Water Treatment Plants

Water Treatment Plants

Thought Of The Day

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Water Flow

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Water Consumption

Water provided for human consumption requirestreatment in order to make it• safe (potable)• pleasant to taste (palatable)

Modern technology offers remarkable capabilitiesto accomplish these goals• introduction of new and different pollutants• cost of treating to required levels is a challenge

for the water supply industry

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Water Demand

• Municipal water supplies are treated tobe both palatable and potable,regardless of their intended use

• If each person uses about 100 litres ofwater per day

• Commercial and industrial users mayincrease that demand by more than 5times

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Drinking Water - Quality

Our water supply comes from two sources

• surface waters i.e. rivers, lakes and reservoirs

• groundwater, which is stored below the earth's surface

Each source presents its own problems

• Surface water has elevated levels of soil particles and algae, making the water turbid

• may contain pathogens

• Groundwater has higher levels of dissolved organic matter (yellow color) and minerals such as iron

• Both sources may have high levels of calcium and magnesium (hardness)

• both can be contaminated by toxic chemicals

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Water Treatment Process

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Drinking Water Plant

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Untreated to Treated Water

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Conventional Surface Water Treatment

Screening

Coagulation

Flocculation

Sedimentation

Filtration

Disinfection

Storage

Distribution

Raw water

AlumPolymers Cl2

sludge

sludge

sludge

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Screening

• Removes large solidslogs

branches

rags

fish

• Simple processmay incorporate a mechanized trash removal system

• Protects pumps and pipes in Water Treatment Plants

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Coagulation

• Small particles are not removed efficiently by sedimentation because they settle too slowly

• they may also pass through filters

• easier to remove if they are clumped together

• Coagulated to form larger particles, but they don'tbecause they have a negative charge

• repel each other (like two north poles of a magnet)

• In coagulation• we add a chemical such

as alum which produces positive charges to neutralize the negative charges on the particles

• particles can stick together• forming larger particles • more easily removed• process involves addition of

chemical (e.g. alum) • rapid mixing to dissolve the

chemical• distribute it evenly

throughout water

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Coagulants

• Aluminum Sulfate Al2(SO4)3

• Ferrous Sulfate FeSO4

• Ferric Sulfate Fe2(SO4)3

• Ferric Chloride FeCl3• Lime Ca(OH)2

Aluminum salts arecheaper but iron salts aremore effective over widerpH range

Factors for choosing a coagulant?1. Easily available in all

dry and liquid forms2. Economical 3. Effective over wide

range of pH4. Produces less sludges5. Less harmful for

environment6. Fast

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Flocculation

• Now the particles have a neutralcharge

• can stick together

• The water flows into a tank withpaddles that provide slow mixing

• bring the small particlestogether to form largerparticles called flocs

• Mixing is done quite slowly andgently in the flocculation step

• If the mixing is too fast, theflocs will break apart into smallparticles that are difficult toremove by sedimentation orfiltration.

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Sedimentation

• water flows to a tank called asedimentation basin

• gravity causes the flocs tosettle to the bottom

• Large particles settle morerapidly than small particles

• It would take a very long timefor all particles to settle outand that would mean we wouldneed a very large sedimentationbasin.

• So the clarified water, withmost of the particles removed,moves on to the filtration stepwhere the finer particles areremoved

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Filtration

• The filtration apparatus is a concrete box which contains sand (which does the filtering), gravel (which keeps the sand from getting out) and underdrain (where the filtered water exits)

• After the filter is operated for a while, the sand becomes clogged with particles and must be backwashed

• Flow through the filter is reversed and the sand and particles are suspended

• The particles are lighter than the sand, so they rise up and are flushed from the system. When backwashing is complete, the sand settles down onto the gravel, flow is reversed and the process begins again

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Raw water

Coagulation

Aeration

Flocculation

Sedimentation Tank

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Disinfection

• With particles removed, it only remains to provide disinfection, so that no pathogens remain in the water

• Protozoan pathogens are large in size and have been removed with other particles

• Bacteria and viruses are now destroyed by addition of a disinfectant

Chlorination• Enough chlorine is added so that

some remains to go out in the water distribution system, protecting the public once the water leaves the plant

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Softening

• Areas where water comes into contact with limestone, there may be high levels of calcium and magnesium present

• these chemicals make the water "hard"

