AIROLI, NAVI MUMBAI – 400 708 2011 – 2012
Civil Engineering Department A Project Visit Report on:
Bhandup Complex – Water treatment Plant
Name: __________________________ _______________________________________ __________________________ ________________ ___ Class: ___________ Div: __________ Roll No: _______ Batch: ________
A report submitted in partial fulfillment of the requirements of UNIVERSITY OF MUMBAI In ENVIRONMENTAL ENGINEERING - I
GENERAL The Municipal Corporation of Greater Mumbai was formed way back in the year 1865 1865 as Mumbai’s civic civic body. The M.C.G.M. is variably variably the cradle of
Local Self Government of India.
It embodies the principle of democracy democracy of
“Governance “Governance of the People, by the people, for the people”.
Through the multifarious civic and recreational services that it provides, the M.C.G.M. has always been committed to improve the quality of life of Mumbai. M.C.G.M. covers an area over 437.71 square Kilometers, catering to the civic needs of over 1.25 crores Citizens. The Corporation operates an annual tilizati outlay of more than Rs.9,000/- crores. Most of the functions carried out by this Corporation are service oriented. The service offered includes Sanitation, Health (Public Health Care and Secondary Health Care Services through its Hospitals, Maternity, Child Health Care Units, Dispensaries and Field Services) Water, Community service, Primary Education and Town Planning etc. The Hydraulic Engineer’s Department is the one responsible for supply of
potable to the city of Mumbai. The present water sources are – Tulsi
18 MLD
0.5 %
Vihar
90 MLD
2.6 %
Tansa
440 MLD
13.10 %
Modak Sagar
455 MLD
13.10 %
Upper Vaitarna
635 MLD
18.85 %
Bhatsa
1830 MLD
51.82 %
TOTAL
3368 MLD
100%
DRINKING WATER STANDARDS As per BUREAU OF OF INDIAN STANDARDS STANDARDS (BIS 10500: 1991) Sr.
Substance or Characteristic Characteristic
No
Requirement
Permissible Permissible Limit
(Desirable Limit)
in the absence of Alternate source source
ESSENTIAL CHARACTERISTICS 1.
Colour Hazen units, Max
5
25
2.
Odour
Unobjectionable Unobjectionable
Unobjectionable Unobjectionable
3.
Taste
Agreeable
Agreeable
4.
Turbidity NTU, Max
5
10
5.
pH Value
6.5 to 8.5
No Relaxation
6.
Total Hardness (as CaCo3) mg/lit., Max
300
600
7.
Iron (as Fe) mg/l, Max
0.3
1.0
8.
Chlorides (as Cl) mg/l, Max.
250
1000
9.
Residual free chlorine mg/l, Min
0.2
--
DESIRABLE CHARACTERISTICS 10. Dissolved solids mg/l, Max
500
2000
11. Calcium (as Ca) mg/l, Max
75
200
12. Copper (as Cu) mg/l, Max
0.05
1.5
13. Manganese (as Mn) mg/l, Max
0.10
0.3
14. Sulfate (as SO4) mg/l, Max
200
400
15. Nitrate (as NO3) mg/l, Max
45
100
16. Fluoride (as F) mg/l, Max
1.9
1.5
17. Phenolic Compounds (as C6H5OH) mg/l, Max
0.001
0.002
18. Mercury (as Hg) mg/l, Max
0.001
No relaxation
19. Cadmiun (as Cd) mg/l, Max
0.01
No relaxation
20. Selenium (as Se) mg/l, Max
0.01
No relaxation
21. Arsenic (as As) mg/l, Max
0.05
No relaxation
22. Cyanide (as CN) mg/l, Max
0.05
No relaxation
23. Lead (as Pb) mg/l, Max
0.05
No relaxation
24. Zinc (as Zn) mg/l, Max
5
15
Water treatment describes those processes used to make water more
acceptable for a desired end-use. These can include use as drinking water, industrial processes, medical and many other uses. The goal of all water treatment process is to remove existing contaminants in the water, or reduce the concentration of such contaminants so the water becomes fit for its desired enduse. One such use is returning water that has been used back into the natural environment without adverse ecological impact. The processes involved in treating water for drinking purpose may be solids separation using physical such as settling and filtration, chemical such as disinfection and coagulation. Biological processes are also employed in the treatment of wastewater and these processes may include, for example, aerated lagoons, activated sludge or slow sand filters . There are two major water treatment plants namely Bhandup Complex within the Mumbai City and Pise- Panjrapur Complex about 25 kms. from the Mumbai City Limits. Limits.
