2
Question
Assertion: The sewage treated in STPs can be released into the river after secondary treatment
Reason: The secondary treatment involves the addition of chemicals to the sewage
Assertion: The sewage treated in STPs can be released into the river after secondary treatment
Reason: The secondary treatment involves the addition of chemicals to the sewage
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Solution
The correct option is C Assertion is true but the reason is false
Sewage, also called municipal waste water, contains human excreta, organic wastes and various pathogens (disease causing microorganisms). Releasing it directly into the water bodies poses a high threat to aquatic life and causes water pollution.
Sewage treatment plants (STPs) are specifically designed to treat this sewage to make it less polluting. The treatment is carried out in two stages, namely
Primary treatment: It involves filtration and sedimentation to remove the suspended solids of varying sizes from the sewage. The filtration process is carried out by allowing the sewage to pass through progressively smaller pores. The filtrate obtained is kept in large settling tanks, in which the solids settle down. The sediment is called primary sludge and the supernatant is called effluent.
Secondary treatment: The effluent is taken to aeration tanks where this fluid is agitated mechanically and air is constantly pumped into it. A large number of heterotrophic aerobic microbes grow in this aeration tank. These microbes digest a major amount of this organic matter, converting it into microbial biomass. These are transferred to a final settling tank, where microbes form sediment called activated sludge. The effluent or supernatant is passed to rivers or streams. Hence the assertion is true.
It is evident from the above explanation that the secondary treatment involves the digestion of the organic matter with the help of microbes but chemicals are not added in the secondary treatment of sewage. Hence the reason is false.
The effluent produced after the secondary treatment can be further treated chemically by chlorine or ozone.
Sewage, also called municipal waste water, contains human excreta, organic wastes and various pathogens (disease causing microorganisms). Releasing it directly into the water bodies poses a high threat to aquatic life and causes water pollution.
Sewage treatment plants (STPs) are specifically designed to treat this sewage to make it less polluting. The treatment is carried out in two stages, namely
Primary treatment: It involves filtration and sedimentation to remove the suspended solids of varying sizes from the sewage. The filtration process is carried out by allowing the sewage to pass through progressively smaller pores. The filtrate obtained is kept in large settling tanks, in which the solids settle down. The sediment is called primary sludge and the supernatant is called effluent.
Secondary treatment: The effluent is taken to aeration tanks where this fluid is agitated mechanically and air is constantly pumped into it. A large number of heterotrophic aerobic microbes grow in this aeration tank. These microbes digest a major amount of this organic matter, converting it into microbial biomass. These are transferred to a final settling tank, where microbes form sediment called activated sludge. The effluent or supernatant is passed to rivers or streams. Hence the assertion is true.
It is evident from the above explanation that the secondary treatment involves the digestion of the organic matter with the help of microbes but chemicals are not added in the secondary treatment of sewage. Hence the reason is false.
The effluent produced after the secondary treatment can be further treated chemically by chlorine or ozone.
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