CUET UG Biology Booster Test 2-Microbes in Sewage Treatment -

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CUET UG Biology Booster Test 2-Microbes in Sewage Treatment

⏱️ 30 Minutes

❓ 20 Questions

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET UG Biology Booster Test 2-Microbes in Sewage Treatment

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QUESTION 1 OF 20

Evaluate the following statements about municipal waste components:
Statement 1: Municipal waste-water contains minor amounts of organic matter and microbes.
Statement 2: A major component of this waste water is human excreta.

Answer Review

1 Evaluate the following statements about municipal waste components:
Statement 1: Municipal waste-water contains minor amounts of organic matter and microbes.
Statement 2: A major component of this waste water is human excreta.

A Statement 1 is true, Statement 2 is false.

B Statement 1 is false, Statement 2 is true.

C Both statements are true.

D Both statements are false.

💡 Short Explanation

Municipal wastewater is heavily polluted with organic matter and microbes. Human excreta is the defining major component of domestic sewage. Statement 1 underestimates the pollutant load.

✅ Correct Answer Explanation

Municipal wastewater, or domestic sewage, contains large—not minor—amounts of organic matter and pathogenic microbes. Statement 2 is correct because human excreta is the primary organic constituent that gives municipal sewage its high polluting potential. Therefore, Statement 1 is false and Statement 2 is true.

❓ Why Other Options Are Incorrect

Option A → Incorrect because Statement 2 is factual, not false.
Option C → Incorrect because Statement 1 falsely labels the high pollutant load as "minor."
Option D → Incorrect because Statement 2 is a well-established fact of sewage composition.

🎯 Strategy

Used: Elimination

Application: Evaluate each statement against the NCERT definition of domestic sewage as a "major" source of pollution.

Final Logic: Once Statement 1 is identified as false, Option B becomes the only valid choice.

🧠 Memory Trick

Sewage = MAJOR pollution (not minor).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

2 Because sewage contains many pathogenic microbes, what essential requirement must be met before disposing of it into natural water bodies?

A It must be treated in sewage treatment plants (STPs) to make it less polluting.

B It must be directly heated to kill pathogens.

C It must be converted entirely into biogas.

D It must be mixed with fresh river water to dilute the pathogens.

💡 Short Explanation

Untreated sewage causes water-borne diseases and pollution. STPs utilize microbes to reduce organic load and pathogens. Dilution is not an effective or standard treatment Strategy.

✅ Correct Answer Explanation

Sewage treatment in STPs is the mandatory industrial process designed to remove organic pollutants and reduce microbial load before effluent is discharged into rivers. This prevents the spread of water-borne diseases and protects the health of natural water bodies. Other options like heating or mixing (dilution) are technically impractical or ineffective on a municipal scale.

❓ Why Other Options Are Incorrect

Option B → Large-scale heating of millions of liters of water is energy-prohibitive and impractical.
Option C → Anaerobic digestion only treats sludge, not the entire volume of municipal wastewater.
Option D → Dilution is "the solution to pollution" fallacy; it does not remove pathogens or organic matter.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Identify the specific industrial process (STPs) described in the NCERT for this purpose.

Final Logic: STPs are the standardized environmental solution provided in the text.

🧠 Memory Trick

Sewage Problem = STP Solution.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

3 Match the target waste component with its correct physical removal technique during primary treatment:

Column 1	Column 2
1. Floating debris	P. Forms the effluent
2. Soil and pebbles	Q. Sequential filtration
3. Supernatant liquid	R. Forms primary sludge
4. Settled solids	S. Sedimentation

A 1-Q, 2-P, 3-S, 4-R

B 1-S, 2-Q, 3-R, 4-P

C 1-Q, 2-S, 3-P, 4-R

D 1-P, 2-S, 3-Q, 4-R

💡 Short Explanation

Debris = Filtration (Q). Soil/Pebbles = Sedimentation (S). Supernatant = Effluent (P). Settled solids = Sludge (R).

✅ Correct Answer Explanation

Floating debris is removed by sequential filtration (1-Q). Soil and pebbles (grit) are removed via sedimentation (2-S). The supernatant liquid that remains is called the effluent (3-P). The solids that settle at the bottom constitute the primary sludge (4-R). Option C aligns these perfectly.

