Microbes in sewage treatment:

Sewage is a term that is often used for waste water including feaces, urine, laundry waste and many more other forms of municipal waste. Now-a-days, it has become the biggest problem of world. Sewage is treated in sewage treatment plants (STPs). It has many microbes and organic matter.  Ganga action plan and Yamuna action plan are first initiatives to solve this major problem.

This sewage treatment is carried in two ways:

Primary treatment or physical treatment:

• It is the physical treatment of large and small particles from sewage. Firstly floating debris are removed by filtration.
• Then soil and pebbles are removed by sedimentation in large settling tanks.
• The sediment is called primary sludge and remaining waste water is called effluent, which is taken for secondary treatment.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          

Secondary treatment and biological treatment:

• Primary effluent is taken into large aeration tanks with full oxygen supply.
• Here, aerobic bacteria grows and form flocs (Combination of bacteria with fungal filaments).
• These microbes consume organic materials and thus reduce BOD of water.
• Then this secondary effluent passes to settling tanks. In these settling tanks, flocs get settle down and sediment is called activated sludge.
• A small part of sludge is used as an inoculum (starter) in aeration tanks. In the digesters, heterotrophic microbes in the absence of oxygen digests bacteria and fungi in sludge and produce biogas.
• Biogas typically refers to a mixture of different inflammable gases produced by the breakdown of organic matter in the absence of oxygen and used as a natural fuel.
• Biogas contains a mixture of gases like methane, hydrogen sulphide and co₂ which form the biogas.