Table 1.

Recent studies in microalgae employed for the production of biofuel

S. no.	Algal species	Reactor/growth conditions and products	References
1	Chlamydomonas reinhardtii GY-D55	Flat-plate airlift photobioreactor. Production rate 0.000959 kg H2/kg dry cells/h	[142]
2	Nannochloropsis gaditana	Down-flow type supercritical water gasification reactor. Product composed of hydrogen (52.0%), methane (17.9%) and CO2 (23.0%) with 97.4 wt% gasification efficiency	[143]
3	Chlorella vulgaris	Supercritical water gasification of microalgal hydrothermal liquefaction for hydrogen production. Non-stirred batch stainless steel Parr reactor produced 30 mol H2/kg algae	[144]
4	Laminaria digitate, Chlorella pyrenoidosa, Nannochloropsis oceanica	Two-stage batch co-fermentation resulted in 6.6 and 70.9% energy conversion efficiencies during hydrogen fermentation and combined H2–CH4 production, respectively. Hydrogen yield of 94.5–97.0 mL/g volatile solids	[145]
5	Chlamydomonas sp., Chlorella sp., Chlorella vulgaris TISTR 8580 and Chlorella protothecoides	Biophotolysis-based hydrogen and lipid production using crude glycerol as an exogenous carbon source. The optimal conditions were glycerol concentration of 16 g/L, initial pH 6.8, and light intensity of 48 μmol photon/m2 s, yielding 11.65 ± 0.65 mL/L hydrogen along with lipid content > 40% in the microalgal biomass	[146]
6	Scenedesmus dimorphus	Combination of separate hydrolysis and fermentation and simultaneous saccharification and fermentation found most effective. Lipid-extracted biomass yielded 0.26 g bioethanol/g lipid-extracted biomass at pH 5, temperature of 34 °C, and microalgae biomass loading at 18 g/L	[147]
7	Dunaliella sp.	Microalgae used as a feedstock for bioethanol production. 72 h of incubation at substrate concentration of 30 g/L microalgal biomass and 3 mL inoculums at pH 6 yielded 7.26 g/L bioethanol	[148]
8	Scenedesmus dimorphus	Microalgae used as a feedstock for bioethanol production. Fermentation conducted at pH 5, temperature of 34 °C, and microalgae biomass loading at 18 g/L via simultaneous saccharification and fermentation resulted in a theoretical yield of bioethanol that exceeded 90%	[149]
9	Mixed microalgae cultures	Fermentation of the glucose after enzymatic hydrolysis yielded 0.46 g ethanol/g glucose	[150]
10	Porphyridium cruentum	Freshwater biomass produced ethanol more efficiently than the sea water biomass with ethanol conversion yields of 70.3 and 65.4%, respectively, after 9 h. Simultaneous saccharification and fermentation processing was superior to separate hydrolysis and fermentation processing for bioethanol production	[31]
11	Scenedesmus acutus	Purified lipids were catalytically deoxygenated to yield liquid product consisting of 99 wt% hydrocarbons and diesel-like (C10–C20) hydrocarbons	[151]
12	Dunaliella tertiolecta	Carbon nanotube (CNT)-supported metal catalyst for hydrothermal liquefaction of Dunaliella tertiolecta to produce bio-oil. Bio-oil conversion and yield increased to 95.78 and 40.25 wt%, respectively, when Co/CNTs were employed as catalysts	[13]
13	Euglena sanguinea	Catalyst calcinated from natural white mussel shell at 1000 °C used in the transesterification process. The algal biodiesel showed the presence of saturated fatty acids: C16:0, C18:0, C22:0, C24:0 and monounsaturated fatty acids C18:1	[41]