One of the oldest life forms, algae, holds the highest potential for future energy generation. This third generation (3G) biofuel holds some major advantages over other biomass but it has not yet taken off as once expected. With increased focus and attention, innovative techniques in research and development, and political will, algae can return to the fore-front of future biofuel production.
Higher biofuels yields are a major advantage of algae over first generation (1G) plant crops such as sugar beet or wheat, and second generation (2G) sources for biofuels such as vegetable or animal waste streams. Estimates provided by Rocca et al (2015) in table 1 below indicate the stark differences in estimated oil yield potential per unit area for different terrestrial crops and microalgae. Microalgae also have rapid growth potential and can double their biomass in as short as 3.5 hours, and are capable of year-round grow (Cheng, 2018).
There is a diverse range of biofuels that can be derived from algae. Biomethane, bioethanol and biobutanol can be derived from macroalgae or seaweeds. Biodiesel, biomethane, bioethanol, bio-oil and bio-hydrogen can be derived from microalgae (Rocca, et al., 2015). Microalgae species are favourable for fuel production due to high lipid contents of 50 – 70 % (Khan, et al., 2018). Algae cultivation can be done in open systems such as ponds and lakes, and in more advanced closed-loop systems on land unsuitable for food crops, removing the concern of competition with food producers. Closed-loop systems offer the added advantage of additional control over variables such as light, temperature, nutrients, pH, and the particular species grown, to enable producers to maximize crop production. Algal growth can be combined with wastewater treatment systems to recycle waste nutrients such as nitrogen and phosphorous to help mitigate greenhouse gas emissions and protect our environment. Microalgae also produce valuable coproducts such as proteins and pigments, and the left-over biomass after oil extraction can be used as feed, fertilizer, or fermented to produce methane or ethanol (Cheng, 2018).
With so many advantages it is clear that algae have been held back from their high expectations as no commercial algae-based biofuel currently exists. It can often require more energy to remove moisture from algal biomass to enable lipid separation, than the energy the end product provides. This has long been a point of friction and research continues into a much-needed energy-intensive drying process that would enable algal biofuels to compete for market share. The high operational, maintenance, harvesting and conversion costs, have meant that it has not yet become feasible as a biofuel (Khan, et al., 2018). Rising CO2 prices as a result ofstringent CO2 stabilizing techniques make the economics of microalgal biofuel unattractive, and production and combustion of microalgal diesel releases as much CO2 as is captured from anthropogenic sources and assimilated by microalgae (Takeshita, 2011). There is at present no comprehensive analysis on the deployment potential of optimized harvesting methods at large scale, from the point of view of technical viability, environmental impacts and cost effectiveness (Rocca, et al., 2015). Environmental and social concerns raised by the production of biofuels from algae include the high demands on key resources such as energy, nutrients, water and CO2’ along with the availability of land with suitable characteristics including climatic conditions and an adequate supply of resources (Rocca, et al., 2015).
There is no doubt there are major challenges to be overcome before biofuels from algae are a viable alternative. The potential is there however and with focus on energy efficient and low-cost harvesting and dewatering techniques, there is a positive future ahead for algae biofuel production.
Cheng, J., 2018. Biomass to Renewable Energy Processes. 2 ed. s.l.:CRC Press.
Khan, M., Shin, J. & Kim, J., 2018. The promising future of microalgae: current status challenges, and optimization of a suatainable and renewable industry for biofuels, feed, and other products. Microbal Cell Factories, 16(36).
Rocca, S., Agostini, A., Giuntoli, J. & Marelli, L., 2015. Biofuels from algae: technology options, energy balance and GHG emissions, s.l.: European Union.
Takeshita, T., 2011. Competitiveness, role, and impact of microalgal biodiesel ain the global energy future. Applied Energy, 88(10), pp. 3481 – 3491.