SUMMER TRAINING REPORT 2015

DONE BY,

SAUNAK SARKAR&SYAMONTOK MUKHERJEE (BOTH FROM H.E.T.C M.E BATCH 2012-2016)AT,

NEWTOWN KOLKATA MECHANICAL DIVISION,PUBLIC HEALTH ENGINEERING DEPARTMENT,GOVERNMENT OF WEST BENGAL.

SUBMITTED TO,

DEPARTMENT OF MECHANICAL ENGINEERINGHOOGHLY ENGINEERING AND TECHNOLOGY COLLEGE(http://www.hetc.ac.in/)VIVEKANANDA ROAD,PIPULPATI ,HOOGHLY,PIN-712103,WEST BENGAL

ACKNOWLEDGEMENT

It is real pleasure to remind of those personalities who have immensely helped us throughout engineering curriculum both in theoretical and practical ways.First of all, I would like to thank Dr. Avijit Patra, Principal and HoD of mechanical engineering of H.E.T.C and all the class teachers as well as technical assistants for their guidance and encouragement to undergo this industrial training program.The Training and placement department of H.E.T.C has done a great job for us by coordinating this training program. So, a big thanks for them.I would also like to express my sincere gratitude to Mr. Tanay Banerjee, Executive engineer, P.H.E. Department, Newtown Kolkata Mechanical Division without whose helping hand and wholehearted effort this training program would not see the daylight.Mr Roney Sarkar and Mr. Mangal Bag are those two personalities who have actively arranged and fine tuned this training program in spite of their busy schedule just to satisfy our knowledge hunger. So, We have no language to express our deep gratitude towards them.And Last but not the least, It is time to thank all the employees of P.H.E Dte. for displaying an extremely sound professional work-culture to make our industry experience a memorable one.

SCOPE

This summer training has been prepared based on the training at Public Health Engineering . The scope of this project that the report which is restricted to study of organisation profile and project profile . Also the information regarding the project is restricted to the work package under Public Health Engineering . The data collected during the training is strictly is confidential and will be used only for the academic purpose.

INTRODUCTION

After completing our third year sixth semester ,we were getting training . Also the reason was that to see the practical work and how much theory is related to the practical work in Mechanical Engineering . So we want to try to organize training and with help of college authority we were sent to the Public Health Engineering .And, at the end , we can definitely claim that we have done a very good and helpful training .

CONTENTSTOPICPAGE NO.

About WBPHED6

Sewage and Drainage Pumping System Related Definitions9

Objective of collection & Disposal 10

Sewer material10

Sewer material-Advantage & Disadvantage 11

Quantity estimation of sewage13

Quantity estimation of storm water15

Sewer Appurtenances 15

Pumping Stations(Sewage & Drainage)15

Type , Efficiency & materials of pumps16

Pumping system design18

Types of pumping stations(wet & dry well)19

Structure of pumping stations20

Undesirable Operation of Pumps21

Gates , valves , actuators 23

Sluice Gate-Dos & Donts23

Gate Valves , NRV , Butterfly valves24

Actuators26

Electrical & Instrumentation facilities28

Sewage Pumping Station - As we saw it35

Drainage Pumping Station As we saw it36

Conclusion38

References39

W.B.P.H.E.DPublic Health Engineering Department(PHED)was created as an independent full-fledged Department in 1987 vide Home (C & E) Departments Notification No. 16664-AR dated 2.9.1987. Earlier Health & Family Welfare Department of the State Government had a Public Health Engineering Wing. As per Rules of Business of the State Government, Public Health Engineering Department controls the Water Supply & Sanitation Budget of the State Government(major head 2215/4215)and undertakes programmes of implementation of water supply and sanitation services mainly through Public Health Engineering Directorate under its administrative control.Currently, however, Panchayet & Rural Development Department controls the Budget of Rural Sanitation and has been made the Nodal Department for Rural Sanitation. The Municipal Affairs and Urban Development Departments are now looking after activities of Urban Sanitation and Sewerage Sector. Therefore, main activities of PHED are now related to Rural and Urban Water Supply Sectors. In the Urban Water Supply Sector, sectoral activities are mostly limited within areas of the State outside Kolkata Metropolitan Area (KMA). PHED also controls partially the Budget of Hill Area Development(major head 2551)so far as provision for water supply is concerned. Budgetary control is also exercised by PHED on Loans to Urban Local Bodies for implementation of Urban Water Supply Schemes(major head 6215).PHED has to arrange for water supply and sanitation measures in fairs and festivals for which fund is provided undermajor head 2250of Social Welfare Department. PHED has to carry out original works of Health & Family Welfare Department undermajor heads 4210 and 2210so far as water supply in hospitals and health institutions is concerned. PHED is also involved in maintenance of non-residential Government buildings under themajor head 2059 of PWD.PHEDhas to operate and maintain three Sewerage & Drainage schemes ( Kalyani, Berhampur and Nabadwip ) completed under Ganga Action Plan ( Phase I). Implementation of Sewerage & Drainage schemes for 4 (four) more towns has been entrusted to Public health Engineering Department. Public Health Engineering Department is continuing operation and maintenance of 21 water supply and drainage schemes belonging to other Departments. Above all, Natural Calamities, like flood or drought, demands safe water supply for the people and Public Health Engineering Department always rises to such occasion. Fund is provided under Relief Departmentsmajor head 2245.

Vision 2020

To provide Safe, Sustainable and Adequate Water Supply to All Humans and Livestock in West Bengal by 2020

Objectives

To ensure permanent drinking water security @70 lpcd (litres per capita per day) in rural West Bengal. To ensure drinking water security through emphasis on piped water supply schemes with an objective to complete shift from hand pump tubewells to piped water supply schemes in a phased manner, provision for house to house connection, conjunctive use of groundwater, surface-water and rain water harvesting. Delivery of services by the system for its entire design period of quality of water in conformity with the prescribed standards at both the supply and consumption points. Issue of potability, reliability, sustainability, convenience, equity and consumers preference to be the guiding principles while planning for a community based water supply system To enable communities to monitor and maintain surveillance on their drinking water sources; To ensure that all schools and anganwadis have access to safe drinking water; To provide enabling environment for Panchayat Raj Institutions and local communities to manage their own drinking water sources and systems; To provide access to information through online reporting mechanism with information placed in public domain to bring intransparency, accountability andinformed decision making;

Paradigm Shift

It is observed that water supply schemes designed to provide 40 lpcd for the entire population in a habitation are often not providing adequate drinking water to people living at the tail end of the schemes or throughout the year. As such there is a need to move ahead from the conventional norms of litres per capita per day (lpcd) norms to ensure drinkingwater security for allin the community. While initiating this move from lpcd to drinking water security at the State, District and Village levels, it is important to ensure that the basic minimum requirement at the household level for drinking and cooking needs and also for other household needs and cattle are met. Water supply for drinking and cooking should maintain quality as per the prescribed BIS standards and for other household and animal needs, the water should be of acceptable standard. To prevent contamination of drinking water in the conveyance system, it is advisable to adopt 24 x 7 supply where ever possible. The cost of water supply provision beyond the basic minimum need must be borne by the consumers. To ensure this, it is important to maintain potability and reliability of drinking water quality standards both at the production (water treatment plant) as well as at the consumption points (household level). Focus on personal hygiene, and proper storage at the house hold level i.e. at the family level will ensure reduction of disease burden leading to improved quality of life and well being of the community. For ensuring quality of water. Bureau of Indian Standard (BIS) IS: 10500 was formulated in 1990. World Health Organization has also issued modified Guidelines for Drinking Water Quality (2004) and Guidelines for safe use of wastewater and grey water (2006). Both the guidelines adopted health based target setting approach. Health based target is based on the total exposure of an individual to contamination and moves from reliance on end product testing of water quality to risk assessment and risk management of water supplies commonly known as 'water safety plan'. Water safety plan links the identification of a water quality problem with a water safety solution. It includes both water quality testing and also sanitary inspection to determine appropriate control measures. It is a quality assurance tool that ensures protection of the water quality from the catchment to the consumer and from the tap to the toilet. Health based target needs to be established for using groundwater, surface water, rainwater and reused/recycled water. For each, the use rather than the source should determine the quality of the water supplied. This therefore emphasizes the need to establishquality assurance programmes for water supplies to reduce the potential risk of contamination ofwater supply. This has been indicated under 'Water Quality Monitoring & Surveillance Programme.

