1. Biogas Production
1.1. Sources
1.1.1. All type of biomass (containing carbohydrates, proteins, fats, cellulose, and hemicelluloses as main components)
1.1.2. Eg. plants, algae,sewage sludge, animal wastes and industrial effluents
1.2. Mechanisms
1.2.1. 1) Hydrolysis
1.2.1.1. Initial attack of complex polymers (polysaccharides, protein, lipids) into monomers
1.2.1.2. By hydrolytic enzyme such as lipase, protease, cellulase
1.2.1.3. Eg. Clostridia, Bifidobacteria, Streptococci and Enterobacteriaceae
1.2.2. 2) Acidogenesis
1.2.2.1. Converison of the monomers into volatile fatty acids (VFAs), acetic acid, CO2 and H2.
1.2.3. 3) Acetogenesis/Dehydrogenation
1.2.3.1. Conversion of VFAs into more acetic acid, CO2 and H2
1.2.3.2. Eg. Acetobacterium woodii and Clostridium aceticum
1.2.4. 4) Methanation
1.2.4.1. Production of methane from carbon dioxide and hydrogen gas or acetic acid
1.2.4.2. Eg. Methanosarcina barkeri, Metanonococcus mazei, and Methanotrix soehngenii.
1.3. Advantages
1.3.1. Energy-efficient and environmentally friendly
1.3.1.1. Drastically reducing GHG emission
1.3.2. Digestate (process by-product) can be used as organic fertilizer
1.3.2.1. Substituting chemical fertilizer
1.3.3. Simple and cost effective
1.3.4. Alternative to natural gas and fossil fuels in power and heat production
1.4. Limitations
1.4.1. Contain impurities
1.4.1.1. Causing corrosion of engine if used as biofuel in automobile
1.4.2. Few technological advancements
1.4.2.1. Unaccessible to large scale production and lack of investment
1.4.3. Less suitable for urban areas
1.4.3.1. Feasible in area where raw materials are in plentiful supply
1.4.4. Effect of temperature on biogas production
1.5. Applications
1.5.1. Biogas upgrading
1.5.1.1. Concentrating methane in biogas to the same standard as fossil natural gas
1.5.2. Biogas-grid injection: From biogas plant to combined heat and power (CHP) plant
1.5.2.1. Transportation of gas to consumers for on-site generation which reduce the loss of energy during transportation
1.5.3. Biogas in transport
1.5.3.1. Eg. Biogas-powered train (Biogaståget Amanda in Sweden), Biogas-powered automobiles (in Europe)
1.5.4. Biogas generate heat or electricity
1.5.4.1. In a CHP gas engine where the waste heat is used for heating the digester, cooking, space heating, water heating and process heating.
1.6. References
1.6.1. Weiland, P. (2010). Biogas production: current state and perspectives. Applied microbiology and biotechnology, 85(4), 849-860.
1.6.1.1. https://link.springer.com/article/10.1007/s00253-009-2246-7
1.6.2. Ramaraj, R., & Dussadee, N. (2015). Biological purification processes for biogas using algae cultures: a review. International Journal of Sustainable and Green Energy. Special Issue: Renewable Energy Applications in the Agricultural Field and Natural Resource Technology, 4(1-1), 20-32.
1.6.2.1. http://www.build-a-biogas-plant.com/PDF/10.11648.j.ijrse.s.2015040101.14.pdf
