DHANALAKSHMI COLLEGE OF ENGINEERING, CHENNAI

DEPARTMENT OF CIVIL ENGINEERING

CE6605 ENVIRONMENTAL ENGINEERING

UNIT – I : PLANNING FOR SEWERAGE SYSTEMS

PART – A (2 MARKS)

1. What do you mean by time of concentration? State its significance in sewer design.

It is defined as the longest time without unreasonable delay that will be required for a drop of water

to flow from the further point of drainage area.

2. State the pollution control board norms for effluent discharge into streams. (M/J -11)

Impurities Inland Surface Water

Public Sewers Land for Irrigation Marine outfall

SS 100 600 200 100

Grease and Oil 10 20 10 20

BOD 30 350 100 100

3. What are the typical characteristics of sewage from South Indian Cities?

The typical characteristics of sewage are listed as follows :

Constituent Concentration

BOD (at 20°C) (400 mg/u)

TOC (290 mg/u)

COD (1000 mg/d)

Chlorides 100 mg/u

Solids 1200 mg.l

4. Explain the meaning and significance of “time of concentration”. (N/D -11)

Time required for the flood discharge to reach to the maximum limit. It is used to indicate the

(a) Inlet time (b) Outlet time

(c) Peak time (d) Maximum Runoff

5. Differentiate between dry weather flow and wet weather flow.

DWF – Dry Weather flow is defined as the flow of sewage, consists of domestic sewage (or

sanitary sewage) and industrial sewage and mentioned as DWF.

WWF - The flow of storm water is called Wet-Weather Flow and mentioned as WWF.

6. State the necessity of legal requirements and effluents disposal of sewage. (N/D -12)

Necessity of Legal Requirements for Effluent Disposal:

All types of effluent needs to be treated and disposed off safely.

Parameters like DO, BOD, COD, suspended solids, other solids content needs to be reduced

to the permissible level.

Toxicity levels must be eliminated to a non-hazardous state and then disposed off.

7.Name sewage characteristics with which organic matter concentration is expressed. BOD, COD

8. State the effluent standards for any four parameters recommended by the pollution control board.

(M/J -13)

TCS<100 mg/u TOS<2100 mg/u

pH = 5.5 to 9.0

BOD < 30 mg/u

COD<250 mg/u

9. Why do the analyses BOD and COD usually give different results for the same wastewater?

Both the BOD and COD tests are a measure of relative oxygen – depletion of a waste contaminant.

Naturally sewage contains bacteria and nutrients almost will initiate bio chemical reactions(BOD)

The chemicals are also broken by down using oxidizing agents(COD).

Result is oxygen content will be N/Dreased and varies.

10. What is the effect of suspended solids on water bodies? (N/D -13)

Effect on suitability of water bodies for reactional activities.

Effect on aquatic defect fishes.

Water becomes warmer good and oxygen penetration.

Bad odour of taste.

11. What is sanitary engineering? Sanitary Engineering is defined as the branch of public health engineering and it deals about the

collection conveyance, treatment and safe disposal of waste for preventing the communicable diseases.

12. What are the objectives of Sanitary Engineering?

(a) To maintain the environments and to prevent the effect of sewage to public health in general.

(b) To prevent the effect of disposal of sewage on land or nearby water bodies from pollution.

(c) To prevent the environment from mosquitoes, flies, bacteria etc

(d) To dispose the human excreta to a safe place(septic tank) before it starts N/Domposition and

M/J cause insanitary conditions in the locality.

13. What are the stages of Sanitary Engineering?

(a) Collection of sewage

(b) Conveyance of sewage

(c) Treatment of sewage

(d) Disposal of sewage

14. Define (i) Refuse (ii) Sewage (iii) Sullage (iv) Storm Water.

(i) Refuse : All waste materials either in liquid ,semi solid (or) solid coming out from residential,

industrial and commericial buildings is generally known as refuse.

(ii) Sewage : Sewage is defined as the liquid waste from community and which includes discharges

from latrines, urinals, bathrooms, kitchens, industrial waste and storm water.

(iii) Sullage: Sullage is defined as the waste water from domestic buildings especially from

bathrooms, kitchens etc.

(iv) Storm water: is defined as the rain water flowing on the ground surface in a locality.

15. What is DWF and WWF? Differentiate.

DWF – Dry Weather flow is defined as the flow of sewage, consists of domestic sewage (or

sanitary sewage) and industrial sewage and mentioned as DWF.

WWF - The flow of storm water is called Wet-Weather Flow and mentioned as WWF.

16. What are the impurities present in sewage?

Physical impurities (such as large solid particles etc)

Chemical impurities (dissolved solids, acid chlorides etc)

Biological (or) Bacteriological impurities (bacteria and other micro organism)

17. What are the three sewerage systems?

(a) Sewerage system

(b) Combined system

(c) Partially separate system.

18. What are the factors affecting the quantity of storm water or DWF?

(a) Population

(b) Rate of water supply

(c) Industries and its type

(d) Infiltration and exfiltration.

19. Define Infiltration and Exfiltration?

Infiltration is the leakage of water from the ground surrounding the sewer.

Exfiltration is the leakage of sewage from the sewer into the ground surrounding the sewer.

20. Define Impermeability factors?

Impermeability factor(or) run-off co-efficient is defined as the ratio of precipitation to run-off.It is denoted by “k”.

