Read the passage and answer the following questions:
Sewage, which is a major component of urban wastewater, contains a significant amount of human excreta, organic matter, and pathogenic microbes. Disposing of such a large quantity of sewage directly into natural water bodies like rivers and streams is not feasible due to its polluting nature. Therefore, sewage undergoes treatment in sewage treatment plants (STPs) to reduce its pollution levels before disposal. The treatment process involves two main steps. The primary treatment focuses on physically removing both large and small particles from the sewage through processes like filtration and sedimentation. Initially, floating debris is removed through sequential filtration. The secondary treatment, also known as biological treatment, involves passing the primary effluent into large aeration tanks. These tanks are mechanically agitated and air is pumped into them, creating an environment suitable for the growth of beneficial aerobic microbes. These microbes form mesh-like structures called flocs, which consist of bacteria associated with fungal filaments. As these microbes grow, they consume a significant portion of the organic matter present in the effluent. This process leads to a reduction in the Biochemical Oxygen Demand (BOD) of the effluent. BOD is a measure of the organic matter content in the water and indicates its pollution potential. The sewage water is treated until the BOD is sufficiently reduced. Overall, sewage treatment plants play a crucial role in reducing the pollution level of sewage by removing particles and organic matter, thereby ensuring that the treated water can be safely disposed of without causing harm to the environment or public health.
Given below are two statements:
Statement I: The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams.
Statement II: Untreated sewage discharged directly into rivers leads to their pollution and an increase in air-borne diseases.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Statement I is true but Statement II is false
Treated sewage can be let into rivers safely, but untreated sewage pollutes them and spreads disease through the water. This is why more sewage treatment plants are needed as towns grow.
Statement I: The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams. — True. After its organic matter and BOD have been reduced, the effluent from secondary treatment is generally released into rivers and streams.
Statement II: Untreated sewage discharged directly into rivers leads to their pollution and an increase in air-borne diseases. — False. Untreated sewage pollutes rivers and increases water-borne diseases. The pathogens in sewage spread through the water, not through the air.
NCERT Extract:
Microbes in Sewage Treatment – “… The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams. … You are aware that due to increasing urbanisation, sewage is being produced in much larger quantities than ever before. However the number of sewage treatment plants has not increased enough to treat such large quantities. So the untreated sewage is often discharged directly into rivers leading to their pollution and increase in water-borne diseases.”