The procedure of lifting of wastewater or sewage is termed as Sewage Pumping. The necessity of Sewage Pumping arises under the circumstances – (i) When some area is low-lying and it can’t drain sewage by gravity into mains / submains. (ii) In flat countries, sewage pumping is adopted because it is more economical. This is because excavation for laying drains at designed grade will become more expensive. (iii) Pumping is restored when outfall sewer is at lower level than the water-body into which it is to be discharged. Also when the outfall is lower than the entrance to the treatment works. (iv) Pumping thus used to take out sewage from cellers or basement of building; when the level of celler is lower than the level of sewer which is drainage pipe.

Also know about how maintenance of sewers is done?

Problems in Sewage Pumping

The pumping of sewage is not as easy as the pumping of water. Therefore one has to face lots of problems during the pumping of sewage. Some special problems are as below –

• Sewage has foul characteristics.
• Rate of flow of sewage varies continuously and hence pumping operations needed to adjust accordingly.
• Sewage contains lots of suspended and floating materials. These generally cause frequent clogging of the pumps.
• The size of sump is finite, therefore the provision of sump is to give only a little storage space.
• Sewage contains organic and inorganic waste. These results in corrosion of parts of pump, thus reduces the life of pumps.
• Pumps should be of high order reliability. Since failure of pumps will lead to flooding which may cause unbearable nuisance.
• Sewage contains disease causing germs / bacteria / organisms. Thus it may cause health hazard to the persons working at pumping station.

Pumping Stations

Location of pumping stations –

Proper location of pumping station requires a comprehensive study of the area to be served to ensure that the entire area can be adequately drained. If the large amount of sewage is to be pumped, the site should be near the stream in which the sewage used to discharge. So that the sewage needs to be thrown directly into it, during emergencies such as break-down of pumping plant, failure of power etc. If we avoid this precaution, the flood will arise in pumping stations. Thus the site is also aesthetically satisfactory. Therefore it needs to design so that it does not gets flooded anytime.

Elements of pumping stations –

Apart from the structure of the pump house, a sewage pumping station consists of the following elements –

• Grit channel or detritus pit
• Coarse and fine screens
• Sumps or wet well
• Pump room or dry well
• Pumps with driving engine or motor
• Miscellaneous accessories – pipes, valves, float switch arrangements, flow recorders, emergency overflows, ventilation arrangements, such as extraction fans etc. etc.

Pump house structure –

The pump house structure is always design to withstand flotation forces. However the sub-structure is made up of mass-concrete or R.C.C. While super-structure can be of any material. The internal wall and floors should be designed –

• to bear the weight of machines and live load of 5 kN/m2.
• planned while keeping in view the future expansion.
• having enough ventilation so that foul gases, moisture can easily escape.
• safe against vibrations caused by pumping machinery.
• minimize humidity thus to control the corrosion.
• dust-proof, water-proof, fire-proof, explosion-proof etc.
• have stairs instead of ladders (avoid spiral-stairs) between different floors.

Types of pumps used in Sewage Pumping

1. Centrifugal pumps –

Centrifugal pumps are most widely used for sewage pumping and storm water. As it is easy to install this in pits, sumps. It can thus transfer the suspended matter present in sewage quickly without getting clog too often. However these pumps work on the principle of centrifugal force. It generally has 2 parts – (i) the casing and (ii) the impeller. The impeller rotates with high speed inside the casing. The clearance between the vane is so large thus prevents the clogging. Such pumps are therefore termed as non-clog pumps.

There are three classes of centrifugal pumps –

• dis-integrator pumps
• full way pumps
• free way pumps

Centrifugal pumps can be classified under –

• Axial flow pumps
• Mixed flow pumps
• Radial flow pumps or centrifugal pumps

	Axial flow pumps	Mixed flow pumps	Radial flow pumps or Centrifugal pump
1	Head developed by propelling action of the impeller vanes.	The head developed by both centrifugal action and propelling action of the impeller vanes.	Head developed by centrifugal force only.
2	Single inlet impeller.	Single inlet impeller.	Either single suction or double suction inlet impeller.
3	Flow enters axially, discharges axially.	In this the flow enters axially, discharges both axially and radially.	Flow leaves the impeller radially and normal to the shaft axis.
4	Usual capacity range is greater than 2000 m3/hr.	Usual capacity range is greater than 100 m3/hr.	Any range of capacity can be obtained.
5	Head value is less than 9 m.	Used for medium heads of 8 to 15 m.	Any range of head can be obtained.
6	Kilowatts decrease with capacity.	KWs remains flat with the change in capacity.	Kilowatts increase with capacity.
7	Specific speed range lies between 8000 to 16000.	Specific speed range lies between 4200 to 9000.	Range of specific speed lies below 4200(for single suction) and 6000 (for double suction).

