Environmental Studies · General Awareness

Water Quality and Pollution

1,263 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

BOD stands for

  1. Biological organism death

  2. Biochemical organic matter decay

  3. Biotic oxidation demand

  4. Biochemical oxygen demand
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Biochemical Oxygen Demand (BOD) is the oxygen in milligrams required  for 5 days in one litre of water at 20 degree centigrade for the micro organisms to metabolise organic wastes present in water.

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

Which of the following does not occur when the sewage is discharged into water?

  1. Increase in $O _2$

  2. Cyanophycean blooms occur
  3. Depletion of $O _2$ layers

  4. Eutrophication
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Decomposition of organic matter by microbes requires oxygen. Degree of impurity of water due to organic matter is measured in terms of Biochemical oxygen demand or (BOD). 

BOD is the oxygen required by microorganisms to completely metabolise organic wastes present in water. 
When untreated sewage is directly discharged into water bodies, it is called organic loading. Organic loading is one source for increased nutrient concentration in water bodies (or eutrophication). It results in increase in BOD and explosive multiplication of blue green alga, called as algal bloom. Algal bloom and increased consumption of oxygen by sewage metabolising microorganisms results in decrease in level of dissolved oxygen in water.

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

A lake with an inflow of domestic sewage rich in organic waste may result in:

  1. Drying of the lake very soon due to algal bloom.

  2. An increased production of fish due to lot of nutrients.

  3. Death of fish due to lack of oxygen.

  4. Increased population of aquatic food web organisms.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Domestic sewage leads to organic loading or occurrence of excess organic matter inside water. Its putrefaction decreases dissolved oxygen. Blue green algae present in the bloom also release toxins. Both toxicity and decreased oxygen level kill aquatic animals. Anaerobic putrefaction produces pollutants like methane, hydrogen sulphide, and ammonia. They kill the bloom forming plants as well. The water body comes to have foul smell, brown colouration, bad taste and oil.

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 O$ _{2}$ concentration.
  2. Decrease in the dissolved O$ _{2}$ concentration.
  3. Maintenance of dissolved O$ _{2}$ concentration at the same level.
  4. No effect on dissolved O$ _{2}$ concentration.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Organic loading is occurrence of excess organic matter inside water due to sewage disposal and eutrophication. This leads to an increase in biological oxygen demand (BOD) for putrefaction. Explosive multiplication of alga leads to algal bloom. These conditions result in decrease in dissolved oxygen in water. Both toxicity due to algal toxins and decreased levels of dissolved oxygen kill aquatic animals.

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

What will be the effect of addition of organic material on water?

  1. COD remain unaffected

  2. BOD remain unaffected

  3. Increases BOD

  4. Reduces BOD
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Decomposition of organic matter by microbes requires oxygen. Degree of organic impurity of water is measured in terms of 'Biological Oxygen Demand' or BOD. BOD is the oxygen in milligrams required by microorganisms to metabolise organic wastes. When more organic matter are added to water, the BOD of the water will increase.

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 releases micro nutrients 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

Organic loading is occurrence of excess organic matter inside water due to sewage disposal and eutrophication. This leads to an increase in biological oxygen demand (BOD) for putrefaction by microorganisms. Also explosive multiplication of blue green alga leads to algal bloom. These conditions result in decrease in dissolved oxygen in water. Both toxicity due to algal toxins and decreased levels of dissolved oxygen kill aquatic animals.

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

Measuring 'Biochemical Oxygen Demand' is used for

  1. Estimating the amount of organic matter in sewage water.

  2. Working out the efficiency of oil driven automobile engines.

  3. Measuring the activity of Saccharomyces cerevisiae in producing curd on a commercial scale.

  4. Working out the efficiency of R.B.Cs. about their capacity to carry oxygen.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Degree of pollution or impurities in water due to organic matter is measured in terms of 'Biological Oxygen Demand' or BOD. Biological oxygen demand or BOD is the oxygen in milligrams required for five days in one litre of water at 20 degree centigrades for the microorganisms to metabolise organic waste. 

Low pollution level is indicated by below 1500 mg/lit, medium pollution level is indicated by 1500 to 4000 mg/lit and high organic pollution level is indicated by above 4000 mg/lit.

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

Which of the option shows following examples in ascending order in terms of BOD?
(i) Distilled water (ii) Tap water(iii) Sewage wastes drained in river

  1. ii- i- iii

  2. i- ii- iii

  3. iii- i- ii

  4. iii- ii- i
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

BOD is the oxygen required by microorganisms to metabolise organic wastes in the water. Biological treatment of wastewater will reduce the organic impurities or an organic load of polluted water, thus curtail the level of BOD. The greater the content of organic waste in the water greater will be the BOD. Organic waste will be maximum in the sewage waste. Hence it will have the highest BOD. Thus the correct answer is option B.

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

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

  1. < 3.0 ppm

  2. <10 ppm

  3. < 100 ppm

  4. < 30 ppm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

BOD is Biological oxygen demand. It is the total amount of oxygen required by the microorganisms present in a water body to break down the organic matter. If BOD is more, it means that there is abundance of microorganisms in that water body and hence it is polluted with organic matter.

Water with BOD level 1 - 2 ppm is considered to be good water, if the BOD is 3 - 9, then the water is considered to be slightly polluted, and if the water has BOD more than 100 ppm, then the water is greatly polluted.
The Central Pollution Control Board has prescribed the limit of BOD for the discharge of industrial and municipal waste in order to regulate the water pollution and for efficient water treatment, and it is <10 ppm.

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

Drained sewage has B.O.D.

  1. More than that of water

  2. Less than that of water

  3. Equal to that of water

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

BOD refers to the biological oxygen demand by the microbes to decompose the organic matter present in the water body. The drained sewage is rich in organic waste that will be decomposed by the bacteria. So, the drained sewage will be deficient in oxygen than the normal water. The oxygen demanded by the microbes will be higher in sewage water.

Hence, the correct answer is 'More than that of water'.

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

BOD (biological oxygen demand) is

  1. Amount of oxygen consumed by microorganisms for decaying organic matter per unit volume of water
  2. Amount of $CO _2$ consumed by microorganisms per unit of sewage water

  3. Amount of oxygen required by aquatic plants for survival

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Biological oxygen demand refers to the amount of oxygen required for the complete decomposition of the organic mass present in the water body by the decomposing bacteria. More the amount of the organic mass, higher will be the BOD and more will be the level of pollution in the water body. As more and more oxygen will be consumed, the aquatic animals, especially fishes will die due to hypoxia. Their dead bodies will further enhance the organic mass.  

Hence, the correct answer is 'Amount of oxygen consumed by microorganisms for decaying organic matter per unit volume of water'

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

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

  1. $< 3.0$ ppm
  2. $< 10$ ppm
  3. $< 30$ ppm
  4. $< 100$ ppm
Reveal answer Fill a bubble to check yourself
B Correct answer
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'
Multiple choice biology human influences on the environment effects of water pollution effect of water pollution water pollution and its control

High BOD indicates

  1. Highly polluted water

  2. Less pollution in water

  3. Less sewage

  4. Less microorganisms
Reveal answer Fill a bubble to check yourself
A Correct answer
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'.

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'.