Science · Class 7
Wastewater Story
Sewage treatment, sanitation, and wastewater reuse.
4 sections15–25 min read6 MCQs · 2 examples
Chapter Overview
Wastewater from homes and industries must be treated before release. This chapter covers sewage composition, treatment steps, septic tanks, vermi-processing toilets, and sanitation diseases.
Wastewater Composition
- Sewage: human excreta, soaps, oils, chemicals
- Contaminates drinking water — spreads cholera, typhoid, hepatitis
- Open defecation major health risk
Treatment Process
- Bar screen: remove large debris
- Grit removal; sedimentation tank: sludge settles
- Aeration: bacteria decompose organic matter
- Chlorination disinfects; treated water released
Sanitation at Home
- Septic tank: anaerobic decomposition underground
- Composting toilets; vermi-processing with worms
- Do not flush plastics, oils, chemicals
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Waterborne disease
How does untreated sewage cause cholera?
- 1Pathogens in faeces enter water
- 2People drink contaminated water
- 3Vibrio bacteria cause severe diarrhoea
Answer
Contaminated water spreads disease
Treatment step
Why is aeration done in treatment plant?
- 1Adds oxygen for aerobic bacteria
- 2Bacteria break down organic waste
- 3Reduces harmful content
Answer
Biological decomposition of organics
Key Points to Remember
- ✓ Swachh Bharat focuses on sanitation
- ✓ Underground sewerage in cities
- ✓ 3 D's: defecation free, safe disposal, dignity
Exam Tips
- • List stages of wastewater treatment
- • Distinguish septic tank and sewer system
- • Name diseases from contaminated water
Practice MCQs — Wastewater Story
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Question 1 of 6Score: 0/0
Sewage contains: