Class 9 Science Chapter 13 Wastewater Story Previous Year Questions with Answers (2020–2025)

Reading your NCERT textbook or revision notes once more feels productive—but it doesn't train your exam brain. When you solve past year questions, three things happen: (1) You immediately identify which topics examiners love—sewage sources and treatment plants dominate, while housekeeping practices appear less often. (2) You learn the exact language and depth examiners expect; a 1-mark answer on 'sources of sewage' should list 3–4 sources (residential, industrial, hospitals, agriculture), not write 10 lines. (3) You build confidence through repetition—solving the same question type 3–4 times makes exam day feel familiar. Studies show students who solve 10–15 past papers score 15–20% higher than those who only revise. For Class 9 Science, the pattern is stable: expect 1–2 questions on sewage treatment steps, 1 on disease links, and at least one application question on housekeeping or sanitation. Start now with questions below, and use cbsetutor.ai's guided solutions to fill knowledge gaps in real time.

One-mark questions test definition, identification, and simple recall. These five questions have appeared (in nearly identical forms) across multiple CBSE papers and sample papers. **Q1. Name the major sources of sewage.** Ans: Residential areas (houses, apartments), commercial establishments (shops, offices), hospitals, and agricultural runoff are the main sources of sewage. **Q2. What is the primary function of a septic tank?** Ans: A septic tank is a watertight chamber where solid particles settle at the bottom and bacterial decomposition breaks down organic matter, while cleaner water flows to the drain field. **Q3. Which type of organism causes cholera and how is it transmitted?** Ans: Cholera is caused by the bacterium *Vibrio cholerae*, transmitted through contaminated water and food, especially in areas with poor sanitation. **Q4. Name one housekeeping practice that prevents waterborne diseases.** Ans: Boiling drinking water kills pathogens; or using a water filter; or maintaining proper toilet hygiene and handwashing. **Q5. What is the purpose of a primary settlement tank in a treatment plant?** Ans: It removes suspended solids (sand, grit, and larger particles) from sewage through sedimentation, allowing heavy particles to settle.

Three-mark questions require explanation, comparison, or listing 2–3 related points. Examiners expect clear reasoning and textbook-aligned language. **Q1. Explain how untreated sewage can contaminate groundwater and cause disease. (3 marks)** Ans: Untreated sewage contains pathogenic bacteria, viruses, and parasites. When sewage leaks from broken pipes or seeps through soil, these microorganisms reach the water table. People who drink contaminated groundwater ingest these pathogens, causing diseases like typhoid, dysentery, and hepatitis A. Poor septic tank design or lack of proper lining accelerates this contamination in rural areas. **Q2. Describe the two main stages of wastewater treatment in a municipal treatment plant. (3 marks)** Ans: (1) Primary treatment: Raw sewage enters a primary settlement tank where heavy solids (sand, grit) settle to the bottom (sludge) and are removed. Oils and lighter particles float and are skimmed. This removes ~30% of pollutants. (2) Secondary treatment: The clearer liquid from primary treatment flows to an aeration tank where oxygen-loving bacteria decompose remaining organic matter into CO₂ and water. A secondary settlement tank then removes the dead bacteria, leaving cleaner effluent. **Q3. Why is chlorination the final step in wastewater treatment? Explain briefly. (3 marks)** Ans: Chlorine is a disinfectant that kills remaining disease-causing bacteria and viruses that survived primary and secondary treatment. Although secondary treatment removes most organic pollutants, some pathogens survive. Chlorination ensures the discharged water is safe for the environment and downstream water bodies. It is the final safety barrier before treated water re-enters rivers or groundwater. **Q4. How do better housekeeping practices reduce waterborne diseases in a community? Give two examples. (3 marks)** Ans: Better housekeeping includes proper waste segregation, safe water storage, hygiene practices, and sanitation awareness. Example 1: Storing water in clean, covered containers prevents mosquito breeding and keeps pathogenic bacteria out. Example 2: Regular handwashing with soap before eating and after toilet use stops fecal-oral transmission of diseases like diarrhea and cholera. Communities with these practices report 40–60% fewer waterborne disease cases. **Q5. Compare the role of aeration tanks and settlement tanks in wastewater treatment. (3 marks)** Ans: Aeration tanks introduce air and microorganisms to decompose dissolved organic matter aerobically, reducing BOD (biochemical oxygen demand). Settlement tanks allow particles and dead microorganisms to settle by gravity, clarifying the water. Aeration tanks are 'treatment agents' (active decomposition), while settlement tanks are 'separation units' (passive sedimentation). Together they remove ~90% of pollutants.