SEWAGE & DRAINAGE PUMPING SYSTEMSome definitionsSanitary sewage: Sewage originated from the residential buildings comes under this category.This is very foul in nature. It is the wastewater generated from the lavatory basins, urinals and water closets of residential buildings, office building, theatre and other institutions. It is also referred as domestic wastewater.Sewage: It indicates the liquid waste originating from the domestic uses of water. It includes sullage, discharge from toilets, urinals, wastewater generated from commercial establishments, institutions, industrial establishments and also the groundwater and storm water that may enter into the sewers. Its decomposition produces large quantities of malodorous gases, and it contains numerous pathogenic or disease producing bacteria, along with high concentration of organic matter and suspended solids.Sewer: It is an underground conduit or drain through which sewage is carried to a point of discharge or disposal. There are three types of sewer systems that are commonly used for sewage collection. Separate sewers are those which carry the house hold and industrial wastes only. Storm water drains are those which carry rain water from the roofs and street surfaces.Combine sewers are those which carry both sewage and storm water together in the same conduit. House sewer (or drain) is used to discharge the sewage from a building to a streetsewer. Lateral sewer is a sewer which collects sewage directly from the household buildings.Branch sewer or sub main sewer is a sewer which receives sewage from a relatively small area.Main sewer or trunk sewer is a sewer that receives sewage from many tributary branches andsewers, serving as an outlet for a large territory. Depressed sewer is a section of sewerconstructed lower than adjacent sections to pass beneath an obstacle or obstruction. It runs fullunder the force of gravity and at greater than atmospheric pressure. The sewage enters andleaves the depressed sewer at atmospheric pressure. Intercepting sewer is a sewer laidtransversely to main sewer system to intercept the dry weather flow of sewage and additionalsurface and storm water as may be desirable. An intercepting sewer is usually a large sewer, flowing parallel to a natural drainage channel, into which a number of main or outfall sewersdischarge. Outfall sewer receives entire sewage from the collection system and finally it isdischarged to a common point. Relief sewer or overflow sewer is used to carry the flow inexcess of the capacity of an existing sewer.Sewerage: The term sewerage refers the infrastructure which includes device, equipment andappurtenances for the collection, transportation and pumping of sewage, but excluding worksfor the treatment of sewage. Basically it is a water carriage system designed and constructedfor collecting and carrying of sewage through sewers.Stormwater: It indicates the rain water of the locality.Subsoil water: Groundwater that enters into the sewers through leakages is called subsoilwater.Sullage: This refers to the wastewater generated from bathrooms, kitchens, washing place andwash basins, etc. Composition of this waste does not involve higher concentration of organicmatter and it is less polluted water as compared to sewage.Wastewater: The term wastewater includes both organic and inorganic constituents, in solubleor suspended form, and mineral content of liquid waste carried through liquid media. Generallythe organic portion of the wastewater undergoes biological decompositions and the mineralmatter may combine with water to form dissolved solids.SOURCES OF SEWAGEThe wastewater generated from the household activities contributes to the major part of thesewage. The wastewater generated from recreational activities, public utilities, commercialcomplexes, and institutions is also discharged in to sewers. The wastewater discharged fromsmall and medium scale industries situated within the municipal limits and dischargingpartially treated or untreated wastewater in to the sewers also contributes for municipalwastewater.OBJECTIVES OF SEWAGE COLLECTION AND DISPOSALThe objective of sewage collection and disposal is to ensure that sewage discharged fromcommunities is properly collected, transported, treated to the required degree so as not to causedanger to human health or unacceptable damage to the natural environment and finallydisposed off without causing any health or environmental problems. Thus, efficient seweragescheme can achieve the following: To provide a good sanitary environmental condition of city protecting public health. To dispose the human excreta to a safe place by a safe and protective means. To dispose of all liquid waste generated from community to a proper place to prevent afavorable condition for mosquito breeding, fly developing or bacteria growing. To treat the sewage, as per needs, so as not to endanger the body of water orgroundwater or land to get polluted where it is finally disposed off. Thus, it protects thereceiving environment from degradation or contamination.Important Factors Considered for Selecting Material for SewerFollowing factors should be considered before selecting material for manufacturing sewer pipes:a. Resistance to corrosionSewer carries wastewater that releases gases such as H2S. This gas in contact with moisture canbe converted into sulfuric acid. The formation of acids can lead to the corrosion of sewer pipe.Hence, selection of corrosion resistance material is must for long life of pipe.b. Resistance to abrasionSewage contain considerable amount of suspended solids, part of which are inorganic solids suchas sand or grit. These particles moving at high velocity can cause wear and tear of sewer pipeinternally. This abrasion can reduce thickness of pipe and reduces hydraulic efficiency of thesewer by making the interior surface rough.c. Strength and durabilityThe sewer pipe should have sufficient strength to withstand all the forces that are likely to comeon them. Sewers are subjected to considerable external loads of backfill material and traffic load,if any. They are not subjected to internal pressure of water. To withstand external load safelywithout failure, sufficient wall thickness of pipe or reinforcement is essential. In addition, thematerial selected should be durable and should have sufficient resistance against naturalweathering action to provide longer life to the pipe.d. Weight of the materialThe material selected for sewer should have less specific weight, which will make pipe light inweight. The lightweight pipes are easy for handling and transport.e. ImperviousnessTo eliminate chances of sewage seepage from sewer to surrounding, the material selected forpipe should be impervious.f. Economy and costSewer should be less costly to make the sewerage scheme economical.g. Hydraulically efficientThe sewer shall have smooth interior surface to have less frictional coefficient.Materials for SewersAsbestos Cement Sewers These are manufactured from a mixture of asbestos fibers, silica and cement. Asbestosfibers are thoroughly mixed with cement to act as reinforcement. These pipes are available in size 10 to 100 cm internal diameter and length up to 4.0 m. These pipes can be easily assembled without skilled labour with the help of specialcoupling, called Ring Tie Coupling or Simplex joint. The pipe and joints are resistant to corrosion and the joints are flexible to permit 12odeflection for curved laying. These pipes are used for vertical transport of water. For example, transport of rainwaterfrom roofs in multistoried buildings, for transport of sewage to grounds, and for transportof less foul sullage i.e., wastewater from kitchen and bathroom.Advantages These pipes are light in weight and hence, easy to carry and transport. Easy to cut and assemble without skilled labour. Interior is smooth (Mannings n = 0.011) hence, can make excellent hydraulicallyefficient sewer.Disadvantages These pipes are structurally not very strong. These are susceptible to corrosion by sulphuric acid. When bacteria produce H2S, inpresence of water, H2SO4 can be formed leading to corrosion of pipe material.Plain Cement Concrete or Reinforced Cement ConcretePlain cement concrete (1: 1.5: 3) pipes are available up to 0.45 m diameter and reinforcementcement