21. Define pH. pH of sewage is defined as the negative log of hydrogen ion concentration present in sewage

22. Define BOD/COD ratio and state its significance.

The quantity of BOD5 to the COD is referred as BOD/COD ratio and it is always less than 1.0. But it

M/J reach 1.0 with N/Dreasing amount of Non Biodegradable Organics (NBO’s) . This ratio is very

important for N/Diding the quantity and type of treatment given to waste water for the safe disposal.

23. Define COD/TOC ratio and state its significance.

The total carbonaceous organic present in a given waste water can be estimated by calculating

TOC of the waste water, by converting the organic carbon to CO2.This can be measured by Infra-Red

analysis, and converted to the original organic compound.(COD/TOC) ratio is used to monitor the water

treatments.

pH = - log(H+)

24. What is relative stability?

The term relative stability of a sewage effluent M/J be defined as the ratio of oxygen available in

the effluent (as D.O. nitrate or nitrite) to the total oxygen required to satisfy its first stage B.O.D demand.

Relative stability = S= 100 [1-(0.794)t 20]

S=100 [1-(0.630)t(37)]

25. Define sanitary project.

The sanitary project is proceeded by the water supply schemes and before the project is finalized,

the various important points are to be considered. It is the usual practice to give the advantages of sanitary

project in stages. For this purpose, the locality is divided into suitable zones and one by one is taken for the

installation of sanitary facilities. The bye-laws of the locality are also so framed as to maintain adequate

sanitation in the structure.

26. What are the major effluent standards for disposal?

Impurities Inland Surface Water

Public Sewers Land for Irrigation Marine outfall

SS 100 600 200 100

Grease and Oil 10 20 10 20

BOD 30 350 100 100

27. What is population equivalent? 28. Define bio-degradable organic matter.

The organic matter, N/Domposed by bacteria under biological action is called bio-degradable organic matter.

PART – B (16 MARKS)

1. What is meant by population equivalent? State its uses. Calculate the population equivalent of a city

given

a) The average sewage from the city is 95*109 l/day

b) The average 5day BOD is 300mg/l

(A/M-11)

2. The BOD of a sewage incubated for one day at 30°C has been found to be 110mg/l. What will be the 5

day 20°C BOD? Assume K1 = 0.1 at 20°C.

(A/M -11)

3. Explain the estimation storm run off and factors influencing it.

(M/J -13)

4. The BOD5 of waste water is 150mg/l at 20°C. The k value is known to be 0.23 per day. What would

BOD8 be, if the test was run at 15°C?

(M/J -12)

5. A population of 30,000 is residing in a town having an area of 60hectares. If the average coefficient of

runoff for this area is 0.60, and the time of concentration of the design rain is 30minutes, calculate the

discharge for which the sewers of a proposed combined system will be designed for the town. Take

80% of water supply, rate of water supply = 120lt/day/person.

(M/J -12)

6. Explain the legal requirements and standards regarding treatment of sewage.

(N/D -11)

7. List the information to be collected while planning for sewerage systems. How will you use the

corrected information?

(N/D -11)

8. Write about 10 effluent quality standards as per Tamil Nadu pollution control board.

(N/D -12)

9. Estimate the storm runoff from 10hectares of a surface having the following characteristics if the

maximum rain intensity in the area is 5cm/hr.

Nature of

surface

Roof Pavements Paved

yards

Maccadam

roads

Lawns &

gardens

Thick

vegetation

Areal

distribution

(% of total)

30 10 5 25 25 5

Coefficient

of runoff

0.90 0.85 0.80 0.40 0.1 0.05

(8)

10. Calculate the combined flow discharge of sewage for the following date.

Area to be served = 150hectares

Population of the locality = 50,000

Time of entry = 15min

Time of flow = 20min

Rate of water supply = 135litres/capita/day

Impermeability factor = 0.45

Assume 80% of water supplied turns in to sewer and peak factor as 1.5

UNIT – II: CONVEYANCE SYSTEM

PART A (2 MARKS)

1. List the factors influencing the fixing of design period.

The factors influencing the fixing of design period are :

Weather flow conditions

Rate of water supply

Type of area served

Population growth

2. Give the design flow value for separate, combined and storm sewers. (M/J -11)

The design values are given as follows:

Separate Sewers 1.0

Combined Sewers 1.0

Storm Sewers 0.5 to 0.8

3. How is the capacity of the wet well in a sewage pumping station determined?

The capacity of sump well is determined on the basis of a minimum detention period of about 15 to

30 minutes of the peak flow. If its capacity is less, the operation of the power unit shall have to be done at

frequent intervals and it M/J result in the increase of the operation cost.

4. Distinguish between “Self Cleansing Velocity” and Non-scouring velocity. (N/D -11)

Self Cleansing Velocity Non-Scouring

Defined as the velcocity at which the solid particles

will remain in suspension without settling at the

bottom of the sewer.

Defined as the minimum velocity which allows the

particle to stick to the invert (i.e.) (No scouring

occurs)

The velocity doesn’t not depends upon the material

sed for construction of sewer.

The velocity depends upon the construction material

of sewer.

5. Enumerate the various steps involved in the layout and construction of sewers.

The various steps involved in the layout and construction of sewer lines are :

(a) Setting out

(b) Alignment and formation of gradient

(c) Excavation of trenches

(d) Laying and Jointing

(e) Testing

(f) Backfilling

6. Reciprocating pump is not widely used in the sewage pumping – state true or false and justify your

answer. (N/D -12)

Reciprocating pumps is used for pumping sewage because high effects are required for

transporting sewage which consists of great fluctuations.

It is more economical.

It is also used for sewage flow where it is varied.

7. Define “sewerage system”. List out the components of it.

Sewerage system is a system for collection conveyance and disposal of sewage. As sewerage

system consists of a network of sewers, for carrying the sewage from individual units (homes and

industries) to the sewage treatment plant.