Five-mark questions demand detailed explanation, diagrams, or multi-step problem-solving. These are typically case-study or application-based. **Q1. A village with 5,000 people has no sewage treatment plant. Explain the health and environmental risks, and propose two solutions using the sewage treatment concept. (5 marks)** Full Solution: Health Risks: (1 mark) Untreated sewage contains pathogenic bacteria (*Vibrio cholerae, Salmonella*), viruses (hepatitis A, polio), and parasites. Open defecation or poorly maintained pit latrines contaminate groundwater. Residents drinking this water develop diarrhea, typhoid, and jaundice. Children and elderly are most vulnerable. Environmental Risks: (1 mark) Raw sewage discharged into rivers depletes dissolved oxygen, killing fish and aquatic life. Algal blooms form due to nutrient overload (eutrophication). The river becomes unfit for downstream irrigation and drinking. Solution 1—Decentralized Treatment: (1.5 marks) Build small modular treatment plants in clusters. Raw sewage undergoes primary sedimentation (settle tank removes solids), then secondary treatment using constructed wetlands (plants and soil bacteria decompose organic matter naturally). This suits rural settings with space. Solution 2—Improved Sanitation: (1.5 marks) Construct septic tanks with soak pits for every household. Ensure regular desludging (removal of accumulated sludge). Train community on handwashing and water storage. Educate on not defecating in open spaces. This reduces pathogen load entering groundwater by 70–80%. **Q2. Draw and label the flow of wastewater through a municipal treatment plant. Explain what happens at each stage. (5 marks)** Full Solution: Diagram Flow: (1 mark) Sketch boxes in sequence: Raw Sewage → Screening (removes large solids) → Primary Settlement Tank → Aeration Tank (Secondary Treatment) → Secondary Settlement Tank → Chlorination → Discharge. Stage 1—Screening (0.5 marks): Removes plastic bags, sticks, stones, and grit using a coarse filter. Prevents damage to pumps and machinery. Stage 2—Primary Settlement (1 mark): Solids settle to the bottom as sludge (25–30% of pollutants removed). Fats and oils float and are skimmed. The clear liquid (supernatant) moves to secondary treatment. Stage 3—Aeration/Secondary Treatment (1.5 marks): The liquid is mixed with oxygen and aerobic bacteria (e.g., *Bacillus, Pseudomonas*) decompose dissolved organic matter. BOD decreases from 200 mg/L to ~50 mg/L. Takes 4–6 hours in the tank. Stage 4—Secondary Settlement (0.5 marks): Dead bacteria and fine particles settle out. Clear water flows to chlorination. Stage 5—Chlorination (0.5 marks): Chlorine kills remaining pathogens. The effluent is now safe to discharge into rivers or reuse for irrigation. **Q3. A region experiences recurring outbreaks of cholera. The municipal water supply tests positive for *Vibrio cholerae*. Propose a comprehensive public health response combining treatment, sanitation, and housekeeping measures. (5 marks)** Full Solution: Immediate Treatment Response (1.5 marks): Increase chlorination dosage in water treatment plants from 0.5 mg/L to 2 mg/L to kill *Vibrio cholerae*. Flush all water pipes to remove stagnant water. Set up emergency water distribution points with pre-boiled or pre-treated water. Distribute water purification tablets (e.g., potassium permanganate) to households. Sanitation Infrastructure (1.5 marks): Repair broken sewage pipes (a major source of contamination). Upgrade septic tanks in slum areas and ensure regular desludging. Build household toilets with proper sealing to prevent groundwater leakage. Construct a secondary sewage treatment plant if the existing one is overloaded (treating more sewage than designed capacity causes raw sewage discharge). Housekeeping Practices (1.5 marks): Launch a public awareness campaign: (1) Boil drinking water for 1 minute before consumption; (2) Wash hands with soap for 20 seconds after using the toilet and before eating; (3) Store water in clean, covered containers away from contamination; (4) Use ORS (oral rehydration solution) if diarrhea develops; (5) Report suspected cholera cases to health authorities immediately. Monitoring and Enforcement (0.5 marks): Test water supply twice weekly. Monitor sewage treatment plant efficiency. Conduct surprise inspections of water vendors and food handlers. Track disease cases through hospital reports. This three-pronged approach (treatment + infrastructure + behavior change) has reduced cholera outbreaks by 80% in similar settings.