❓ Why Other Options Are Incorrect

Options A, B, and D mismatch the physical components with their correct process or nomenclature.

🎯 Strategy

Used: Option Grouping

Application: Match the pairs you are 100% certain about (e.g., Debris=Filtration) to filter out wrong options.

Final Logic: Only Option C provides a 100% correct cross-reference.

🧠 Memory Trick

Debris-Q, Grit-S, Effluent-P, Sludge-R.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

4 Which of the following processes is NOT involved in the primary treatment of sewage?

A Sequential filtration

B Physical removal of particles

C Sedimentation of grit

D Biological breakdown of organic matter

💡 Short Explanation

Primary treatment is physical. Biological treatment occurs in the secondary stage. Filtration and sedimentation are physical techniques.

✅ Correct Answer Explanation

Primary treatment is strictly a physical process involving filtration and sedimentation to remove solid particles. The biological breakdown of organic matter is the defining characteristic of "Secondary Treatment" (biological treatment), which occurs in the aeration tank.

❓ Why Other Options Are Incorrect

Option A → Filtration is the first physical step.
Option B → Physical removal is the goal of primary treatment.
Option C → Sedimentation is the physical method used for grit removal.

🎯 Strategy

Used: Elimination

Application: Differentiate between Physical (Primary) and Biological (Secondary) stages.

Final Logic: Since the process is physical, the biological option is the outlier.

🧠 Memory Trick

Primary = Physical, Secondary = Biological.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

5 What directly differentiates primary sludge from the primary effluent?

A Primary sludge contains pathogenic microbes, while effluent is completely sterile.

B Primary sludge consists of settled solids, while effluent is the supernatant liquid.

C Primary sludge is passed to aeration tanks, while effluent goes to anaerobic digesters.

D Primary sludge is formed by biological flocs, while effluent is formed by grit.

💡 Short Explanation

Sludge = Bottom solids. Effluent = Top liquid (supernatant). This is the fundamental split in primary treatment.

✅ Correct Answer Explanation

The primary settling process physically separates sewage into two parts: the dense solid waste that accumulates at the bottom (primary sludge) and the clearer liquid that stays on top (supernatant or primary effluent). Option B is the only accurate physical description of this separation.

❓ Why Other Options Are Incorrect

Option A → Effluent is not sterile; it still contains high organic loads.
Option C → Sludge goes to digesters, while effluent goes to aeration tanks.
Option D → Flocs are biological, whereas primary output is physical.

🎯 Strategy

Used: Substitution

Application: Define the physical outputs of a settling tank as per the chapter.

Final Logic: Sludge=Solids, Effluent=Liquid.

🧠 Memory Trick

Sludge (Solid) vs. Effluent (Liquid).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

6 Arrange the pathway of the primary effluent:
1. Passed into large aeration tanks
2. Separation from primary sludge in the settling tank
3. Subjected to biological treatment

A 1 → 2 → 3

B 2 → 3 → 1

C 3 → 1 → 2

D 2 → 1 → 3

💡 Short Explanation

Step 1: Physical separation (2). Step 2: Transfer to aeration tank (1). Step 3: Biological process (3).

✅ Correct Answer Explanation

The process begins with the physical separation of the effluent from the sludge in the primary settling tank (2). This effluent is then passed into the large aeration tanks (1), where it undergoes secondary biological treatment (3). The order 2 → 1 → 3 follows the plant workflow accurately.

❓ Why Other Options Are Incorrect

Option A → Passing into the tank cannot happen before physical separation.
Option B → Biological treatment must follow the tank placement.
Option C → Biological treatment cannot occur before the effluent is passed into the tank.

🎯 Strategy

Used: Substitution

Application: Follow the liquid path in a Sewage Treatment Plant.

Final Logic: Separate → Transfer → Treat.

🧠 Memory Trick

Separate → Transfer → Treat.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

7 Analyze the following regarding the aeration tank process:
I. It involves constant mechanical agitation.
II. It requires air to be pumped into the sewage.
III. It primarily supports anaerobic bacteria.

