Says about the Water treatment plants in kerala

1. WATER TREATMENT PLANTS
KWA, ARUVIKKARA

2. CONTENTS
 INTRODUCTION
 75 MLD PLANT
 86 MLD PLANT
 74 MLD PLANT
 72 MLD PLANT

3. INTRODUCTION
 INTAKE SOURCE
 The water for the treatment purpose is taken from the Aruvikkara dam reservoir supported by
Peppara Reservoir Dam.
 It was built by the Kerala Water Authority in 1983 has a catchment area of 83km² and receives an
average rainfall of 481 cm.
 It is the main drinking water supply to Thiruvananthapuram city and suburban areas.

4.  RAW WATER PUMP HOUSE
 There are two raw water pumping stations for the intake. One is located near the dam and the
other is constructed in the Chithirakunnu region.
 The one located near the dam is used to pump water to the 75 and 72 MLD treatment plants
and the latter is used for pumping water to the 86 MLD and the 74 MLD plants.

5. 75MLD PLANT
 The 75- MLD water treatment plant has different levels of process in it
 Intake
 Aeration
 Flash Mixer
 Flocculator
 Clarifier (lamella clarifier)/plate settler
 Filtration
 Disinfection
 Clear Water Pumping

6. HYDRAULIC FLOW DIAGRAM OF 75MLD PLANT

7. INTAKE
 Using 600 Hp centrifugal motors the water is transported to the aerator of the 75 MLD plant through
1000mm diameter pipes. The raw water pump house uses 2 type of motors, Submersible motor with 537
Hp and centrifugal motors with 600 Hp, for pumping the water to the water treatment plants.

8. AERATION

9. FLOCCULATOR
 The flocculator helps to flock the impurities present in the water after the aeration. Before flocculation
the water is mixed with alum and lime to adjust the pH level of the water. The alum and lime used in the
mixing are first grade.

10. CLARIFIER
 The clarifier type used in 75 MLD plant is lamellar type. In this level the filtration and settlement of the
flocks and other heavy materials present in the water is done by flowing the water through the lamellae
present.
 As the water flows through lamellae the heavier particles present in the water will settle in the bottom
part of the lamellae as the arrangement of the lamellae is in a certain angle which will settle the heavier
particle.
 Cleaning of the clarifiers are done every day by removal of the lamellae and cleaning them individually.

11. FILTRATION
 The filtration process in the 75 MLD plant is so basic, done in old times, which is sand filtration. The filter
bed uses different size of gravels and sand for the filtration process.
 The filter media is set up so that the first layer is made up of 50mm x 38mm gravel that is 100mm deep,
the second layer is made up of 38mm x 12mm gravel that is 100mm deep, the third layer is made up of
12mm x 6mm gravel that is 100mm deep, the fourth layer is made up of 6mm x 2.5mm grit that is
150mm deep, and the top layer is made up of sand that is 0.7 mm in effective size.
 The sand is usually cleaned by forcing the air to pass through them from the bottom of the sand bed for
a short time and next by flowing pressurized water form the bottom layer, this process will wash out all
the impurities present in the filter bed.

12. DISINFECTION
 After the filtration the water is flown to the main pipe to the clear water pump house. When
the water reaches the main pipe the disinfection process takes place.
 The disinfection is done by mixing the water with a certain amount of chlorine in it. By doing
this the small microorganisms, like bacteria and other amoebic bodies, would die and the
water is good for drinking purpose.
 The amount of chlorine used is decided by the amount of E coli present in the water.

13. CLEAR WATER PUMPING
 After these processes the water reaches the clear water pump house where the cleared and filtered
water, which is ready to use, is pumped to the brake pressure tank. The clear water pump house uses 470
Hp motors to pump the water to the tank.

15. 86 MLD PLANT
 GENERAL
 INTAKE
 AERATION & CHEMICAL ADMINISTRATION
 CLARIFLOCCULATION
 FILTRATION
 DISINFECTION

17. GENERAL
 The 86 MLD WTP was commissioned on 1999 January 26.It is located at Chithirakunnu region of
Aruvikkara.

18. INTAKE
 Two horizontal centrifugal pumps with a combined power of 637 HP each are used for the intake at the
raw water pump house. The pump spins at a speed of 740 rpm and can discharge 3999.96 m3 per hour.
Through a 1200 mm cast iron pipe the raw water is released into the intake channel.

