Rejuvenation of the Slow Sand Filters at Palta for Augmentation of Water Supply of Calcutta City

Old is gold. This is specially true with the 59 slow sand filter beds which were constructed during the year 1868 through 1956 and are still working and even at this age it leaves enough scope for rejuvenation. The original design capacity of the filters was 99 mgd. With the aging, the output of the filters gradually decreases. This is quite natural but the decline of the filtration rate from 99 mgd. to the present 66 mgd. is rather unusual.