DIRECTORATE OF TECHNICAL EDUCATION

GUINDY, CHENNAI-25

BOARD EXAMINATIONS – APRIL 2018

CIVIL ENGINEERING

ANSWER KEY

QUESTION PAPER CODE: 387

SEMESTER : V

YEAR : III

SUBJECT CODE : 31052

SUBJECT NAME : ENVIRONMENTAL ENGINEERING AND

POLLUTION CONTROL

Prepared by,

A.ANBUKKARASI, B.E LECT / CIVIL

276-PERIYAR CENTENARY POLYTECHNIC COLLEGE. VALLAM.

PART-A Note: Each question carries two marks 1. Name any five methods used to forecast the population.

Arithmetical increase method Geometrical increase method Incremental increase method Decreasing rate method Simple graphical method Comparative graphical method Master plan method

2. What is continuous system of supplying water? In continuous system of water supply the water is supplied for all the 24 hrs. Advantages of continuous system of supply.

1. Most ideal 2. No separate storage by the consumers is required. 3. Adequate supply is always available for fire-fighting. 4. Wastage is minimum. 5. Small size pipes are sufficient for distribution.

3. What is circular system of distribution layout? Ring system also called circular of rectangular system in which the distribution area is divided

into number of rectangular or circular black and main pipes are laid on the periphery of these blocks.

Such a ring system is very suitable for towns and cities having well planned roads. 4. Define the term sewerage.

The entire system of collecting, treating and finally disposing through sewer is known as the sewerage.

5. What is the necessity of cleaning of sewer? The sewers should be properly cleaned and maintained. Once the sewers are laid and buried, they are liable to corrosion, deterioration, erosion etc. For the following reasons, the sewers are to be cleaned.

1. Breakage of sewers 2. Clogging of sewers 3. Odours in the sewers

6. Name the classification of solid waste. Food waste Rubbish Ashes and residues Demolition and construction wastes Special wastes Treatment plant wastes Agricultural waste Hazardous wastes

7. What is meant by pollutants? A pollutant is a substance or energy introduced into the environment that has undesired effects, or adversely affects the usefulness of a resource.

8. Mention the permissible limits of (a) pH value (b) Turbidity (c) Chlorides (d) Hardness. (a) pH value – 6.5 to 8.5 (b) Turbidity – 5 NTU (c) Chlorides – 1000mg/l (d) Hardness – 600mg/l PART – B

Note: Each question carries three marks 9. Mention any six factors which affect the per capita Consumption.

Size of the city Climatic Conditions. Habits of people. Industrial and commercial activities. Quality of water supplies. Pressure in distribution system. Development of sewerage facilities. System of supply. Cost of water. Policy of metering and method of charging.

10. Write short notes on cement concrete pipe. The cement concrete pipes may be precast or cast-in-situ. They may be plain, reinforced or

prestressed up to 15m head, plain concrete pipes are used. RCC pipes are used up to a head of 75m. Beyond 75m head, only prestressed concrete pipes

are adopted. RCC pipes are cast for safe pressure of 0.2, 0.4, and 0.6N/mm2.

Advantages: The inside surface can be made smooth. Low Maintenance cost Durable Have least coefficient of thermal expansion. Unaffected by atmospheric actions. Cast-in-situ pipes eliminate transport charges. Can be easily cast either in factories or at site.

Disadvantage: Affected by acids, alkalies, and salty waters. Repairing is very difficult. Cost of transportation and laying is more due to heavy weight. Difficult to make connections in them. May crack during handling and transport. Porosity may cause leakage. If not reinforced cannot withstand high pressure and tensile stresses.

11. State any three functions of service reservoir.

To store water for emergencies like breakdown of pumps, fires, power supply failures etc. To equalise the rates of flow due to variation between the rate of supply and rate of demand. To maintain pressure in the distribution system. To facilitate constant rate of pumping and thus reduce pumping hours. Under gravity system of supply, to minimise the diameter of mains. To make the design and construction of treatment units and distribution system Economical.

12. Write short notes on joints in sewer lines. Suitable joints will have to be formed to make a continuous sewer line. The type of joint will

be decided by considering the pipe material, internal pressure, external loads etc. Its construction should be such that tree roots cannot penetrate through it. It should be capable of resisting the effects of acidic, alkaline or gaseous actions of the sewage. It should be cheap and economical. It should be easy to construct. It should be non- absorbent and durable. It should be flexible in nature. It should be water tight so that infiltration of ground water and exfiltration of sewage are

prevented.

