4.4 Microalgae and other microorganisms

Seaweeds are one form of large algae, but there are also single-celled aquatic microalgae and cyanobacteria that photosynthesise. Designs for bioreactors to enable microalgae to be used as an energy source have been suggested, as shown in Figure 8.

Maximise

Figure 8 A possible bioreactor design for use of microalgae as an energy source

They could potentially make a very attractive bioenergy source because:

• they grow in water, and are tolerant of wide ranges of salinity and temperature
• they do not occupy land that could be used for other products
• under appropriate conditions, the cells of the algae can contain high percentages of oils, and the cyanobacteria can excrete oil into their surroundings: the microbial residues after oil extraction can also be used as an energy source
• it is possible that they could be used simultaneously to clean up waters polluted with plant nutrients, and the resulting biomass, including the oil, used for energy (Clarens et al., 2010)
• some microalgae forms are also seen as candidate material for the capture of carbon dioxide from power plants.

Can leftover products from non-energy uses be used as additional ‘secondary’ bioenergy sources? You look at that question next.