The water from Tansa, Modak Modak Sagar, Upper Vaitarna and
part of Bhatsa (Injection) is treated at Bhandup Complex having capacity of 1910 MLD. French company Degremont Suez, which had set up the 1910 MLD water treatment plant at Bhandup in 1981, is Asia’s largest wa ter treatment plant. This plant is continuously working from last 28 years. This plant controls 70 per cent of the city ’s water supply and was recently awarded the ISO 9001-2000 certification for consistent high quality water treatment. The application of new techniques helps to reduce the wastage of water and the plant can treat t he 2100 MLD water which is greater than its designed capacity.
The combination of following processes is used for m unicipal drinking water treatment worldwide:
Pre-chlorination – for algae control and arresting any biological growth
Aeration – along with pre-chlorination for removal of dissolved iron and manganese
Coagulation – for flocculation
Coagulant aids also known as polyelectrolytes – to improve coagulation and for thicker floc formation
Sedimentation – for solids separation, that is, removal of suspended solids trapped in the floc
Filtration – for removal of carried over floc
Disinfection – for killing bacteria
Purification of water at Bhandup Water Treatment Plant Prechlorination of Raw water from the sources
Supply of Raw water from through 1 km Horse shoe tunnel to the plant
Aeration
Feeding of Coagulant (PAC) and Mixing
Flocculation cum Sedimentation
Filtration (Rapid Gravity Filters)
Disinfection (Postchlorination)
Storage and Distribution from MBR
1. Prechlorination: The addition of chlorine at the head works of a treatment plant prior to other treatment processes. Done mainly for disinfection and control of tastes, odours, and aquatic growths, and to aid in coagulation and settling, The normal dosage of this treatment plant for pre chlorination of water is 3.0 mg/l. After giving dosage to the water the water is flowed to the 1 km long horse shoe type formation tunnel in which contact of chlorine with raw water takes place.
2. Supply of Raw Waters from Sources to the plant: Raw water from different sources are brought to the plant in a 1 km long Horse shoe type tunnel by means of 4 water mains. Generally raw water of turbidities 40 – 45 NTU during normal flow and 80 NTU during the rains. The water is treated so as to achieve turbidity less than 5 NTU. After reaching the treatment plant the Raw water is divided into 2 types Inlet bays one of 3 m depth and other of less than 3 m. The water is divided into four streams/sections A, B, C & D.
3. Aeration: Aeration is a unit process in which air and water are brought into intimate contact. Turbulence increases the aeration of flowing streams. In industrial processes, water flow is usually directed countercurrent to atmospheric or forceddraft air flow. The contact time and the ratio of air to water must be sufficient for effective removal removal of the unwanted gas. Aeration as a water treatment practice is used for the following operations:
Carbon dioxide reduction.
Oxidation of iron and manganese found in many well waters (oxidation tower).
Ammonia and hydrogen sulfide reduction (stripping).
Aeration is also an effective method of bacteria control.
Types of Aerators:
Four types of aerators are in common use: (i)
Gravity aerators
(ii)
Spray aerators
(iii)
Diffusers, and
(iv)
Mechanical aerators
The Treatment plant in Bhandup uses Gravity aerators in which cascade type arrangement is made for the purpose of aeration.
Spray Aerators
4. Feeding of Coagulant and Mixing: Accepters extensive range of high performance organic and inorganic coagulants have been developed to significantly enhance the coagulation of suspended solids across a range of industrial applications involving process water treatment, treatment, wastewater and effluent treatment. At this treatment plant the alum was used as a coagulant. But due to advantages of PAC (Poly-Aluminum Chloride) over Alum such as efficiency and dosage required, now a days PAC is used as coagulant. After pre chlorination and aeration, the water comes in mixing basing. In mixing basin PAC coagulant is added and mixed in water by creating the turbulence by freefall of water from 0.9 m height. After this the water is pumped in to Clariflocculator.
