Define sewage .How are Microbes used in sewage treatment plant.

Sewage treatment in Sewage plants

• Sewage is municipal waste containing large amounts of organic matter, Human excreta, and pathogenic bacteria.

• Generally sewage is drained into water bodies like rivers, ponds etc. Before discharging into water bodies, sewage is made less polluting so sewage is treated in sewage treatment plants.

• Sewage treatment is carried out in two steps. Physical treatment and Biological treatment. 

Physical treatment in sewage plants

• Physical treatment includes removal of large and small particles by filtration by passing through a wire mesh.

• The grit, soil, pebbles are removed by process of sedimentation in a tank. After physical treatment, the supernatant is known as effluent.

• This effluent is undergone the Biological treatment.

Biological treatment in sewage plants

• In biological treatment, the effluent is passed into an aeration tank where aerobic microbes are grown rapidly and form a group.

• This group of aerobic microbes is called flocs. Flocs are masses of bacteria and look like a mesh -like structure.

• These aerobic bacteria consumes organic matter present in sewage and reduces Biochemical  oxygen demand (BOD).

• BOD refers to the amount of oxygen required for consumption  of all organic matter in one litre of water oxidised by microbes.

• BOD measures the amount of organic matter in water measuring the rate of oxygen uptake by microbes.

• Once  Biochemical  oxygen demand is reduced then effluent is called as activated sludge.

• This sludge is passed out in anaerobic sludge digesters. In these digesters, heterotrophic microbes are grown anaerobically to digest the pathogenic bacteria and fungi.

• In the digesters, during this process a mixture of gases such as methane hydrogen sulphide and carbon dioxide are released that are stored as biogas.

• In 1985, Ministry of Finance and Environment started Ganga and yamuna action plan.

• Under this plan, sewage treatment plants have been set up near the major river to protect from water pollution

• Sewage treatment plants make seewage water from more polluted to less polluted before discharging into water.