pipes are available up to 1.8 m diameter. These pipes can be cast in situ or precast pipes.Precast pipes are better in quality than the cast in situ pipes. The reinforcement in these pipes canbe different such as single cage reinforced pipes, used for internal pressure less than 0.8 m;double cage reinforced pipes used for both internal and external pressure greater than 0.8 m;elliptical cage reinforced pipes used for larger diameter sewers subjected to external pressure;and Hume pipes with steel shells coated with concrete from inside and outside. Nominallongitudinal reinforcement of 0.25% is provided in these pipes.Advantages of concrete pipes Strong in tension as well as compression. Resistant to erosion and abrasion. They can be made of any desired strength. Easily molded, and can be in situ or precast pipes. Economical for medium and large sizes. These pipes are available in wide range of size and the trench can be opened andbackfilled rapidly during maintenance of sewers.Disadvantages These pipes can get corroded and pitted by the action of H2SO4. The carrying capacity of the pipe reduces with time because of corrosion. The pipes are susceptible to erosion by sewage containing silt and grit.The concrete sewers can be protected internally by vitrified clay linings. With protection liningthey are used for almost all the branch and main sewers. Only high alumina cement concreteshould be used when pipes are exposed to corrosive liquid like sewage.Vitrified Clay or Stoneware SewersThese pipes are used for house connections as well as lateral sewers. The size of the pipeavailable is 5 cm to 30 cm internal diameter with length 0.9 to 1.2 m. These pipes are rarelymanufactured for diameter greater than 90 cm. These are joined by bell and spigot flexiblecompression joints.Advantages Resistant to corrosion, hence fit for carrying polluted water such as sewage. Interior surface is smooth and is hydraulically efficient. The pipes are highly impervious. Strong in compression. These pipes are durable and economical for small diameters. The pipe material does not absorb water more than 5% of their own weight, whenimmersed in water for 24 h.Disadvantages Heavy, bulky and brittle and hence, difficult to transport. These pipes cannot be used as pressure pipes, because they are weak in tension. These require large number of joints as the individual pipe length is small. Brick SewersThis material is used for construction of large size combined sewer or particularly for stormwater drains. The pipes are plastered from outside to avoid entry of tree roots and groundwaterthrough brick joints. These are lined from inside with stone ware or ceramic block to make themsmooth and hydraulically efficient. Lining also makes the pipe resistant to corrosion.Cast Iron SewersThese pipes are stronger and capable to withstand greater tensile, compressive, as well asbending stresses. However, these are costly. Cast iron pipes are used for outfall sewers, risingmains of pumping stations, and inverted siphons, where pipes are running under pressure. Theseare also suitable for sewers under heavy traffic load, such as sewers below railways andhighways. They are used for carried over piers in case of low lying areas. They form 100% leakproof sewer line to avoid groundwater contamination. They are less resistant to corrosion; hence,generally lined from inside with cement concrete, coal tar paint, epoxy, etc. These are joinedtogether by bell and spigot joint. IS:1536-1989 and IS:1537-1976 provides the specifications forspun and vertically cast pipes, respectively.Steel PipesThese are used under the situations such as pressure main sewers, under water crossing, bridgecrossing, necessary connections for pumping stations, laying pipes over self supporting spans,railway crossings, etc. They can withstand internal pressure, impact load and vibrations muchbetter than CI pipes. They are more ductile and can withstand water hammer pressure better.These pipes cannot withstand high external load and these pipes may collapse when negativepressure is developed in pipes. They are susceptible to corrosion and are not generally used forpartially flowing sewers. They are protected internally and externally against the action ofcorrosion. Ductile Iron PipesDuctile iron pipes can also be used for conveying the sewers. They demonstrate higher capacityto withstand water hammer. The specifications for DI pipes is provided in IS:12288-1987. Thepredominant wall material is ductile iron, a spheroidized graphite cast iron. Internally these pipesare coated with cement mortar lining or any other polyethylene or poly wrap or plastic bagging/sleeve lining to inhibit corrosion from the wastewater being conveyed, and various types ofexternal coating are used to inhibit corrosion from the environment. Ductile iron has proven to bea better pipe material than cast iron but they are costly. Ductile iron is still believed to bestronger and more fracture resistant material. However, like most ferrous materials it issusceptible to corrosion. A typical life expectancy of thicker walled pipe could be up to 75 years,however with the current thinner walled ductile pipe the life could be about 20 years in highlycorrosive soils without a corrosion control program like cathodic protection. Plastic sewers (PVC pipes)Plastic is recent material used for sewer pipes. These are used for internal drainage works inhouse. These are available in sizes 75 to 315 mm external diameter and used in drainage works.They offer smooth internal surface. The additional advantages they offer are resistant tocorrosion, light weight of pipe, economical in laying, jointing and maintenance, the pipe is toughand rigid, and ease in fabrication and transport of these pipes. High Density Polythylene (HDPE) PipesUse of these pipes for sewers is recent development. They are not brittle like AC pipes and otherpipes and hence hard fall during loading, unloading and handling do not cause any damage to thepipes. They can be joined by welding or can be jointed with detachable joints up to 630 mmdiameter (IS:4984-1987). These are commonly used for conveyance of industrial wastewater.They offer all the advantages offered by PVC pipes. PVC pipes offer very little flexibility andnormally considered rigid; whereas, HDPE pipes are flexible hence best suited for laying in hillyand uneven terrain. Flexibility allows simple handling and installation of HDPE pipes. Becauseof low density, these pipes are very light in weight. Due to light in weight, they are easy forhandling, this reduces transportation and installation cost. HDPE pipes are non corrosive andoffer very smooth inside surface due to which pressure losses are minimal and also this materialresist scale formation.Glass Fiber Reinforced Plastic PipesThis martial is widely used where corrosion resistant pipes are required. Glass fiber reinforcedplastic (GRP) can be used as a lining material for conventional pipes to protect from internal orexternal corrosion. It is made from the composite matrix of glass fiber, polyester resin andfillers. These pipes have better strength, durability, high tensile strength, low density and highcorrosion resistance. These are manufactured up to 2.4 m diameter and up to 18 m length(IS:12709-1989). Glass reinforced plastic pipes represent the ideal solution for transport of anykind of water, chemicals, effluent and sewage, because they combine the advantages of corrosionresistance with a mechanical strength which can be compared with the steel pipes. Typicalproperties that result in advantages in GRP pipes application can be summarized as follows: Light weight of pipes that allows for the use of light laying and transport means. Possibility of nesting of different diameters of pipe thus allowing additional saving intransport cost. Length of pipe is larger than other pipe materials. Easy installation procedures due to the kind of mechanical bell and spigot joint. Corrosion resistance material, hence no protections such as coating, painting orcathodic are then necessary. Smoothness of the internal wall that minimizes the head loss and avoids the formationof deposits. High mechanical resistance due to the glass reinforcement. Absolute impermeability of pipes and joints both from external to internal a

