ROSENFELD IMAGES LTD / SCIENCE PHOTO LIBRARY ROSENFELD IMAGES LTD / SCIENCE PHOTO LIBRARY
Sewage treatment. Bacterial anaerobic treatment of sewage in aluminium-clad buildings at a sewage treatment plant. Sewage is added to the closed chambers or digesters. Organic catalysts (enzymes) are added to the sewage to make the solid sewage sludge soluble. The sewage is then fermented by bacteria which reduce it to simple organic acids. These organic acids are then converted into methane and carbon dioxide by bacteria. The methane can be collected and used as fuel. After spending between 10 and 30 days in the digesters, the humus-like residue of the sludge is removed and passes onto the next stage of treatment. Photographed at Munich in Bavaria, Germany.
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