Algae, cyanobacteria and aquatic plants for production of biofuels
"Algae and aquatic biomass has the potential to provide a new range of "third generation" biofuels, including jet fuels. Their high oil and biomass yields, widespread availability, absent (or very reduced) competition with agricultural land, high quality and versatility of the by-products, their efficient use as a mean to capture CO2 and their suitability for wastewater treatments and other industrial plants make algae and aquatic biomass one of the most promising and attractive renewable sources for a fully sustainable and low-carbon economy portfolio." (Source: European Algae Biomass Association - EABA).
- Download the EBTP Value Chain Fact Sheet #7 Aquatic Biomass (353 Kb)
Photomicrograph of Botryococcus species, with oil droplets being released.
Algae have the potential to produce considerably greater amounts of biomass and lipids per hectare than terrestial biomass, and can be cultivated on marginal lands, so do not compete with food or other crops. Algae can be cultivated photosynthetically using sunlight for energy and CO2 as a carbon source. They may be grown in Shallow lagoons or raceway ponds on marginal land (e.g. Sapphire Energy, Aurora BioFuels, Live fuels) or closed ponds (e.g. Green Star). Green Star also produces a micronutrient formula to greatly increase the rate of algal growth.
A number of closed photobioreactors are being investigated, including: Horizontal tubes (e.g. AlgaeLink NV), Vertical (e.g. BioFuel Systems SL), Thin film, Open/Closed systems (e.g.Parabel, Cellana). See also Subitec, Germany.
Productivity is higher in the controlled, contained environment of a photobioreactor, but capex and opex are also both substantially higher than for open systems. Significant investment in research is required before high levels of productivity can be guaranteed on a commercial scale.
Algae to biofuels plants may be developed on land adjacent to power stations, for converting the carbon dioxide from exhausts into fuel.
Algae may be used to produce biofuels in several ways:
- Conversion to bioethanol (e.g. Algenol)
- Exraction of oils (e.g. SGI, Solixalgredients, Sapphire Energy, Algasol).
- Production of oils from feedstock via dark fermentation (e.g. Solazyme)
- Conversion of whole algae to biocrude via pyrolysis (e.g. BioFuel Systems SL)
- "Green crude" (e.g. Sapphire Energy, Muradel)
- Algal biorefinery - biofuels and other products (Parabel, Cellana)
Following extraction, algal oils may be further refined (e.g. by hydrocracking and hydrogenation) to produce gasoline or jet fuels.
In addition to producing oils, algae are rich sources of vitamins, protein and carbohydrates. The following steps have been identified for development of microalgae biorefineries.
- Development of mild and efficient cell disruption, extraction and fractionation technologies
- Effective technologies for separation of carbohydrates, proteins and lipids
- Lipid /oil refining technologies
- Improvement of energy consumption and environmental performance, decrease of capital costs
- Integrate knowledge & facilities for oil, food and fine chemical industry
- Biomass provision (quantity and quality)
EABA - European Algae Biomass Association aims to act as a catalyst for fostering synergies among scientists, industrialists and decision makers in order to promote the development of research, technology and industrial capacities in the field of algae.
Algal Biomass Association (US) - promotes the development of viable commercial markets for renewable and sustainable commodities derived from algae.
Proterro has developed a patented method using modified cyanobateria in bioreactors to produce sugars, which could be used as feedstock for advanced biofuels. Proterro says that the system potentially offers higher productivity (per acre of land used) and costs less than producing sugar from corn, cellulose or sugar cane.
Researchers at the Biodesign Institute, Arizona State University have modified cyanobacteria (photosynthetic bacteria) to excrete oil, which can be collected without killing the cells. The technique could be used to optimise microbial oil production for conversion into biofuels. The Biodesign Institute is also carrying out research to optimise Photobiorectors (e.g. phosphorous, CO2 light irradience) for cyanobacetria.
Researchers at J. Craig Venter Institute in Rockville, Md. and Waseda University in Tokyo have modified the circadian clock of cyanobacteria to remain in its daytime state and hence increase productivity. Researchers on the project include Professor Carl H. Johnson, Vanderbilt University.
Aquatic plants with potential as biomass feedstocks
Aquatic plants, such as Spirodela polyrhiza, commonly called Greater Duckweed, have low levels of cellulose and lignin and have the potential to be converted to biofuel at a cost competitive with fossil fuels. In 2014 the genome was being investigated by researchers at the Waksman Institute of Microbiology, with a view to optimising the pond plant as a future feedstock. Thermochemical Conversion of Duckweed to gasoline, diesel, and jet fuel - the 'duckweed biorefinery' concept - is also being studied by Department of Chemical and Biological Engineering, Princeton University, and the Institute of Process Engineering, Chinese Academy of Sciences et al.
A recent IEA Bioenergy report "State of Technology Review - Algae Bioenergy" (2017) gives an international update on the status and prospects for using micro-and macroalgae as feedstocks as bioenergy feedstocks.