Question

SCIENTIFIC LITERACY
WASTE WATER
Given below is a newspaper article published in Hindustan Times: 15th April 2019.
At least four sewage cleaners/workers choked to death while cleaning septic tanks in Tamil Nadu's Tirupurdistrict on Sunday, the police said. When one of the victims fell unconscious inside the tank after inhaling toxicgases, others who tried to save him also died. The fire department personnel rushed to the spot to rescuethem, but their attempts failed as the men died immediately after inhaling the poisonous gases. Thedeceased were cleaning three tanks which were filled with sewage. The fatal incident happened while the second tank was being cleaned.

Q1. The given figure presents a diagrammatic view of the flow of wastewater through a septic tank of a given city. Given below in jumbled order is the sequence of events that take place inside the tank. Choose the option that best describes the sequence of the flow: a) Slowly, the solid wastes settle as sludge at the bottom of the tank. b) With time, the oil and grease float to the top as scum. c) Sewage enters through the inlet. d) Now, this treated/clarified wastewater goes to a drain field. Nature cleans it up further. e) Next, the aerobic bacteria present in the wastewater consume human waste, food waste, soaps and other unwanted matter remaining in the wastewater in the tank. Tick the correct sequence:
( i) c, a, d, b, e
(ii) c ,a ,e ,b ,d
(iii) c ,a ,b ,e ,d
(iv) c ,b, a, d ,e

Q2. From the options given below, choose a pair of poisonous gases that workers could have inhaled when they were inside the septic tank:
(a) Hydrogen sulphide (H2S), Methane (CH4 )
(b) Oxygen (O ), Methane (CH4)
(c) Carbon monoxide (CO), Sulphur dioxide (SO)
(d) Nitrogen (N2) and Oxygen(O2)

Q3. The incident inside the septic tank was unfortunate and cost the lives of four men. The efforts of the fire department to save the sewage cleaners also went in vain. What could have been the possible reasons for the fatal incident to have occurred while the cleaning of the 'second tank' was in progress? a) Workers had already inhaled toxic gases in septic tank-1,while entering tank b) Concentration of gases may have increased leading to the death. c) More concentration of toxic gases around/inside tank2
i) a) only
ii) b) only
iii) c) only
iv) all the above

Q4. A Septic tank can last for several years as long as it is properly maintained and regularly pumped. Excess sludge and scum need to be removed periodically as it prevents the aerobic breakdown of wastes and leads to the formation of “sewer gases” in the tanks. How do you think poisonous gases are formed inside the septic tanks?
a) Anaerobic respiration/decomposition of wastes in the sewage
b) Aerobic respiration of wastage in the sewage
c) Respirationof wastes in the sewage
d) None of the above
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Answer 1

Answer:

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Answer 2

Answer:

I don't know

Explanation:

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