Xenobiotic and Biogas question discussion

1. Xenobiotic Metabolism and Biogas
Exam Questions Discussion

2. Question 1

3. Explanation
 Microbial degradation is the best method to degrade
xenobiotic compounds founds in disposal pits, sewage
treatment plants etc., as the microorganisms are used to
degrade xenobiotic compounds is the best method. It can
degrade all the pollutants efficiently, thereby causing no
harm to the environment. Chemical degradation is harmful
to the environment, water degradation doesn’t remove any
pollutants and using physical agents it is very difficult to
remove or separate the pollutants.

4. Question 2

5. Explanation
Municipal and residential waste is a good substrate for biogas
production. E-waste and metallic waste do not consist of
carbon compounds. Gaseous effluents are not used to
produce biogas.

6. Question 3

7. Explanation
 Biogas is produced from biomass by Anaerobic
fermentation. Produced from raw organic materials such as
agricultural waste, manure, plant material, sewage and
food waste.

8. Question 4

9. Explanation
Xenobiotics are those man made chemical substances
which are present in environment at unnaturally high
concentration and are not produced in living system.

10. Question 5

11. Explanation
 Methanogens like Methanobacterium are anaerobic
bacteria that can act upon organic matter like
cellulose, releasing a mixture of gases composed of
hydrogen, carbon dioxide and methane. Small amount
of hydrogen sulfide (H2S) is also produced during
methanogenesis.

12. Question 6

13. Explanation
o Xenobiotic compounds are often toxic to life and are also
often hard for microorganisms to metabolize (because they
contain molecular arrangements that not normally
encountered in nature).

14. Question 7

15. Explanation

16.  Hydrolysis- the first step in the conversion of organic material
to biogas. In this stage, certain bacteria break down organic
polymers like carbohydrates into simple sugars so that the next
group of bacteria can further process the material.
 Acidogenesis- the second step in the conversion of organic
material to biogas. In this stage, certain bacteria called
acidogenic bacteria convert the simple sugars and amino acids
into carbon dioxide, hydrogen, ammonia, and organic acids.
 Acetogenesis- the third step in the conversion of organic
materials to biogas. In this stage, certain bacteria called
acetogenic bacteria convert the organic acids into acetic acid,
carbon dioxide, and hydrogen.
 Methanogenesis- the final step in the conversion of organic
materials to biogas. In this stage, certain single-celled organisms
called methanogens convert the intermediate products produced
in the preceding stages into biogas (primarily methane and
carbon dioxide). The solid and liquid leftover from this process,
digestate, consists of material that the microbes cannot use as
well as dead bacteria.

17. Question 8

18. Explanation
 Hydrolysis is the first step in the anaerobic
decomposition of organic matter. It involves the
conversion of polymeric organic matter (e.g.,
polysaccharides, lipids, proteins) to monomers (e.g.,
sugars, fatty acids, amino acids) by hydrolases secreted
to the environment by microorganisms.

19. Question 9

20. Explanation
 Acetogenesis is the third step of anaerobic digestion.
Products from fermentation (organic acids, alcohols)
are converted into hydrogen (H2), carbon dioxide
(CO2) and acetic acid (CH3COOH). To produce acetic
acid, acetogenic bacteria need oxygen and carbon.

21. Question 10

22. Explanation
 The anaerobic digestion process produces gas
composed of methane (CH4) and carbon dioxide
(CO2), known as biogas. These gases are produced
from organic wastes such as livestock manure, food
processing waste, etc.

23. Question 11

24. Explanation
 Biogas consists mainly of methane and carbon dioxide.
It can also include small amounts of hydrogen
sulphide, hydrogen, siloxanes and some moisture. The
relative quantities of these vary depending on the type
of waste involved in the production of the resulting
biogas.

25. Question 12

26. Explanation
 Methanogens are microorganisms that produce
methane as a metabolic byproduct in anoxic
conditions. Methanogens belong to Archaebacteria.

27. Question 13

28. Explanation
 Organic waste enters fermentation tank from the
upper part, and the sensors can automatically senses
temperature and oxygen content, so as to provide a
favorable condition for microorganism activity in
organic waste.

29. Question 14

30. Explanation
 Biomagnification refers to increase in concentration of
toxicant at successive trophic levels. This happens
because a toxic substance accumulated by an organism
cannot be metabolised or excreted, and is thus passed
on to the next higher trophic level. This phenomenon
is well-known for mercury and DDT.

31. Question 15

32. Explanation
Types of recalcitrant Xenobiotic compounds
 These are categorized in to 6 types.
 Halocarbons
 Polychlorinated biphenyls
 Synthetic Polymers
 Alkylbenzyle sulphonates
 Oil mixtures
 Other xenobiotic Compound

33. Question 16

34. Explanation
 It is observed that the level of DDT increases as the
food chain progresses. It means, the primary
consumers will have more DDT concentration than
the producers, the secondary consumers will have
more than primary consumers, and so on. The highest
concentrations will be seen in the top carnivore.

35. Question 17

36. Explanation
 The metabolism of many xenobiotics is fundamental
to many toxic processes such as carcinogenesis,
teratogenesis, and tissue necrosis. They are extremely
toxic in nature. Many xenobiotic compounds in the
environment have medium to long-term stability in
soil, their persistence resulting in significant impact
on the functioning of soil ecosystems.

37. Question 18

38. Explanation
 Polychlorinated biphenyls (PCBs) are toxic
chemicals, recalcitrant to degradation,
bioaccumulative and persistent in the environment,
causing adverse effects on ecosystems and human
health. They consist of the biphenyl structure with two
linked benzene rings in which some or all of the
hydrogen atoms have been substituted by chlorine
atoms. PCBs were used mainly as coolants and
lubricants in transformers, capacitors, and other
electrical equipment.

39. Question 20

40. Explanation
 Anaerobic digestion is widely used as a source of
renewable energy. The process produces a biogas,
consisting of methane, carbon dioxide, and traces of
other 'contaminant' gases. Biogas is the gas produced
when bacteria break down organic matter in the
absence of oxygen.

41. Question 20

42. Explanation
 It is observed that the level of DDT increases as the
food chain progresses. It means, the primary
consumers will have more DDT concentration than
the producers, the secondary consumers will have
more than primary consumers, and so on. The highest
concentrations will be seen in the top carnivore.

43. Question 21

44. Explanation
 Biogas is considered an ideal fuel because of the
following reasons: (i) Biogas does not cause air
pollution as the combustion process is smoke free. (ii)
Biogas produces a large amount of heat per unit mass
and thus has high calorific value. (iii) Biogas is an
environmentally-friendly, renewable energy
source produced by the breakdown of organic matter
such as food scraps and animal waste. (iv) The
technology used to produce biogas is quite cheap.

45. Question 22

46. Explanation
 Biomagnification is a process causing the
concentration of a substance (crosses) to increase at
higher levels of the food chain.

47. Question 23

48. Explanation
 The composition of biogas varies depending upon the
substrate composition, as well as the conditions within
the anaerobic reactor (temperature, pH, and substrate
concentration).

49. Question 24

50. Explanation
• The bacteria which produce the gaseous mixture are
collectively known as methanogens.
• Methanobacterium is one such methanogen.

51. Question 25

52. Explanation
 Certain bacteria which produce biogas like the
methanogens particularly grow anaerobically
on cellulosic material to produce large amounts of
methane with carbon dioxide and hydrogen.

53. THANK YOU