Cultivation of algae as advanced biofuel feedstocks and conversion to biofuels

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.

Algal Biorefineries

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)

Source: Wageningen University, Netherlands