A I and II are correct

B II and III are correct

C I and III are correct

D All are correct

💡 Short Explanation

Agitation and air are essential for oxygen. Oxygen supports aerobic, not anaerobic, bacteria. Statement III is false.

✅ Correct Answer Explanation

Aeration tanks require constant mechanical agitation and air pumping (I and II) to maximize dissolved oxygen, which is essential for the growth of aerobic microbes. Statement III is incorrect because the aeration tank supports aerobic, not anaerobic, bacteria. Therefore, only I and II are correct.

❓ Why Other Options Are Incorrect

Option B → Includes Statement III, which is false.
Option C → Includes Statement III, which is false.
Option D → Includes Statement III, which is false.

🎯 Strategy

Used: Elimination

Application: Eliminate all options containing Statement III (the anaerobic claim).

Final Logic: Only Option A remains after excluding the false anaerobic statement.

🧠 Memory Trick

Aeration = Aerobic (Anti-Anaerobic).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

8 Which of the following outcomes is NOT a direct result of air pumping in the aeration tank?

A Vigorous growth of useful aerobic microbes

B Formation of flocs

C Decrease in the biochemical oxygen demand

D Immediate release of methane gas

💡 Short Explanation

Methane is produced by anaerobic digestion. Methane is NOT produced in the aerobic aeration tank. Air pumping promotes aerobic processes.

✅ Correct Answer Explanation

Air pumping promotes the growth of aerobic microbes (A), the formation of flocs (B), and the reduction of organic matter which decreases BOD (C). Methane production is characteristic of anaerobic sludge digesters, not the aerobic aeration tank. Thus, D is the correct answer.

❓ Why Other Options Are Incorrect

Option A → This is the primary intended result of aeration.
Option B → Flocs are the aggregation of these aerobic microbes.
Option C → Consuming organic matter lowers the BOD.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Match the result to the specific tank type (Aerobic vs. Anaerobic).

Final Logic: Aerobic tanks do not produce methane.

🧠 Memory Trick

Aeration = No Methane.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

9 How do fungal filaments contribute to the structure of biological flocs?

A They consume the bacteria to reduce their population.

B They associate with bacterial masses to form mesh-like structures.

C They produce oxygen for the bacteria to survive.

D They mechanically agitate the effluent.

💡 Short Explanation

Flocs are bacterial and fungal associations. They form a mesh. This mesh traps organic matter.

✅ Correct Answer Explanation

Biological flocs are defined in the NCERT as masses of bacteria associated with fungal filaments to form mesh-like structures. This structure allows the microbes to effectively capture and consume organic particles in the effluent.

❓ Why Other Options Are Incorrect

Option A → Fungi do not consume the bacteria; they live symbiotically in the floc.
Option C → Fungi do not produce oxygen; oxygen is provided by air pumping.
Option D → Mechanical agitation is performed by the aeration tank equipment.

🎯 Strategy

Used: Substitution

Application: Extract the definition of flocs from the textbook description.

Final Logic: "Mesh-like structures" is the key identifying feature.

🧠 Memory Trick

Floc = Bacteria + Fungi (Mesh).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

10 What is the primary function of the microbes within the biological flocs as they grow?

A To consume the major part of the organic matter in the effluent.

B To produce inflammable biogas.

C To remove grit and small pebbles.

D To form the primary sludge.

💡 Short Explanation

Flocs are the active biological treatment agents. They consume organic matter. This reduction in organic matter lowers the BOD.

✅ Correct Answer Explanation

As the flocs grow in the aeration tank, their metabolic activity consumes the significant organic load present in the primary effluent. This biological consumption is the mechanism that reduces the BOD of the sewage water.

❓ Why Other Options Are Incorrect

Option B → Biogas is produced by anaerobic bacteria in digesters, not aerobic flocs.
Option C → Grit is removed in primary treatment (physical).
Option D → Primary sludge is the result of primary treatment (physical).

🎯 Strategy

Used: Substitution

Application: Recall the primary goal of the "Secondary Treatment" (Biological) stage.

