04-12-2012, 03:02 PM
Modern sewage treatment
Modern sewage treatment2.pptx (Size: 67.29 KB / Downloads: 56)
Based on biological principles of sewage purification where purification is brought about by the aerobic and anerobic bacteria
Treatment may be divided into
Primary
Secondary
Primary treatment
SCREENING
Sewage arriving at a disposal work is first passed through a metal screen which intercepts large floating objects such as pieces of woods wrags.
There removal is necessary to prevent clogging of treatment plant
The screen consists of vertical steel bars 5 cm apart
In some plant they are moving type
GRIT CHAMBER
Sewage is then passed through long narrow chamber 10- 20 cm in length
Constant velocity of 1 foot per second
Detention period of 30 seconds to 1 minute
Function is to allow the settlement of heavier solid but organic matter can pass through
PRIMARY SEDIMENTATION
Sewage is now admitted into a huge ps tank
It is a large tank holding 1/4th to 1/3rd the dry weather flow
sewage is made to flow very slowly across the tank at a velocity of 1-2 feet per min
Detention period is 6-8 hrs
During this purification takes place through sedimentation of suspended matter
50 -70 % settle under gravity
Reduction of 30-40 % in no. of coliform organism is obtained
The organic matter which settles down is called sludge
Small amount of biological action takes place in sewage
A certain amount of fat and greece rise to surface called scum
Sewage is also treated with lime ,aluminium sulphate
Trickling filter method
It is a bed of crushed stones 1 to 2m deep 2 to 30m in diameter
Effluent from PS tank is sprinkled uniformly on surface on the bed by a revolving device
The device consists of hollow pipes with holes
The pipes keep rotating and sprinkling
ACTIVATED SLUDGE PROCESS
The heart of activated sludge process is the aeration tank
The effluent from ps tank is mixed with sludge drawn from the final settling tank
In the proportion of 20-30 %
Detention period is 6-8 hrs
The aeration is accomplished either by mechanical agitation or by forcing compressed air from bottom of the tank