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Microbes play a dual role when used for ...

Microbes play a dual role when used for sewage treatment as they not only help to retrieve usable water but also generate fuel. Write how this happens?

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Sewage is treated in sewage treatment plants to make it less polluting . This treament is carried out in two stage .
(i) Primary treatment : Primary treatment is a physical process of removal of small and large particles through filtration and sedimentation.
ii. Secondary treatment : It is a biological process, that employs the heterotrophic bacteria naturally present in the sewage .
The bacterial flows are allowed to sediment, that is called activated sludge . The remaining major part of the sludge in pumpen into large tanks called anaerobic sludge digesters.
During this digestion, bacteria produce a mixture of gases.
Here these gases form biogas and can be used as source of energy as inflammable.
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