19. AERATION AND CHEMICAL ADMINISTRATION
 Through perforated PVC pipes, the appropriate amounts of the chemicals , alum and lime are added into
the inflow channel . The water is then run through an RCC Parshall flume mostly for aeration purposes.
The water is then poured through gravity into a second mixing container with two compartments.

20. CLARIFLOCCULATION
 The RCC flash mixer of dimensions 3x3x3.4 meters, with a capacity of 30 m3 receives the water from the
mixing chamber. There is an overflow tank available that serves as a warning in the event of a
clariflocculator overflow and prevents one.
 Water is poured into the centrally driven bucket type clariflocculator after being mixed.
 There are two RCC clariflocculators, each measuring 43 MLD.
 Each clarifier has a 43.2 meter diameter, a 4.5 meter side water depth (SWD), and a 192 minute
detention time.
 There are 4 flocculator agitators in each clariflocculator. If the NTU value is greater than 50, only
one agitator is used. If it is greater than 100 NTU, 150 NTU and 200 NTU, two, three and four
agitators are used respectively. The bridge is rotated 1 time per 8 hours if the NTU value is greater
than 200.

21. FILTRATION
 For filtering, there are six twin quick RCC gravity sand filters with 14 MLD and sizes 4.2 m x 12.0 m each .
 The filter media is set up so that the first layer is made up of 50mm x 38mm gravel that is 100mm deep,
the second layer is made up of 38mm x 12mm gravel that is 100mm deep, the third layer is made up of
12mm x 6mm gravel that is 100mm deep, the fourth layer is made up of 6mm x 2.5mm grit that is
150mm deep, and the top layer is made up of sand that is 0.7 mm in effective size and is 700 Out of the
4 WTPs, the filtration rate is 5.8 m3/m2/hr., which is the highest.
 The backwashing is done at suitable intervals depending on the turbidity. There are 3 numbers of air
blowers 30 HP each and 2 number of wash water pump each of 40 HP for backwashing purpose. An RCC
wash water tank is provided with a capacity 750 m3 is constructed for storing wash water.

22. DISINFECTION
 Through a chlorinator, chlorine gas is used to disinfect. The 86 MLD chlorination unit is equipped with
chlorine gas leak absorption system. Following chlorination, water is kept in a 29.5 m × 30 m x 6 m clear
water RCC sump before being pumped into the BPT's top chamber.

23. 74 MLD PLANT
 GENERAL
 INTAKE
 CHEMICAL ADDITION, AERATION & MIXING
 PULSATOR TYPE FLOCCULATOR
 FILTRATION
 DISINFECTION

25. GENERAL
 This 74 MLD plant, located at Chithirakunnu, was inaugurated by Sri. V S Achuthanandan, former Chief
Minister of Kerala, on 18th May 2010 and is under Japan International Cooperation Agency (JICA)
assisted Kerala water supply project. It was designed, built and is operated by SUEZ Degremont Pvt LTD.
The company uses its patented pulsator technology in this treatment plant.

26. INTAKE
 The intake is done by 3 centrifugal pumps with 2 working and 1 standby .Here also an additional 5-10
MLD can be pumped using submersible pump at raw water pumping house.

27. CHEMICAL ADDITION, AERATION & MIXING
 Chemicals, alum and lime, stored in chemical house is added in the inlet channel and allowed for
aeration and mixing in the mixing chamber.
 The chemicals are prepared in respective dosing unit .
 But with respective to dosing units in other plants, here there is another mechanism called saturator for
lime, where it provides clearer solution of lime. There are 2 such saturators and is equipped with a
constant head tank, which will indicate the level of solution in saturator and prevent from overflowing.

