Chapter 4: Biofuels from Algae and Seaweeds By Dr Ku Syahidah Ku Ismail

Biofuels from Algae

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

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

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

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)

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.

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.

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.

Biofuels from Seaweed

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.

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

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

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