Tag: effects of water pollution

Questions Related to effects of water pollution

Limit of BOD prescribed by Central Pollution Control Board for discharge of industrial and municipal waste waters into natural surface waters is

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. $< 3.0$ ppm

  2. $< 10$ ppm

  3. $< 30$ ppm

  4. $< 100$ ppm

Show answer
Correct Option: B
Explanation:
BOD or Biochemical oxygen demand is the amount of oxygen required to decompose the organic matter in one litre of polluted water. More BOD means more organic matter is present in the water. Hence, a high BOD value means that the water is heavily polluted. 
According to Central Pollution Control Board, limit of BOD for discharge of industrial and municipal waste waters into natural surface waters is less than 10 ppm i.e. < 10 ppm.
So, the correct answer is '< 10 ppm'

High BOD indicates

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. Highly polluted water

  2. Less pollution in water

  3. Less sewage

  4. Less microorganisms

Show answer
Correct Option: A
Explanation:

BOD or the Biological Oxygen Demand that is created when there is a large concentration of the organic matter in the water. To decompose this organic mass, the decomposing bacteria will be activated and there would be consumption of the dissolved oxygen in this process. So, more the organic matter, higher will be the BOD and as a result more will be the pollution in the water body. This causes severe decrease in the dissolved oxygen and kills the aquatic animals.

Hence, the correct answer is 'Highly polluted water'.

Biochemical oxygen demand in a river water 

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. Remains unchanged when algal bloom occurs

  2. Increases when sewage gets mixed up with river water

  3. Has no relationship with concentration of oxygen in water

  4. Gives a measure of Salmonella in water

Show answer
Correct Option: B
Explanation:
Biochemical oxygen demand or BOD is the amount of oxygen required to decompose organic matter in one litre of polluted water.
If the water is more polluted, more will be the BOD because more will be the organic matter present in it and hence, more oxygen will be required to decompose it.
Hence, BOD in a river water will increase if sewage gets mixed up with the river water because more organic matter will be added in the river.
So, the correct answer is 'Increases when sewage gets mixed up with river water'.

BOD of eutrophied lake will be

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. Lower

  2. Moderate

  3. Higher

  4. Same as any other lake

Show answer
Correct Option: C
Explanation:
Eutrophication is the phenomenon of nutrient enrichment of nitrogen and phosphorus in a water body that supports a dense growth of plants and animal life. Due to nutrient enrichment, excess growth of algae occurs which is called algal bloom. When these algae die, their organic matter gets decomposed and this results in the depletion of oxygen leading to death of aquatic animals. This process is called eutrophication. 
Biochemical oxygen demand or BOD is the amount of oxygen required to decompose organic matter in one litre of polluted water.
Hence, BOD of a eutrophied lake will be higher as it will have more organic matter and more oxygen will be needed to decompose it.
So, the correct answer is 'Higher'.

BOD level in fresh water should not exceed beyond

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. $5$ ppm

  2. $10$ ppm

  3. $25$ ppm

  4. $50$ ppm

Show answer
Correct Option: A
Explanation:
BOD or Biochemical Oxygen Demand is the amount of oxygen required to decompose organic matter present in one litre of polluted water.
More the value of BOD,more will be the amount of organic matter in the water. Hence, a high BOD value means heavily polluted water.
Water with BOD value of 1-2 ppm is considered clean. 
In freshwater, BOD value should not exceed 5 ppm as the dissolved oxygen will be used up in the decomposition of organic matter and will not be available for the survival of aquatic organisms which will lead to their death.
So, the correct answer is '5 ppm'. 

When domestic sewage mixes with river water, __________

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. Small animals like rats will die after drinking river water

  2. The increased microbial activity released micronutrients such as iron

  3. The increased microbial activity uses up dissolved oxygen

  4. The river water is still suitable for drinking as impurities are only about $0.1\%$

Show answer
Correct Option: C
Explanation:

Domestic sewage contains large amounts of organic matter. When domestic sewage mixes with river water, organic matter will content will increase in the river. This will lead to increase in BOD or Biochemical Oxygen Demand. 

BOD is the amount of oxygen required by bacteria to decompose organic matter in one litre of polluted water.
If the water is more polluted, more will be the BOD because more will be the organic matter present in it and hence, more oxygen will be required to decompose it.
Hence, the dissolved oxygen will be used up by the bacteria to decompose the organic matter.
So, the correct answer is 'The increased microbial activity uses up dissolved oxygen'.