28. PULSATOR TYPE FLOCCULATOR
 Once the chemicals are mixed with the raw water, it is taken to the pulsator unit. The pulsator unit
consists of a total of 4 pressure chamber .
 In each pulsator, water first enters a central vacuum chamber which consists of air compressor and a
vacuum breaker valve.
 The air compressor runs continuously whereas the valve keeps opening and closing. There are 2 air
compressors in chamber where one will be working and other is a standby. When the valve closes, the
running blower/ air compressor generates a sucking action inside the chamber causing the water to rise
up in it.
 Once the water reaches a level, the valve opens and atmospheric air enters the chamber pushing the
water down. This creates a pulsating action of water within the chamber. The water from the chamber
flows through a channel with a lateral perforated pipe.
 The perforations are present only at the bottom. In between adjacent laterals, above them, stilling plates
are provided so that the upcoming water’s energy is reduced. The perforated pipes are laid at the
bottom of a rectangular pulsating chamber. The pulsating action in the central vacuum chamber is
reproduced in this chamber leading to the formation of a sludge blanket. Sludge blanket can be defined
as a layer of high concentration of impurities. Once the water fills the chamber, the solid particles begin
to settle. This settling is interrupted by the pulsating action and they remain in suspension. The sludge
blanket is formed at a height of approximately 1.5m from the bottom.

31. FILTRATION
 74 MLD uses Aquazur V filter. There are 6 such filters with a sand depth of about 1m. Uniform sand with
an effective size of about 0.95 is used. The use of uniform sand helps in utilization of the complete depth
of sand layer.
 The advantage of V-filters is that it minimizes the amount of water required for backwash. The unfiltered
particles coming up with the water may settle back before reaching the central channel resulting in a
larger amount of time for backwash. To prevent this, side wash is provided by passing raw water through
the V shaped inlet. This will ensure better flow towards the central channel and since raw water is used
for the purpose, water requirement will also be low.
 This filter needs a backwashing every 72 hours and a backwashing time of approximate 30 minutes.
Another merit in this WTP is that it recycles the backwashing water and uses again as raw water for
treatment.

32. Filtration Process Backwash Process

33. DISINFECTION
 Disinfection is done in two stages- pre chlorination & post chlorination in chlorine contact tanks. The
chlorinated water is stored in the sump tank and pumped to BPT.

34. 72 MLD PLANT
 GENERAL
 INTAKE
 AERATION & CHEMICAL ADMINISTRATION
 COAGULATION
 CLARIFLOCCULATION
 FILTRATION
 DISINFECTION

36. GENERAL
 This is the first and oldest water treatment plant under the Trivandrum Water Supply Scheme. It was
commissioned on 7th February 1973 by Shri. C Achutha Menon, the former chief minister of Kerala.
Earlier the plant consisted of a capacity of 48 MLD only and later due to more demand additional 24
MLD was added to it.

37. INTAKE
 As mentioned earlier, the intake of water from the Karamana River for this 72 MLD plant is from the
pump house situated near the dam with 6 centrifugal pumps. Suitable screening devices are present. A
sampling pump is also present near the intake channel for the purpose for sampling raw water to the
chemical laboratory.

38. AERATION AND CHEMICAL ADMINISTRATION
 During the commissioning, the water doesn’t contain any particles found for the purpose of aeration
during chemical testing. Even though for the aeration purpose the water is allowed to pass through a
venturi portion called Parshall flume in the water channel which acts as a component of aeration, causes
turbulence under gravity and removes odor and other gases during the turbulence. This is done after
adding lime and alum.

39. COAGULATION
 Based on the findings from chemical lab i.e., turbidity and pH ,calculated quantity of alum as coagulant
and lime as coagulant aid is added to the water. The alum and lime is stored in the chemical building
and required quantity of alum and lime solutions is made in respective tanks .Then it is conveyed to the
inlet channel through PVC pipes .Then the coagulation is achieved by a rapid mixer with mixing time of 1
minute.

40. CLARIFLOCCULATION
 After the flash mixing, the water is allowed to enter the inner ring portion of the clariflocculator through
gravity. At the inner or central portion, flocculation is achieved through the slow mixer. After that in the
outer ring the sedimentation happens and the clear water enters to the edge of the clarifloculator. If the
turbidity is greater than the specified limit, the bridge is rotated for the collection of flocs. In this WTP,
there are 3 clariflocculators of capacity 24 MLD each.

41. FILTRATION
 The clear water from the clariflocculator then passes to the filtration bed. There are 10 RCC twin rapid
sand filters of 1.75MLD. Backwashing is done in an interval of 23hrs and for a period of 1 hr.
DISINFECTION
 The disinfection is done by chlorination after the water is being filtered

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