PLAGIARISM DECLARATION FORM

Student Name:

Registration No:

Module No and Title of the module:

Assignment no and Title of the Assignment:

Section H2 of the Royal University of Bhutan’s Wheel of Academic Law provides the following definition of academic dishonesty:

“Academic dishonesty may be defined as any attempt by a student to gain an unfair advantage in any assessment. It may be demonstrated by one of the following:

Collusion: the representation of a piece of unauthorized group work as the work of a single candidate.

Commissioning: submitting an assignment done by another person as the student’s own work.

Duplication: the inclusion in coursework of material identical or substantially similar to material which has already been submitted for any other assessment within the University.

False declaration: making a false declaration in order to receive special consideration by an Examination Board or to obtain extensions to deadlines or exemption from work.

Falsification of data: presentation of data in laboratory reports, projects, etc., based on work purported to have been carried out by the student, which have been invented, altered or copied by the student.

Plagiarism: the unacknowledged use of another’s work as if it were one’s own.

Examples are:

verbatim copying of another’s work without acknowledgement paraphrasing of another’s work by simply changing a few words or altering the order of presentation, without

acknowledgement ideas or intellectual data in any form presented as one’s own without acknowledging the source(s) making significant use of unattributed digital images such as graphs, tables, photographs, etc. taken from test books,

articles, films, plays, handouts, internet, or any other source, whether published or unpublished submission of a piece of work which has previously been assessed for a different award or module or at a different

institution as if it were new work use of any material without prior permission of copyright from appropriate authority or owner of the materials used”

Student DeclarationI confirm that I have read and understood the above definitions of academic dishonesty. I declare that I have not committed any academic dishonesty when completing the attached piece of work.

Signature of Student: Date: 24-08-15

1/ Discuss the relative merits of the separate and the combined systems of sewage, and give theconditions favorable for the adoption of each one of them.

Separate Sewer System Combined Sewer Systemdo not require on-site pre-treatment or storage of the wastewater

do not require on-site pre-treatment or storage of the wastewater

It provides high level of comfort and hygiene for the users.

It provides high level of comfort and hygiene for the users.

It doesn’t provide breeding ground for vectors.

It produces no smell, mosquitoes or flies

Stormwater can be harvested for domestic purpose.

Storm water and wastewater can be managed at the same time

Moderate operation cost Moderate operation and maintenance costsLimited or no risk of sewerage overflow Risk of sewerage overflow as all the wastewater

are collected by one single pipeSurface runoff and rainwater can be collected separately and can be used for landscaping and agricultural purpose

Storm water or rainwater cannot be collected separate for the purpose of landscaping or agriculture.

2/ Write short notes on: financing the sewage projects and types of sewerage.

Financing sewer projects

When the project is being initiated, the funding is done by the government. All the expenditure starting from the digging trenches to the laying of pipe is done by the government.

After its construction it`s responsibility is the city corporation where its running, maintenance and operation is being looked after. For the maintenance and operation cost, the money has to come from the users. It is being collected in terms of taxation.

Tax is being collected on the basis of the amount of water being consumed by a particular household for example. It’s done on the basis of water consumed as it is rational logic that sewage produced is directly proportional to the water consumed.

Types of Sewer

i. Combined sewers

It’s a large network of underground pipe network where all the wastewater from the industries, domestic, stormwater runoff are collected in one pipe.

The wastewater collected are transported to the wastewater treatment plant where all the collected wastewater are treated together and discharged to a water body.

The sewer is designed to maintain a certain velocity so that the waste particles will not accumulate in the pipe. It is generally maintained at a velocity of 0.6 to 0.75 m/s. if the slope cannot be maintained, pumping stations are being installed.

The primary sewer is laid at a depth of 1.5 to 3 m.

It is suitable for urban areas with resources to implement, operate and maintain the system.

ii. Separate Sewers

It is used to transport the wastewater and stormwater in separate ways.

The construction costs can be higher than the combined sewer system because two separated networks are necessary.

Especially suitable in areas where irregular, heavy rainfall is expected to avoid frequent combined sewer overflows

iii. Simplified Sewer

This system has smaller diameter pipes laid at a shallower depth and at a flatter gradient than conventional sewers.