Quantity Estimation of SewageVariation in Sewage FlowVariation occurs in the flow of sewage over annual average daily flow. Fluctuation in flowoccurs from hour to hour and from season to season. The typical hourly variation in the sewageflow is shown in the Figure 4.1. If the flow is gauged near its origin, the peak flow will bequite pronounced. The peak will defer if the sewage has to travel long distance. This is becauseof the time required in collecting sufficient quantity of sewage required to fill the sewers andtime required in travelling. As sewage flow in sewer lines, more and more sewage is mixed init due to continuous increase in the area being served by the sewer line. This leads to reductionin the fluctuations in the sewage flow and the lag period goes on increasing. The magnitude ofvariation in the sewage quantity varies from place to place and it is very difficult to predict.For smaller township this variation will be more pronounced due to lower length and traveltime before sewage reach to the main sewer and for large cities this variation will be less.Figure 4.1 Typical hourly variations in sewage flow.

For estimating design discharge following relation can be considered:Maximum daily flow = Two times the annual average daily flow (representingseasonal variations)Maximum hourly flow = 1.5 times the maximum daily flow (accounting hourlyvariations)= Three times the annual average daily flowAs the tributary area increases, peak hourly flow will decrease. For smaller population served(less than 50000) the peak factor can be 2.5, and as the population served increases its valuereduces. For large cities it can be considered about 1.5 to 2.0. Therefore, for outfall sewer thepeak flow can be considered as 1.5 times the annual average daily flow. Even for design of thetreatment facility, the peak factor is considered as 1.5 times the annual average daily flow.The minimum flow passing through sewers is also important to develop self cleansing velocityto avoid silting in sewers. This flow will generate in the sewers during late night hours. Theeffect of this flow is more pronounced on lateral sewers than the main sewers. Sewers must bechecked for minimum velocity as follows:Minimum daily flow = 2/3 Annual average daily flowMinimum hourly flow = minimum daily flow= 1/3 Annual average daily flowThe overall variation between the maximum and minimum flow is more in the laterals and lessin the main or trunk sewers. This ratio may be more than 6 for laterals and about 2 to 3 in caseof main sewers.Design PeriodThe future period for which the provision is made in designing the capacities of the variouscomponents of the sewerage scheme is known as the design period. The design period dependsupon the following: Ease and difficulty in expansion, Amount and availability of investment, Anticipated rate of population growth, including shifts in communities, industries andcommercial investments, Hydraulic constraints of the systems designed, and Life of the material and equipment.Following design period can be considered for different components of sewerage scheme.1. Laterals less than 15 cm diameter : Full development2. Trunk or main sewers : 40 to 50 years3. Treatment Units : 15 to 20 years4. Pumping plant : 5 to 10 yearsQuantity Estimation of Storm WaterFactors Affecting the Quantity of StormwaterThe surface run-off resulting after precipitation contributes to the stormwater. The quantity ofstormwater reaching to the sewers or drains is very large as compared with sanitary sewage.The factors affecting the quantity of stormwater flow are as below:i. Area of the catchmentii. Slope and shape of the catchment areaiii. Porosity of the soiliv. Obstruction in the flow of water as trees, fields, gardens, etc.v. Initial state of catchment area with respect to wetness.vi. Intensity and duration of rainfallvii. Atmospheric temperature and humidityviii. Number and size of ditches present in the areaMethods for Estimation of Quantity of Storm Water1. Rational Method2. Empirical formulae methodSewer AppurtenancesThe structures, which are constructed at suitable intervals along the sewerage system to helpits efficient operation and maintenance, are called as sewer appurtenances. These include:(1) Manholes, (2) Drop manholes, (3) Lamp holes,(4) Clean-outs, (5) Street inlets called Gullies, (6) Catch basins,(7) Flushing Tanks, (8) Grease & Oil traps, (9) Inverted Siphons, and(10) Storm Regulators.Sewage And Storm water Pumping StationsThere are certain locations where it is possible to convey sewage by gravity to a centraltreatment facility or stormwater is conveyed up to disposal point entirely by gravity.Whereas, in case of large area being served with flat ground, localities at lower elevation orwidely undulating topography it may be essential to employ pumping station for conveyanceof sewage to central treatment plant. Sewage and stormwater is required to be lifted up from alower level to a higher level at various places in a sewerages system. Pumping of sewage isalso generally required at the sewage treatment plant.Pumping of sewage is different than water pumping due to polluted nature of the wastewatercontaining suspended solids and floating solids, which may clog the pumps. The dissolvedorganic and inorganic matter present in the sewage may chemically react with the pump andpipe material and can cause corrosion. The disease causing bacteria present in the sewagemay pose health hazard to the workers. Sedimentation of organic matter in the sump wellmay lead to decomposition and spreading of foul odour in the pumping station, requiringproper design to avoid deposition. Also, variation of sewage flow with time makes it achallenging task.Pumping stations are often required for pumping of (1) untreated domestic wastewater, (2)stormwater runoff, (3) combined domestic wastewater and stormwater runoff, (4) sludge at awastewater treatment plant, (5) treated domestic wastewater, and (6) recycling treated wateror mixed liquor at treatment plants. Each pumping application requires specific design andpump selection considerations. At sewage treatment plant pumping is also required forremoval of grit from grit chamber and pumping may be required for conveying separatedgrease and floating solids to disposal facility.Generally pumping station should contain at least three pumping units of such capacity tohandle the maximum sewage flow if the largest unit is out of service. The pumps should beselected to provide as uniform a flow as possible to the treatment plant. All pumping stationsshould have an alarm system to signal power or pump failure and every effort should be madeto prevent or minimize overflow. Flow measuring device such as venturimeter shall beprovided at the pumping station. In all cases raw-sewage pumps should be protected byscreens or racks unless special devices such as self cutting grinder pumps are provided.Housing for electric motors should be made above ground and in dry wells electric motors should be provided protection against flooding. Good ventilation in dry well should beprovided, preferably of forced air type, and accessibility for repairs and replacements shouldbe ensured.The site selection for the pumping station is important and the area selected should never getflooded. The station should be easily accessible in all weathers. The stormwater pumpingstation should be so located that the water may be impounded without causing damage to theproperties. Location of the pumping station should be finalize considering the futureexpansion and expected increase in the sewage flow. There need to be enough space in thepumping station to replace low capacity pump with higher capacities as per the need infuture. The capacity of the pumping station is based on the present and future sewage flow.Generally design period up to 15 years is considered for pumps. The civil structure and thepipelines shall be adequate to serve for the design period of 30 years.Types of PumpsFollowing types of pumps are used in the sewerage system for pumping of sewage, sewagesludge, grit matter, etc. as per the suitability:a. Radial-flow centrifugal pumpsb. Axial-flow and mixed-flow centrifugal pumpsc. Reciprocating pistons or plunger pumpsd. Diaphragm pumpse. Rotary screw pumpsf. Pneumatic ejectorsg. Air-lift pumpsOther pumps and pumping devices are available, but their use in environmental engineeringis infrequent.Radial-Flow Centrifugal pumps: These pumps consist of two parts: (1) the casing and (2)the impeller. The impeller of the pump rotates at high speed inside the casing. Sewage isdrawn from the suction pipe into the pump and curved rotating vanes throw it up throughoutlet pipe because of centrifugal force. Radial-flow pumps throw the liquid entering thecenter of the impeller out into a spiral volute or casing. The impellers of all centrifugal pumpscan be closed, semi open, or open depending on the application. Open impeller type pumps are more suitable because suspended solids and floating matter present in the sewage can be easily pumped without clogging. These pumps can have a horizontal or vertical design.These pumps are commonly used for any capacity and head. These pumps have low specificspeed up to 4200.Axial- flow Centrifugal pumps: Axial-flow designs can handle large capacities but only withreduced discharge heads. They are constructed vertically. The vertical pumps have positivesubmergence of the impeller. These are used for pumping large sewage flow, more than 2000m3/h and head up to 9.0 m. These pumps have relatively high specific speed of 8000 16000. The water enters in this pump axially and the head is developed by the propellingaction of the impeller vanes.Mixed flow pumps: These pumps develop heads by combination of centrifugal action and thelift of the impeller vane on the liquid. They are having single impeller. The flow enters thepump axially and discharges in an axial and radial direction into volute type casing. Thespecific speed of the pump varies from 4200 to 9000. These are used for medium headsranging from 8 m to 15 m.Most water and wastewater can be pumped with centrifugal pumps. They should not be usedfor the following: Pumping viscous industrial liquids or sludges, where the efficiencies of centrifugalpumps are very low, and therefore positive displacement pumps are used for suchapplications. Low flows against high heads. Except for deep-well applications, the large number ofimpellers needed is a disadvantage for the centrifugal design.The rotational speed of impeller affects the capacity, efficiency, and extent of cavitation.Even if the suction lift is within permissible limits, cavitations can be a problem and shouldbe checked. Centrifugal pumps are classified on the basis of their specific speed (Ns) at thepoint of maximum efficiency. The specific speed of the pump is defined as speed of theimpeller in revolution per minute such that it would deliver discharge of 1 m3/min against 1.0m of head. The pumps with low specific speed are suitable for more suction lift than the pumps withhigh specific speed. The axial flow pumps with high specific speed will not work with anysuction lift; rather these pumps require positive suction head and some minimumsubmergence for trouble free operation. It is advisable to avoid suction lift for the centrifugalpumps. Hence pumps are generally installed either to work submerged in the wet well orinstalled in the dry well at such a level that the impeller will be below the level of the liquidin the wet well.Positive displacement pumps: These pumps include reciprocating piston, plunger, anddiaphragm pumps. Almost all reciprocating pumps used in environmental engineering aremetering or power pumps. A piston or plunger is used in a cylinder, which is driven forwardand backward by a crankshaft connected to an outside driving unit. Adjusting metering pumpflow involves merely changing the length and number of piston strokes. A diaphragm pumpis similar to a reciprocating piston or plunger, but instead of a piston, it contains a flexiblediaphragm that oscillates as the crankshaft rotates. Plunger and diaphragm pumps feedmetered amounts of chemicals (acids or caustics for pH adjustment) to a water or wastewaterstream. These are not suitable for sewage pumping because solids and rugs present in thesewage may clog them. These pumps have high initial cost and very low efficiency.Rotary Screw Pumps: In this type, a motor rotates a vane screw or rubber stator on a shaft tolift or feed sludge or solid waste material to a higher level or the inlet of another pump. Theseare used in the square grit chamber for removal of grit.Air Pumps: These pumps include pneumatic ejectors and airlifts. In pneumatic ejectorwastewater flows into a receiver pot and an air pressure system then blows the liquid to atreatment process at a higher elevation. The air system can use plant air (or steam), apneumatic pressure tank, or an air compressor. This pumping system has no moving parts incontact with the waste; thus, no clogging of impeller is involved. Ejectors are normallymaintenance free and operate for longer time. Airlift pumps consist of an updraft tube, an airline, and an air compressor or blower. Airlifts blow air at the bottom of a submerged updrafttube. As the air bubbles travel upward, they expand reducing density and pressure within thetube. Higher flows can be lifted for short distances in this way. Airlifts are used in wastewatertreatment to transfer mixed liquors or slurries from one process to another. These pumpshave very low efficiency and can lift the sewage up to small head.

