Sewage Clarification Plant for Calcutta

History. Sewage and storm water of Calcutta, since the inception of the waterborne drainage system in the City in 1869 used to be discharged into the river Bidyadhari about 5 miles to the east of the City-in its crude form. This river being a tidal one sewage and storm water used to be stored in a large reservoir about five miles in length and were discharged into the river during the period of low tides. The reservoir had the storage capacity of 8 hours sewage flow plus the storm water for 8 hours at the rate of 1/4" rainfall per hour. The above system of disposal of Calcutta's sewage and rainfall worked satisfactorily for a considerable period of time-without causing any appreciable nuisance by forming sludge banks in the river or causing any harm to the fish life in the same.