Components

1. House Sewer

2. Lateral Sewers

3. Branch Sewers

4. Mains Sewers

5. Trunk Sewers

6. Manholes

7. Catch basins etc.

8. What are the situations where the pumping of sewage becomes essential is sewage management.

(M/J -13)

Pumping from low lying areas.

To lift the sewage in treatment plants for making the flow under gravity

Pumping at specified intervals in flat country

The place where the basement level of the houses are lower than the invert level of the sewer.

When a sewer has to pass across a high ridge.

9. What is the significance of self cleansing velocity in sewer design .

Deposition takes place and if it is not removed it will obstruct free flow causing further deposition

and finally leading to complete blocking of sewer. So checking at least once a day is important.

10. Name any two softwares used in sewer design. (N/D -13)

Sewer CAD

Storm CAD

11. Define a sewerage system.

Sewerage system is a system for collection conveyance and disposal of sewage. As sewerage

system consists of a network of sewers, for carrying the sewage from individual units(homes and

industries) to the sewage treatment plant.

12. What is self cleansing velocity?

Self cleansing velocity is defined as the velocity at which the solid particles will remain in

suspension without settling at the bottom of the sewer.

13. Define Non-scouring velocity?

The maximum velocity at which the scouring action of sewer surface is not happened that velocity

is called Non-scouring velocity.

14. What is time of concentration? State its importance while designing of sewers.

It is defined as the longest time without unreasonable delay that will be required for a drop of water

to flow from the further point of drainage area. It is used to find out the discharge through storm sewer.

15.What are the advantages of circular sewer over other sewer sections?

Advantages of Circular Sewer

a) From hydraulic point of view circular section provides more hydraulic mean depth(or

maximum area per unit wetted perimeter)

b) Construction cost and material requirement is less.

16. What are the disadvantages of egg-shaped sewers?

Disadvantages of egg-shaped sewers

a) The egg-shaped sewer is less stable than the circular section,

b) the construction is difficult.

17. What are the factors governing the types of joint?

Type of sewer

Type of sewerage system

Strength and flexibility of joint

Internal pressure

External Load

Type of Support etc

18. What are the requirements of an ideal joint?

a) Water tight joint

b) Easy for construction

c) Cheap and economical

d) Flexible

e) Non-absorbent

f) High durability

19. Name the various types of joint.

1. Cement mortar joint

2. Collar Joint

3. Flexible or bituminous joint

4. Mechanical joint

5. Open joint

20. Name the type of joint used to join the metallic sewers.

Mechanical Joint

21. Name the tests used for sewer pipes.

a) Water Test

b) Straightness Test

c) Smoke Test

d) Air Test

22. What are the various forces acting on the sewer pipes?

Internal Pressure

External Load

o Back fill loads

o Super-imposed Loads

Temperature Stresses

Flexural Stresses

23. Why the pumping capacity is to be adjusted in sewage pumping?

The rate of flow of sewage is not a constant one and varies continuously, hence the pumping

capacity is be adjusted with rate of flow.

24. What is the purpose of providing a reflux valve and air valve?

Reflux valve is used to open the flow in one direction only.Air valve is used to release the air or

pressure, while the pump is working .

25. Name any three mechanical tools used for cleaning of sewer.

Double worm screw

Drain Brush

Wire Brush

26. Define Blocks and inspection chamber.

Blocks : Sewer line is divided into small lengths are called blocks.

Inspection Chamber : Smaller diameter, shallow depth manholes are located in non-traffic areas

and located only at start of the branch sewer, is called Inspection Chamber.

27. What is a clean out?

A clean-out is an inclined pipe, which is connected to the underground sewer, used to remove any

obstruction present inside the sewer.

28.Where inlets are located?

The inlets are located by the sides of roads at a distance of about 30m to 60 m. They are also

located at the inlet of the storm water regulators.

29. How the sand and small sized particles are removed in a oil and grease trap?

The grease, oil and small particles are very light in weight and floating on the surface of the

sewage. If sand is desired to be excluded from sewage, the space should be kept at bottom of chamber for

sand to be deposited.

30. What is a storm water regulator?

The structures constructed to divert the part of sewage in case of combined sewers are known as

the storm water regulators, and they come into operation when discharge exceeds a certain value.

31. How the inner and outer surfaces of the bricks sewer are covered?

Brick sewers should be plastered on their outer surface to prevent the entry of root, and to prevent

the entry of root, and to prevent the entry of ground water.

The inner surface of the brick surface is to be lined by using ceramic block or stone war to make it

smooth.

The cement plastering should not be inside the brick sewer in order to avoid crown corrosion, as in

cement concrete sewer.

32. Write the purpose of using non-circular sewer sections?

To reduce the cost of construction

To increase the velocity of flow (at low discharge)

To provide the space for cleaning and maintenance

To increase the strength

To simplify the method of construction

33. Mention the problems occurring, while pumping of sewage.

The pumping of sewage is not simple as pumping of water,for the following problems:

(a) Sewage has lot of suspended and floating of solids and they cause clogging of pumps.

(b) Sewage contains organic and inorganic matters and they M/J corrode the pumping units

and reduce their life.

(c) Biological life of sewage, including disease producing bacteria are dangerous for health.

Hence any slackness with sewage pumping has to be attended immediately.

(d) The rate of flow of sewage is not a constant one, and varies continuously, hence pumping

capacity is to be adjusted with rate of flow.