Efficiencies of PumpsEfficiencies of the pumps range from 85% for large capacity centrifugals (radial-flowcentrifugals and axial-flow and mixed-flow centrifugals) to below 50% for many smallerunits. For reciprocating pistons or plunger pumps efficiency varies from 30% onwarddepending on horsepower and number of cylinders. For diaphragm pumps, efficiency is about30%, and for rotary screw type, pneumatic ejectors type and air-lift pumps it is below 25%.

Materials for Construction of PumpsFor pumping of water using radial-flow centrifugals and axial-flow and mixed-flowcentrifugal type pumps normally bronze impellers, bronze or steel bearings, stainless orcarbon steel shafts, and cast iron housing is used. For domestic wastewater pumping usingradial-flow centrifugals and axial-flow and mixed-flow centrifugal type pumps similarmaterial is used except that they are often made from cast iron or stainless steel impellers. Forindustrial wastewater and chemical feeders using radial-flow centrifugal or reciprocatingpiston or plunger type pumps, a variety of materials depending on corrosiveness are used. Indiaphragm pumps the diaphragm is usually made of rubber. Rotary screw type, pneumaticejectors type and air-lift pumps normally have steel components.

Pumping System DesignTo choose the proper pump, the environmental engineer must know the capacity, headrequirements, and liquid characteristics. This section addresses the capacity and headrequirements.

CapacityTo compute capacity, the environmental engineer should first determine average system flowrate, then decide if adjustments are necessary. For example, when pumping wastes from acommunity sewage system, the pump must handle peak flows roughly two to five times theaverage flow, depending on community size. Summer and winter flows and future needs alsodictate capacity. Population increase trends and past flow rates should also be considered inthis evaluation. The capacity of the pumping station should be so determined that the pumpof minimum duty should also run for at least 5 min. In addition, the capacity of the wellshould be such that with any combination of inflow and pumping, the cycle of operation foreach pump will not be less than 5 min and the maximum detention time in the wet well willnot exceed 30 min at average flow.The capacity of the pumps installed should meet the peak flow rate with about 100% standby.Two or more number of pumps should be provided. The size and number of pumps for largerpumping station is so selected that variation in the flow rate can be adjusted by manipulatingspeed of the pump or throttling the delivery valve, without starting or stopping the pumps toofrequently. The general practice is to provide three pumping sets in small stations consistingof one pump of capacity equal to dry weather flow (DWF), second pump with capacity of 2times DWF and third pump of capacity 3 times DWF. For larger pumping stations five pumpsets are provided with capacities of 2 units of 0.5 DWF, 2 pumps of 1 DWF and one pump of3 DWF.

Head RequirementHead describes pressure in terms of lift. The discharge head on a pump is a sum of thefollowing contributing factors:1) Static Head (hd) - The vertical distance through which the liquid must be lifted i.e. thelowest water level in wet well and highest point on the discharge side.2) Friction Head (hf) - The resistance to flow caused by friction in the pipes, valves, andbends. Entrance and transition losses shall also be included. The loss of head in friction in thepipes is estimated from the well known equation hf = fLv2/(2gD)3) Velocity Head (hv) - The head required to impart energy into a fluid to induce velocity.Normally this head is quite small and can be ignored unless the total head is low. This isestimated as v2/2g.4) Pressure Head (hp) - The pressure differential that the pump must develop to deliver wateron the delivery side under higher pressure. The pressure on water in sump well is usuallyatmospheric pressure, whereas when pumping into sewers there would be potential head atthe point of delivery, against which the pump have to deliver. Thus, this is the differencebetween pressures on the liquid in the wet well and at the point of delivery.Total Head (H) of pumping is thus expressed by the following equation:H = hd + hf + hv hp (2)

Suction LiftThe amount of suction lift that can be handled must be carefully computed. It is limited bythe barometric pressure (which depends on elevation and temperature), the vapor pressure(which also depends on temperature), friction and entrance losses on the suction side, and thenet positive suction head (NPSH) - a factor that depends on the shape of the impeller and isobtained from the pump manufacturer.

HorsepowerThe horsepower required to drive the pump is called brake horsepower (BHP). The followingequation determines the brake horsepower:BHP = (w.Q.H)/(75.p. m) (3)Where, Q = discharge (m3/s); H = head of water (m); w = Density of water (kg/m3); p =Efficiency of the pump; and m = efficiency of the driving motor.

Types of Pumping StationsPumping stations can be configured in a wide variety of arrangements, depending on size andapplication. The classifications for such pumping-station configurations are: wet well/drywell, wet well only with submersible pumps, and wet well only with non-submersible pumps.

Wet well and dry well: In this configuration, two pits (wells) are required: one to hold thefluid, and one to house the pumps and appurtenances (Figure 9.1). This is required for fluidsthat cannot be primed or conveyed long distances in suction piping, this option is typicallyused to pump large volumes of raw wastewater, where uninterrupted flow is critical andwastewater solids could clog suction piping. While construction costs of this type may behigher and a heating, ventilation, and cooling (HVAC) system is necessary due to installationbelow ground. This configuration is best for operation and maintenance activities becauseoperators can see and touch the equipment.