13. Draw the flow diagram of sewage treatment.

14. State any three preventive measures of water pollution.

Setting up effluent treatment plants to treat waste. Recycling of water must be encouraged. Industrial wastes must be treated before discharge. Educate public for preventing water pollution and the consequences of water

Pollution. Strict enforcement of water pollution control act. Continuous monitoring of water pollution at different places. Developing, economical method of water treatment. River, streams, lakes and other water reservoirs must be well protected from being

Polluted.

15. What are the objects of environmental impact assessment? The environmental impact assessment (EIA) server one or more of the purposes such as

decision making choosing among various alternatives, integrating environmental cost into project cost.

The main objective of EIA is to ensure the development to sustained with minimal environmental degradation.

16. Mention any six methods of solid waste disposal. The methods of solid waste disposal are:

Dumping Sanitary land filling Incineration Composting Ploughing in fields Grinding and discharging into sewers Salvaging Fermentation or Biological digestion

PART – C

17. (a) From the following population records, Compute the probable population by arithmetical increase method in the years 2020, 2030 and 2040.

Solution:

YEAR POPULATION INCREASE IN POPULATION (x)

1980

1990

2000

2010

20,000

31,000

39,000

49,500

11,000

8000

10,500

TOTAL 29,500

Average increase per decade (푥̅)

(푥̅) = 29500 = 9,833 3

(3 Marks)

The future populations are now computed by the equation. Pn = Po + n. 풙 (1 Mark)

(a) Population after 1 decade beyond 2010 P2020 = P1 = P2010 + 1. 풙 = 49,500 + 1 x 9833 = 59,333 (2 Marks)

(b) Population after 2 decades beyond 2010 P2030 = P2 = P2010 + 2. 풙 = 49,500 + 2 x 9833 = 69,166 (2 Marks)

(c) Population after 3 decades beyond 2010 P2040 = P3 = P2010 + 3. 풙 = 49,500 + 3 x 9833 = 78,999

(2 Marks)

[OR]

YEAR 1980 1990 2000 2010 POPULATION 20000 31000 39000 49500

17. (b) Explain with neat sketch reservoir intake.

Reservoir intake is located near the upstream side of the dam, where maximum depth of water is available.

It consists of an intake well which is connected to the top of the dam by a gangway. The well is empty except the intake pipes. The intakes are provided with bell mouth

entry and are covered by the screens to exclude any floating matter. They are located at different levels with a common vertical pipe. Such a location of the

intakes ensure supply of water even when the water level in the reservoir fluctuates. The valves of the intakes are operated from the top. The outlet pipe is taken out through

the body of the dam and it suitably supported. When the valve of an intake pipe is opened, water is drawn from the reservoir.

(7 Marks)

Fig: Reservoir Intake

(3 Marks)

18. (a) Compare slow sand filter with rapid sand filter. (10 Marks)

ITEM NO.

ITEM SLOW SAND FILTERS RAPID SAND FILTERS

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Pre-treatment Compactness Filter media (i)Effective (ii)uniformity coefficient (iii)Grain size distribution (iv) Quantity (v) Quality Base material Size of each unit Rate of filtration Method of cleaning Time required for cleaning Interval for cleaning Bacterial removal Removal of turbidity Post treatment Economy (a)Initial cost (b)Cost of operation and maintenance (c)Overall cost (d)Depreciation cost Ease in construction Skilled supervision

Not required Require more area 0.25 to 0.35mm 2 to 3 Uniform throughout the depth Except the top 100 to 150mm To be laid with finer variety Require more Finer 3 to 65mm size gravel for 0.3 to 0.75m depth Large surface area 100 to 2000m2 or more Small 100 to 200/m2/hr Laborious, scraping and removing top 20 to 30mm thick layer and washing and replacing with new sand More 1 to 3 months Good 98 to 99% Poor (30%) Not essential High Low High Low Simple for small construction Not required

Require coagulation flocculation and sedimentation. Require small area 0.35 to 0.6mm 1.2 to 1.7 Laid in layers. Smallest grain size at the top and coarsest grain Size at the bottom. Require less Slightly close 3 to 40mm size gravel for 0.45 to 0.9 m depth. Small surface area 110 to 80m2

Large 3000 to 6000/m2/hr Easy agitating the sand grains with or without compressed air and back washing. Less than about 15 minutes 1 to 3 days Poor 80 to 90% Good (100%) Disinfection with chlorination is essential. Low High Low High Suitable for major construction Essential

[OR]

