ASTRID & HANNS-FRIEDER MICHLER / SCIENCE PHOTO LIBRARY ASTRID & HANNS-FRIEDER MICHLER / SCIENCE PHOTO LIBRARY
Sewage treatment. View of methane gas bubbling from a sample of sewage being broken down with bacteria. In this process household and industrial sewage is treated by bacteria in anaerobic (oxygen deficient) conditions. Before this, fat, sand and stone are removed from the raw sewage. Water is then removed and treated separately. The sewage is then placed in a tank where the bacteria are added under anaerobic conditions. Methane gas is released as the bacteria breakdown the sewage. This gas is used to heat the tank. The treated sewage can be used as fertiliser. Photographed in South Germany.
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