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Microalgae production for biofuels. Worker tending to ponds being used to culture Chlorella vulgaris microalgae. This site composts household waste to produce methane, which is burned to produce electricity. The carbon dioxide released from the combustion of the waste is used to help grow microalgae, which are then used for biofuel production. The carbon dioxide is pumped into ponds (seen here) to promote photosynthesis and therefore growth of the algae. Photographed in France. (KEYSTONE/SCIENCE PHOTO LIBRARY/PASCAL GOETGHELUCK/SCIENCE PHOTO LIBRARY)