Consider the following statements regarding "Aerobic Bacteria": 1. They function effectively in the absence of oxygen. 2. They consume soaps and food waste left in clarified water. 3. They remain permanently suspended in the water and never settle. Which of the statements given above is/are correct?

The correct option is (b). Explanation Aerobic bacteria are microorganisms that require oxygen for respiration and metabolic processes. In the context of wastewater treatment, they are utilized in the secondary (biological) treatment stage to decompose organic impurities. Statement-wise Analysis: - Statement 1 is Incorrect. By definition, aerobic bacteria require the presence of oxygen to survive and function effectively. Bacteria that function in the absence of oxygen are classified as anaerobic bacteria. - Statement 2 is Correct. During the biological treatment phase (specifically in aeration tanks), air is pumped into the water to support the growth of aerobic bacteria. These bacteria consume organic contaminants, including human waste, food waste, soaps, and other biodegradable matter remaining in the clarified water. - Statement 3 is Incorrect. These bacteria do not remain permanently suspended. After they have consumed the organic matter, the water is transferred to a settling tank. Here, the bacterial flocs (masses of bacteria) settle at the bottom to form activated sludge, allowing the treated water to be separated from the top. Key Takeaway: Aerobic bacteria require oxygen to decompose biodegradable organic matter during the secondary stage of wastewater treatment and subsequently settle as activated sludge.

NCERT Class 7 Environment & Ecology — Chapter 2: Wastewater story

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Consider the following statements regarding "Aerobic Bacteria":

They function effectively in the absence of oxygen.
They consume soaps and food waste left in clarified water.
They remain permanently suspended in the water and never settle.

Which of the statements given above is/are correct?

Official previous-year question

Verified 1 Aug 2026.

Options

A1 only
B2 only
C1 and 3 only
D1, 2 and 3

Did you get this right?

Solution

The correct option is (b).

Explanation

Aerobic bacteria are microorganisms that require oxygen for respiration and metabolic processes. In the context of wastewater treatment, they are utilized in the secondary (biological) treatment stage to decompose organic impurities.

Statement-wise Analysis:

Statement 1 is Incorrect. By definition, aerobic bacteria require the presence of oxygen to survive and function effectively. Bacteria that function in the absence of oxygen are classified as anaerobic bacteria.
Statement 2 is Correct. During the biological treatment phase (specifically in aeration tanks), air is pumped into the water to support the growth of aerobic bacteria. These bacteria consume organic contaminants, including human waste, food waste, soaps, and other biodegradable matter remaining in the clarified water.
Statement 3 is Incorrect. These bacteria do not remain permanently suspended. After they have consumed the organic matter, the water is transferred to a settling tank. Here, the bacterial flocs (masses of bacteria) settle at the bottom to form activated sludge, allowing the treated water to be separated from the top.

Key Takeaway:
Aerobic bacteria require oxygen to decompose biodegradable organic matter during the secondary stage of wastewater treatment and subsequently settle as activated sludge.

Your note

More from Chapter 2: Wastewater story

With reference to the composition of sewage, consider the following statements: 1. It is a liquid waste consisting entirely of dissolved impurities. 2. It contains nutrients such as phosphorus and nitrogen. 3. It is devoid of any saprophytic or disease-causing bacteria. Which of the statements given above is/are correct?

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Consider the following statements regarding the impurities found in sewage: 1. Urea and pesticides are classified as organic impurities. 2. Nitrates and phosphates are classified as organic impurities. 3. Vegetable waste and animal waste are classified as organic impurities. Which of the statements given above is/are correct?

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Consider the following statements regarding the physical treatment of wastewater: 1. Bar screens are used to remove large objects like rags and sticks. 2. The speed of wastewater is increased in the grit and sand removal tank to facilitate filtration. 3. Sedimentation tanks are designed to increase the flow speed to prevent settling of solids. Which of the statements given above is/are correct?

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With reference to unit operations used in wastewater treatment, the role of a skimmer is to:

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Consider the following statements regarding "Activated Sludge": 1. It consists of suspended microbes that settle at the bottom of the tank after aeration. 2. It contains a very low percentage of water, being mostly solid. 3. A part of it is pumped back into the aeration tank to serve as an inoculum. Which of the statements given above is/are correct?

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The correct option is (b).

Explanation

Statement-wise Analysis:

Statement 1 is Incorrect. By definition, aerobic bacteria require the presence of oxygen to survive and function effectively. Bacteria that function in the absence of oxygen are classified as anaerobic bacteria.
Statement 2 is Correct. During the biological treatment phase (specifically in aeration tanks), air is pumped into the water to support the growth of aerobic bacteria. These bacteria consume organic contaminants, including human waste, food waste, soaps, and other biodegradable matter remaining in the clarified water.
Statement 3 is Incorrect. These bacteria do not remain permanently suspended. After they have consumed the organic matter, the water is transferred to a settling tank. Here, the bacterial flocs (masses of bacteria) settle at the bottom to form activated sludge, allowing the treated water to be separated from the top.

Key Takeaway:
Aerobic bacteria require oxygen to decompose biodegradable organic matter during the secondary stage of wastewater treatment and subsequently settle as activated sludge.