The main objective of wastewater treatment is to remove as many suspended solids as possible before returning the remaining water, known as effluent, to the environment. As solid matter decays, it consumes oxygen, which is required by the plants and animals that live in the water.
“Primary treatment” removes approximately 60% of the suspended solids from wastewater. Aerating (stirring up) the wastewater to add oxygen is also part of this treatment. Secondary treatment removes over 90% of suspended solids.
Download PDF of Class 7 Chemistry Worksheet on Chapter 18 Wastewater Story – Set 2
CBSE Class 7 Chemistry Worksheet Chapter 18 Wastewater Story – Set 2
Q1. Chemical used to treat wastewater is ___.
a.) Chlorine
b.) Ozone
c.) Ammonia
d.) None of the above
Q2. Which step is chlorination in the wastewater treatment plant?
a.) First
b.) Second
c.) Second last
d.) Last
Q3. Which of the following is a characteristic of wastewater?
a.) Foul smell
b.) Dark colour
c.) Bad taste
d.) All of the above
Q4. Which of the following is a part of the inorganic impurities of the sewage?
a.) Excreta
b.) Garbage
c.) Phosphate
d.) Vegetable waste
Q5. Which of the following is not a water-borne disease?
a.) Cholera
b.) Typhoid
c.) Tuberculosis
d.) Diarrhea
Q6. Fill in the blanks.
a.) Nitrates and phosphates are ___ impurities.
b.) The last step of wastewater treatment is ___.
c.) Aerobic bacteria feed on organic matter and produce ___.
Q7. State True or False.
a.) Open drains are the breeding spot for mosquitoes and other microbes.
b.) Sludge is the solid impurities settled at the bottom of the clarifier.
c.) Sewage water can be reused.
Q8. Name the type of microbes present in sewage that causes diseases.
Q9. Define sewage.
Q10. Justify why the open drain is a big concern nowadays.
Q11. What do you understand about wastewater treatment?
Q12. What is the importance of microbes in sewage?
Q13. Why is chlorine passed into the wastewater treatment plant?
Q14. What are some of the alternatives for sewage disposal?
Q15. What is the composition of sewage?
Q16. Explain why it is harmful to discharge untreated sewage into rivers or seas.
Q17. Describe various housekeeping practices for efficient working of the sewage system.
Q18. Explain the relationship between sanitation and disease.
Q19. What do you understand by the term chemical toilet?
Q20. Describe the steps involved in getting clarified water from wastewater.
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