Allows for a more flexible design associated with lower costs and a higher number of connected households

iv. Solids-free Sewers

it is similar to conventional sewers, except that the wastewater is presettled and solids removed before entering the system. As the solids are removed before hand, the diameter of the pipe can be smaller.

3/ Note down the various problems of sewer works observed at field. Document how the problems areresolved. Various problems of sewer observed in the field are:

I. Pitch/slope of the sewer is not maintainedII. Leakages form the sewer pipes contaminating the surrounding.

III. The sewer pipes are not joint firmly.IV. Bell side of the sewer facing downwards.V. Destroying power cables and other pipes while digging trenches.

4/ Differentiate between sanitary sewage and storm sewage. Discuss and explain the Rational Formulaand its limitations in calculating the quantities of storm sewage.

Sanitary Sewage Storm SewageIt is for the conveyance of domestic wastewater It is for stormwater runoffIt needs pumping Pumping is optional

Rational Formula

Rational method is used in calculating the peak flows from small drainages less than 200 acres. It is most accurate for runoff estimates from small drainages with large amounts of impervious area.

The Rational Formula is:

Q = Cf C i A

Where:

Q = Peak flow in cubic feet per second (cfs)

Cf = Runoff coefficient adjustment factor to account for reduction of infiltration and other losses during high intensity storms

C = Runoff coefficient to reflect the ratio of rainfall to surface runoff

i = Rainfall intensity (in/hr)

A = Drainage area in acres (ac)

Limitation of Rational Method

I. It cannot applied to larger areas larger than 200 acresII. The average rainfall intensities used in the formula have no time sequence relation to the actual

rainfall pattern during the storm.

5/ Mention the various aspects you would keep in view when designing a sewer.

We should consider the following aspects while designing the system:

Correct estimation of sewage discharge is necessary to know the proper diameter of the sewer. The flow velocity inside the sewer should not be large as it require heavy excavation and high lift

pumping. It should not be so small causing deposition of the solid in the sewers. The sewers should be laid at least 2 to 3 m deep to carry sewage from basement. The sewage in sewer should flow under gravity with 0.5 to 0.8 full at designed discharge, i.e. at

the maximum estimated discharge. Treatment plant should be designed taking into consideration the quality of raw sewage

expected and to meet the discharge standards. The sewers provided should be adequate in size to avoid overflow and possible health hazards. The sewerage system is designed to remove entire sewage effectively and efficiently from the

houses to the point of treatment and disposal.

6/ What are the advantages of the egg-shaped section, and under what conditions of flow, does it become useful? Will you recommend its use for sanitary sewers, and if not, why?

The advantages of using egg-shaped section are:

It gives 2 to 15% higher velocities than provided by hydraulically equivalent circular sections.

The solids are less likely to be deposited.

It is used where there is low discharge. So this shape increases the discharge as it increases the velocity of flow. This happens due to the shape which becomes narrower at the bottom which increases the hydraulic mean depth, and the wastewater flowing at the bottom experiences a pressure from above. The oval form of sewer is to be preferred when the volume of sewage matter is subject to fluctuations.

I would recommend this for sanitary sewer because the deposition rate of the solids in the sewer is not very high, which means that there will be no blockages.

Proportionate DepthProportionate Velocity

in circular sewers in egg-shaped sewers0.25 0.701 0.698

0.2 0.615 0.6270.15 0.517 0.544

0.1 0.401 0.440.05 0.257 0.295

7/ Explain the importance of (1) self-cleansing velocity; and (2) non-scouring velocity.

Self-cleansing velocity: Sewage consists of considerable amount of organic and inorganic solids,

which remain floating or suspended. If velocity of flow in the sewer is less, these solids get deposited

at the invert of the pipe and cause obstruction to the flow of sewage. Hence, it is necessary to

maintain a minimum velocity of flow at which no solids get deposited in the sewer. The velocity of

flow that prevents settlement of solids is known as self-cleansing velocity. This velocity should be

maintained at least once in a day during the peak flow at all sections of the sewerage system.