• Hardness is removed by a process called softening

• Two chemicals (lime, CaO and soda ash, Na2CO3 ) are added to water

• causing the calcium and magnesium to form precipitates

• solid substance is then removed with the other particles by sedimentation and filtration

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Synthetic Organic Chemicals

• Water supplies can be contaminated with synthetic organic chemicals (SOCs) from agricultural runoff or commercial and industrial sources

• such as the leaking underground storage tank

• These chemicals are not efficiently removed by the simple water treatment process

• These chemicals can be removed by passing the water through a layer of activated carbon in a column

• The carbon granules strongly attract organic chemicals removing them from the water by a process called adsorption

• When the carbon is full and can't hold any more chemical, it is removed from the column, heated to burn off contaminants and can then be re-used.

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Distribution

• Pumping of the clean water produced at the treatment plant to the community is called distribution

• This can be done directly or by first pumping the water to reservoirs or water storage tanks

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Onsite TreatmentColor, Taste and Odor

• The activated carbon technology used in municipal drinking water treatment can be applied in homes as well

• the carbon is contained in a "household-sized" column

• water passes through the carbon removing organic matter (which can cause a yellow color) and also compounds which cause unpleasant taste and odor

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Onsite TreatmentAt The Tap

• Home water treatment systems may also be installed at the tap

• Although the technologies vary somewhat among products, they typically include pre-filtration

• hardness and metals removal by ion exchange

• organic matter removal with activated carbon

• post-filtration

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US Bottled Water Sales

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Decrease in Tap Water Consumption

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Bottled Water vs Filtration System

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The Plastic Planet

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Implement A Project

Low Cost• Water Conservation• Water Treatment• Wastewater Treatment• Safe Drinking Water

for Flood Effected People

• Rainwater HarvestingOr • Any Smart Idea related

to Public Health Engineering

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Rawal Lake Water Treatment Plant

Water Supply

• Water supply in Potohar region

• Groundwater- major source

• Groundwater is supplemented with treated

surface water

• Disinfectants

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Sources of Drinking Water in Rawalpindi

Two main sources of water in Rawalpindi.Groundwater

• Groundwater with Tube wells

• located throughout the city

• 290 tube wells in WASA controlled area

• supplying approximately 28 MGD water to the residentsof Rawalpindi.

Surface water in the form of lakes• Surface water is supplied from Khanpur Dam (14.6 MGD)

through Sangjani Water Treatment Plant

• Rawal Lake through Rawal Lake Water Filtration Plant (23MGD).

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Ground- vs. Surface Water

Groundwater

• constant composition

• high mineral content

• low turbidity

• low color

• low or no D.O.

• high hardness

• high Fe, Mn

Surface water

• variable composition

• low mineral content

• high turbidity

• colored

• D.O. present

• low hardness

• taste and odor

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History

Initial Construction 1962-63

Capacity 14 MGDExecuting Agency WAPDAContractor WABAG, Germany

First Extension (7 MGD) 1975-79

Extended Capacity. 21 MGDExecuting Agency PHED, Govt. of PunjabContractor M/S Federal Const. Corp. Lahore.

Second Extension (7 MGD) 2000-2002

Extended Capacity. 28 MGDExecuting Agency PMU, WASA/RDAContractor VA TECH. WABAG GmbH,

Austria.

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Main Components

• Screening• Coagulation• Aeration• Flocculation• Sedimentation• Filtration• Disinfection or Chlorination• Lime Dosing

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ComponentsScreening• 3 Bar Screens. • large pieces• form of branches of trees• leaves• clothes• plastic bags• dead animal

Aeration• 2 Blowers. Air flow @ 6 m3/min.• remove taste and odor problems from incoming raw water• Dissolved Oxygen (DO) level of water is enhanced by this process

Coagulation• 2 geared drives• shaft mounted mixers for alum mixing• coagulant delivery pipes• alum is added and rapidly mixed with water• remove suspended particles in the form of turbidity

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Components

• Flocculation• Clarifier # 1 to 3

• 3 Mechanical Flocculation mounted on a central rotating fullbridge with sludge scraper rotating bridge

• Clarifier Area = 475 m2

• Up flow velocity = 2.55 m/hr.• Total flow = 336 L/s

• Clarifier # 4• 4 flat bottom clarifiers Hydraulic flocculators (Vertical baffles)

16 sludge concentrator Cones• Clarifier Area = 4 x 190 = 760 m2

• Up flow velocity = 2.2 m/hr.• Total flow = 475 L/ s

• Coagulant is mixed through vertical baffling arrangements

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Components

Sedimentation• large flocs are removed by gravity settling• clear water is collected from the surface• settled material (sludge) removed from sedimentation tank• rotating vipers and sludge valves

Filtration• removal of suspended non settleable solids from the drinking water• supernatant water after sedimentation• passed through a 1.4 meter column of silica sand• effective size of 0.95mm ( 10 %)• filtration rate of 5.4 m/hr. (average)-6.5 m/hr (Max)(110-130 glns/ft2. /hr.)