Match and find the correct option.

I II III
(a) BOD (i) Supernatant as effluent (p) Useful aerobic microbes 
(b) Flocs (ii) Measure of organic matter (q) All settled solids
(c) Primary sludge (iii) Masses of bacteria associated with fungi (r) Methane hydrogen sulphide carbon dioxide
(d) Biogas (iv) Anaerobic sludge digester (s) Polluting water has more BOD
biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. a-ii-s, b-iii-p, c-i-q, d-iv-r

  2. a-ii-p, b-i-r, c-iv-q, d-iii-s

  3. a-i-s, b-iii-q, c-iv-p, d-ii-r

  4. a-iv-r, b-ii-s, c-iii-p, d-i-q

Show answer
Correct Option: A
Explanation:

(a)BOD - (ii)Measure of organic matter-(s)Polluting water has more BOD-Biochemical Oxygen Demand is the amount of dissolved oxygen needed by aerobic microbes to break down organic material present in a given water sample at certain temperature over a specific time period. Polluting water has more organic matter thus required more oxygen for the breakdown. Hence polluting water has more BOD.

(b)Flocs- (iii)Masses of bacteria associated with fungi -(p)Useful aerobic microbes-Flocs are the masses of bacteria associated with fungi. Flocs are helpful in increasing the decomposition rate and are put in the aeration tank while the secondary sewage treatment process is in effect
(c)Primary sludge-(i)Supernatant as effluent-(q)All settled solids-Primary sludge includes settleable solids removed during primary treatment in primary clarifiers.
(d)Biogas-(iv)Anaerobic sludge digester-(r)Methane, hydrogen sulfide, carbon dioxide-Biogas is the mixture of gases(Methane, hydrogen sulfide, carbon dioxide)- produced by the breakdown of organic matter in the absence of oxygen(I.e from anaerobic sludge digesters).

Water above the dissolved $O _2$ content may be considered uncontaminated.

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. $0.8$ mg/l

  2. $0.008$ mg/l

  3. $8.0$ mg/l

  4. 8 $\mu$g/l

Show answer
Correct Option: C
Explanation:
The microorganisms in water decompose organic matter using dissolved oxygen. More the amount of dissolved oxygen in the water, more is its purity and vice versa. Water below 5mg/l is considered contamined and water above 8mg/l is considered as uncontaminated.

So, the correct answer is "8.0mg/l".

Water pollination is best assessed by determining.

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. DO and BOD

  2. BOD and turbidity

  3. Do and acidity

  4. BOD and alkalinity

Show answer
Correct Option: A
Explanation:

 D.O. is the dissolved gaseous form of oxygen that is essential for respiration of fish and other aquatic organisms. Wastewater from sewage treatment plants often contains organic materials that are decomposed by microorganisms. The amount of oxygen consumed by these organisms in breaking down the waste is known as the biochemical oxygen demand or BOD. BOD directly affects the amount of dissolved oxygen in rivers and streams. The greater the BOD, the more rapidly oxygen is depleted in the stream, thus reducing the oxygen available to higher forms of aquatic life. Pollution, therefore, increases the BOD of a water body. So, the water pollution status of a water body can be assessed by studying the dissolved oxygen (DO) and biological oxygen demand (BOD) of the water body. So, the correct option is 'DO and BOD'.

Two bottles were half filled with water from Ganga ('P') and Kaveri ('Q') and kept under identical airtight conditions for 5 days. The oxygen was determined to be 2% in bottle ('P') and 10% in bottle ('Q'). What could because of this indifference?

biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

  1. Ganga is more polluted than Kaveri

  2. Both the rivers are equally polluted

  3. Kaveri is more polluted than Ganga

  4. Kaveri has more minerals than Ganga

Show answer
Correct Option: A
Explanation:
Biochemical oxygen demand or BOD is the amount of dissolved oxygen needed by the aerobic bacteria present in water in a given amount of time. Given that 'P' has 2% oxygen and 'Q' has 10% oxygen dissolved after 5 days in an airtight condition. So, one can conclude that the aerobic bacteria present in 'P' is more than 'Q' as BOD of 'P' is much more than 'Q'. So Ganga is more polluted than Kaveri.