(e) The size of sump is limited since the large sized sumps will result in the settlements of silt

and organic matter at its bottom. The provision of sump or wet well is made to give only a little storage

space.

34. Draw the sketch of rectangular surface drain.

35.Draw the sketch of semi-circular surface drain.

36. Draw the sketch of U-Shaped and V-shaped surface drain.

PART – B (16 MARKS)

1. Discuss with neat sketch a drop manhole and indicate where it is used.

(M/J -12)

2. Explain the laying of sewer in the field for the desired alignment and gradient.

(M/J -13)

3. Determine the diameter of separate sewer section running 0.7times at maximum discharge for a

population of 50,000 persons. Water is supplied at a rate of 140lt/capita/day. Assume 80% of water

supplies turn as sewage. Take peak factor as 2.25 and manning’s constant n = 0.013 at all depth of

flow. The permissible slope is 1 in 700.

(M/J -13)

4. Design a sewer section running 0.7times at maximum discharge for a population of 90,000 persons.

Water is supplied at a rate of 200lt/capita/day. Take slope 1 in 400, manning’s constant n = 0.013 at all

depth of flow and peak factor as 85% of water supplied.

(M/J -12)

5. Explain the various system of plumbing used in drainage.

(M/J -13)

6. Compare the formation, advantages and disadvantages of one pipe and two pipe plumbing system.

(M/J -11)

7. A town has a population of 1,00,000 persons with a per capita water supply of 200lt/day. Design a

sewer running 0.7times at maximum flow conditions. Take n = 0.013, slope 1 in 500 and peak factor of

3.

(M/J -11)

8. Discuss the choice available and the factors to be considered while selecting pumps and pipes for a

sewerage system.

(N/D -11)

9. Explain the significance of maximum and minimum velocities of flow in design of sewers.

(N/D-12)

10. State the hydraulic formulae adopted in design of sewers.

(N/D -12)

UNIT – III PRIMARY TREATMENT OF SEWAGE

PART A (2 MARKS)

1. What is grey water and grey water harvesting?

Greywater is generally defined as, the waste water generated from wash basins, showers and bath.

Greywater harvesting is defined as the waste water treatment of onsite sanitation applied to grey waters.

2. Distinguish between grit chamber and plain sedimentation tank. (M/J -11)

Grit Chamber Plain Sedimentation

They are used to remove inorganic particles. They are used to treat the industrial waste

It works on pump setting It works on flocculent settling

Chemicals are not needed to aid settling Chemicals are needed for flocculent settling

It depends on sourcing and settling velocity It depends on the surface loading and detention

time

3. What are the differences in the functions of “Screen Chamber” and “Grit Chamber” in sewage treatment?

Grit Chamber Screen Chamber

They are used to removed inorganic particles. To remove floating particles.

It works on settling of particles. It works on pores where it traps the particles

Chemicals are required for settling Its not required

4. What is meant by Grey water Harvesting? (N/D -11)

Greywater harvesting is defined as the waste water treatment of onsite sanitation applied to grey waters.

5. Differentiate between unit operations and unit processes in wastewater treatment.Give at least two

examples in each.

Unit Operations Unit Process

Methods of treatment in which the application of

physical forces predominate are called as unit

operations

Methods of treatment in which the removal of

contaminants is brought about by chemical or

biological reactions

It is mere physical process Includes addition of chemicals

Example : Grit Removal, Sedimenation Example :

Coagulation,Flocculation,Filtration,Activated Sludge

Process,Disinfection

6. State the necessity of velocity control devices in grit chamber. Name the devices used.

(N/D -12)

Flow velocity should neither be too low as to cause the settling of lighter organic matter nor should it

be so high as not to cause the settlement of the entire slit and grit present in sewage.

A flow velocity of about 0.25 to 0.3 m/sec is adopted for the design of put basins.

7. What do you mean by on-site sanitation? Brief it.

System of sanitation where the means of storage and treatment are contained with the plot occupied

by leveling and its immediate surroundings.

8. State the objectives of grey water harvesting. (M/J -13)

1) Conservation of water

2) Recycle of waste water

3) Reducing load on septic tank

4) Top soil nitrification

5)

9. Give the design criteria for screen chamber.

Coarse Screens – Spacing 50 mm/6 litres of solids

Medium Screens – Spacing 6 to 40 mm (30 to 90 litres of sewage)

Fine Screens – 1.5mm – 3m space opening

20% of SS is removed .

10. What are the objectives of grey water harvesting?

1) Conservation of water

2) Recycle of waste water

3) Reducing load on septic tank

4) Top soil nitrification

11. What are the stages of sewage treatment?

Preliminary Treatment

Primary Treatment

Second (Biological) Treatment

Advanced or final treatment

12. What are the functions of primary treatment?

Removal of oils and greases etc.

Removal of larger settlable in-organic solids

Reduction of BOD of sewage about 25%.

13. What is the difference between unit operations and unit processes?

Unit Operations Unit Process

Methods of treatment in which the application of

physical forces predominate are called as unit

operations

Methods of treatment in which the removal of

contaminants is brought about by chemical or

biological reactions

It is mere physical process Includes addition of chemicals

Example : Grit Removal, Sedimenation Example : Coagulation, Flocculation, Filtration,

Activated Sludge Process, Disinfection

14. What are the types of screens?

According to size of openings

Coarse Screen

Medium Screen

Fine Screen

According to movement

Fixed Screens

Movable Screens

Moving Screens

15. What are the general methods employed for disposal of screenings?

Burial

Incineration

Disintegration

Fertilizer

16. Define Incineration.

Incineration is defined as the process of burning the screenings at high temperatures normally about

760°C to 840 °C.

