ROBERT BROOK / SCIENCE PHOTO LIBRARY ROBERT BROOK / SCIENCE PHOTO LIBRARY
Waste water treatment. A demonstration of the use of algae and plants in waste water treatment. The plants and algae are grown, without soil, on the sewage. Bacteria digest ammonia in the sewage and turn it into nitrates for use by the plants. The plants also absorb phosphorous from the sewage. Oxygen is pumped into the water (upper centre) for use by the aerobic bacteria that live in the water and on the roots of the plants. These bacteria convert the organic matter in the sewage to carbon dioxide and other stable chemicals. Photographed at the Earth centre, Doncaster, UK.
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