Wet well with submersible pumps: In this configuration, one well holds both the pumps andthe wastewater being pumped. The pump impeller is submerged or nearly submerged in thewastewater. Additional piping is not required in this type to convey the wastewater to theimpeller. This option is common worldwide, and the submersible centrifugal pumps can beinstalled and operated cost-effectively. When vertical pumps are installed the driving motoris mounted on the floor above the ceiling of the wet well.

Wet well with non-submersible Pumps: In this configuration, one well holds the wastewater.The pumps are installed above the water level in wet well. This option is used in areas wherethe wastewater can be pulled through suction piping e.g., treated or finished water or whereshutdowns or failures would not be immediately critical e.g., a package plants rawwastewater lift stations, equalization of secondary treated wastewater, etc.In selecting the best design for an application, environmental engineers should consider thefollowing factors: Many gases are formed by domestic wastewater, including some that are flammable.When pumps or other equipment are located in rooms below ground level, the possibilityof explosion or gas buildup exists, and ventilation is extremely important. When wastewater is pumped at high velocities or through long lines, the hammeringcaused by water can be a problem. Valves and piping should be designed to withstandthese pressure waves. Even pumps that discharge to the atmosphere should use checkvalves to cushion the surge. Coarse bar screens shall be provided ahead of pumpingstation when centrifugal pumps are installed. Most of the places dry-well design is preferred. The pumping station must be able toadjust the variation of wastewater flow. The smallest capacity pump should be able topump from the wet well and discharge at a self cleansing velocity of about 0.6 m/s.Pumping stations typically include at least two pumps and a basic wet-well level controlsystem. One pump is considered a standby pump, although the controls typically cycleback and forth during normal flows so they receive equal wear.

TYPES AND STRUCTURE OF PUMPING STATIONS

The type of pumping stations can be (a) Horizontal pumps in dry pit, (b) Vertical pumps in dry pit, (c) Vertical pumps in suction well and (d) Submersible pumps in suction sump. All these types include a sewage-receiving sump, which is called suction sump or wet well. These types of pump arrangements are shown in Figure

Undesirable OperationsThe following undesirable operations should be avoided:A. Operation at higher headA pump should never be operated at a head higher than the maximum recommended head otherwise such operation may result in excessive recirculation in the pump, and overheating of the sewage and the pump. Another problem that arises if a pump is operated at a head higher than the recommended maximum head is that the radial reaction on the pump shaft increases causing excessive unbalanced forces on the shaft, which may cause failure of the pump shaft. As a useful guide, appropriate marking should be made on the pressure gauge. Efficiency at a higher head is normally low and such an operation is also inefficient.B. Operation at lower headIf a pump is operated at a lower head than the recommended minimum head, the radial reaction on the pump shaft increases causing excessive unbalanced forces on the shaft, which may cause premature wear of bearings and possibly shaft failure if persisted. As a useful guide appropriatemarking should be made on both pressure gauge and ammeter. Efficiency at a lower head isnormally low, hence such an operation is inefficient. In such cases, it is advisable to throttle thedelivery side valve to create more head to work within safe head. This will also reduce the power. If this is a design flaw additional head has to be created at tail end by elevating the delivery. However, these are not energy efficient solutions; change of impeller to suit the actual head is the solution. C. Operation on higher suction liftIf a pump is operated on suction lift higher than the permissible value, pressures at the eye of impeller and the suction side fall below vapour pressure. This results in flashing of sewage into vapour. These vapour bubbles collapse during passage, resulting in cavitation in the pump, causing pitting on the suction side of impeller and casing, and excessive vibrations. In addition to mechanical damage due to pitting, pump discharge also reduces drastically. Typical damage to impeller and sometimes to the casing is shown in Figure. Fig. Typical Cavitation Damage of an ImpellerD. Operation of the pump with low submergenceMinimum submergence above the bell-mouth or foot-valve is necessary to prevent entry of air into the suction of the pump, which gives rise to the vortex phenomenon, causing excessive vibration, overloading of bearings, reduction in discharge and in the efficiency. As a useful guide, the lowest permissible sewage level should be marked on the water level indicator. Usually the pump manufacturer indicates the minimum height of submergence. In the case of submersible pumps, the minimum depth is needed to ensure cooling of the motor while running.E. Operation with occurrence of vorticesIf vibration continues even after taking all precautions, vortex may be the cause. Vortex should be stopped by using anti vortex fittings as described in chapter 4 of Part A of the manual: A well-planned maintenance programme for pumping systems can reduce or prevent unnecessary equipment wear and downtime. (The following maintenance information applies to both sewage and solids pumping systems.)The following is a maintenance checklist for a basic pumping-station: Check the wet well level continuously (whenever necessary). Record each pumps run time hours (as indicated on the elapsed-time meters) at least once in a day and confirm that the pumps running hours are equal. Ensure that the control-panel switches are in their proper positions. Ensure that the valves are in their proper positions. Check for unusual pump noises. At least once a week, manually pump down the wet well to check for and to remove debris that may clog the pumps. Inspect the float balls and cables and remove all debris to ensure that they operate properly. Twisted cables are to be released that may affect automatic operations. If a pump is removed from service, adjust the lead pump selector switch to the number that corresponds to the pumps remaining in operation.GATES, VALVES AND ACTUATORS

Sluice GateA sluice gate (Figure 3.3) is traditionally a wooden or metal plate, which slides in grooves in the sides of the guide channel. Sluice gates are commonly used to control sewage levels in STPs.

Dos for sluice gates Operate the gate at least once in every three months. Check the nuts of all construction and foundation bolts once in a year. Tighten the bolts, if loose. Examine the entire painted surface for any signs of damage to the protective paint.

Donts for sluice gates

Do not remove lock plates until the gate has been properly installed.

Do not keep the gate out of operation for more than three months.

Do not forget to set the stop nut in the correct position.

Do not disturb the adjustment of wedge block bolts/studs.

Do not over torque the crank handle/hand wheel.ValveOn the delivery side of centrifugal pumps, a non-return valve is necessary to prevent back-pressure from the delivery head on the pump, when the pump is shut off. To avoid water-hammer, which is likely to be caused by the closure of the valve, the valve may be provided with an anti-slam device, which may be either a lever and dead-weight type, a spring-loading type or the dash pot type.Pumps may be run in parallel with different permutation of the standbys. Isolation valves would be needed to isolate those pumps, which are to be idle. Generally, the isolating valves are gate valves,which should preferably be of the rising stem type, since this type offers the advantage of visual indication of the valve-position. For exterior underground locations, gate valves are generally used.