18.(b) Explain about the various layouts of distribution. The various layouts of distribution system are

Dead end or tree system Grid iron system or interlaced system or reticulation system Circular or ring system Radial system

Dean End system: It consists of (i) One main supply pipe (ii) Number of sub mains (They are generally laid at an angle of 90 to the main pipe) (iii) Number of branch pipes (they are laid at an angle of 90 or other than 90 to the sub main pipes. Through the branches water is supplied to the consumers through various house service connections. (iv) The branch pipes are also called laterals. Advantages: (i)The distribution network can be solved easily. (ii) There are less number of cut off valves provided. (iii) The length of the pipe used in this system is very shorter when compared with the other System. Therefore, it is very easy to lay and to operate. (iv) This system is cheap and simple and can be extended easily. Disadvantages: (i) If any damage or repair takes in any pipe line then it will completely stop the water supply in the area fed by that pipe. (ii) The number of dead ends in this system prevents the free circulation of water.

(3 Marks) Grid iron system or interlaced system or reticulation system: In this system the main pipe, submain pipe and branch pipes are interconnected with each other. Advantages: (i) During repair of any one pipe system, it is possible to change the route and to distribute the water to consumers. (ii) During fire and other emergency cases more water can be diverted towards the affected area. (iii) In this system since there are different interconnections, the dead ends are completely eliminated. (iv) In this system the friction loss and size of the pipe get reduced.

Disadvantages: (i)It requires more length of pipe line and therefore it requires large number of cut off valves. (ii) The construction cost is very high. (iii) Design is difficult.

(3 Marks) Ring system or Rectangular or Circular system:

Ring system are also called circular or rectangular system in which the distribution area is divided into number of rectangular or circular block and main pipes are laid on the periphery of these blocks.

Such a ring system is very suitable for towns and cities having well planned roads.

(2 Marks) Radial system:

In this system water is taken from the main pipe and pumped into the distribution reservoir placed at different centres.

The water is then supplied through radially laid distribution pipes. This system is suitable if a city or town is having a system of radial roads emerging from

different centre.

Advantages:

This system is most suitable for non- supply hours. This system is more efficient and ensure high pressure. Calculation for design of sizes of pipe also very simple.

(2 Marks) 19. (a) Compare conservancy system with water carriage system.

S.NO ITEM OF COMPARISON CONSERVANCY SYSTEM WATER CARRIAGE SYSTEM

1. 2. 3. 4. 5. 6. 7.

Initial cost Maintenance cost Consumption of water Odour Location Employment of labour Transportation

Less More Less Foul smell with always be there from such latrines. Latrines should be located outside the building More Transported through trucks and trollies.

More Less More There is no foul smell from water closets Can be located within the building itself Less Transported through closed conduits.

8. 9. 10. 11. 12.

Revenue from manure Skilled person Cleanliness Pollution of underground water Out -break of epidemic

More Not required skilled personal to supervise Poor Possible Possible

Less Required skilled person to supervise High Impossible Impossible

(10 Marks) [OR]

19. (b) Explain about drainage arrangements in buildings. House drainage is the collection and conveyance of liquid refuse from the public drain and sewers. Certain part of the building are set apart for this purpose. The drainage lines from the places of collection, leading to the sewer are also shown on the plan with necessary appurtenances. Sanitary conveyances include lavatory blocks comprising of water closets, urinals and bathrooms. (2 Marks) Principles of House Drainage: For proper design and construction of house drainage system, the following general principles are adopted.

The entrances to drains should be outside the building. The drainage systems should have proper ventilation. The drains should not pass through buildings but should pass by the side of the building. The drains should not be laid close to trees, since they are subject to damage by their roots. The drains should be laid at gradients for self-cleansing. If this is not possible, automatic

flushing system should be provided to them. The drains should be laid straight between points of access. All changes of direction or

gradient should be opened for inspection. Branch drains should be as small as possible. All the connections should be oblique so that the incoming drain faces the direction of flow of

the sewage. The size of the drains should be just sufficient to meet the requirements. The pipe joints should be water tight and made from non- absorbent materials. The house drains should be connected to public sewer only. When the public sewer is deeper

than the house drain. The house drains should contain sufficient number of traps at suitable points. The house drains should be separated from the public sewer by a trap to prevent the entry of

foul gas. (8 Marks) 20. (a) Describe standard trickling filter with neat sketch. Construction: Shape: Trickling filters may be circular, square or rectangular in shape. Filter Media:

The filter media consists of coarser materials such as cubically broken stone or slag. It should be free from dust and small pieces. The size of the material should be between 25 to 75mm. Before using the filtering material, it should be washed. The depth of the filter media varies between 2 to 3 m. Under drainage system: The under-drainage system consists of ‘U’ Shaped hall-round channels, cast in the concrete floor. During construction, a slope of about 1 in 100 to 1 in 50, towards the drain is given for the remaining floor to collect the treated sewage. The under-drainage system should be self-cleaning and easily accessible. It should be opened to the atmosphere. Ventilation:

(a) Sufficient natural ventilation should be provided for the successful working of the trickling filter. Natural draft ventilation may be provided by (i)By connecting the ends of under-drains to a chimney for circulation of air through them. (ii) By constructing the filters above ground with open sides. (iii) By providing vent pipes at the periphery of filter. (iv) By keeping the ends of under drains open.

(b) Sometimes forced ventilation may be provided by forcing the air upwards through the filter. Distribution system: Sewage is sprayed on the surface of trickling filters from moving or fixed distributors through nozzles. Moving distributors: There are two types of moving distributors

Rotary distributors Rectilinear distributors

Rotary distributors: They are provided with distributing arms, usually four in number. These arms rotate around a central support. These distributors are suitable for circular filters. Rectilinear distributors: They move back and forth from one end to the other. They are supported on rails. They are suitable rectangular trickling filters. (3 Marks) Working:

After primary treatment the sewage trickles over the filtering media by means of moving arms. While it moves down through the contact media, it is acted upon by bacteria’s.

The dissolved and colloidal organic matters are precipitated and flocculated by the bacterial action.

A gelatinous film or slime layer called zoogloeal film is formed on the surface of the contact media.

The aerobic bacteria gets oxidised and it to sulphates, phosphates, nitrates etc. With passage of time the slime layer becomes thicker and heavier. It moves towards the bottom of the trickling filter and passes out with the effluent.

Then it settles in the secondary settling tank. The phenomenon of losing this slime layer is referred to as sloughing. (3 Marks)

Performance and efficiency of standard rate trickling filters: The effluent obtained from a standard rate trickling filter plant is highly nitrified and

stabilized. The removal of B.O.D is 75% and suspended solids is 80%. The sludge obtained in the secondary settling tank is with 92% moisture content.

The efficiency of a standard rate trickling filter plant can be expressed by

η (%) = 100 1 + 0.0014√푈 Where η = Efficiency of the filter, U = Organic loading in N/ha.m/day Advantages: (i)The effluent is highly nitrified and stabilised. Hence it can be easily disposed. (ii) Flexible in operation. (iii) Moisture content of sludge obtained is as high as 92% (iv) Self-cleaning (v) Cheap and simple in operation (vi) Mechanical wear and tear is very small. Dis advantages: (i)High loss of head warrants automatic dosing of the filters. (ii) Nuisance due to odour and psychoda fly. (iii) Require less land area. (iv) Require preliminary treatment. (v) Costly (2 Marks)

STANDARD TRICKLING FILTER (2 Marks)

[OR] 20. (b) What are the methods of solid waste disposal? Explain any four methods.

The methods of solid waste disposal are: (2 Marks) Dumping Sanitary land filling Incineration Composting

Ploughing in fields Grinding and discharging into sewers Salvaging Fermentation or Biological digestion

Dumping: In this method the refuse is dumped in low lying areas partly as method of reclamation of land. As a result of bacterial action, refuse decreases considerably in volume and is converted into humus. Drawbacks: (i)The refuse is exposed to files and rodents. (ii) It is a source of nuisance from smell and unsightly appearance. (iii) The loose refuse is dispersed by the action of wind. (iv) Drainage from dumps contributes to the pollution of surface and ground water. Sanitary land filling: A sanitary land fill is a well-designed, Operated and controlled facility for the disposal of the solid waste on land. Basically, land filling consists of following steps: (i)Refuse is deposited at the working area. (ii) The refuse is spread into thin layers and compacted by heavy equipments. (iii) The refusal layers are covered with earth material and compacted every day. The depth of refuse before sealing may vary between 2 to 15 feet or more. Incineration:

It involves in burning of combustible refuse in an incinerator. All sorts of bacteria, insects are destroyed and the remaining non-combustible ashes, metals etc. have little sanitation problems.

The heat produced during burning of the refuse can be utilised for the production of stream and other purposes.

