Which of the following statements represent(s) advantages of the separate system of sewerage? Statement I: The load on treatment units becomes less. Statement II: Sewers are large in diameter. Statement III: Maintenance costs are reasonable.
- AOnly II
- BOnly III
- COnly ICorrect
- DOnly II and III
Solution
Concept
In a separate system, only sanitary sewage goes to the treatment plant, so the load on treatment units is small. Sewers are also small in size.
Step-by-step solution
1. A separate system carries sewage and storm water in two different sets of pipes. 2. Only sewage reaches the treatment plant, so the load on treatment units is less. Statement I is true. 3. Sewers carry only sewage, so they are small in diameter, not large. Statement II is false. 4. Two pipe systems are needed, and small sewers often need flushing, so maintenance cost is high. Statement III is an advantage of the combined system, not the separate one. 5. So only Statement I is correct. The answer is C.
Explanation
In a separate system, storm water does not go to the treatment plant, so the treatment load is less. Sewers are small, not large. Maintenance cost is higher because two sets of pipes are kept and small sewers need flushing.
Why the other options are wrong
A: Sewers in a separate system are small, not large. B: Reasonable maintenance cost is an advantage of the combined system. D: Both II and III are wrong.
Shortcut
Separate system = small pipes, less treatment load, higher maintenance cost.
Common mistake
Mixing up the advantages of the combined system (large sewers, easy cleaning, lower maintenance) with those of the separate system.
Correct answer: C) Only I