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Q8:
What is the key difference between primary and secondary sewage treatment?
Solution :
Definition of Sewage Treatment Paradigms
Sewage treatment is the process of removing contaminants from wastewater to produce an environmentally safe fluid waste stream. The process is bifurcated into physical and biological phases based on the mechanism of pollutant removal.
Step 1: Analysis of Primary Sewage Treatment (Physical Treatment)
Primary treatment functions strictly through physical mechanisms. The objective is to remove large and small particles from the sewage by sedimentation and filtration.
- Filtration: Large debris is removed sequentially through wire mesh screens. [Principle: Size exclusion]
- Sedimentation: The sewage is placed in settling tanks where grit (sand, pebbles) and solid organic matter settle down due to gravity. [Per Stokes' Law: Velocity of settling is proportional to particle size/density].
- Resultant Output: The supernatant is known as the primary effluent, while the settled solids are termed primary sludge.
Step 2: Analysis of Secondary Sewage Treatment (Biological Treatment)
Secondary treatment utilizes biological organisms to reduce the Biological Oxygen Demand (BOD) of the primary effluent.
- Aeration: The effluent is agitated in large aeration tanks, promoting the growth of aerobic microbes into flocs (masses of bacteria associated with fungal filaments). [Biological Principle: Microbial degradation of organic matter].
- BOD Reduction: As these microbes consume organic matter, the BOD of the water decreases significantly. [Definition: BOD refers to the amount of $O_2$ that would be consumed if all organic matter in 1 liter of water were oxidized by bacteria].
- Sedimentation: The mixture is passed into a settling tank where the flocs are allowed to sediment. This sediment is called activated sludge.
Step 3: Comparative Analysis of Key Differences
| Feature | Primary Treatment | Secondary Treatment |
|---|---|---|
| Mechanism | Physical (Sedimentation/Filtration) | Biological (Microbial degradation) |
| Role of Microbes | Negligible | Essential (Aerobic/Anaerobic) |
| Target | Floating debris and grit | Dissolved organic matter |
| BOD Impact | Minimal change | Significant reduction |
Visual Representation of Treatment Hierarchy
Final Solution: The fundamental difference is that primary treatment is a purely physical process involving the removal of large solid particles through sedimentation and filtration, whereas secondary treatment is a biological process involving the use of aerobic microorganisms to oxidize and decompose dissolved organic waste, thereby significantly lowering the Biological Oxygen Demand (BOD) of the water.
More Questions from Class 12 Biology Microbes in Human Welfare EXERCISES
- Q1: Bacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes with the help of a microscope, which sample would you carry and why?
- Q1: Bacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes with the help of a microscope, which sample would you carry and why?
- Q2: Give examples to prove that microbes release gases during metabolism.
- Q2: Give examples to prove that microbes release gases during metabolism.
- Q3: In which food would you find lactic acid bacteria? Mention some of their useful applications.
- Q3: In which food would you find lactic acid bacteria? Mention some of their useful applications.
- Q4: Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
- Q4: Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
- Q5: In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
- Q5: In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
- Q6: Name any two species of fungus, which are used in the production of the antibiotics.
- Q6: Name any two species of fungus, which are used in the production of the antibiotics.
- Q7: What is sewage? In which way can sewage be harmful to us?
- Q7: What is sewage? In which way can sewage be harmful to us?
- Q8: What is the key difference between primary and secondary sewage treatment?
- Q9: Do you think microbes can also be used as source of energy? If yes, how?
- Q9: Do you think microbes can also be used as source of energy? If yes, how?
- Q10: Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
- Q10: Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
- Q11: Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled \(A\), \(B\) and \(C\); but the laboratory attendant did not note which was which. The BOD values of the three samples \(A\), \(B\) and \(C\) were recorded as 20mg/L, 8mg/L and 400mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?
- Q11: Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled (A), (B) and (C); but the laboratory attendant did not note which was which. The BOD values of the three samples (A), (B) and (C) were recorded as (20mg/L), (8mg/L) and (400mg/L), respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?
- Q12: Find out the name of the microbes from which Cyclosporin \(A\) (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.
- Q12: Find out the name of the microbes from which Cyclosporin (A) (an immunosuppressive drug) and Statins (blood cholesterol lowering agents) are obtained.
- Q13(a): Find out the role of microbes in the following and discuss it with your teacher. (a) Single cell protein (SCP)
- Q13(a): Find out the role of microbes in the following and discuss it with your teacher. (a) Single cell protein (SCP)
- Q13(b): Find out the role of microbes in the following and discuss it with your teacher. (b) Soil
- Q13(b): Find out the role of microbes in the following and discuss it with your teacher. (b) Soil
- Q14: Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer. Biogas, Citric acid, Penicillin and Curd
- Q14: Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer. Biogas, Citric acid, Penicillin and Curd
- Q15: How do biofertilisers enrich the fertility of the soil?
- Q15: How do biofertilisers enrich the fertility of the soil?
CBSE Solutions for Class 12 Biology Microbes in Human Welfare
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Evolution
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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