1. Chapter 4: Biofuels from Algae and SeaweedsBy
Dr Ku Syahidah Ku Ismail

3. Biofuels from Algae

4. Algal biomass conversion process
Microalgal Biomass
Biochemical Conversion
Dark fermentation
Ethanol, Hydrogen
Anaerobic Digestion
Methane, Hydrogen
Photo-fermentation
Biophotolysis
Hydrogen
Thermochemical Conversion
Gasification
Hydrocarbon gas
Pyrolysis
Oil, gas, charcoal
Liquefaction
Oil
Chemical Separation
Solvent Extraction
Direct combustion
Power generation
Electricity or Power

5. Combustion and thermochemical conversions
Harvested algal biomass (80-95% moisture content) can be dried and combusted to generate electricity.
However, drying process is expensive
Moreover, combustion of algal biomass destroys the nitrogen fertilizer content and elevates the emissions of NOx.
Combustion of algal biomass is more expensive compared to combustion of woody biomass or coal
Thus, the more promising options are to recover biofuels from the wet algal biomass directly after harvest

6. Methane Production by Anaerobic Digestion
Anaerobic digestion – conversion of organic matter to biogas (a mixture of methane, CO2, water vapour, hydrogen sulfide and sometimes hydrogen)
The yield of methane were typically around 0.31 per gram of volatile solids destroyed.
This low yield is due to recalcitrance of some algal species to biodegradation, and the inhibition of the microbiological conversion by ammonia released from the biomass.
This problem can be solved by adding carbon-rich wastes to the microalgal biomass to double the methane yields
Or develop bacterial cultures that are resistant to ammonia inhibition

7. Ethanol and other solvent fermentation
Carbohydrate storage such as starch in green algae, glycogen in cyanobacteria, or glycerol by Dunaliella can be converted to ethanol by yeast fermentation.
However, the yield of ethanol is very low (about 1% of the biomass converted to ethanol)

8. Hydrogen production
Hydrogen can be generated by microalgae via dark fermentation, photo-fermentation and biophotolysis
Dark fermentation involves the anaerobic conversion of starch, glycogen, glycerol in the algae into hydrogen.
The process is carried out by either an anaerobic bacteria or by the microalgae itself.
However, the yield is low.

9. Oil production
Many microalgae, in particular green algae and diatoms can accumulate significant quantities of neutral lipids eg. Triacylglycerols
These lipids can be extracted from the biomass and converted into biodiesel or green diesel
Synthesis of lipid is triggered under condition when cellular growth is limited eg. Nutrient deficiency
Botrycoccus braunii is a green microalgae which produces up to more than 50% of its dry weight as pure hydrocarbon. Unfortunately its growth rate is very low.

10. Advantages of Algae to Biofuel
Greater productivity over higher plants, because they grow in water, thus no water and nutrients limitation.
Algal cultivation does not require arable land, and can be carried out in shallow ponds or open ocean.

11. Biofuels from Seaweed

13. Anaerobic Digestion of Seaweeds
Seaweed washed up on shore was used.
To boost the overall process, the methane produced can be blended with natural gas and subsequently converted into electricity.

14. Seaweed to Ethanol
Extracts from Laminaria hyperborea can be fermented to ethanol by conversion of mannitol and laminaran (by products of alginate production)
Microorganisms to produce ethanol from seaweed are bacterium Zymobacter palmae and yeast Pichia angophorae

15. Limitations of Biofuels from Algae and Seaweed
Scientific and technological challenges remain to be improved to make it more economically viable.
Providing nutrients to ocean-farming either by pumping deep ocean waters or providing synthetic fertilizers is very expensive and environmentally unacceptable.
Cultivation area is a challenge – coastlines are limited resources and competes with societal needs

16. Test Yourself
What are the advantages of biofuel production from algae/seaweed compared to lignocellulosic materials?