1.6.3. Advantages and Disadvantages of Biogas
2. Bioethanol
2.1. Bioethanol Production from Algae
2.1.1. Reason why algae is used instead of other feedstock
2.1.1.1. Rapid growth
2.1.1.2. No competition with food products in land or in water
2.1.1.3. High carbohydrate contents lead to easy fermentation to bioethanol.
2.1.1.4. Low level of hemicellulose and no lignin, thereby increases the efficiency of hydrolysis and fermentation yields
2.1.1.4.1. Low production cost of bioethanol
2.1.1.5. Algae able to utilize Carbon dioxide from environment
2.1.1.6. Rapid production and harvesting cycle (1–10 days)
2.1.1.6.1. Sufficient supplies to meet demand for bioethanol
2.1.2. Classification of Algae
2.1.2.1. Macroalgae (multicellular)
2.1.2.1.1. Type of macroalgae
2.1.2.2. Green (Chlorophyceae)
2.1.2.3. Eg. of species used for bioethanol production
2.1.2.3.1. Ulvalactuca
2.1.2.3.2. Kapphaphycus alvarezii
2.1.2.3.3. Sargassum fulvellum
2.1.2.4. Microalgae (unicellular)
2.1.2.4.1. Type of microalgae
2.1.2.4.2. Eg. of species used for bioethanol production
2.1.3. Strategies employed for enzymatic hydrolysis and fermentation
2.1.3.1. i. Separate hydrolysis and fermentation (SHF),
2.1.3.2. Eg. Trichoderma reesei, which secrets enzyme for hydrolysis; Saccharomyces cerevisiae has the ability to ferment hexoses while Scheffersomyces stipitis have the ability to use pentose sugars
2.1.3.3. ii. Simultaneous saccharification and fermentation (SSF),
2.1.3.4. iii. Simultaneous saccharification and co-fermentation (SSCF)
2.1.4. Recent advances in bioethanol production
2.1.4.1. Using Consolidated Bioprocessing Microbial Consortium that consists of an enzyme producing strain having the ability to hydrolyze the available biomass and two other different strains which have potential to ferment five carbon and six carbon sugars into ethanol
2.1.4.2. Obstacle of this approach
2.1.4.2.1. Control of consortium
2.1.4.2.2. Finding microbes with identical fermentation condition
2.1.5. Challenges:
2.2. General processes of bioethanol production from algae feedstock
2.2.1. 1st: Drying of Algae
2.2.2. Large quantity of water is required for industrial-scale production
2.2.3. 2nd: Hydrolysis
2.2.3.1. Cell wall is depolymerize first in order to obtain polysaccharides that can be converted into monomers through hydrolysis
2.2.3.2. 2 ways of hydrolysis
2.2.3.2.1. Chemical Hydrolysis (Acid Hydrolysis)
2.2.3.2.2. Enzymatic Hydrolysis
2.2.4. 3rd: Fermentation
2.2.4.1. To obtain bioethanol while water and carbon dioxide is released as by-product by fermentation using microbes utilizing mannose, galactose, glucose, xylose, and arabinose from algal biomass obtained by hydrolysis.
2.2.4.2. Microbes involved
2.2.4.2.1. 1) Yeast (Saccharomyces cerevisiae)
2.2.4.2.2. 2) Bacterium Zymomonas mobilis
2.2.5. 4th: Purification
2.2.5.1. Involves distillation, rectification and dehydration
2.3. Reference
2.3.1. Nadeem, H. (2019). Microbial Production of Ethanol. Materials Research Foundations, 46. doi:10.21741/9781644900116-12
2.3.1.1. https://www.researchgate.net/publication/331072641_Microbial_Production_of_Ethanol
3. Renewable Hydrogen (Biohydrogen)
3.1. Microalgae
3.1.1. Indirect photolysis of water
3.1.1.1. Equation:
3.1.1.1.1. 12 H2O + 6 CO2 → light → C6H12O6 + 6 O2 C6H12O6 + 12 H2O → 12 H2 + 6 CO2
3.1.1.2. Method
3.1.1.2.1. Two-stage
3.1.1.3. Advantage
3.1.1.3.1. Does not generate any undesirable, toxic or environmentally harmful by-products
3.1.1.4. Disadvantage
3.1.1.4.1. Hydrogen production limited with time, the yield of hydrogen decreases after 60 hours of production
3.1.2. Direct photolysis of water
3.1.2.1. Equation
3.1.2.1.1. 2 H2O → light → 2 H2 + O2
3.1.2.2. Method
3.1.2.2.1. Continuous mode
3.1.2.3. Advantage
3.1.2.3.1. More efficient than two-stage method
3.1.3. Parameters that influence microalgae cultivation for hydrogen production efficiency
3.1.3.1. Light intensity
3.1.3.2. Chlorophyll concentration
3.1.3.3. pH
3.1.3.4. Culture mixing
3.2. Application
3.2.1. Sent to fuel cells where it is recombined with oxygen to power houses or fuel vehicles
3.3. Limitations
3.3.1. Sensitivity of hydrogenase enzyme to O2 and H2 partial pressure severely decreases the efficiency of the processes
3.3.2. Insufficient knowledge on the metabolism of H2 producing microorganisms and the levels of H2 concentration tolerance of these microorganisms.
3.3.3. Lack of understanding on the improvement of economics of the process by combination of H2 production with other processes
3.3.4. No clear contender for a robust, industrially capable microorganism that can be metabolically engineered to produce more hydrogen
3.4. Solutions
3.4.1. Development of bioreactor design
3.4.2. Engineering of hydrogenase enzyme
3.4.3. Genetic modification of microorganism
3.5. References
3.5.1. Microorganisms as Direct and Indirect Sources of Alternative Fuels | IntechOpen
3.5.2. Levin, D. B., Pitt, L., & Love, M. (2004). Biohydrogen production: prospects and limitations to practical application. International journal of hydrogen energy, 29(2), 173-185.
