Class 7 Science

Chapter 18: Wastewater Story

STAGE 0: Foundation / Basics

Water used in homes, schools, and industries becomes dirty.

This dirty water is called wastewater.

What is Wastewater?

Wastewater contains dirt, human waste, soaps, oils, and chemicals.

It must be cleaned before releasing into rivers.

Sewage

Wastewater that flows through drains is called sewage.

Untreated sewage can cause diseases.

Sewage Treatment Plant (STP)

A Sewage Treatment Plant cleans wastewater.

Main steps:

• Screening – removal of large objects
• Sedimentation – heavy particles settle
• Aeration – air is pumped to help bacteria
• Chlorination – kills harmful germs

Sludge

Solid waste that settles at the bottom is called sludge.

It can be used to produce biogas or manure.

Sanitation and Hygiene

Proper sanitation keeps people healthy.

• Use toilets
• Do not throw waste in water bodies
• Keep surroundings clean

Reuse of Treated Water

Treated water can be reused for:

• Gardening
• Cleaning roads
• Industries

STAGE 2: NCERT Textbook Questions & Answers

Q1. What is wastewater?

Water that becomes dirty after use is called wastewater.

Q2. Why should sewage be treated?

To remove harmful substances and prevent water pollution.

Q3. What is sludge?

Solid waste that settles at the bottom during treatment.

STAGE 3: Exam-Oriented Questions

Fill in the blanks:

• Dirty water is called __________.
• Solid waste that settles is called __________.

Very Short Answer:

Name one step of sewage treatment.
Answer: Screening

Quick Revision Points

• Wastewater must be treated
• Sewage contains harmful substances
• STP cleans wastewater
• Clean water protects health