Question

Following is the sewage treatment. In which of the following options, the correct word for all four numbers (1, 2, 3, and 4) are indicated?     

A. 1 - Large aeration tanks; 2 - Chemical agitation; 3 - High; 4 - Anaerobic
B. 1 - Large aeration tanks; 2 - Mechanical agitation; 3 - Low; 4 - Anaerobic
C. 1 - Large aeration tanks; 2 - Chemical agitation; 3 - Low; 4 - Aerobic
D. 1 - Large aeration tanks; 2 - Mechanical agitation; 3 - High; 4 - Anaerobic

Answer 1

Hint: Sewage treatment is the method of removing waste and contaminants from wastewater of the city, society, colony etc. This wastewater primarily contains household sewage along with certain industrial wastewater. In sewage treatment plants various approaches are used like physical, chemical, and biological approaches to eliminate contaminants and produce treated wastewater that is safe to discharge into the environment.

Complete step-by-step answer:
Sewage contains a vast number of toxic organic matter. Microorganisms are widely used in sewage treatment plants to remove this toxic organic matter. A sewage or wastewater treatment plant is comprised of two stages ie primary and secondary or biological treatment.
Primary Treatment involves the removal of large or small-sized ingredients in wastewater by physical processes.
The secondary treatment eliminates dissolved organic substances by the use of biological agents. This is also known as biological treatment. Primary effluent is passed into the big aeration tanks with constant mechanical agitation and air supply. Aerobic microbes grow quickly and form flocs. Flocs are masses of bacteria that consume organic substances and thus decrease the biochemical oxygen demand(BOD). When the BOD of sewage has decreased, the effluent is passed into the settling tank. Here, the bacterial flocs settle, and sediment is known as activated sludge. A small portion of the sludge is used as an inoculum in the aeration tank and the remaining portion is passed into larger tanks known as anaerobic sludge digestors. In the digesters, heterotrophic microbes anaerobically digest fungi and bacteria in sludge that produces a mixture of gases like carbon dioxide, hydrogen sulphide, and methane which form the biogas.

Therefore the correct answer is OptionB .
Note: Human health and the environment are influenced by the direct disposal of human and industrial effluents into natural resources without any treatment. Sewage treatment is necessary to decrease the toxicity of sewage and maintain a healthy and safe environment, and also promote human welfare.