17. What are types of settling?

Type I Settling (Discrete settling)

Type II Settling (Flocculent Settling)

Type III Settling (Hindred or Zone Settling)

Type IV Settling (Compression settling)

18.Explain Stoke’s law of settling velocity.

19. What is the purpose of providing velocity control in grit chambers? (or) How can you control the velocity

in Grit chambers?

Flow velocity should neither be too low as to cause the settling of lighter organic matter nor should it

be so high as not to cause the settlement of the entire slit and grit present in sewage.

A flow velocity of about 0.25 to 0.3 m/sec is adopted for the design of put basins.

20. Define Skimming Tank.

Skimming tanks are the structures used to remove the grease and oil from the sewage, by diffusion

of air through the sewage.

21. Define Sedimentation Tank

Sedimentation tank are the treatment units of sewage treatment, used to reduce the strength and to

settle the solids of the sewage.

Settling Velocity Vs =

22. Define Detention or Retention Time.

The detention time of a primary settling tank is defined as the average theoretical time required for the

sewage to flow through the tank.

23. What is Surface Loading or Overflow rate?

The surface loading rate or over flow rate is defined as the ratio of discharge (Q) to the plan area(BL) and

it is also termed as surface loading .

Surface Loading(or) Overflow rate =

24. Define Weir Rate.

Weir loading rate is defined as the amount of sewage leaving the settling tank per unit length of the weir.

It is measured in terms of m3/m/day.

25. What are the advantages of secondary sedimentation?

It is more effective than the plain sedimentation.

Space requirement is very low

Simple operations

More effective for reduction of BOD, colour and turbidity.

26. What is septic tank?

A septic tank is a primary sedimentation tank and an unit of on-site sanitation, with a longer detention

period (12 to 36 hours) with an additional provisions for digestion of the settled sludge.

Weir loading rate =

27. What is on site santiation?

On site sanitation is the treatment process and disposal of domestic waste water that cannot be

carried away by an off-site sanitation system.

28. Give Hazen’s equation for discrete particles.

Settling Velocity,

29. How the oils and grease matters are removed from sewage?

Grease in sewage includes fats, waxes, free fatty acids, calcium and magnesium soaps are removed

form sewage by either by flotation or as a scum or sludge by using air diffusion and skimming tank.

30.Define grey and black water .

Grey water is generally defined as the waste water generated from wash basins, showers and both.

Black water is the waste water containing human fecal waste.

31.What are the applications of recycled grey water?

Recycled grey water can be used for,

(a) Irrigational purposes

(b) In-door uses(such as flushing toilets etc)

32. Write the difference between coagulation and flocculation?

Coagulation is the process of adding the chemicals (coagulants) in order to precipitate the smaller

and finer particles, where as flocculation is the formation of flocs during sedimentation process.

33. Define washing of grit.

Washing of grit is defined as the process of separating or removing the organic matter from the grit

and returning it to the treatment plant. The washing of grit should be carried out immediately after its

collection in the grit chamber.

34. Name the treatment units work on the principle of sedimentation.

Sedimentation Tank

Imhoff Tank

Septic Tank

Chemical Precipitaion Tank

Secondary Settling Tank

PART – B (16 MARKS)

1. With the help of neat sketch discuss the component parts, functioning, advantages and disadvantages of a

septic tank. Discuss various methods of disposal of septic tank effluent.

(M/J-12)

2. a) Explain the working of grit chamber and their types.

b) Discuss in brief the various types of settling and design consideration of sedimentation tank.

(M/J-12,13)

3. a) What is surface overflow rate (SOR). Derive the relationship between SOR and settling velocity of a

particle for the removal of such particle.

b) Explain the designing of a screen chamber.

(M/J-13)

4. a) Describe the on – site sanitation methods

b) Design a septic tank for a colony population of 100persons. Assume suitable data wherever

necessary. (M/J-13)

5. Design a septic tank for on site sanitation of a housing colony with 120 population. Assume suitable design

criteria and draw a neat sketch of the designed tank. (N/D-11)

6. Design a circular primary sedimentation tank to treat an average sewage flow of 5000m3/day, suitably

assuming the design criteria. Draw a neat sketch of the designed tank.

7. a) Design a rectangular sedimentation tank for treating 4.5million litres per day adopting L:B ratio as 2,

overflow rate 20m3/d.m2 and detention time of 3hours.

b) Determine the settling velocity of spherical particle of specific gravity 2.65, diameter

0.18mm. Take kinematic viscosity of water 1.01*10-6m2/sec.

(A/M-11)

7. Design a sedimentation tank. Assume all necessary data.

(N/D-11)

8. What is meant by preliminary treatment of waste water? Enumerate various unit operation falling

under this. (N/D-10)

9. a) What is meant by treatment of waste water? Draw a outline of various treatment process.

b) What is meant by plain sedimentation? Describe the design principle of a typical sedimentation

tank? (N/D-09)

UNIT – IV: SECONDARY TREATMENT OF SEWAGE

PART – A (2 MARKS)

1. State the objective and functioning principle of a secondary treatment unit.

The general principle is to remove pollutants from the water by getting them either to settle or

to float of then removing the material.

The waste water is mixed with a controlled population of bacteria and oxygen there by

removing suspended solids and soluble organic materials.

2. State the advantages of UASB Reactors. (M/J -11)

The advantages are :

The treated water can be used for irrigation purposes.

Sludge disposal is easier and cheaper .

The power requirement is very less.

The cost of treatment is low.

