Environmental Studies · General Awareness

Water Quality and Pollution

1,303 Questions

Water Quality and Pollution examines the sources, mechanisms, and impacts of contaminants in aquatic ecosystems. It covers crucial environmental concepts like eutrophication, biochemical oxygen demand, and thermal pollution. This subject frequently appears in general science and environmental studies sections of various examinations.

Eutrophication CausesThermal Pollution EffectsBiochemical Oxygen DemandSynthetic Fertilizer ImpactsWastewater SourcesAquatic Ecosystem Toxicity

Water Quality and Pollution Questions

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

Biochemical oxygen demand in a river water 

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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'.
Multiple choice biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

BOD of eutrophied lake will be

  1. Lower

  2. Moderate

  3. Higher

  4. Same as any other lake
Reveal answer Fill a bubble to check yourself
C Correct answer
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'.
Multiple choice biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

BOD level in fresh water should not exceed beyond

  1. $5$ ppm
  2. $10$ ppm
  3. $25$ ppm
  4. $50$ ppm
Reveal answer Fill a bubble to check yourself
A Correct answer
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'. 
Multiple choice biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

When domestic sewage mixes with river water, __________

  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 $0.1\%$
Reveal answer Fill a bubble to check yourself
C Correct answer
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'.

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

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

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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).

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

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

  1. $0.8$ mg/l
  2. $0.008$ mg/l
  3. $8.0$ mg/l
  4. 8 $\mu$g/l
Reveal answer Fill a bubble to check yourself
C Correct answer
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".
Multiple choice biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

Water pollination is best assessed by determining.

  1. DO and BOD

  2. BOD and turbidity

  3. Do and acidity

  4. BOD and alkalinity
Reveal answer Fill a bubble to check yourself
A Correct answer
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'.

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

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?

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.    
Multiple choice biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

Multiple Choice Questions
BOD in river water

  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. Give a measure for Salmonella in water.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Biochemical Oxygen Demand or BOD is the amount of dissolved oxygen needed by aerobic microbes to break down organic matter present in a particular water sample at a certain temperature over a specified period of time. Value of BOD increases, given that the organic matter content is high in the water sample. Sewage is rich in organic residues thus it increases BOD of river water upon mixing.

So, the correct answer is option B, increases when sewage gets mixed up with river water.

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

Multiple Choice Questions
BOD is a measure of

  1. Industrial wastes passed into water bodies

  2. amount of carbon monoxide combined with haemogloblin

  3. extent of pollution with organic matter

  4. amount of oxygen required by plants during night.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

BOD or Biochemical Oxygen Demand measures the degree of impurity of a water body or sample due to organic matter. BOD is the amount of dissolved oxygen needed by aerobic microbes to breakdown the organic matter present in the water body.

So, the correct answer is extend of pollution with organic matter.

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

Limit of B.O.D. prescribed by Central Pollution Control Board for the discharge of industrial and municipal waste waters into natural surface waters, is 

  1. < 30 ppm

  2. < 3.0 ppm

  3. < 10 ppm

  4. < 100 ppm
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period. The central pollution control board prescribed the BOD limit for the discharge of industrial and municipal waste water as < 10ppm

So, the correct answer is '< 10 ppm'

Multiple choice biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control
In a survey conducted in Delhi, on the efforts being made to clear the Km patch in Yamuna, it was observed that the BOD in 2003 was 13 mg/litre while it was 18 mg/litre in 2004. 
What inference can you draw from the following data?

  1. The pollutants in the river has decreased due to efforts by Delhi government.

  2. Despite efforts there are still dissolved minerals in the river.

  3. Although efforts are being made, the pollution is still on an increase in Delhi.

  4. There is an algae in the river.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period. As the level of BOD increases, this shows that efforts are being made to clean Yamuna river but pollution is still on an increase in Delhi. 

Therefore, the correct answer is option C.

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

Increase of BOD in water leads to

  1. Increase in the dissolved oxygen concentration

  2. Decrease in the dissolved oxygen concentration

  3. Maintenance of dissolved oxygen concentration at the same level

  4. No effect on dissolved oxygen concentration
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. Domestic sewage primarily contains biodegradable organic matter, which readily decomposes by micro-organisms, which can multiply using these organic substances as substrates and hence utilise some of the components of sewage. It is possible to estimate the amount of biodegradable organic matter in sewage water by measuring biochemical oxygen demand (BOD). Micro-organisms involved in biodegradation of organic matter in the receiving water body consume a lot of oxygen, and as a result there is a sharp decline in dissolved oxygen downstream from the point of sewage discharge. This causes mortality of fish and other aquatic creatures. 

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

Sewage drainage into water bodies is harmful for fishes because

  1. Excessive CO$ _2$ is added in water.

  2. It gives off a bad smell.

  3. It removes the competition with fishes to dissolved oxygen.

  4. It increase competition of fishes for dissolved oxygen.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Domestic sewage primarily contains biodegradable organic matter, which readily decomposes by bacteria and other micro-organisms, which can multiply using these organic substances as substrates and hence utilise some of the components of sewage. It is possible to estimate the amount of biodegradable organic matter in sewage water by measuring biochemical oxygen demand (BOD). Micro-organisms involved in biodegradation of organic matter in the receiving water body consume a lot of oxygen, and as a result there is a sharp decline in dissolved oxygen downstream from the point of sewage discharge. This causes mortality of fish and other aquatic creatures. 

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

In a sewage plant, BOD is indicated as high. After sometime it shows a decrease then

  1. There is increase in bacterial growth but decrease in oxygen.

  2. There is decrease in bacterial growth but increase in oxygen.

  3. There is increase in bacterial growth but increase in oxygen.

  4. There is decrease in bacterial growth but decrease in oxygen.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. BOD can be used as a gauge of the effectiveness of wastewater treatment plants. It is listed as a conventional pollutant in the U.S. Clean Water Act.

Higher the BOD, more is the pollution.
Thus, if BOD had reduced, it shows decrease in bacterial growth which consumes the oxygen present and ensures increase in oxygen level.
Therefore, the correct answer is option B.