Filter Backwashing• Conventional backwashing system includes• Compressed air• Air and Water• Water• Approximate time 12 to 20 minutes

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Filter Backwash

• Sand is backwashed when• It becomes clogged• Turbidity of filtered water gets too high

• During backwash, water is pumped upwards through the sand bed

• Sand becomes “fluidized”, and particles are flushed from the sand

• Dirty backwash water is pumped into a settling pond and either• Recycled back into plant or• Disposed

• Backwashing can consume 1% to 5% of a plant’s production

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Raw water

Coagulation

Aeration

Flocculation

Sedimentation Tank

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Components

Disinfection or Chlorination• Liquid chlorine is used for this purpose• dosage rate varies from 1.5 to 2.0 mg chlorine per

liter of water• depending upon the level of contamination, pH, and

temperature• ensuring the residual chlorine upto 0.3-0.5 mg/l.

Lime Dosing• last unit process applied at Rawal Lake water

filtration plant• lime is used to adjust the pH of water

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Disadvantages of Chlorination

Chlorine is a dangerous chemical because1. it irritates the respiratory system2. it irritates the eyes3. can form Trihalomethanes, THMs, which are possible

carcinogens

Other disinfectant chemicalsOzone gas (O3)Ultraviolet light (UV)

Not as desirable becauseMore expensive than chlorineCan’t maintain a residual concentration

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Water Quality Monitoring Program

• Water quality analysis laboratory• regularly monitor and analyze the quality of

water supplied through plant• equipped with latest instruments and chemicals • to test all the basic physico-chemical and

biological parameters • recommended by the World Health Organization• Urban Water Supply & Sanitation Project Phase

I

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Serial No. Water Quality ParameterPHYSICAL PARAMETERS

1 Appearance

2 Color

3 Odor

4 Taste

5 Temperature

6 Turbidity

CHEMICAL PARAMETERS

7 pH

8 Alkalinity

9 Hardness as CaCO3

10 Electrical Conductivity

11 Sulphate

12 Calcium

13 Magnesium

14 Total Dissolved Solids

15 Chlorides

16 Residual Chlorine

17 Nitrate as NO3-

18 Nitrite as NO2-

BACTERIOLOGICAL PARAMETERS

19 Total Coliform Count

20 Fecal Coliform Count

TOXIC SUBSTANCES

21 Arsenic as As +3/+5

22 Cyanide as CN-

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Treated Water Quality

• Turbidity. 1-3 NTU

• Color. Colorless

• Odor Unobjectionable

• pH 7.5 to 9.5

• Residual Chlorine. 0.3 to 0.5 mg/L

(at WW 1 and Topi WW)

• Coliform Bacteria Nil/100 ml

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Rawal Lake Catchment Area

Diplomatic

Enclave

Malpur

Village

Lakhwal

Village

Q.A.

University

Bari Imam

Poultry Waste from

Murree

Bani Gala

Village

Noor Pur Shahan

Filtration Plant

WASA

Kurrang

River

Chatter Park

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Upstream

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Shahdra Kass

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Bari Imam

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Bari Imam

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Bari Imam

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Bari Imam

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Human Activities at Korang River

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Quaid-e-Azam University

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Pictorial View - Filtration Plant

RAWAL LAKE FILTRATION PLANTWater Treatment Plants 57

Intake Structure

WASA WASA

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Main Building

WASA

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Main Electrical Control Panel

WASA

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Circular and Rectangular Clarifiers

Rectangular

ClarifierCircular

Clarifier

Filtration Media

WASA

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Filtration System

WASA WASA

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Filtered Water Collection System

WASA

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Lime Dosing System

WASA

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Safe Drinking Water

How can you ensure that your drinking water is safe?

a) Boilingb) Storing it safelyc) Drinking water from safe sourcesd) All of above

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Thank You