This is the based on the suspended growth process in which an adequate biological mass in suspension with in the tank,is maintained by either natural or mechanical mixing.Activated sludge process is am improved method of secondary treatment of the effluent from primary sedimentation tank.The sludge of the sewage which is previously agitated under areobic conditions containing full of areobic bacteria is called "activated sludge".
In the activated sludge process the primary effluent is mixed with activated sludge and then areated so as to oxidize the organic matter and converted into settable flocs.These flocs can be removed in the secondary sedimentation tank.
What are the construction and operation activated sludge
The conventional Activated sludge process consists of a rectangular tank 3 to 4.5m deep and about 6m wide and 10 to 20m long.This tank has an arrangement of sending diffused air from bottom or mechanical agitator.
The primary effluent is mixed with the portion of returned sludge and then aollowed into the tank.This mixed liquor is then areated or mechanically agitated in the presence of air.The areobic bacteria kept in suspension oxidize the sludge.The oxidized sludge is with drwan and sent to secondary clarifier for sedimentation process.The operation is a continuous process.The recycling of the returned sludge.
The various methods are available to bring about aeration of sewage are:
1.Diffued areation which can be further be classified as
a.Ridge and furrow type areation.
b.spiral flow tank areation.
2.Mechanical areation.They are two types of mechanical areation namely.
a.Simplex areation
b.Haworth paddle system
c.Link belt areation
d.kenser brush areation
What are the advantages of activated sludge process
1.High efficiency in the removal of B.O.D and solid by about 90%.
2.Free from fly nuisance and bad smell.
3.Area required for construction is small.
4.Initial cost is very less.
5.Loss of head in the process is small.
What are disadvantages of activated sludge process
1.It operation cost is high.
2.Skilled supervision is necessary.
3.The Change in the quality and quantity of effluent upsets the process.
4.Large volume of sludge is produced.