3. What are the objectives of Secondary and Tertiary treatment of Sewage?

Secondary Treatment:This involves further treatment of the effluent coming from the primary

sedimentation tank

Tertiary Treatment :This is accomplished through biological N/Domposition of organic matter.

4. What is the operational principle of waste stabilization ponds? (N/D -11)

Stabilisation ponds are open-flow-through earthernbasins(or ponds),specially designed and

constructed for the treatment of sewage and bio-degradable industrial waste waters.

Stabilisation ponds provide long detention periods up to several days and these period, the waste

get stabilized by the action of natural forces.

5. Distinguish between suspended growth processes and attached growth processes.

Suspended Growth Process Attached Growth Process

Microorganisms grow in suspension.

Example: Activated Sludge Process

Microorganisms get attached to an inert media.

Example : Trickling fiters

6. State the main objectives of providing advanced treatment of sewage. How it is different from

conventional treatment system. (N/D -12)

Objectives of Advanced Treatment :

To remove the organic load left after the secondary treatment

To kill the pathogenic bacteria.

Conventional Treatment Advanced Treatment

Used to separate the floating materials and

heavy settleable inorganic solids

Used to remove pathogens and the remaining

very fine dissolved organic matter

Reduces BOD by 15% Microorganism removal rate 30 – 100%`

7. When you will opt/prefer the anaerobic treatment of sewage over an aerobic process.

While the BOD value/organic strength is very high anaerobic treatment preferred.

8. Waste stabilization ponds are applicable for sewage management in rural areas only.Comment on this

statement and justify your comment. (M/J -13)

Statement is correct. Reason is the land required will be very large and cost of treatment is also

less.

9. What is the significance of sludge solids retention time in ASP design?

Sludge solids retention time M/J be defined as average time for which the mass of suspended

solids remain under aeration.

Though the hydraulic retention time M/J be only few hours, the residence time of biological solids is

much greater and while the sewage passes through the aeration tank only once within the hydraulic

retention time, the resultant biological growth and the extracted organic solids are repeatedly recycled from

the secondary settling tank back to aeration tankthere increasing the retention time of solids.

10. How do you determine hydraulic loading rate of a trickling filter? (N/D -13)

The quantity of sewage applied per unit of surface area of the filter per day.

11. What are the classifications on secondary treatment of sewage?

(a) Filtration Process

(b) Activated sludge Process

12. Define activated sludge.

The sludge coming from the secondary sedimentation tank is called activated sludge and contains

more quantity of microbes.

13. What are the advantages of Aerobic N/Domposition over anaerobic N/Domposition?

Aerobic N/Domposition does not produce bad smells and gases.

More active than anaerobic bacteria – the rate of doing work by aerobic bacteria – the rate of doing work by

aerobic bacteria is three times the work doing by anaerobic bacteria at 30°C.

14. Name the difference types of filters used in secondary treatment of sewage?

o Contact beds

o Intermittent sand filters.

o Trickling filters

o Other filters

15. Define First contact period.

In the filtration process of secondary treatment of sewage, the sewage is kept in contact media of

the contact for a certain period and that period termed as first contact period.

16. Define Second contact period in contact beds.

In order to provide sufficient oxygen available for the growth of (aerobic) bacteria, the filter is left

empty for a period called second contact period.

17. What are the advantages of contact beds?

Contact Bed can be operated without exposing the sewage to view.

Contact bed consumes relatively small amount of head.

No nuisance of filter files.

Odour problems are also very less.

18. What are the disadvantages of contact beds?

For effective working of contact bed, primary treatment of sewage is necessary otherwise,

the contact bed will be easily clogged.

The cost of the contact bed is relatively more.

The operation of contact bed requires skilled supervision

The rate of treatment of sewage is very low.

It requires long rest period (about 8 hours)

19. Howan intermitted sand filter differs from Contact Beds?

Intermittent sand filters are larger in size when compare with contact beds.

The filter media is finer than that in the contact beds.

There is no concrete lining around the filter media, as was there in contact beds.

20. What are the advantages of intermitted sand filters?

The effluent obtained from this filter is of good quality with suspended solids level of less than 10

mg/L and BOD of less than 5 ppm.

21. What are the factors affecting the rate of filtration ofan intermittent sand filter?

a. Depth and size of filtering material.

b. Nature of the influent

c. Quality of the effluent required.

22. What is a trickling filter?

Trickling filters are also called as percolated or sprinkling filters, consists of tanks of filter media.

The filter media M/Jbe of crushed stone (or) gravel or slag of larger size over the filter media, the sewage is

allowed to sprinkle or trickle down by means of spray nozzles or rotary distributors.

23. Define “Sloughing in trickling filter”.

The break up or detachment of biomass(biological solids) from the slime layer is known as

Sloughing, in trickling filter.

24. What are the types of high rate trickling filter?

Accelo-filter system

Aero-filter system

Alternating double filtration

Bio filtration

Enclosed filtration

25. Define “Ponding”.

Sometimes, the voids in the filter media gets clogged due to the heavy growth of fungi and algae. This is

called ponding of filter, over filter bed. This problem can be eliminated by chlorinating the sewage, which

kills the algae. By adding Copper Sulphate also controls the ponding problems.Ponding at the surface is

most common during winter months.

26. Draw the flow diagram for aero-filter-single stage treatment.

Filter

Digester

Secondary Clarifer

Primary Clarifer Sludge

Recirculated Flow

Sludge

Influent Effluent

27. Name any four methods of advanced sewage treatments.

Depth Filtration

Adsorption

Gas-stripping

Ion-Exchange

Advanced oxidation process

28. Define “Depth filtration”

Depth filtration is an advanced waste water treatment method, which is involves the removal of

particulate material suspended in sewage and also used to remove chemically precipitated phosphorus.

