steel reactor	Maximum bio-oil yield of 43% and highest heating value of 39 MJ/kg at 350°C	[135]
	Spirulina platensis	1.8L reactor fitted with agitation impeller (300 rpm), 500-750ml algal slurry with 10-50% solids, 200-380°C, 0–120 min, nitrogen carrier gas with initial pressure of 2 MPa	Maximum bio-oil yield of 39.9% at 350°C, 20% solids and 60 min	[133]

Table 2. Microalgae cell composition.

	Composition (% dry matter)
Microalgae Species	Protein	Lipids	Carbohydrates	Reference(s)
Anabena cylindrica	43-56	4-7	25-30	[136]
Aphanizomenon flos-aquae	62	3	23	[137]
Chaetoceros calcitrans	36	15	27	[39]
Chlamydomonas rheinhardii	48	21	17	[38]
Chlorella vulgaris	51-58	14-22	12-17	[138]
Chlorella pyrenoidosa	57	2	26	[39]
Chlorella protothecoides	-	-	50	[139]
Chlorella zofingiensis	-	65.1	-	[140]
Chlorococcum sp.	-	39.8-41	-	[141]
Diacronema vlkianum	57	6	32	[142]
Dunaliela salina	57	6	32	[39]
Dunaliela bioculata	49	8	4	[41]
Euglena gracilis	39-61	22-38	14-18	[39,41]
Haematococcus pluvialis	48	15	27	[142]
Isochrysis galbana	50-56	12-14	10-17	[39]
Porphyridium cruentum	28-39	9-14	40-57	[39,41]
Prymnesium parvum	28-45	22-38	25-33	[41]
Scenedesmus obliquus	50-56	12-14	10-17	[38,42]
Scenedesmus dimorphus	8-18	16-40	21-52	[39,41]
Scenedesmus quadricauda	47	1.9	21-52	[41]
Spirogyra sp.	6-20	11-21	33-64	[41]
Spirulina maxima	60-71	6-7	13-16	[39]
Spirulina platensis	46-63	4-9	8-14	[39]
Synechococcus sp.	63	11	15	[38]
Tetraselmis maculata	52	3	15	[41]

Figure 2. Microalgae bio-refinery model.

Table 3. Biodiesel production and characteristics of various sources. Adapted from [94,138].

Type of source	Biomass Oil content (wt %)	Yield (L oil/ha year)	Land required (m^2/kg biodiesel year)	Biodiesel production (kg/ha year)
Corn	44	172	66	152
Hemp	33	363	31	321
Soybean	18	636	18	562
Jatropha	28	741	15	656
Camelina	42	915	12	809
Rapseed	41	974	12	862
Sunflower	40	1070	11	946
Castor	48	1307	9	1156
Palm Oil	36	5366	2	4747
Microalgae	30	58,700	0.2	51,927
Microalgae	50	97,800	0.1	86,515
Microalgae	70	136,900	0.1	121,104

Table 4. LC-PUFA composition of various microalgae species. Adapted from [143].

LC-PUFA	Chlorella vulgaris (green)	Chlorella vulgaris (orange)	Diacronema vlkianum	Haematococcus pluvialis	Isochrysis galbana	Spirulina maxima
ALA	661 ± 12	3665 ± 1	14 ± 1	3981 ± 2	421 ± 5	40 ± 0.1
DHA	16 ± 1	80 ± 1	836 ± 41	-	1156 ± 40	-
EPA	19 ± 1	39 ± 1	3212 ± 57	579 ± 6	4875 ± 108	-
Total ω-3 PUFA	971 ± 14	4781 ± 2	5407 ± 146	5770 ± 14	6461 ± 153	58 ± 35

Table 5. Pharmacological effects of micro-algal carbohydrates.

Microalgae species	Type of carbohydrate	Pharmacological effects	Ref
Chlorella stigmatophora	Crude polysaccharide	Anti-inflammatory, immuno-modulating	[144]
Chlorella vulgaris	Crude polysaccharide	Anti-oxidant	[145]
Gyrodinium impudicum KG-03	Sulfonated polysaccharide	Anti-viral	[80,146]
Haematococcus lacustris	Water-soluble polysaccharide	Immuno-stimulating	[77]
Phaeodactylum tricornutum	Crude polysaccharide	Anti-inflammatory, immuno-modulating	[144]
Porphyridium sp.	Crude polysaccharide	Anti-oxidant	[78]
	Sulfonated polysaccharide	Anti-inflammatory	[79]
Rhodella reticulata	Extracellular polysaccharide	Anti-oxidant	[147]
Scenedesmus quadricuada	Crude polysaccharide	Anti-oxidant	[145]

Table 6. List of bio-refinery studies conducted on microalgae.

Feedstock	Extracted compounds	Ref
Dunaliella tertiolecta	Lipids such as beta-carotene, fatty acids and phytosterol followed by pyrolysis to obtain char and bio-oil from defatted biomass	[148]
Isochysis galbana	Polar lipids and carotenoids such as fucoxanthin	[149]
Nannochloropsis gaditana	Proteins, carotenoids and biodiesel	[150]
Nannochloropsis sp.	Lipids fraction such as carotenoids and fatty acids followed by bio-hydrogen	[151]
Scenedesmus sp.	Amino acids with biogas	[152]
Defatted algal biomass	Short chain carboxylic acids and biohydrogen production from algal biomass post lipids extraction	[153]

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