Final Logic: Consuming organic matter is the goal of secondary treatment.

🧠 Memory Trick

Flocs = Organic Matter Consumers.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

11 Which of the following statements about BOD is INCORRECT?

A BOD measures the rate of uptake of oxygen by micro-organisms.

B A greater BOD indicates a lower polluting potential of waste water.

C BOD is indirectly a measure of the organic matter present in water.

D Sewage water is treated until the BOD is reduced.

💡 Short Explanation

BOD stands for Biochemical Oxygen Demand. High BOD = High organic matter = High pollution. Low BOD = Low organic matter = Low pollution.

✅ Correct Answer Explanation

BOD is the amount of oxygen required by aerobic microorganisms to break down organic matter in a sample of water. A higher BOD signifies a larger concentration of organic pollutants that require more oxygen for decomposition. Therefore, stating that greater BOD indicates a "lower" polluting potential is scientifically incorrect.

❓ Why Other Options Are Incorrect

Option A → This is the correct definition of how BOD is measured in laboratory conditions.
Option C → Since microbes consume organic matter for respiration, the oxygen demand is directly proportional to the amount of organic substrate available.
Option D → The primary goal of secondary treatment is to reduce BOD to a level safe for discharge.

🎯 Strategy

Used: Elimination

Application: Identify the direct inverse relationship between BOD and polluting potential.

Final Logic: Since high BOD equals high pollution, Option B is clearly the INCORRECT statement.

🧠 Memory Trick

High BOD = High Pollution.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

12 Match the condition of the water sample with its corresponding BOD status:

Column 1	Column 2
1. High concentration of organic matter	P. Very high BOD
2. After extensive secondary treatment	Q. Highly reduced BOD
3. Pure river water	R. Very low BOD
4. Untreated sewage	S. High BOD polluting potential

A 1-S, 2-R, 3-P, 4-Q

B 1-P, 2-R, 3-Q, 4-S

C 1-Q, 2-P, 3-S, 4-R

D 1-S, 2-Q, 3-R, 4-P

💡 Short Explanation

High organic matter = High polluting potential (S). After treatment = Reduced BOD (Q). Pure water = Very low BOD (R). Untreated sewage = Very high BOD (P).

✅ Correct Answer Explanation

High concentration of organic matter correlates to high polluting potential (1-S). Extensive secondary treatment effectively removes organic material, leading to a highly reduced BOD (2-Q). Pure, unpolluted river water naturally has very low BOD (3-R). Untreated sewage, being the most contaminated, has a very high BOD (4-P). Option A provides this mapping accurately.

❓ Why Other Options Are Incorrect

Options B, C, and D contain incorrect associations based on the standard BOD levels for these water types.

🎯 Strategy

Used: Option Grouping

Application: Anchor the definitions (e.g., Pure water = Lowest BOD) and eliminate distractors.

Final Logic: Option A correctly reflects the gradient from raw sewage to treated or pure water.

🧠 Memory Trick

Sewage (High) → Treated (Low) → Pure (Lowest).

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

13 Under what condition are the bacterial 'flocs' allowed to sediment to form activated sludge?

A Before the primary effluent enters the aeration tank

B Immediately after grit sedimentation

C Once the BOD of the sewage is reduced significantly

D After the production of biogas in digesters

💡 Short Explanation

Aeration allows microbes to consume organic matter. BOD reduces during this consumption. Settling follows the reduction of BOD.

✅ Correct Answer Explanation

The aeration process continues until the aerobic microbes have consumed the majority of the organic matter, which directly correlates to a significant reduction in BOD. Only after this reduction are the flocs allowed to settle in a secondary tank to form the "activated sludge," which is rich in active microbes.

❓ Why Other Options Are Incorrect

Option A → Primary effluent is the input, not the output of the aeration phase.
Option B → Grit is physical; activated sludge is biological.
Option D → Biogas is produced from sludge, not before sludge is activated.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Sequence the stages of biological treatment as defined in the textbook.

Final Logic: Treatment (BOD reduction) must precede settling.

🧠 Memory Trick

BOD Reduction First → Settling Second.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

14 Which of the following statements is NOT a valid description of the inoculum used in secondary treatment?

A It consists of a small part of the activated sludge.