The CBSE rationalized the Class 9 curriculum in 2024–25, removing some content and emphasizing applied learning. For Wastewater Story, here are the key shifts to expect: Increased Focus on Application: The board is moving away from pure rote learning. Expect fewer questions asking 'Define secondary treatment' and more asking 'How would you treat sewage in a remote village with no electricity?' This means understanding *why* each treatment step works, not just *what* it is. Practice case-study questions above; they model the new pattern. Emphasis on Sanitation-Disease Link: The 2026–27 syllabus explicitly connects poor sanitation to disease spread. Examiners will ask: 'How does open defecation cause typhoid?' rather than just naming the disease. Study the mechanism—fecal matter contaminating water supplies, ingestion of pathogens, infection. Environmental Angle: Expect more questions on how untreated sewage damages rivers, kills aquatic life, and causes eutrophication. The board wants students to see sewage treatment not as a public health issue alone, but an environmental necessity. Less on Treatment Plant Machinery, More on Design Choices: Questions won't ask the exact diameter of an aeration tank. Instead: 'Why is aeration necessary in secondary treatment?' or 'Why do you need both a primary and secondary settlement tank?' Focus on principle, not specification. Shorter Answers, Sharper Points: With board exams now reducing space and time, answers must be concise. A 5-mark answer should hit 4–5 key ideas in 150–180 words, not ramble. Review the solved questions above for this structure.

Exam performance depends not just on knowledge but on how you tackle questions. Use this three-step strategy: **Step 1—Read and Categorize (30 seconds per question):** As you open the paper, quickly scan all Chapter 13 questions. Mark them as (a) Definition/recall (1–2 marks), (b) Explanation/comparison (3 marks), (c) Application/case-study (5 marks). This tells you which questions to attempt first. **Step 2—Tackle Easy Ones First (1-mark questions, 5–7 minutes total):** One-mark questions are high-confidence wins. List sewage sources in 20 seconds, define septic tank in 15 seconds. Each correct answer builds momentum. Common 1-mark patterns: name the disease caused by contaminated water, state a sewage source, define a term, name a housekeeping practice. Refer to the five 1-mark questions above; examiners rarely ask anything beyond these. **Step 3—Outline Before Writing 3 & 5-Mark Answers (2 minutes planning, 6 minutes writing per question):** For 3-mark questions, jot down three bullet points (e.g., 'Primary treatment: settles solids → Secondary treatment: bacteria decompose organics → Chlorination: kills pathogens'). Then expand each point into 2–3 sentences. This ensures you hit all three marks without repeating yourself. For 5-mark questions, use the CRADLE method: Context (what's the situation?), Reasoning (why does this happen?), Action (what's the solution?), Details (give examples), Linked (connect back to the question). The sample 5-mark solutions above follow this structure. **Step 4—Check for Diagram Clues:** If the question asks to 'draw and label,' spend 1.5 minutes on a clear sketch (sewage treatment plant flow, septic tank cross-section). A well-labeled diagram often earns 2–3 marks alone; sloppy sketches lose marks even if your explanation is correct. **Time Allocation (for a 2-hour exam with 40–45 marks for the entire science paper):** Allocate ~25 minutes for all Chapter 13 questions. If Chapter 13 is 1/6 of the paper (6–7 marks), spend 6–8 minutes. If it's 1/4 (10 marks), spend 10–12 minutes. Avoid over-answering; once you've hit the mark-value, move on (a 3-mark question answered in 8 minutes is wasted time). **Common Mistakes to Avoid:** (1) Writing too much for 1-mark questions—four sources of sewage, not a paragraph. (2) Forgetting to name the microorganism (bacteria, virus, parasite) when describing diseases. (3) Describing treatment plant stages out of order (raw sewage doesn't go straight to chlorination). (4) Mixing up primary and secondary treatment roles. (5) Forgetting to mention *why* each step is needed, not just *what* happens. Review the solved questions above to see how answers balance brevity with completeness.