Wastewater Story — Class 7 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 7 Science chapter "Wastewater Story" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 7 Science chapter "Wastewater Story" — 8 important questions with detailed answers for CBSE board exam pre…
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Key Questions Covered:
- What is wastewater? What are its sources?
- What is sewage? Distinguish between sewage and wastewater.
- Describe the main steps in wastewater treatment.
- What is the difference between primary and secondary treatment?
- What is activated sludge? How does it work in treatment?
- What is biosolids or sludge? What is its disposal?
- + 2 more questions in the full chapter
Solutions Summary:
| Question | Status |
|---|---|
| What is wastewater? What are its sources? | ✓ Solved |
| What is sewage? Distinguish between sewage and wastewater. | ✓ Solved |
| Describe the main steps in wastewater treatment. | ✓ Solved |
| What is the difference between primary and secondary trea… | ✓ Solved |
| What is activated sludge? How does it work in treatment? | ✓ Solved |
| What is biosolids or sludge? What is its disposal? | ✓ Solved |
Showing 6 of 8 questions
Q1: What is wastewater? What are its sources?
Wastewater: water from households, industries, and agriculture containing dissolved and suspended impurities and pollutants. Sources:
1. Household: bathrooms, kitchens, laundry (sewage)
2. Industrial: factories, mills, chemical plants
3. Agricultural: runoff from fields containing fertilizers, pesticides, soil
4. Commercial: restaurants, hotels, hospitals
5. Stormwater: rainwater mixed with dust and pollutants
6. Groundwater: mineral-rich water from deep sources
Contains harmful pathogens, chemi...
Q2: What is sewage? Distinguish between sewage and wastewater.
Sewage: wastewater from houses (toilets, sinks, bathrooms) containing feces, urine, and household waste. More concentrated in pollutants.
Wastewater: broader term; includes sewage plus water from industries, agriculture, and other sources.
Both contain pathogens and pollutants. Sewage is most dangerous due to fecal matter containing disease-causing bacteria (E. coli, Salmonella), viruses, parasites. Must be treated before disposal to prevent waterborne diseases and environmental contamination.
Q3: Describe the main steps in wastewater treatment.
Wastewater treatment process:
1. Screening: remove large objects (sticks, rags, plastic)
2. Sedimentation: solid particles settle (primary treatment), sludge collected
3. Aeration: pump air into wastewater, promote bacterial decomposition
4. Secondary settling: remaining suspended particles settle
5. Biological treatment: aerobic bacteria decompose organic matter
6. Filtration: sand/gravel filters remove remaining particles
7. Disinfection: chlorination/UV light kills pathogens
8. Final treatmen...
Q4: What is the difference between primary and secondary treatment?
Primary treatment:
1. Screening: remove large objects
2. Grit removal: separate sand, gravel
3. Sedimentation: heavy solids settle (sludge removed)
4. Purpose: remove 50-60% suspended solids
Secondary treatment:
1. Aeration: introduce oxygen
2. Biological decomposition: microorganisms (bacteria) break down organic matter
3. Settling: remaining solids precipitate
4. Purpose: remove 80-95% organic matter, reduce BOD (biological oxygen demand)
Secondary treatment requires longer time but produces c...
Q5: What is activated sludge? How does it work in treatment?
Activated sludge: mixture of flocculent microorganisms (bacteria, protozoa, fungi) concentrated in wastewater treatment. Formation: primary sludge is aerated to activate microbial growth.
How it works:
1. Microorganisms decompose dissolved organic matter in aeration tank
2. Sludge settles in secondary clarifier
3. Some sludge returned to aeration tank (maintains microbial population)
4. Excess sludge removed (waste sludge)
5. Clarified effluent flows out for disinfection
Advantage: efficient rem...
Q6: What is biosolids or sludge? What is its disposal?
Biosolids (sludge): residual solid matter separated during treatment; contains microorganisms, undecomposed organic matter, mineral nutrients. High in nitrogen and phosphorus.
Disposal methods:
1. Landfill: dump in designated sites
2. Composting: decompose aerobically to form compost for agriculture
3. Land application: spread on agricultural fields as fertilizer (nutrient-rich)
4. Incineration: burn at high temperature (reduce volume, kill pathogens)
5. Drying beds: solar drying reduces moistur...
Showing 6 of 8 questions. Visit the full page for complete solutions.
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