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Question
Select the option that has the correct sequence of the various steps involved during the treatment of waste water.
Select the option that has the correct sequence of the various steps involved during the treatment of waste water.
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Solution
The correct option is C Sequential filtration and sedimentation →Breakdown of the organic matter→Bacterial flocs sediment→Effluent released into the water bodies
The municipal waste water consisting of organic wastes and microbes generated from the cities and towns is called sewage. The sewage cannot be released into the water bodies directly as it can lead to pollution of water making it unfit for drinking. The pathogenic microbes of the sewage also cause harmful diseases. Hence, the sewage is treated in the sewage treatment plants (STPs) before it is released into the water bodies.
Sewage treatment is carried out in two stages: primary treatment and secondary treatment.
Primary treatment: it involves physical removal of particles from sewage through filtration and sedimentation. Floating debris is removed by sequential filtration initially. This is carried out in the filtration tanks. After filtration, the waste water is allowed to stand undisturbed for a certain time. The heavier particles such as soil and small pebbles (grit) settle down under the effect of gravity and form the sediment which is referred to as primary sludge. The supernatant formed is called the effluent and undergoes further biological treatment/secondary treatment.
Secondary treatment: the effluent collected from the primary treatment is mechanically agitated in the aeration tank, with continuous air supply. This results in the growth of a large number of aerobic heterotrophic microbes. These microbes form flocs (mesh-like structures containing masses of bacteria associated with the filaments of fungi). They breakdown the organic matter present in the effluent and reduce the level of organic pollutants in the water. This is then transferred to a final settling tank, where microbes form sediment called activated sludge. The effluent from the secondary treatment plant is discharged into rivers or streams.
The municipal waste water consisting of organic wastes and microbes generated from the cities and towns is called sewage. The sewage cannot be released into the water bodies directly as it can lead to pollution of water making it unfit for drinking. The pathogenic microbes of the sewage also cause harmful diseases. Hence, the sewage is treated in the sewage treatment plants (STPs) before it is released into the water bodies.
Sewage treatment is carried out in two stages: primary treatment and secondary treatment.
Primary treatment: it involves physical removal of particles from sewage through filtration and sedimentation. Floating debris is removed by sequential filtration initially. This is carried out in the filtration tanks. After filtration, the waste water is allowed to stand undisturbed for a certain time. The heavier particles such as soil and small pebbles (grit) settle down under the effect of gravity and form the sediment which is referred to as primary sludge. The supernatant formed is called the effluent and undergoes further biological treatment/secondary treatment.
Secondary treatment: the effluent collected from the primary treatment is mechanically agitated in the aeration tank, with continuous air supply. This results in the growth of a large number of aerobic heterotrophic microbes. These microbes form flocs (mesh-like structures containing masses of bacteria associated with the filaments of fungi). They breakdown the organic matter present in the effluent and reduce the level of organic pollutants in the water. This is then transferred to a final settling tank, where microbes form sediment called activated sludge. The effluent from the secondary treatment plant is discharged into rivers or streams.
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