B It is pumped back into the primary settling tank.

C It serves to maintain the population of aerobic microbes in the aeration tank.

D It contains bacterial flocs.

💡 Short Explanation

Activated sludge is pumped back to the aeration tank. It is NOT pumped into the primary settling tank. Primary settling is for physical separation only.

✅ Correct Answer Explanation

The inoculum consists of activated sludge containing bacterial flocs (A and D). It is recycled into the aeration tank (C) to ensure a steady supply of aerobic microbes to start the treatment process for new batches of effluent. Pumping it into the primary settling tank (B) is incorrect because that stage is dedicated to purely physical sedimentation.

❓ Why Other Options Are Incorrect

Option A → Valid description (it is recycled).
Option C → Valid function of the inoculum.
Option D → Valid composition (the sludge is composed of flocs).

🎯 Strategy

Used: Elimination

Application: Trace the path of the recycled sludge in the STPs diagram.

Final Logic: Activated sludge goes back to the AERATION tank, not the primary one.

🧠 Memory Trick

Inoculum = Recycled to AERATION.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

15 What happens to the remaining major part of the activated sludge inside the anaerobic sludge digesters?

A It is continuously agitated mechanically with air.

B It is pumped directly into natural water bodies.

C Other kinds of anaerobic bacteria digest the bacteria and fungi present in the sludge.

D It is transformed back into primary sludge.

💡 Short Explanation

Digesters use anaerobic bacteria. They break down the organic biomass of the aerobic sludge. Result: Digested sludge + Biogas.

✅ Correct Answer Explanation

The bulk of the activated sludge is moved into anaerobic sludge digesters. In this oxygen-free environment, specialized anaerobic bacteria perform the digestion of the biomass (the bacteria and fungi from the aeration tank), breaking them down to release methane, H₂S and CO₂.

❓ Why Other Options Are Incorrect

Option A → Agitation with air is for the aeration tank, not anaerobic digesters.
Option B → Releasing sludge into water bodies would be a major pollution event.
Option D → Primary sludge is physically separated, not transformed from secondary activated sludge.

🎯 Strategy

Used: Substitution

Application: Define the function of an "anaerobic sludge digester."

Final Logic: The term "digestion" refers to the microbial breakdown of the sludge biomass.

🧠 Memory Trick

Anaerobic Bacteria = Sludge Digesting Engines.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

16 Arrange the sequence of processes leading to biogas production:
1. Bacteria produce a mixture of methane, hydrogen sulphide, and carbon dioxide.
2. Activated sludge is pumped into large anaerobic sludge digesters.
3. Anaerobic bacteria digest the bacteria and fungi in the sludge.

A 3 → 2 → 1

B 2 → 3 → 1

C 1 → 2 → 3

D 2 → 1 → 3

💡 Short Explanation

Step 1: Pump to digester (2). Step 2: Digestion occurs (3). Step 3: Gas release (1).

✅ Correct Answer Explanation

First, the activated sludge is moved to the digesters (2). Next, the anaerobic bacteria carry out the digestion process by breaking down the sludge biomass (3). Finally, as a byproduct of this digestion, the mixture of gases (biogas) is produced and released (1). The sequence 2 → 3 → 1 is logically correct.

❓ Why Other Options Are Incorrect

Options A, C, and D misrepresent the causality of the process (e.g., digestion must occur before the gas is produced).

🎯 Strategy

Used: Substitution

Application: Follow the chronological flow of sludge to biogas conversion.

Final Logic: Transfer → Digestion → Gas Release.

🧠 Memory Trick

Transfer → Digest → Produce Gas.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

📄 Passage

"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."

Based on the passage, what is the fate of the effluent from the secondary treatment plant?

A It is reused as drinking water.

B It is pumped back into the aeration tank.

C It is released into natural water bodies like rivers and streams.

D It is directed to the anaerobic sludge digester.

💡 Short Explanation

Passage text: "effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams." This is the final step in the treatment cycle.

