Microbes in Human Welfare Test - 16

A major component of this waste-water is human excreta. This municipal waste-water is also called as sewage. It contains a large amount of organic matter and microbes. Many of which are pathogenic.

STP stands for sewage treatment plants. Before the disposal of waste-water into the natural water bodies, sewage is treated in STPs to make it less polluting.

The treatment of waste-water in STPs is carried out in two stages namely primary treatment and secondary treatment. Treatment of waste-water is done by the heterotrophic microbes naturally present in the sewage.

In primary treatment, initially floating debris is removed by sequential filtration. Then grit and small pebbles are removed by sedimentation. All solids that settle form the primary sludge while the supernatant forms the effluent.

The constant agitation of primary effluent allows vigorous growth of useful aerobic microbes into flocs which are the masses of bacteria associated with fungal filaments to form mesh-like structures.

BOD refers to the Biochemical oxygen demand. It is the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria.

The sewage water is treated until the BOD is reduced. The BOD test measures the rate of uptake of oxygen by micro-organisms in a sample of water and thus, BOD is indirectly a measure of the organic matter present in the water. The greater the BOD of waste-water more is its polluting potential.

Activated sludge are the sediment bacterial flocs which were present in the effluent. When the biochemical oxygen demand of sewage water is reduced significantly, the effluent is then passed into a settling tank where the bacterial flocs are allowed to sediment.

In the secondary treatment, a small part of the activated sludge is pumped back into the aeration tank to serve as inoculum. The remaining major part of the sludge is pumped into large anaerobic sludge digesters.

Millions of gallons of waste water is treated in various sewage plants where microbes play a major role in decomposing the waste. This methodology has been practised for a century, in almost all parts of the world.