Gate Valve

A gate valve is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid as shown in Figure 3.4 overleaf. The distinct feature of a gate valve is that the sealing surfaces between the gate and seats are planar. The gate faces can form a wedge shape or they can be parallel. Typical gate valves should never be used for regulating flow, unless they are specifically designed for that purpose. Gate valves require maintenance as indicated overleaf:

Non-Return Valve (Check Valve)Normally, a check valve is installed in the discharge of each pump to provide a positive shutoff from force main pressure when the pump is shut off and to prevent the hydraulic force from draining back into the wet well. The most common type of check valve is the swing check valve, which is shown in Figure

This valve consists of a valve body with a clapper arm attached to a hinge that opens when the pump starts operating and closes to seal when the pump is shut off.Check valves must close before the water column in the pipe reverses flow; otherwise, severe water hammer can occur when the clapper arm slams against the valve body seat. If this occurs, an adjustment of the outside weight or spring is usually required. A traditional clapper type of check valve has a lever on the extended shaft, which allows adjustment of the weight on the arm or spring to vary the closing time. Wear occurs within the valve primarily on the clapper hinge-and-shaft assemblies and should be checked annually for looseness.Non-Return Valve (Ball Type)Non-return valve depends on a light weight and suitable coated ball moving inside the flowing pipe to occupy an elevated angular position while the fluid is in pumping and dropping back to close the reverse flow through the pipe. Because it is a sphere sitting over a circular opening, it is expected to seat properly and seal the reverse flow. The material of the ball, the coating and its sturdiness against dents caused by the slide are important aspects. The ball is replaced by opening the top flange after switching off the pump. This can be installed in any position, vertical or horizontal. A non-return valve is shown in Figure.When flow occurs, the ball is lifted into the angular piping and is held there because its weight is lighter than the sewage and the velocity of flow. When the flow stops, it slides back and seals.

Butterfly Valve

Butterfly valves are another type of valve that have been successfully used as suction and discharge isolation valves in pumping stations. They are frequently used in sewage plants where waste streams with a high solids content are encountered, such as in sludge pumping systems. A butterfly valve consists of the valve body and a rotating disc plug that operates through 90 degrees.This is usually a disc rotated by 90 degrees by external handle. In the open position, the disc is in line with the flow. In the closed position, the disc is at 90 degrees to the flow and it stops the flow. Usually, the axis is vertical although horizontal axis arrangement may also be used in smaller sizes.The closing and opening can be manual or mechanized. The butterfly valves occupy less space and are generally preferred for pipe sizes larger than 150 mm.Many agencies specify butterfly valves as opposed to gate valves because they are less susceptible to plugging.

Actuators

These are replacements for physical operation by the operators. Actuators are used for automation of valves. An actuator rotates the valve spindle or lifts and drops the same.A. Electric geared motor actuatorThe actuator consists of a rotor stator unit driving an output shaft through a single stage-worm reduction gear, which incorporates an automatic mechanical device for changing manual drive to power drive. The actuator includes a travel-limit switch unit and a torque switch unit, and is of totally enclosed construction. When power fails, electric motor driven gear actuators retain their positions. When power supply returns, pay attention how the valves move. The electric motor driven gear actuator is shown in Figure

B. SolenoidsSolenoids are the most common actuator components. It consists of a moving ferrous core (a piston) that moves inside wire coil. Normally the piston is held outside the coil by a spring. When a voltage is applied to the coil and current flows, the coil builds up a magnetic field that attracts the piston and pulls it into the centre of the coil. The piston can be used to supply a linear force. Diaphragm valve have small holes on it. The holes should be free from clogging by debris otherwise the diaphragm may not open.C. PneumaticsPneumatic systems have much in common with hydraulic systems with a few key differences. The reservoir is eliminated as there is no need to collect and store the air between uses in the pneumatic system. Also because air is a gas, it is compressible and regulators are not needed to recirculate the flow; however, since the gas is compressible, the systems are not as stiff or strong.In general, the pneumatics are liable to cause accidents such as when the air hose suddenly pulls out of the hose clamp and jets high pressure air on persons nearby. This should be avoided. The electric geared motor type is to be preferred. The pneumatic valve is shown in Figure

D. Hydraulic systemActuator (hydraulic motor and hydraulic cylinder) is operated by hydraulic fluids (hydraulic oil), which is pressurised by hydraulic pump driven by an electric motor. Generally, a smooth movement and variable speed can be achieved. Moreover, the installed relief valve can prevent the system from breakdown. It should be noted that hydraulic oil leaks as pressure increases. Check for oil leakage regularly. Hydraulic system should be kept clean because it is vulnerable to dust or rust. Take precautions to avoid fires because the hydraulic oil is combustible.SCREENScreenings in sewage from the incoming sewer below the ground level need to be separated and lifted above ground level, and removed either by mechanical or manual method.Types of Screens

Coarse ScreensCoarse screens are usually bar screens consisting of vertical or inclined bars spaced at equal intervals across a channel through which sewage flows. The openings are usually 25 mm.Hand-cleaned screens are usually inclined at 45 degrees to the horizontal.

Medium Bar ScreensMedium bar screens have clear openings of about 12 mm.

Fine ScreensFine screens are mechanically-cleaned devices. Fine screens may be of the drum or disc type, mechanically cleaned and continuously operated. They are also used for protecting the beaches where untreated sewage may have to be discharged into the sea for disposal by dilution.

ELECTRICAL AND INSTRUMENTATION FACILITIES

INTRODUCTIONElectrical systems that are to supply electrical power for an entire STP consist of power receiving and transforming equipment, power distributing equipment, cables, drives and standby generators.Instrumentation facilities are also installed for the purpose of measuring and collecting process data such as flow rate, pressure, water qualities, and so on, at all times. These are utilized to monitor and control treatment processes at optimal conditions for a stable treatment. The instrumentation facilities consist of sensors for processes, signal converters, operating devices (actuators), controllers (PLC: Programmable Logic Controller), monitoring devices (PC: personal computer), etc. This section describes the following electrical and instrumentation facilities: A. Power receiving and transforming equipment (Substation & transformers) B. Standby power supply system (Generators, Engines, UPS: Uninterruptible Power Supply) C. Prime movers and motor controllers (Motors, Starters, Cabling) D. Instrumentation system E. Supervisory control and data acquisition system (SCADA)A typical single line diagram (SLD) depicts the entire electrical power flow system of an STP. The single line diagram not only presents the type and number of equipment but also the electrical specifications. This is an important document for an O&M person who would like to refer to it in case of any operational or maintenance need. Every STP should have: A SLD kept for record and displayed properly in the STP facility particularly near the electrical sub-station SLD periodically reviewed and updated suitably in case of any change All those personnel involved in the electrical and instrumentation work should understand the SLD.

POWER SUPPLY SYSTEM

Power supply systems have the following three major functions: Transfer power from the transmission system to the distribution system Reduce the voltage to the specified level (Typical voltage level is 415 volt for STPs) suitable for connection to local loads Protect the entire network by identifying and isolating electrical faults selectivelyPower Receiving and Transforming EquipmentIf the STP facility receives the electrical supply at high voltage i.e., 66kV, 11kV, 6.6 kV, or 3.3 kV, it has to be reduced to the operating voltage level, which is usually 415V. A substation, which is used to step-down high voltage to low voltage, consists of the following equipment or devices:

High Tension (HT) Substation

The HT substation is composed of the following equipment and devices.

Disconnecting Switch

Disconnecting switches are devices to open/close a high voltage circuit when high-voltage equipment are inspected, tested or cleaned. The devices are capable of safely breaking no-load current but not load current. For safe O&M work, be sure to open/close the disconnecting switch only after opening a circuit breaker, which is located on the secondary side, just downstream of the disconnecting switch.

Circuit Breaker

Circuit breakers are switches that open/close electric-circuits in normal and abnormal conditions (especially in short circuit). Therefore, the circuit breakers must be capable of tripping the circuits in conjunction with protective relays and by cutting off the short-circuit current definitely and safely, avoiding accidents due to high current.Circuit breakers for high voltage are categorised into the following types according to their techniques of eliminating arcs: A. Air Circuit Breakers (ACB)B. Vacuum Circuit Breaker (VCB)C. Inert Gas Method (SF6)

Power Fuses

The function of a power fuse is to sense and prevent flow of excess current in electrical devices and electrical wire by melting the fuse element and thereby breaking the electric circuit when subjected to a short-circuit. Power fuses are typically used for smaller electrical systems because they have the capability and speed for breaking the circuit as compared with circuit breakers.A proper O&M, practice is that even if only one fuse melts due to an accident such as a short-circuit in a three phase switch, all power fuses including the melted one should be replaced.