4. Biodiesel production
4.1. Sources
4.1.1. Non-edible biomass
4.1.1.1. Eg: Date palm seeds, jatropha, neem
4.1.2. Agricultural residues
4.1.2.1. Eg: Wheat, rice husk and groundnuts
4.1.3. Algae (especially microalgae)
4.1.3.1. Better sources as microalgae grow very quickly & can utilize salt and waste water streams
4.1.3.2. Eg: Chlorella sp., Dunaliella primolecta, Botrycoccus braunii
4.2. Oil Conversion
4.2.1. Transesterification
4.2.1.1. Oil extracted is mixed with alcohol and an acid/base to produce the fatty acid methyl esters (biodiesel)
4.2.1.2. Extraction method
4.2.1.2.1. Solvent extraction with hexane
4.2.1.2.2. Supercritical fluid extraction
4.3. Applications (microalgae)
4.3.1. Open pond systems
4.3.1.1. Method
4.3.1.1.1. The algae, water and nutrients are circulated around a racetrack. The ponds are kept shallow to keep the algae exposed to sunlight. Carbon dioxide and nutrients are constantly fed to the ponds.
4.3.1.2. Advantage
4.3.1.2.1. Lower cost than photobioreactors
4.3.1.3. Disadvantages
4.3.1.3.1. Contamination with unwanted algal species
4.3.1.3.2. Cannot uptake carbon dioxide efficiently
4.3.2. Photobioreactors
4.3.2.1. Method
4.3.2.1.1. A closed systems which mostly designed as tubular reactors, plate reactors or bubble column reactors
4.3.2.2. Advantage
4.3.2.2.1. Higher biomass
4.3.2.3. Disadvantage
4.3.2.3.1. Unable get light penetration
4.4. Current Issues
4.4.1. Malaysia depends heavily on palm oil as a source for biodiesel production
4.4.2. The algae biofuel production was still too expensive to be commercialized in the near future.
4.4.3. Factors
4.4.3.1. Produces unstable biodiesel with many polyunsaturates
4.4.3.2. High cost of harvesting the algal biomass.
4.5. References
4.5.1. Malaysian Biodiesel Association - About Biodiesel
4.5.2. https://microbewiki.kenyon.edu/index.php/Biodiesel_from_Algae_Oil#Processes_converting_algae_oil_to_biodiesel
5. Biofuel
5.1. Definition
5.1.1. Biofuels are fuels produced from organic materials including plant materials and animal wastes
5.2. Types
5.2.1. Bioethanol
5.2.2. Biogas
5.2.3. Biohydrogen
5.2.4. Biodiesel
5.3. Generation
5.3.1. First Generation
5.3.1.1. Source
5.3.1.1.1. Derived from food crops such as corn, sugar cane and wheat
5.3.1.2. Limitation
5.3.1.2.1. Threaten the food source
5.3.1.2.2. Increased food prices
5.3.1.2.3. Land scarcity
5.3.2. Second Generation
5.3.2.1. Sources
5.3.2.1.1. Derived from non-food crops such as agricultural wastes and lignocellulosic plant biomass.
5.3.2.2. Limitation
5.3.2.2.1. Require sophisticated downstream processing technologies
5.3.2.2.2. High production cost
5.3.3. Third Generation
5.3.3.1. Source
5.3.3.1.1. Derived from algae
5.3.3.2. Advantages
5.3.3.2.1. Use of non-arable land or wastewater resources for the growth of algae
5.3.3.2.2. Rapid biomass yield
5.3.3.2.3. Carbon dioxide sequestration
5.3.4. Fourth Generation
5.3.4.1. Source
5.3.4.1.1. Genetically engineered algae
5.3.4.2. Advantages
5.3.4.2.1. Improve biomass and lipid production
5.3.4.2.2. Optimize fuel properties
5.4. References
5.4.1. Gharabaghi, M., Amrei, H. D., Zenooz, A. M., Guzullo, J. S., & Ashtiani, F. Z. (2015). Biofuels: bioethanol, biodiesel, biogas, biohydrogen from plants and microalgae. In CO2 Sequestration, Biofuels and Depollution (pp. 233-274). Springer, Cham.
5.4.2. https://agsci.oregonstate.edu/sites/agsci.oregonstate.edu/files/bioenergy/generations-of-biofuels-v1.3.pdf
5.4.3. Abdullah, B., Muhammad, S. A. F. A. S., Shokravi, Z., Ismail, S., Kassim, K. A., Mahmood, A. N., & Aziz, M. M. A. (2019). Fourth generation biofuel: A review on risks and mitigation strategies. Renewable and sustainable energy reviews, 107, 37-50.
5.4.3.1. Fourth generation biofuel: A review on risks and mitigation strategies