Which one of the following aspects should be considered at the time of final selection of sewage treatment plant?
- AThe site should be safe from floods for all the timeCorrect
- BThe site should not be situated on the leeward side of wind
- CThe site should be as far as possible far away from the town
- DThe subsoil water level at the site should not remain low even during monsoon
Solution
Concept
Siting a sewage treatment plant
Step-by-step solution
1. The plant must be protected from floods, otherwise the units would be damaged and untreated sewage would escape. 2. It should be located downwind (leeward) of the town so that odours are carried away from it, and not too far from the town (economy of pumping). 3. The water table should be low, not high, even during the monsoon.
Explanation
Flood safety is the essential site requirement. The other statements are reversed or exaggerated.
Why the other options are wrong
(b) is reversed (the plant should be on the leeward side of the town). (c) "as far as possible" ignores the cost of conveying sewage. (d) is the opposite of the requirement (the water table should remain low).
Shortcut
STP site: flood-free, low water table, downwind of town, not too distant.
Common mistake
Choosing the leeward-side statement.
Correct answer: A) The site should be safe from floods for all the time