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Sewage treatment. Storage tower at a sewage works used for the anaerobic bacterial treatment of industrial and domestic effluent. The sewage is treated with an enzyme to make it soluble and then stored in these tanks, which exclude air. It is broken down by bacteria into gases (mainly methane) and a humus-like material before moving on to the next stage of treatment. The methane produced can be used as a fuel. Photographed in Germany.
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