UPSC Prelims 2015 · Question 93 of 98

UPSC Prelims 2015 question on Railway Bio Toilets

With reference to bio-toilets used by the Indian Railways, consider the following statements:

1. The decomposition of human waste in the bio-toilets is initiated by a fungal inoculum.

2. Ammonia and water vapour are the only end products in this decomposition which are released into the atmosphere.

Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2
Show answer

Answer: D. Neither 1 nor 2

Verdict

The answer is neither 1 nor 2. Railway bio-toilets use an anaerobic bacterial inoculum, and the products include methane, not ammonia and water vapour alone.

Analysis

Statement 1 is INCORRECT. Decomposition in the bio-digester is initiated by an anaerobic microbial inoculum, a consortium of bacteria adapted to work at low temperatures, not by a fungal inoculum. Statement 2 is INCORRECT. The digester breaks human waste down into colourless, odourless water and methane gas, the latter being combustible and usable for cooking or heating. Ammonia and water vapour are not the only end products, and the word only makes the statement fail even before the methane point.

Source

The Hindu report on bio-toilets for all trains.

How to crack it

Anaerobic digestion always yields methane, so any statement about a sealed digester that omits methane from the products should look wrong at once. Then note the word only, which converts a partial list into an exhaustive claim and is falsified by a single addition. Two independent routes lead to the same rejection here, which is typical: check the chemistry and check the quantifier, and you rarely need to recall the technology in detail.

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