Voltage Transformer (VT) or Potential Transformer (PT)

Voltage transformers are used mainly in high-voltage distribution equipment to step-down voltage in measurement circuit for safe measurement; single-phase and three-phase types are manufactured. The typical secondary voltage of the voltage transformer is 110 volt (Phase-to-Phase). They are also applied to protective relays.O&M issues to be observed in case of a PT are as follows: If once short circuit occurs on the secondary side of a VT, excess current flows into the primary side and that may cause the fuse on the primary side to blow. The primary fuse has also to be checked when there is a fault trip or metering mismatch.

Current Transformer (CT)

Current transformers are used for stepping down current to be measured safely. It is also applied to protective relays. The typical secondary current of the current transformer is 5 Amp or 1 Amp.O&M issues to be checked are as follows: If the secondary side of CT is open-circuited, all the current flowing to primary side is excited by magnetic saturation and causes damages to the CT by over-heating. Therefore, the secondary side should never be left open-circuited. Even when the downstream instrument is removed for any repair, the secondary should be shorted.

Protective Relay

Protective relays should detect electrical faults promptly, isolate the faults from system and activate alarms when there is a faulty condition sensed in the electrical supply to the circuits or electrical equipment (short circuit, earth fault, single-phase, reverse power flow etc.)The protective relays should have the following three characteristics: A. Certainty: The relay should always be sensing the parameters for action when there is a fault or specified abnormality. B. Selectivity: The relay should obey a selection of the limits beyond which a fault will be judged. C. Promptness: The relay should sense and operate within the shortest possible time.Categories according to protective functions are as follows: A. Over current relay (OCR): Monitor and protect against over load and short-circuit. B. Under voltage relay (UVR) and over voltage relay (OVR): Detect and protect under voltage (power failure) or over voltage. C. Earth fault relay: Protect by detecting current leakage to earth.

Categories according to design as follows.

An electrochemical protective relay converts the voltages and currents to magnetic and electric forces and torques that press against spring tensions in the relay. The tension of the spring and taps on the electromagnetic coils in the relay are the main processes by which a user sets a relay. In a Solid State relay, the incoming voltage and current waveforms are monitored by analog circuits, not recorded or digitized. The analog values are compared to settings made by the user by a potentiometer in the relay. A Digital Relay converts all measured analog quantities into digital signals. Compared to static relays, digital relays introduce Analogue to Digital Converter (A/D conversion) of all measured analogue quantities and use a microprocessor to implement the protection algorithm. The microprocessor may use some kind of counting technique, or use the Discrete Fourier Transform (DFT) to implement the algorithm. Since late 1990s most of the protective relays are of digital type. Advantages of Digital Relays High level of functionality integration Additional monitoring functions Functional flexibility Capable of working under a wide range of temperatures. Internal power requirement is very low. They can implement more complex functions and are generally more accurate Self-checking features and self-adaptability Able to communicate with other digital equipment of contemporary design Less sensitive to temperature-related aging Economical because can be produced in required numbers and can be set at site More accurate Signal storage is possibleLimitations of Digital RelayThe devices have short lifetime due to the continuous development of new technologies. Needs to be protected against power system transients As digital systems become increasingly more complex they require specially trained staff for operation Proper maintenance of the settings and monitoring dataThese limitations are overcome by progressive improvements in design, ruggedness, cost, low power and heat generation factors, standardized modular design, scalability and simpler training to operating staff.

Transformer

A transformer is the most important component in substations. Transformers receive electrical power at high voltage and transform it to lower service voltage. They also provide isolation between high voltage and low voltage supply.Cooling system for oil-immersed transformer: Oil serves as direct cooling medium to disperse the heat that is generated from windings and core. The oil is in turn cooled by indirect cooling medium such as air at the oil radiator.Cooling system for dry transformer: Utilize surrounding air or SF6 as cooling medium.Transformer Efficiency: The efficiency of a transformer varies between 96% and 99%. It not only depends on design, but also on operating load. The transformer losses are mainly attributed to: Constant Loss: This is also called iron loss or core loss, which mainly depends upon the material of the core and magnetic circuit of the flux path. Hysteresis and eddy current loss are two components of constant loss. Variable Loss: This is also called load loss or copper loss, which varies with the square of the load current.The best efficiency of a transformer occurs at a load when constant loss and variableloss are equal. For distribution transformers, installed in an STP, the best efficiency would occur around 50% load.O&M checks to be made are as follows: Check connections of cables for looseness and overheating Check the transformer for abnormal vibration and noise Check oil and winding temperature regularly with respect to manufacturers manual Check for moisture ingress by observing the colour of the silica gel Check for level of oil in the conservator

Low Tension (LT) Panel

LT panels or LT switchboards are designed to distribute stepped-down voltage to power equipment and control panels. They typically consist of moulded case circuit breakers (MCCBs), power contactors (PCs), protective relays (PRs), meters, indication lamps, control switches, etc.

A. MCCB

An MCCB is designed to open/close low voltage feeder circuit or branch circuit at normal condition. It also breaks the circuit automatically in case of abnormal condition such as overload, short circuit, etc.

B. Power Contactor

A power contactor is typically used for on / off control of motors. A relay can be installed on the circuit for overload protection. Electromagnetic force works to open /close the contacts. The O&M checks to be made are as follows: Check for abnormal noise or overheating of exciting coils, abnormal noise and discolouration of contacts (carbonized or worn contact surfaces by arcing) Check for the proper working of all display indicators like voltmeters, ammeters, energy meters.Bus-bar

Bus-bars are conductors to carry power among the various components in the power circuit in an outdoor station or distribution board. They are to be rated to carry the maximum rated current continuously and short-circuit current for a short time without damage.The O&M issues to be cared for: Check connections for looseness and overheating, and check the bus bar for discolouration Check bus bars are properly colour coded (Red, Yellow or Blue) to represent the phases Check bus bars are properly enclosed within panels.

SEWAGE PUMPING STATION AS WE SAW IT

Fig. Layout of Pump House of ISLS-V in NEW TOWN,KOLKATA

DRAINAGE PUMPING STATION-AS WE SAW IT

Drainage pumping station are used to pump out the wastewater and surface water including storm water but not sewerage.This type of pump station are consisted of 1.Sump2.Vertical turbine pumps- 3592 m^3/hour * 8MLC , 150 kw motor.3.Lubricating pumps- 5 m^3/hour * 8 MLC , 22 kw / 3 HP motor. 4.Valves.5.Piping arrangement.6.Step down (11kv/430v) transformer.7.L.T Control Panel.

Fig.1(top) : Layout of a pump station.Fig.2(bottom left & right) : VT Pumps & piping system.

CONCLUSION

In conclusion , We would like to say that , we have tried our level best to carefully and sincerely know all the aspects of Drainage and sewage pumping systems . The operation and management of day to day work done in these systems was the real things to learn . We have prepared this report from our mechanical engineering viewpoint. This training have exposed us to the professional world . We have sensed how to deal real world problems . Overall , we learnt to apply our bookish knowledge to practical field and at the end of the day , we feel much needed completeness of our engineering education in a very successful way due to the training at Public Health Engineering Department.

References

1.Sewage-handbook

2.Course : Wastewater Management Prof. M.M. Ghangrekar,IIT Kharagpur

3.National Programme On Technology Enhanced

Learning, MHRD

4.Central Public Health And Environmental Engineering

Organisation (CPHEEO) Manuals.

5. Flood Control Pumping Stations_US-LOW-web

6. Pumps & Drainage Brochure