5. Clariflocculator: Clariflocculator unit is a combination of both flocculation and clarification in a single tank. This unit consists of concentric circular compartments. The inner compartment is the flocculation chamber and the outer compartment is the clarifier. The chemically dosed water is uniformly distributed over the surface of the flocculation compartment for effective effective
tilization of the the available available volume for
flocculation. The specially designed flocculating paddles enhance flocculation of the feed solids. As heavy particles settle to the bottom, the liquid flows radially outward and upward and the clarified liquid is discharged over a peripheral weir into the peripheral launder. The deposited sludge is raked to the bottom near the central pocket from which it can be easily discharged. At this Treatment plant the rectangular Sedimentation tank with the circular flocculation tank in center of it and its size is 44 m length, 44m breadth, 7.5m depth in center and 5.5m depth in corners. The Clariflocculator is of 17m diameter and it consists of sludge removal pump and scrapers rotating on 2-3 rpm for
removal of sludge. This treatment plant has 20 Clariflocculator of this size and its capacity of each one is 12.5 MLD water. The water comes into the flocculation tank from mixing basin. Some amount of raw water is aided in to flocculator for proper formation of floc. Then water goes in clarifier (sedimentation tank) for sedimentation. sedimentation. The detention period of flocculator is 15 minutes and that of clarifier is 2 hours 15 minutes. Thus the total detention time of this Clariflocculator is 2 hours and 30 minutes. The quantity of sludge formed in this process is around 3% of raw water. The process of removal of sludge is done at night only. The water is then passed to Rapid gravity filters for filtration.
Em t
Full
Night View
Different Views of Clariflocculator
6. Filtration: Filtration is the most relied water treatment process to remove particulate material from water. Coagulation, flocculation, and settling are used to assist the filtration process to function more effectively. The coagulation and settling processes have become so effective that sometimes filtration may not be necessary. However, where filtration has been avoided, severe losses in water main carrying capacity have occurred as the result of slime formation in the mains. Filtration is still essential. Rapid Sand filters are used to serve the purpose of filtration in BWTP. Rapid sand filters use relatively coarse sand and other granular media to remove particles and impurities that have been trapped in a floc through the use of flocculation chemicals – typically salts of aluminum or iron. Water and flocs flows through the filter medium under gravity or under pumped pressure and the flocculated material material are trapped in the sand matrix. Rapid sand filters must be cleaned frequently, once in a day, by backwashing, which involves reversing the direction of the water and adding compressed air. During backwashing, the bed is fluidized and care must be taken not to wash away the media. The process, called “BACKWASHING”, involves several steps. First, the filter is taken off line and the water is drained down to the filter bed. Then, the air wash cycle is started which pushes air up through the filter material causing the filter bed to appear to boil. This breaks up the compacted filter bed and forces the accumulated particles into suspension. After the air wash cycle stops, the backwash cycle starts with water flowing up through the filter bed. Clean water is passed through the filter bed in order to wash the material and remove most of the accumulated particles. This cycle continues a fixed time or until the turbidity of backwash water is below a set value. In some cases, the additional step of
air/water wash (simultaneously) is done after air wash cycle and followed by rinse water wash. This useless water compared to traditional step and has higher removal efficiency efficiency which results in the cleaner filter. This treatment plant is having 4 stakes of rapid sand filters and each stake is consisting of 18 numbers of rapid sand filters. Thus this plant is having total 72 numbers of rapid sand filters. The size of each filter is 15m x 11m and it filters around 300 liter water per second. Each filter are having 8000 numbers of filtering nozzles and filter media of 5cm thick 4mm sand and 90cm thick 0.8mm sand. The depth of this filters are 2.5m up to the top of filter media.
Rapid Gravity Filter
7. Disinfection: Chlorination became the accepted means of disinfection, and it is the single most important discovery in potable water treatment. Recently, however, the concern over disinfection by-products (DBPs) produced by chlorine has given new impetus to investigating alternative disinfectants. Disinfection of potable water is the specialized treatment for destruction or removal of organisms capable of causing disease; it should not be confused with sterilization, which is the destruction or removal of all life. Pathogens (disease producing organisms) are present in both groundwater and surface water supplies. These organisms, under certain conditions, are capable of surviving in water supplies for weeks at temperatures near 21° C, and for months at colder temperatures. Destruction or removal of these organisms is essential in providing a safe potable water supply. Post-chlorination is done to filtered water at Bhandup water treatment plant is done at CCT (Chlorine Contact Tank), where more chlorine is aided to the water for disinfection purpose and to remove pathogenic bacteria from water. The detention period of this tank is 30 minutes.
