Table 3 Possible biofuels from microalgae and conversion processes

Bioethanol, biobutanol, biomethanol, bioaceton

Simultaneous saccharification and fermentation (SSF)

Separate hydrolysis and fermentation (SHF)

Simultaneous saccharification and co-fermentation (SSCF)

Separate hydrolysis and co-fermentation (SHCF)

Dark fermentation

Photo fermentation

Anaerobic fermentation

Acetone–butanol–ethanol (ABE) fermentation

Consolidated bioprocessing

Fe₂O₃, CeO₂-CNT and others

[42, 49, 85,86,87,88,89]

Biodiesel

Lipid hydrolysis and chemical, physical, enzymatic transesterification

Interesterification

Acidolysis

Alcoholysis associated with glycerolysis

Folch method (use of chloroform–methanol)

Bligh and dyer method (use of chloroform–methanol)

Modified method of the Folch/Bligh and dyer methods (use of methyl-tert-butyl-ether)

Superior solvent extraction method (use of chloroform)

Direct or in situ supercritical transesterification

Post-transesterification

Wet extraction method

Deep eutectic solvent (DES) method

ZrO₂, TiO₂, Al₂O₃, CeO₂, SiO₂, Fe₂O₃, CaO-NPs and others

[46, 77, 78, 90,91,92,93,94,95,96,97,98,99,100]

Syngas

Gasification

Pyrolysis

Direct combustion

Bio-electrochemical fuel cells

Supercritical water gasification (SCWG)

Hydrothermal gasification

TiO₂, CeO₂ and others

[88, 101,102,103,104,105]

Bio-electricity

Bio-electrochemical system contain anode, cathode and electrode

Direct combustion

Fe₂O₃, CeO₂-CNT, CaO-NPs and others

[106,107,108]

Biomethane

Anaerobic digestion

Catalytic hydrothermal gasification

SiO₂, nano-particles of platinum (Pt), nickel (Ni), cobalt (Co), iron (Fe) and others

[46, 109,110,111,112]

Bio-hydrogen

Solid-state anaerobic digestion

Biophotolysis

Photobiological hydrogen production

Dark fermentation

Photo fermentation

Solid-state fermentation

Suspended fermentation

TiO₂, CeO₂ and others

[113,114,115,116,117,118]

Bio-oil and bio-char

Hydrothermal (thermochemical) liquefaction

Pyrolysis

Expeller press

Bead beating

Ultrasound assisted extraction method

Microwave extraction method

Electroporation/electropermeabilization

Slow pyrolysis

Fast pyrolysis

Torrefaction

Hydrothermal carbonization

Hydrothermal liquefaction

Ion exchange

Wet imprgenation

Catalytic hydropyrolysis

Hydrogenation

Hydrodeoxygenation

CeO₂-CNT, SiO₂-MgO nanohybrids and others

[46, 90, 119,120,121,122,123,124,125,126,127]