✅ Correct Answer Explanation

The text explicitly states that the secondary treatment effluent is generally discharged into natural water bodies. While STPs aim to reduce the polluting load, this is the final disposal point for the liquid effluent after biological treatment.

❓ Why Other Options Are Incorrect

Option A → Standard STPs do not treat water to drinking quality standards.
Option B → Inoculum is recycled, but the bulk effluent is not.
Option D → Digesters only treat the sludge, not the secondary effluent.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Locate the exact sentence in the passage regarding the effluent fate.

Final Logic: Direct reading comprehension confirms C.

🧠 Memory Trick

Effluent → River.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

📄 Passage

What is cited as the primary reason for untreated sewage being discharged directly into rivers?

A The number of sewage treatment plants not increasing enough to match sewage production.

B The failure of sequential filtration techniques.

C The Ministry of Environment and Forests mandating direct discharge.

D A decrease in urbanisation in recent years.

💡 Short Explanation

The passage mentions rising urbanization produces more sewage. Infrastructure (STPs) growth is lagging. This imbalance is the cause.

✅ Correct Answer Explanation

The passage clearly states: "the number of sewage treatment plants has not increased enough to treat such large quantities." This disparity between rapid sewage production and limited treatment infrastructure is the reason provided for the direct discharge of untreated sewage.

❓ Why Other Options Are Incorrect

Option B → The passage does not discuss filtration failure.
Option C → The Ministry's action plans aim to STOP direct discharge, not mandate it.
Option D → The passage actually cites "increasing urbanisation," not a decrease.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Extract the cause-effect relationship from the passage text.

Final Logic: STP growth < Sewage production = Untreated discharge.

🧠 Memory Trick

Too much sewage, too few STPs.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

19 What is the core Strategy proposed under the Ganga and Yamuna Action Plans to prevent river pollution?

A To physically remove floating debris from the river surface using nets.

B To convert the entire river water into biogas.

C To introduce pathogenic organisms to compete with existing microbes.

D To build a large number of STPs so that only treated sewage is discharged.

💡 Short Explanation

Plans = Infrastructure. Infrastructure = STPs. Goal = Discharge ONLY treated sewage.

✅ Correct Answer Explanation

The core Strategy of these national action plans is the systematic construction of a large number of sewage treatment plants. This ensures that municipal waste is effectively processed so that only treated, non-polluting effluent enters the river systems, fulfilling the plans' environmental objectives.

❓ Why Other Options Are Incorrect

Option A → Net removal is a surface-level temporary measure, not a comprehensive treatment Strategy.
Option B → Converting river water to biogas is scientifically impossible and not a proposed plan.
Option C → Introducing pathogens would worsen the contamination.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Identify the core "proposal" as described in the chapter/passage.

Final Logic: The goal is treatment through construction of STPs.

🧠 Memory Trick

Action Plan = More STPs.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

20 By implementing the Yamuna Action Plan, what is the expected outcome for the river ecosystem?

A An increase in primary sludge sedimentation within the river.

B A continuous supply of activated sludge to the river banks.

C Increased mechanical agitation of the river water.

D A decrease in water-borne diseases due to the discharge of only treated sewage.

💡 Short Explanation

Treated sewage = Reduced pathogen load. Reduced pathogen load = Reduced water-borne diseases. Outcome = Improved public health.

✅ Correct Answer Explanation

The primary ecological and public health benefit of ensuring only treated sewage reaches the river is the removal of the pathogenic microbial load. By reducing pathogens, the incidence of water-borne diseases in populations relying on the river water is significantly decreased.

❓ Why Other Options Are Incorrect

Option A → Sludge sedimentation is meant for the STP, not the river bed.
Option B → Activated sludge should stay within the STP cycle; dumping it elsewhere would pollute the environment.
Option C → Mechanical agitation is a part of the aeration process, not a goal for a river.

🎯 Strategy

Used: Substitution

Application: Link the treatment process to its ultimate public health benefit.

Final Logic: Fewer pathogens = Less disease.

🧠 Memory Trick

Treated Sewage = Cleaner Water = Fewer Diseases.

📚 Class XII – Biology – Chapter: Microbes in Human Welfare – Topic: Microbes in Sewage Treatment

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