It is recommended for crowded cities and populated areas due to lack of suitable land. Composting: Composting is the biochemical degradation of the organic fraction of solid waste, having as its end product that is used, primarily for soil conditioning. There are five basic steps involved in all composting practices: (i)Preparation: Typical preparation step may include the sorting of soluble material, the removal of non-combustibles, Shredding, Pulping, Grinding and the addition of waste water sludge. (ii) Digestion: Basically, Composting system falls into two categories (a)Wind-row Composting in open wind-row: In wind-row composting, the refuse is grind and moistered and then conveyed to an outdoor decomposition area where it is placed in windrows. The wind-rows are turned once or twice each week during the composting period. (b)Mechanical composting in closed digestors: The digesters which is 37 feet in diameter and 10feet deep and usually contains 3 to 8 feet of solid waste. The solid waste enters the digester on its perimeter and is continuously mixed and slowly moved to the center discharge point. (iii) Curing: The amount of curing required at the initial stabilization depends on the proposed use of composted material. The curing periods for

Windrow composting – 2 weeks Mechanical composting – 3 weeks

(iv) Finishing: The amount of finishing required is also dependent upon the final marketing of the compost. (v) Storage or disposal: Storage is necessary because the use of composting is seasonal, with greatest demand the spring and fall. Ploughing in fields: This method of refuse disposal is used only on small scale. The land is ploughed and the solid waste are buried and it is disposed off. Grinding and discharging to sewers: In this method the refuse is well ground in home or commercial grinders and is discharged into the sewer. It is used in America and other western countries. Salvaging: It is the removal of certain elements such as paper, rogs, glass, plastics, scrap metals, etc, from sewage having markable value. Separation of solvable materials from refuse is usually done by hand pickers at smaller plants and by means of mechanical devices at larger ones. Fermentation or biological digestion: In this method the garbage is placed in air tight sealed tanks for 10 days, and in the presence of air for 15 to 20 days. The digested residue is stable and it is used as a soil conditioner. (8 Marks) 21. (a)(i) What are the preventive measures of water pollution?

Setting up effluent treatment plants to treat waste. Recycling of water must be encouraged. Industrial wastes must be treated before discharge. Educate public for preventing water pollution and the consequences of water

Pollution. Strict enforcement of water pollution control act. Continuous monitoring of water pollution at different places. Developing, economical method of water treatment. River,streams, lakes and other water reservoirs must be well protected from being

Polluted. (5 Marks) 21.(a)(ii) What is called green house effect? Give the remedial measures of green house Effect. Green House Effect: Greenhouse gases in the lower levels of the atmosphere act like the glass of a green house.

Like glass, they are transparent to the near infrared rays but are opaque to the heat radiated by the heated earth and trap them.

By not letting the solar rays to escape into outer space, greenhouse gases add to the heat that is already present on the earth’s surface. This results in an increase in temperature and is commonly known as the greenhouse effect. (3 Marks)

Remedial measures of greenhouse effect: Reduction in consumption of fossil fuels such as coal and petroleum Use of bio-gas plants Use of nuclear power plants Increasing forest cover

Use of unleaded petrol in automobiles Installation of pollution controlling devices in automobiles (catalytic converter) and industries

(Electro Static Precipitators, Bag filters, Wet scrubbers etc.) (2 Marks) [OR]

21.(b)(i) State the limitations of EIA. Many EIAs lack a central, Conceptual or analytical theme or recognisable investigative design

to guide the collection and interpretation of data. Predictions, if made, are commonly vague and of questionable to project decision-making. Similarly, significance levels and probabilities are rarely indicated except in the most

superficial. EIA is often applied as a reactive and discrete activity, only loosely related to the broader

process of environmental decision-making. EIA is almost exclusively applied to the project-specific developments and not to the other,

more complex and more common categories of environmental problems. EIA cannot handle the cumulative effects of piecemeal development. EIA is inappropriate for resolving environmental issues. EIA is inappropriate for many, major environmental problem such as ozone depletion, toxic

waste disposal. (5 Marks) 21.(b)(ii) How the environmental impact statement is prepared? Ideally, the content of an EIS should have the following

Executive Summary Policy, legal and Administrative frame work. Description of the environment. Description of the proposed project in detail. Significant Environmental impacts. Socio-economic analysis of project impacts. Identification and analysis of alternative. Mitigation action/Mitigation Management plan. Environmental Management plan. Monitoring program Knowledge gaps. Public involvement List of Reference.

Appendices including Reference documents, photographs, unpublished data. Terms of Reference Consulting team composition Notes of public consultation sessions. (5 Marks)