Wastewater Story Class 7 important questions with answers PDF download
FAQs on CBSE Important Questions for Class 7 Science Wastewater Story - 2025-26
1. What are some important short-answer questions from Chapter 13, Wastewater Story, for the CBSE Class 7 exam 2025-26?
Some important short-answer (2 or 3-mark) questions include defining sewage, explaining the role of a bar screen in a Wastewater Treatment Plant (WWTP), and listing two diseases caused by poor sanitation and contaminated water. Another expected question is to explain what sludge is and how it is treated.
2. What is a likely 5-mark question from the Wastewater Story chapter?
A common 5-mark question for the 2025-26 exam would be to describe the complete process of wastewater treatment in a Wastewater Treatment Plant (WWTP). The answer should cover all the key stages in the correct order:
Primary Treatment: Bar screens, grit and sand removal, and sedimentation in a clarifier.
Secondary Treatment: Aeration to promote bacterial growth for consuming waste.
Tertiary Treatment: Disinfection using chlorine or UV light before releasing the treated water.
3. Why is it a bad practice to throw cooking oils and fats down the drain? What is its impact on the wastewater system?
It is a bad practice because oils and fats can harden and block the pipes, leading to clogs. In the sewer system, they can interfere with the wastewater treatment process by clogging the soil pores in drains, which reduces the effectiveness of water filtration. This is a frequently asked HOTS (Higher Order Thinking Skills) question.
4. How does the aeration step in a WWTP help in cleaning water, and what would happen if it were skipped?
The aeration step involves pumping air into clarified water to help aerobic bacteria grow rapidly. These bacteria are crucial as they consume the remaining organic human waste, soaps, and other unwanted matter. If this step were skipped, the organic contaminants would not be effectively removed, and the discharged water would remain polluted, causing harm to aquatic life and the environment.
5. Explain the terms 'sewage' and 'sludge'. How are they different?
Sewage is the liquid waste, or wastewater, released from homes, industries, hospitals, and other sources. It contains dissolved and suspended impurities. Sludge, on the other hand, is the solid material that settles down at the bottom of a sedimentation tank or clarifier during wastewater treatment. The key difference is that sewage is the incoming wastewater, while sludge is the separated solid byproduct of its treatment.
6. What are some expected Multiple Choice Questions (MCQs) from the Wastewater Story chapter?
Expected MCQs often test specific knowledge. For instance, a question might ask which of the following is used to disinfect water at the end of the treatment process (options: chlorine, oxygen, carbon dioxide, nitrogen). Another could be about the useful byproduct of sludge treatment, which is biogas. Questions about the definition of contaminants and types of sewers (sanitary, storm) are also common.
7. As an active citizen, what important practices can you adopt to minimise wastewater pollution?
This is an important value-based question. As an active citizen, you can adopt the following practices:
Do not dispose of cooking oils, fats, or grease down the kitchen sink.
Avoid flushing solid wastes like sanitary towels, plastics, or chemical-laden items down the toilet.
Use natural cleaning products instead of harsh chemicals to reduce the chemical load on the WWTP.
8. Compare the function of a bar screen and a clarifier in a WWTP. Why is their operational order important?
A bar screen is used at the very beginning of the treatment process to physically remove large objects like rags, sticks, and plastic bags from the wastewater. A clarifier (or sedimentation tank) is used later to allow smaller, suspended solids like faeces to settle at the bottom as sludge. The order is critical because removing large objects first prevents damage and blockages to the pumps and equipment used in the subsequent clarifier and aeration stages, ensuring the plant runs efficiently.











