1. Choose the correct option.
a. Read the statements carefully and choose the correct option.
Statement I – The organic impurities present in wastewater are nitrates, sulphates, phosphates and metals.
Statement II – The inorganic impurities present in wastewater are dead plants and spoiled vegetables, human faeces, etc.
i. Statement I is correct while statement II is incorrect.
ii. Statement II is correct while statement I is incorrect.
iii. Both the statements are correct.
iv. Both the statements are incorrect.
- Answer: (iv) Both the statements are incorrect.
b. Which of the following is a component of industrial wastewater, but not domestic wastewater?
i. Detergent
ii. Oil
iii. Arsenic
iv. Faecal matter
- Answer: (iii) Arsenic
c. In a wastewater treatment plant, after passing the wastewater through a grit and sand removal tank, the water is allowed to settle in a large tank. The solids that settle at the bottom of the large tank are called activated:
i. sludge
ii. sewage
iii. scum
iv. vermi-cakes
- Answer: (i) sludge
d. Which of the following statement is incorrect for a vermi-processing toilet?
i. It has been tested and developed in India.
ii. It is a novel, low water use toilet that is safe for processing of human waste.
iii. The human excreta is treated by roundworms and cockroaches.
iv. Vermi-cakes are high quality manure.
- Answer: (iii) The human excreta is treated by roundworms and cockroaches.
e. Which of the following diseases can be prevented by consuming safe drinking water?
i. Asthma
ii. Typhoid
iii. Malaria
iv. Tuberculosis
- Answer: (ii) Typhoid
2. Assertion-Reasoning questions.
(i)
- Assertion (A): We should not consume contaminated water.
- Reason (R): Contaminated water contains toxic chemicals and germs that can cause diseases.
- Answer: (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
(ii)
- Assertion (A): Chromium and lead contamination are found in wastewater of some industries.
- Reason (R): Chromium and lead present in the industrial effluents can kill the aquatic life of rivers and oceans.
- Answer: (b) Both Assertion (A) and Reason (R) are true, and Reason (R) is not the correct explanation of the Assertion (A).
3. Answer the following questions in one sentence.
a. What is the wastewater released by houses called?
Answer: The wastewater released by houses is called sewage or domestic wastewater.
b. What is scum?
Answer: Scum is the waste material that is lighter than water and floats on its surface, such as oil and grease.
c. What is the function of bar screens in wastewater treatment plants?
Answer: The function of bar screens is to remove large solid objects like plastic bags, cans, and sticks from the wastewater.
4. Answer the following in 2-3 sentences.
a. What is an industrial effluent?
Answer: Industrial effluent is the wastewater discharged from industrial and commercial establishments. It often contains harmful chemicals like acids, alkalis, heavy metals, and oils, which are not typically found in domestic sewage.
b. What is the purpose of bubbling air into the aeration tank during the treatment of sewage?
Answer: Air is bubbled into the aeration tank to promote the growth of aerobic bacteria. These bacteria consume the harmful human waste, food waste, and other organic matter still present in the water, thereby cleaning it.
c. Why should chemicals not be released into the drains?
Answer: Chemicals should not be released into the drains because they can kill the beneficial bacteria that are essential for breaking down waste in the water treatment process. Furthermore, these toxic chemicals can contaminate water bodies, poisoning aquatic life and polluting water sources.
5. Answer the following questions in 3-4 sentences.
a. Explain how sludge is treated during primary treatment in WWTP.
Answer: During primary treatment, the sludge that settles at the bottom of the settling tank is first scraped out. This sludge is then transferred to a separate tank where it is decomposed by anaerobic bacteria. The resulting biogas can be used as a fuel, and the dried sludge is used as manure, often called vermi-cake if processed with worms.
b. Vermi-processing toilets are beneficial. Justify this statement.
Answer: Vermi-processing toilets are highly beneficial. They are a low-water-use system, which conserves water. They safely process human waste by using earthworms to convert it into vermi-cake, a high-quality manure that can be used in agriculture. This method is also hygienic and prevents the contamination of groundwater.
c. Why is the disposal of sewage into water bodies very dangerous for aquatic animals and plants?Answer: Disposing of sewage into water bodies is dangerous because it enriches the water with nutrients, leading to excessive algae growth (eutrophication). When this algae dies, its decomposition by bacteria consumes dissolved oxygen in the water. This creates oxygen depletion, leading to the death of fish and other aquatic animals. Sewage also introduces harmful pathogens and toxins that can directly poison aquatic life