29. What are the methods used for aeration in Activated Sludge Process?

Diffused Aeration

Mechanical Aeration

Combined Diffused and Mechanical Aeration

PART – B (16 MARKS)

1. a) Explain the components and operational principles of activated sludge process.

b) Design an oxidation ditch for community of 7500 with per capita sewage contribution of 90Lpcd

and BOD 250mg/l. The desired BOD of the treatment sewage is 30mg/l

(N/D-11)

2. a) With the help of a neat sketch explain the function and operation of USAB.

b) Determine the surface area of a low rate trickling filter to treat 10MLd of average sewage flow

with a BOD of 300mg/L at an organic loading rate of 0.2kg BOD/m3/day.

(N/D-11)

3. Define and explain the different loading criteria, based on which aeration tank of ASP is operated.

(A/M-11)

4. Determine the size of a high rate trickling filter for the following data:

Sewage flow = 4.5 million litres per day

Recirculation ratio = 1.5

BOD for raw sewage = 230mg/l

BOD removal in PST = 30%

BOD of treated effluent required = 25mg/l (16)(A/M-11)

5. a) Explain with sketch the treatment of sewage by activated sludge process. Mention the advantages

and disadvantages of the process.

b) Explain briefly the working principle of waste stabilization ponds. Mention their classifications.

(M/J-12)

6. a) Compare conventional and high rate trickling filter.

b) Design an oxidation pond for treating sewage from a hoe climatic residential colony with 5000

persons, contributing sewage at 120litres per capita per day. The BOD5 of sewage is 300mg/l.

(M/J-12)

7. Determine the size of a high rate trickling filter for the following data: (M/J-13)

Flow = 4.5mld

Recirculation = 1.4

BOD of raw sewage = 250mg/l

BOD removal in primary clarifier = 25%

Final effluent BOD designed = 30mg/l

a) Sketch the vertical section of trickling filter. Explain the biological process involved in it.

b) Differentiate aerobic from anaerobic process. What is meant by secondary sedimentation tank?

State its significance.

(N/D-10)

8. a) Explain the operational principle of oxidation tank.

b) Discuss the different waste water reclamation techniques.

(N/D-09)

9. Design a conventional activated sludge plant to treat domestic sewage with diffused air aeration

system, given the following data:

Population = 35000

Average sewage flow = 180lpcd

BOD of sewage = 220mg/l

BOD removed in primary treatment = 30%

Overall BOD reduction desired = 85% (N/D-09)

UNIT – V: DISPOSAL OF SEWAGE AND SLUDGE

PART A (2 MARKS)

1. Define the treatment “sludge conditioning “.

Thickening is a procedure used to increase the solids content of sludge by removing a

portion of liquid fraction.

The sludge is thickened to 14% solids where a five fold increase in surge volume is

achieved.

2. List out the methods of minimizing sewage sickness. (M/J -11)

The methods adopted are:

Bio filters

On-site waste water treatment

Sludge management

Composting

Surface Disposal

Sub surface Disposal

3. What are the concerns in the application of sewage on to land?

It is used for sewage farming.

For irrigation purposes

For pre-treatment process

For production of cotton,groundnut sugar cane.

4. How does one improve the dewaterability of sludge? (N/D -11)

Dewatering techniques are adopted to improve the dewaterability of sludge.

Vaccum filtration – vaccum is being conveyed and mixed with sludge

High speed centrifuges for drying of raw sludges

Elutriation – Before dewatered it is washed to remove the organic and fatty acids from

sludge water.

5. State the purpose of sludge thickening.

Purpose of Sludge thickening

To remove moisture content from the sludge (98% of moisture and 2% solids content)

To dewater or dry the raw/digested sludge.

To prevent foul smelling

To reduce the land area.

6. What do you mean by sewage sickness? (N/D -12)

When sewage is applied continuously on a piece of land, the soil pores or voids M/J get

filled up and clogged with sewage matter.

Full circulation of air will be prevented and aerobic N/Domposition of organic matter will

stop and anerobicN/Domposition will start.

This phenomenon of soil getting clogged is called as sewage sickness of land.

7. Name the feed material sources for bio gas recovery in a sewage treatment plant.

Primary Sludge

Secondary sludge

8. What do you mean by sewage farming? (M/J -13)

Sewage effluence is generally disposed by applying on land.

A part of it percolates below the ground of the valids are clogged off which leads to

choking.

9. What are the methods of sludge thickening?

Gravity Thickening

Flotation thickness

Centrifugal thickness

10. What are the methods adopted in India for disposal of sewage? (N/D -13)

(a) Natural method of disposal

(i) By dilution

(ii) Land treatment

(b) Artificial Method of disposal

(i) Primary treatment

(ii) Secondary treatment

11. What is an Oxygen Sag Curve and state its importance?

The quantity of net oxygen balance can be calculated at any stage of the self purification process.

This is represented by oxygen sag curve,

12. Under what circumstances land treatment of sewage is suitable?

a. The area of the land treatment is composed of sandy,loamy or alluvial soils over soft murum.

b. Such soils are easily aerated and it is easy to maintain aerobic condition in them .

c. The depth of water table is more even in rainy season, that there are no chances for pollution

of underground water sources by land treatment.

d. The rainfall in the area is low as it will assist in maintaining good adosorption capacity of soil.

e. There is absence of river or other natural water sources in the vicinity for disposal of sewage.

