DAVID NUNUK / SCIENCE PHOTO LIBRARY DAVID NUNUK / SCIENCE PHOTO LIBRARY
Sewage treatment plant. Aerial photograph of aeration tanks at a sewage works. This stage is used to treat sewage after most of the solid waste (sludge) has been removed in settlement tanks. In an aeration tank, air is blown into the sewage to promote the growth of micro-organisms that feed on harmful bacteria. This is followed by further settlement to remove any remaining solid waste. The cleaned water will be pumped into a river. Sludge can be treated and used as fertiliser or used to produce methane to burn and generate electricity.
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