Chlorine contact chamber
8. Storage and Distribution from MBR: The water is then pumped to the Master balancing (MBR) reservoir from which the water is distributed under gravity type of distribution to other 26 Elevated storage reservoirs (ESR). In distribution reservoirs again chlorination is done for disinfection purpose
in distribution system, this process is called as “Booster Chlorination”. This time the dosage of chlorine is around 2-3 mille grams per liter. In water treatment plant, adequacy of water treatment from health point of view is ensured by maintaining residual chlorine of 0.2 to 0.1 mg/l at the farthest point of distribution system.
Internal View of an MBR
TESTING OF WATER The Water being treated is tested at various stages of treatment which was described above. It has facilities for carrying out tests like: 1.
Turbidity:
Turbidity is measured in NTU: Units.
Nephelometric A
digital
Turbidity laboratory
turbidimeter was used (as shown in figure below) which gives turbidity directly in NTU after placing a test tube containing water to be tested on left side of the device. 2.
Jar Test:
The jar test is a reliable method for determining the proper chemical dosages and conditions for coagulation of water to remove color and turbidity. This method allows adjustments in pH, variations in coagulant or polymer dose, alternating mixing speeds, or testing
of
different
coagulant
or
polymer types, on a small scale in order to predict the functioning of a large scale treatment operation. A jar test simulates the coagulation and flocculation processes that encourage the removal of suspended colloids and organic matter which can lead to turbidity, odor and taste problems.
The jar test procedure involves the following steps:
1. Fill the jar testing apparatus containers with sample water. One container will be used as a control while the other 5 containers can be adjusted depending on what conditions are being tested. For example, the pH of the jars can be adjusted or variations of coagulant dosages can be added to determine optimum operating conditions. 2. Add the coagulant to each container and stir at approximately 100 rpm for 1 minute. The rapid mix stage helps to disperse the coagulant throughout each container. Coagulants are chemical additions, such as metallic salts, which help cause smaller aggregates to form larger particles. 3. Reduce the stirring speed to 25 to 35 rpm and continue mixing for 15 to 20 minutes. This slower mixing speed helps promote floc formation by enhancing particle collisions which lead to larger flocs. These speeds are slow enough to prevent sheering of the floc due to turbulence caused by stirring to fast. 4. Turn off the mixers and allow the containers to settle for 30 to 45 minutes. Then measure the final turbidity in each container. The final turbidity can be evaluate roughly by sight or more accurately using a nephelometer. 3.
Chlorine Content:
The orthotolidine (OT) test permits the measurement of relative amounts of total residual chlorine, free available chlorine, and combined available chlorine. This test has some limitations. Samples containing a high proportion of combined available chlorine may indicate more free available chlorine than is actually present, while samples samples containing a low low proportion of combined combined available chlorine may indicate less free available chlorine than is actually present. Precise results depend on strict adherence to the conditions of the test. The
conditions are the time time intervals between between the addition of reagents reagents and the relative relative concentration of free available chlorine and an d combined available a vailable chlorine in the sample and the temperature of the water. The temperature temperature of the sample under examination should never be above 68°F (20°C). The precision of the test increases with decreasing temperature. EQUIPMENT: Either a disk or slide comparator may be used in
performing the orthotolidine orthotolidine test. A disk comparator comparator is shown in figure. This This comparator consists of a standard color disk and two sample tubes. Water to be tested is placed in both tubes. Reagent is added to one and the resulting color matched with the disk. The other tube is placed behind the disk to eliminate any color error that might be caused by turbidity in the test sample. The only reagent used is a standard orthotolidine solution. 4.
MPN Test: Coliform Bacteria Test
This test is used when the water cannot be filtered due to turbidity, high iron, large amounts of sediment, or high non-coliform bacteria count. This test involves incubation of measured volumes of sample in liquid nutrients which favor the growth of any coliform bacteria present. This is a statistical method of testing based on the number of positive tubes of media after 48 hours of incubation and 48 additional hours of confirmation. The procedure can be represented by the following diagram.
MPN test
CONCLUSION The Site visit to Bhandup Water Treatment plant has given us an opportunity to think in a broader aspect of Water purification and its supply. The in depth knowledge earned by the visit will be very useful with respect to our studies and in the near future too.
Thank you