2. Reciprocating pumps –

The reciprocating pumps have thus become obsolete in modern sewage pumping station. Its initial cost is high and comparatively efficiency is low. Reciprocating pumps are generally of 2 types – (i) ram type and (ii) propeller type.

Diaphragm pump is an example of Ram type Reciprocating pump.

3. Propeller pumps –

The axial flow pump is sometimes called a propeller pump.

4. Air pressure pumps or ejectors –

It works on the action of compressed air. Used in following conditions –

• small quantity of sewage is to be lifted.
• pumping station construction is not possible.
• centrifugal pumps usually clogged.

Power for pumps

1. Steam engines –

Earlier, steam engines were used for operation for the operation of pumps. However Steam power is more reliable., But they are not much in favor due to the following reasons –

• Large initial cost and not economical
• High maintenance cost etc.

2. Internal combustion engines –

The internal combustion engines may run on diesel / gasoline. Initial cost of diesel engine is high and also its difficult to start. Speed is slow also. Operational cost is also very high. These are only used in emergencies, when there is electric power not available.

3. Electric motors –

Pumps are generally operated through electric motors. They are generally very convenient. They are compact, silent in operation, automatic in action and also free from nuisance of smoke.

Maintenance of sewers consists of the removal of obstructions, cleaning of sewers including sewer appurtenances and repair works.

Maintenance of sewers is generally of two types – (i) Preventive / Routine maintenance (ii) Corrective maintenance. Routine maintenance means precautions taken to prevent any breakdown of sewerage facilities. Preventive maintenance is more economical. Whereas corrective maintenance is provided when the breakdown occurs.

Read more about – How testing of sewer is done ?

Problems faced during maintenance of sewers

1. Clogging of sewers
2. Hazards

1. Clogging of sewers

Sewers may get clogged because of the following factors –

• Grit and other detritus may get deposit in the sewer. Thus this will create stagnation resulting in collection of organic matter, which provides bad odour and poisonous gases.
• Roots of nearby plants may penetrate through the joints or cracks in the sewer lines, so this might result in clogging.
• The growth of fungi forms tendrils which starts floating, thus offer an obstruction to the flow.
• Due to improper working of pumps; sewerage gets stagnated and thus clog sewers.

2. Hazards

Persons engaged in operations and maintenance of sewers; are exposed to occupational hazards likewise –

• Physical injuries
• Injuries caused by chemicals and radio-active wastes
• Infections caused by pathogens present in sewage
• danger due to deficiency of oxygen

Safety precautions against gas hazards

While entering with manholes, the following precautions should taken care of –

• Traffic warning signs should be there, thus to avoid accidents.
• No smoking / however open flames allowed nearby.
• Explosion proof electric lighting equipment or mirrors for reflection of light used only.
• Oxygen amount should be taken care of, thus no oxygen deficiency should be there.
• If any noxious gas is found, forced ventilation should be restored.
• Allow safety equipments.
• Use of non-sparking shoes and non-sparking tools.

Safety equipments for maintenance of sewers

Sewer cleaning equipments and devices

1. Portable pump set
2. Sectional sewer rods
3. Flexible sewer rods
4. Ferret used in conjunction with a fire hose
5. Sewer cleaning bucket machine
6. Dredger
7. Rodding machine with flexible sewer rods
8. Scraper
9. Automatic flushing tanks
10. Hydraulically propelled devices (flush bags, sewer balls, sewer pills, sewer scooter)

Ventilation of Sewers

Ventilation of sewers thus done properly for the completion of following purpose –

1. Continuous flow – Ventilation relieves air pressure, caused due to sudden rise or fall of sewage. Due to this, air locks will not be there in it and sewer flow will be continuous flow.
2. Disposal of sewer gases – The sewer has gases like – NH3, CO, CH4, N2, H2S etc. and sometimes includes petrol vapor also. If methane gas (CH4, explosive in nature) is not removed, may blow off manhole’s cover. On the other hand, CO is poisonous in nature. Therefore all the above gases needed to remove by proper ventilation.
3. Prevention of unpleasant odour – Ventilation prevents concentration of unpleasant odour which generally causes nuisance .

