Cleaning is done by________________?

1) scraping and removal in filters slow sand
2) back washing in slow sand filters
3) scraping and removal in filters rapid sand
4) back washing in rapid sand filters

The correct answer is

Double filtration is used_______________?

A. to increase the filtration slow sand filters capacity of
B. to increase the filtration rapid sand filters capacity of
C. for isolated buildings like pools, hotels etc swimming
D. all of the above

The polluted water is one which_______________?

A. contains pathogenic bacteria
B. consists of undesirable substances rendering it unfit for drinking and domestic use
C. is safe and suitable for drinking and domestic use
D. is contaminated

The time of concentration is defined as_______________?

A. the time taken by rainfall water to run from most distant point of water shed to the inlet of sewer
B. the time required for flow of water in sewer to the point under consideration
C. sum of (A) and (B)
D. difference of (A) and (B)