Non-scouring velocity: The velocity of flow in sewer should not be too high, as the suspended solids

will cause wear to contact surface of the pipe and erode the pipe material of sewer. This will reduce

the life of the sewer. The permissible maximum velocity to prevent eroding is termed as non-scouring

velocity and it should be limited to 3.0 m/s.

8/ Write detailed notes on characteristics of partially full sewers.

Some important facts about velocity of flow in partial-flow sewers are as follow:

I. Velocity of flow is equal to full flow velocity when the flow is half full,

II. Velocity of flow is more than full flow velocity when the flow is more than half full,

III. Velocity of flow is rapidly decreasing when the flow is less than half full,

IV. Velocity of flow has to be checked for minimum self-cleansing velocity whenever the sewer is flowing less than half full,

V. Velocity of flow is the maximum when the depth of flow is 0.82 D.

VI. The carrying capacity of the sewer is the maximum when the depth of flow is approximately equal to 0.9D.

9/ Describe in order the various stages followed in the laying of sewers.

The stages followed in laying of sewer are

i. First we should determine the elevation at which the sewer is to be laid. Initial and final elevation is measured at the interior point of the connecting pipe in the middle portion of the pipe.

ii. Then we should calculate the pitch or the fall of the pipe per run. A drop greater than ¼” per foot is not adequate as water will flow faster than solids, while a slope to small, less than 0.003, will be sufficient to carry solids away. The recommended pitch for 4" pipe is 1/8" to 1/4" per foot.

iii. After that trench is dug out and bedding material like sand is being laid if required to reduce the possibility of sag.

iv. After the trench has been dug out, the laying of the pipe is begun. Bell end of the pipe is placed uphill and laying is started from the lower elevation. The pitch should be maintained.

v. After laying, check for any leakages, whether the pipe is damaged in the process.vi. Then place the sand and/or gravel over the pipe, enough to cover at least 10” over the sewer

pipe. Start compacting the material with a rammer or any other compaction equipment suitable for the type of pipe being installed.Note: It is important to install a warning tape over the first layer of compacted soil, so others will be aware when excavating that a pipe is located under the detectable warning tape.

10/ What should be the characteristics of materials to be used for sewers?

The characteristics of the material to be used for the sewer are:

a. Resistance to corrosion: the wastewater in the sewer contains gases like H2S which turns into sulphuric acid when it comes in contact with water. So this acid leads to corrosion of the sewer pipes. Therefore laying of corrosion resistant pipe is important.

b. Resistance to abrasion: Sewage contain considerable amount of sand or grits which moves at a high velocity and can cause wear and tear of sewer material. This action reduces the thickness of pipe and reduces hydraulic efficiency of the sewer by making the interior surface rough.

c. Strength and durability: the sewer pipes that are laid at a great depth and below the traffic/road has to withstand the load of the traffic and backfill. So the pipe should be thick enough to be able to withstand the loads above and the hydrological pressure.

d. Weight of the material: The material selected for sewer should have less specific weight, which will make pipe light in weight. The lightweight pipes are easy for handling and transport.

e. Imperviousness: the sewage pipe should be impervious so that there is no seepage of the wastewater to the outside surrounding.

f. Economy and cost: sewage pipes should be less costly so that the projects costs less.

g. Hydraulically efficient: The sewer shall have smooth interior surface to have less frictional coefficient.

Reference

http://construction.about.com/od/Specifications/ss/Sewer-Pipe-Installation-How-To-Install-A-Sewer-Pipe.htm#showall

http://www.google.bt/imgres?imgurl=http://civilengineerspk.files.wordpress.com/2014/03/combined-sewer-system1.jpg%253Fw%253D620&imgrefurl=http://civil-experts.blogspot.com/2014/05/design-of-sewer

system.html&h=312&w=620&tbnid=Pi9CFEffBWE_hM:&docid=xO1LAeLOEGN8QM&ei=0d_ZVcjNO-uO7QarvqjYCA&tbm=isch&ved=0CCIQMygIMAhqFQoTCIj65vu7v8cCFWtH2wodKx8Kiw

K.N.Duggal, Elements of Public Health Engineering,

Sewer Material, M.M. Ghangrekar, IIT Kharagpur

S.K.Garg, Sewage Disposal and Air Pollution Engineering, Vineet Khanna.