For an understanding of sewage treatment, which of the following concepts are important from the point of view of its practical implementation?
(1) Role of microbes in the degradation of organic substances
(2) Understanding about Biological Oxygen Demand (BOD)
(3) Classification of microorganisms
Choose the correct answer from the codes given below:

Correct option is D

Correct Answer: (d)
Explanation:
Practical sewage treatment mainly depends on microbial activity in degrading organic waste and monitoring BOD to judge pollution levels.
Classification of microorganisms is theoretical and not directly required in practical implementation.
Information Booster:
Sewage treatment uses aerobic and anaerobic microbes.
BOD measures oxygen required for microbial decomposition of organic matter.
Lower BOD = cleaner water; higher BOD = more pollution.
Activated sludge and trickling filters use microbial growth for efficiency.
Microbes convert organic matter → CO₂, water, methane, and biomass.
Additional Information (Incorrect Statement):
(3) Classification of microorganisms is not essential for operating sewage treatment plants; the focus is on function, not taxonomy.