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Chapter: Civil : Environmental Engineering : Disposal Of Sewage And Sludge

Important Question And Answer: Disposal Of Sewage And Sludge

Civil - Environmental Engineering - Disposal Of Sewage And Sludge

Important Question And Answer: Disposal Of Sewage And Sludge



1.                 Define   the   term   'Dilution   Factor'?



The ratio of the quantity of the diluting water to that of the sewage is known as the


Dilution Factor.



2.What are the methods adopted for sewage disposal?



     Dilution is disposal in water.


     Effluent Irrigation or Broad Irrigation or Sewage forming is disposal on land.



3.What are the conditions adopted for disposal by dilution?


        When sewage is comparatively fresh (4 to hr old) and free from floating and settlable solids.


                                When the dilution water has a high dissolved oxygen (D.O.) content.


        When the out fall sewer of the city or the treatment plant is situated near some natural waters having large volumes.



4.What are the natural forces of purification?


        Dilution and dispersion.




        Oxidation -reduction in sun-light.







5.What are the factors affecting self purification of polluted streams?







        Hydrography such as the velocity and surface expanse of the river stream.


        Dissolved oxygen and the amount and type of organic matter.


        Rate of re aeration.


6.What are the types of self purification?


The self purification divided into four zones.



        Zone of degradation.


        Zone of active decomposition.


        Zone of recovery


        Zone of Cleaner water



7. What   is   meant   by   'Self   purification   phenomen



When sewage is discharged into a natural body of


water, the receiving water gets polluted due to waste products, present in sewage effluent. The natural forces of purification such as dilution, sedimentation, oxidation -reduction in sun light go on acting upon the pollution elements and bring back the water into its original condition. This automatic purification of polluted water, in due coarse is called the self purification phenomenon.



8.What is meant by photo synthesis?




The sun light has a bleaching and stabilizing effect of bacteria. It also helps certain micro organisms to derive energy from it and convert themselves into food for other forms of life, thus absorbing Co2 and releasing O2 by a process known as Photo synthesis.

9. What do you mean by Oxidation?




The oxidation of the organic matter prevent in sewage effluents, will start as soon as the sewage out falls into the river water containing dissolved oxygen. The deficiency of oxygen so created will be filled up by the atmospheric oxygen. The process of oxidation will continue till the organic matter has been completely oxidized. This is the most important action responsible for effecting self purification of rivers.



10. What do you understand by Reduction?




Reduction occurs due to hydrolysis of organic matter settled at the bottom either chemically or biologically. An aerobic bacteria will help in splitting the complex organic constituents of sewage into liquids and gases and thus paving the way for their ultimate stabilization by oxidation.



11. Define the term Re-oxygenation curve?




In order to counter - balance the consumption of D.O. due to de-oxygenation, atmosphere supplies oxygen to the water and the process is called re-oxygenation.



12.                    What   is   mean   by   'Oxygen   sag   curve'?




The amount of resultant oxygen deficit can be obtained by algebraically adding the de-oxygenation and re-oxygenation curves. The resultant curve so obtained is called the oxygen sag curve or the oxygen deficit curve.

13. Write the equation for find out the B.O.D. of the diluted water.



B.O.D. of the diluted mixture


C = [ Cs.Qs . CR.QRf  ] / Qs QR





Cs -B.O.D. of sewage


CR - B.O.D. of river



Qs - Sewage discharge



QR- Discharge of the river



14. What is meant by epilimnion zone?




The water of a lake gets stratified during summers and winters. Since such turbulence extends only to a limited depth from below the water surface, the top layers of water in the lake become well mixed and aerobic. This warmer, well mixed and aerobic depth of water is called epilomnion zone.



15. What is meant by hypolimnion zone?




The lower depth of water in the lake which remains cooler, poorly mixed and an aerobic, is called are hypolimnion zone.

16. What do you understand by monocline? Give example.




The water of a lake gets stratified during summers and winters. The change from epilimnion to hypolimnion can be experienced while swimming in a lake. When you swim in top layers horizontally you will feel the water warmer and if you dive deeper, you will find the water cooler. The change line will represent monocline.



17.What are the advantage of land filling methods of dispoal?



        It is simple and economical


        No plant / equipment is required


        There are no by products and hence there is no problem of the disposal of the by-products.


        Separation of varies materials of the refuge is not required.


18.What are the disadvantages of land filling methods of disposal?



        Proper site may not be available near by


        Wind direction map not be favourable.


        Large band areas are required.


        It may be difficult to get large quantities of covering material.


19.What do you understand by pulverization?




In this method, the dry refuse is pulverized into power form, without changing its chemical form. The power can either be used as a poor quality manure, or else be disposed of by land filling.


20.What are the disadvantages of incineration of method of disposal?


        Large initial expenditure.


        Improper operation results in air pollution problems and incomplete reduction of the waste materials.


        Disposal of the remaining residue is required.


        High slacks needed for natural draft chimneys present safety problems.



21. What do you understand by mechanical composting?




The open window method of composting is very laborious and time consuming process. Also it requires large area of land which may not be available in big cities these difficulties are overcome by adopting mechanical composting in which the process of stabilization is expedited by mechanical devices of turning the compost.



22.            What are the methods adopted for composting?



        Composting by trenching.


        Open window composting.


        Mechanical composting.



23.What   is   meant   by   'humus'?




The refuge gets stabilized in about 4.5 months period, and gets changed into a brown coloured odourless innocuous powdery form known as humus, which has high manure value became of its nitrogen content.



24.What are methods adopted for sludge drying?



        Drying the sludge on prepared sand beds.


        Drying the sludge on centrifuges.


        Drying the sludge by heat dryers



25.What is meant by house refuse?




This consists of vegetable and animal waste matters, ashes, cinders, rubbish, debries from cleaning and demolition of structures.

26.What is meant by organic waste?




It includes dry animal and vegetable refuse, cow dung, excreta of birds, tree leaves, sticks, plastic bottles, paper waste, rags. This waste is subject to decay with time and evolve highly offensive odour and gases which are highly detrimental to health.



27.What are the types of preventive measure in adopted for sewage sickness?



        Primary treatment of sewage


        Choice of land


        Under-drainage of sool.


        Giving rest to the land.


        Rotation of crops


        Applying shallow depths.





28.Define   the   term   'Raw   sludge'?




The sludge, which is deposited in a primary sedimentation tank is called Raw sludge. Raw sludge contains highly puterscible organic matter, and is thus, very objectionable.



29.What   is   meant   by   'conditioning'?




Conditioning improves the drainability of digested sludge. Prior conditioning of sludge before application of dewatering methods renders it more amenable to dewatering.



30. What are the purpose of dewatering?




The purpose of dewatering is to further reduce the volume of sludge and thereby increase the solids concentration.


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