Methods of ventilation

1. Man hole covers with gratings – The man hole covers generally have perforations / gratings through which sewer gases escape. The disadvantage of this method is that it mostly causes air pollution by spreading bad odour. It also allows the storm water, dust, debris etc. in it.
2. Ventilating columns or shafts – Ventilating columns or shafts, generally provided at the end of every branch sewer.
3. Proper design and construction of sewer – Sewer should be so design that they run half or 2/3 full. The space above sewage flow will provide ventilation.
4. Proper house drainage system – House vent and soil pipes thus used to ventilate the house drains and lateral sewers.
5. Unobstructed outlets – Unobstructed outlets provide partial ventilation to storm water drains and sewers.
6. Use of mechanical devices – Forced drafts, provided by exhaust fans to expel out foul gases sewers.

After installation of sewer; Sewer Test is subjected before they are put into service. Therefore sewers are under gone through the following tests (i) Test for straightness of alignment and obstruction (ii) Water test (iii) Smoke test (iv) Air test. Let us discuss each test in detail along with test procedures, apparatus and their dimensions, and many more.

Read – what are the types and shapes of sewer?

(i) Test for straightness of alignment and obstruction

As soon as a stretch of sewer is laid, then it is tested for straightness and obstruction. It has two method, described below –

1. At the high end of sewer or drain, a smooth ball of diameter 13 mm less that the pipe bore is insert. If there is no obstruction in the form of yarn or mortar projecting through the joint, then the ball will roll down the invert of the pipe. Thus emerge at the lower end. Alternatively a double disc or solid closed cylinder 75 mm less than internal dimension of the sewer may run. The run through the stretch of the sewer, ensures that it is free from any obstruction.
2. A mirror is placed at one end of the sewer line; lamp at other end. If the pipe line is straight, the full circle of light will observed in mirror. If the pipe line is not straight, this would apparent. The mirror will also indicate any obstruction in the pipe-barrel.

(ii) Water test

Water test is carried out to find out the water tightness of the joints. Sewer Test is carried out after giving sufficient time for the joints to set. In case of concrete and stoneware pipes with cement mortar joints, pipes should be tested three days after the cement mortar joints have been made. If is necessary that the pipelines are filled with water for about a week before commencing the application of pressure to allow for the absorption by the pipe wall.

The sewers are tested by plugging the upper end with a provision for an air outlet pipe with stop cock. The water is filled through a funnel connected at the lower end provided with a plug. Afterwards the air is expelled out, stop cock is closed and the reading is noted after 30 minutes. The pipe line is then inspected. There should not be any leaks in the pipe and joints. Water shall not exceed 15 ml in the smaller dia. and 60 ml in the larger dia. of length 100 mm. Any sewer or part of it; not meeting the test, shall be emptied and repaired and tested again.

(iii) Smoke test

Smoke test is carried out for drainage pipes located in buildings. Thus smoke is produced by burning oil, waste, tar, paper etc. in the combustion chamber of the smoke machine. The pipes are approved gas-tight by the smoke test conducted under pressure of 25 mm of water. It is maintained for 15 minutes after all trap seals have been filled with water.

(iv) Air test

Air testing becomes necessary, particularly in large dia. pipes when the required quantity of water is not available for testing. It is done by subjecting the stretch of pipe to an air pressure of 100 mm of water by means of a hand pump. The pressure is maintained at 75 mm. The joints shall be assumed to be water tight. In case the drop is more than 25 mm, the leaking joints shall be traced and suitably treated to ensure water tightness. The exact point of leakage can be detected by applying soap solution to all the joints in the live and looking for air bubbles.