13. What is sewage sickness? How it can be avoided?

If the sewage is continuously applied over a particular land, the voids and pores of soil get

clogged(or filled up), and the free circulation of air is prevented.

In this stage the organic matter get N/Domposed and foul smelling gases are produced. This phenomenon

is called sewage sickness.

(a) Primary Treatment of sewage

(b) Depth of sewage application

(c) Drainage of soil

(d) Alternate arrangement

(e) Period of application

(f) Rotation of crops

(g) Treatment to land.

14. Name the common methods of sludge disposal.

(a) Disposal on land

(b) Distribution by pipeline

(c) Drying on drying beds.

(d) Incineration

(e)Dumping into sea

(f) Heat-drying

(g) Lagooning or ponding

(h) Filters

(i) Digestion followed by drying

15.What is gravity thickening?

The gravity thickeners are the simplest and most commonly used methods for thickening the

sludge. The gravity thickeners consists of a small circular open tank. Similar to the plain sedimentation tank

except the depth parameters, and thickeners has a heavier ranking mechanism.

16. What is the purpose of sludge digestion?

(a) The digested sludge is having better quality and can be used for various purposes.

(b) The digestion removes the pathogenic bacteria

(c) The digestion gives fertilizer and other useful products.

(d) The digestion produces combustible high calorific gases.

(e) In order to reduce the volume of sludge.

17. What are the impacts of disposal of untreated sewage into water courses?

The fish life is affected by various factors such as light, colour, temperature, chlorides,D.O. etc.

The fish for consumption if grown in polluted water sources, M/J carry the intestinal diseases.

18. What is Elutriation?

Elutriation is defined as the process of washing the sludge, to remove the organic and fatty acids

from the sludge.Washing of sludge is done by plant effluent.The purpose of washing by effluent is

to reduce the sludge’s alkalinity.

19. What is meant by high rate sludge digestion?

In conventional digestion, a detention period of 40 to 50 days is provided, due to which larger

capacity tanks are required. Even during cold and rainy season, it becomes difficult to dispose off the

digested solids, which also require more capacity of tank to retain them in such times. The speed of the

digesters can be only increased, if the conditions permit. The speed of the high rate digestion tank is

increased by the following ways.

1. Bycontinous operation of the tank

2. By providing multi-stage digestion

3. By heating the sludge.

20. List out the factors involved in self purification of streams?

Rate of re-aeration

Type of organic matter present in sewage

Temperature

Velocity of flow

Presence of available oxygen in receiving waters

Sedimentation etc.

21. State the advantages of land disposal of effluent.

It increases the fertilizing capacity of the land.

This method is very cheap, if the availability of land is more.

This is the best method of supplying manure to the soil

The crops grown on land treated with sewage posses high calorific values.

This methods charges the aquifers to some extent.

22. What are the three steps in sludge digestion process?

Acid production stage

Acid regression stage

Alkanine fermentation stage

23. What is need for sludge concentration?

(a) To permit increased loading to the sludge digesters

(b) To increase feed solids concentration to vaccum filters.

(c) To reduce the cost of transport for heavy volume of disposal

(d) To minimize the land requirement

(e) To save the additional fuel required for incineration method of sewage disposal.

24. Define Dilution Factor?

The ratio of the quantity of the diluting water to that of the quantity of sewage is called dilution

factor.

25. Name the treatment methods used to avoid sewage sickness of land?

(a) Primary treatment of sewage

(b) Depth of sewage application

(c) Drainage of soil

(d) Alternate arrangement

(e) Period of application

(f) Rotation of crops

(g) Treatment of land .

Dilution Factor =

26. What is meant by dewatering in sludge management?

Dewatering of sludge is defined as the process of removing or drying the water from the digested

sludge from the digestion tank.

27. Define ripened sludge.

The granular,stable and odourless sludge, formed in the alkaline-fermentation stage of the sludge

digestion is called ripened sludge.

28. What are the factors affecting the sludge digestion.

(a) Temperature

(b) Sludge seeding

(c) Mixing

(d) pH value

(e) Other factors.

PART – B (16 MARKS)

1. With a flow chart explain the various processes involved in sludge treatment.

(A/M -04)

2. Sketch a sludge digestion tank and discuss the stages in sludge digestion process.

(A/M -04)

3. Explain the various actions involved in the self purification process of a stream.

(M/J -13)

4. a) Draw a typical oxygen sag curve and explain.

b) Determine the BOD of river water at the discharge point of the treated sewage from a town

having a BOD of 30mg/L discharged at the rate of 5m3/s in to a river having a flow of 30m3/s and

no BOD.

(N/D -11)

5. a) Explain the Streeter Phelps equation and its application.

b) Determine the volume reduction due to dewatering of sludge from a liquid content of 8% to 15%

(N/D-11)

6. a) Discuss deep well injection.

b) Explain about biogas recovery.

(M/J -13)

7. a) What is sludge sickness? How it is prevented?

b) Discuss the common method of sludge disposal.

(N/D-09)

8. Design a digestion tank for primary sludge with the help of following data:

Average flow = 200Mld

Total suspended solids in raw sewage = 300mg/l

Moisture content of digested sludge = 85%

Assume suitable data.

(N/D-09)

9. a) Explain the mechanism of dewatering of sludge.

b) A sewage containing 200mg/l of suspended solid is passed through primary settling tank,

trickling filter and secondary setting tanks. How much gas will probably be produced in the

digestion of sludge from one million litres of sewage?

10. Explain the disposal of digested sludge. Also explain the use of lagoons in disposal of raw sludge.