Benefits of using Sewer Test

• Save time with the ready to go system
• Provides guarantee to operate system safely
• A positive test for in-filtration or ex-filtration
• Testing can be performed on various types of sewer pipe including newly installed or however pre-existing lines
• Also cost effective solution
• Verifies the integrity of new sewer lines
• Simple, fast and efficient quality control tests
• Can also verify workmanship of newly installed sewer lines

In this vary article, first of all, we are going to throw light on the various shapes of sewer along with their advantages.This, also referred as Types of Sewer. So proceeding with the shapes of sewer, generally circular cross sectional is mostly used among sewer.

Read more about – Joints in Sewers.

Sewer of circular cross section has following advantages –

• Easily manufactured
• Gives the maximum are for given perimeter
• Also gives the greatest H.M.D. while running full / half-full
• Most efficient cross section at all flow conditions
• Most economical section since it utilizes minimum quantity of material
• Due to uniform curvature, it offers less opportunities for deposits

1. Circular Shaped Sewer –

Other than circular, we have non-circular shapes of sewer as following

1. Standard egg shaped / Ovoid section
2. New ovoid section
3. Horse shoe section
4. Parabolic section
5. Semi-elliptic section
6. Semi-circular section
7. U-shaped section
8. Basket handle section
9. Rectangular section

All of the above shapes, except for the the ovoid and rectangular section, however have become practically obsolete. Because there is a lot of difficulty in their construction and non-availability of factory made section of these shapes.

2. Standard Ovoid Section –

3. New Ovoid Section –

However, ovoid shaped sewers are still in use as combined sewers. In combined system, the discharge is thus subject to great variation. In rainy season, the sewers are heavily load while in summer only 5% to 10%. Hence the circular sewer, if provided for combined system, will run with very low depths. In such circumstances, however ovoid shaped sewers are more suitable. Its main advantage is that it gives slightly higher velocity during low flow than a circular sewer of the same capacity.

4. Parabolic Section –

5. Horse shoe section –

6. Semi-elliptic section –

7. Semi-circular section –

8. U-shaped section and Basket handle section

9. Rectangular section

Rectangular sections are mainly used as independent covered storm water surface drains rather than as sewers.

A sewer is an under ground conduit or drain through which sewage is conveyed to the point of discharge or disposal. Therefore it is obvious that joints will be there in it. Joints in sewers can be of the following types –

1. Bell and spigot joint
2. Collar joints
3. Simplex joints
4. Flexible or bituminous joints
5. Mechanical joints
6. Open joints

Want to know, what are sewer appurtenances ?

1. Bell and spigot joint

Such joints are quite common in plain or reinforced concrete pipes of sewers. Each pipe has a spigot end and a bell or socket end. Cement mortar of proportion 1:1 or 1:2 inserted between the space of the bell end and spigot end. Gasket or jute packing may placed in the inner side, to maintain the alignment of the sewer. The mortar caulked joint thus finished at about 45 degree on the outer face.

2. Collar joints

For such a joints in sewers, the plain ends of the consecutive lengths of pipe are kept near each other. A collar of slightly bigger diameter is place’d around. The annular space between the collar and the ends of the pipe then filled with cement mortar of 1:1 proportion. Such joints thus used for concrete pipes of larger diameters.

3. Simplex joints

Simplex joint, also referred as ring tie coupling, is similar to collar joints. These are used for asbestos cement pipes. Thus the joint consists of a pipe sleeve or coupling of asbestos cement. Also it has two rubber rings which then compressed between the exterior of the pipes and interior of the sleeve. Such a joint is quite flexible.

4. Flexible or bituminous joints

Flexible joint is also termed as bituminous joint. The collar joint, using cement mortar is relatively rigid. Such joints crack easily due to even slight movement pipes due to settlement etc. These joints, made flexible by using bitumen instead of cement mortar.

5. Mechanical joints in sewers

Such joints use mechanical devices like flange rings, bolts, screwed ends etc. so that to keep the two ends together. Therefore it, used for metallic sewers made of cast iron, steel etc.

6. Open joints in sewers

If there is no objection to infiltration, open joints can however be adopted in sewers. The bell and spigot ends simply placed together, without inserting filling material in the annular space. Gasket may however be inserted; to maintain alignment. The joint is merely covered with tar paper,this is because to prevent entry of subsoil into the sewer.