WATER TREATMENT PLANT

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WATER

TREATMENT

PLANT INTRODUCTION

Clean and safe water is vital for everyday life. Water is

essential for health, hygiene and the productivity of our

community.

Water treatment is any process that makes water more

acceptable for a specific end-use. The end use may

be drinking, industrial water supply, irrigation, river flow

maintenance, water recreation or many other uses

including being safely returned to the environment.

Water treatment removes contaminants or reduces their

concentration so that the water becomes fit for its

desired end-use.

The water treatment process may vary slightly at

different locations, depending on the technology of the

plant and the water it needs to process, but the basic

principles are largely the same. This section describes

standard water treatment processes. Treatment

for drinking water production involves the removal of

contaminants from raw water to produce water that is

pure enough for human consumption without any short

term or long term risk of any adverse health effect.

Substances that are removed during the process of

drinking water treatment include suspended solids,

CONTENT:

INTRODUCTION

OBJECTIVE OF WAT-

ER TREATMENT

PROCESSES

COD WATER

TREATMENT DATA

DISINFECTION

WATER TREATMENT

IN KARACHI

RECOMMENDATION

APPENDICES

BIBLIOGRAPHY

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bacteria, algae, viruses, fungi, and minerals such as iron and manganese.

The processes involved in removing the contaminants include;

1. Physical processes such as carbon adsorption, distillation 2. Chemical processes such as precipitation, neutralization and oxidation 3. Biological processes such as filtration and radiation

Measures taken to ensure water quality not only relate to the treatment of the

water, but to its conveyance and distribution after treatment. It is therefore

common practice to keep residual disinfectants in the treated water to kill

bacteriological contamination during distribution.

World Health Organization (WHO) guidelines are a general set of standards

intended to apply where better local standards are not implemented.

PROCESSES

A combination selected from the following processes is used for municipal

drinking water treatment worldwide:

1. Pre-chlorination for algae control and arresting biological growth

2. Aeration along with pre-chlorination for removal of dissolved iron and

manganese

3. Coagulation for flocculation or slow-sand filtration

4. Coagulant aids, also known as polyelectrolytes – to improve coagulation

and for thicker floc formation

5. Sedimentation for solids separation that is removal of suspended solids

trapped in the floc

6. Filtration to remove particles from water

7. Disinfection for killing bacteria viruses and other pathogens.

8. UV Radiation

9. Reverse Osmosis

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Coagulation / Flocculation

During coagulation, liquid aluminum sulfate (alum) and/or polymer is added to

untreated (raw) water. When mixed with the water, this causes the tiny particles

of dirt in the water to stick together or coagulate. Next, groups of dirt particles

stick together to form larger, heavier particles called flocs which are easier to

remove by settling or filtration.

Sedimentation

As the water and the floc particles progress through the treatment process, they

move into sedimentation basins where the water moves slowly, causing the

heavy floc particles to settle to the bottom. Floc which collects on the bottom of

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the basin is called sludge, and is piped to drying lagoons. In Direct Filtration, the

sedimentation step is not included, and the floc is removed by filtration only.

Filtration

Water flows through a filter designed to remove particles in the water. The filters

are made of layers of sand and gravel, and in some cases, crushed anthracite.

Filtration collects the suspended impurities in water and enhances the

effectiveness of disinfection. The filters are routinely cleaned by backwashing.

Sludge Drying

Solids that are collected and settled out of the water by sedimentation and

filtration are removed to drying lagoons.

pH Correction

Lime is added to the filtered water to adjust the pH and stabilize the naturally soft

water in order to minimize corrosion in the distribution system, and within

customers’ plumbing.

Disinfection

Water is disinfected before it enters the distribution system to ensure that any

disease-causing bacteria, viruses, and parasites are destroyed.

OBJECTIVE OF WATER TREATMENT

All surface water and some groundwater require treatment prior to consumption to ensure that they do not represent a health risk to the user. Health risks to consumers from poor quality water can be due to microbiological, chemical, physical or radioactive contamination. However, microbiological contamination is generally the most important to human health as this leads to infectious diseases which affect all populations groups, many of which may cause epidemics and can be fatal. Chemical contamination, with the exception of a few substances such as cyanide and nitrate, tends to represent a more long-term health risk. An example of this is nitrate which can cause methaemoglobinaemenia in babies. Substances in water

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which affect the clarity, color or taste of water may make water objectionable to consumers. As many microorganisms are found associated with particles in water, physical contamination may also represent a health risk as it extends microbial survival. Most treatment systems are designed to remove microbiological contamination and those physical constituents which affect the acceptability or promote microorganism survival - largely related to the suspended solids in the water. A disinfectant is nearly always included in treatment plants of any size. This is done for two main reasons: firstly it is added to inactivate any remaining bacteria as the final unit of treatment and, more importantly, to provide a residual disinfectant which will kill any bacteria introduced during storage and/or distribution.

Reduction or inactivation of viruses.

Less than or equal to (≤) one nephelometric turbidity unit (NTU) of turbidity.

No detectable E. coli, fecal Coliform and total coliform.

To control unpleasant taste & appearance of particles.

To remove the unpleasant odor and color.

To extract the undesirable chemicals & dissolved minerals.

WATER TREATMENT IN KARACHI

KWSB (Karachi Water & Sewerage Board) was formed in 1983 before it was

known by the name of Greater Karachi Water Supply (1952). Main Water Source

Providers: There are two water sources that provides water to Karachi City.

1) Indus River/ Kinjhar Lake

2) Hub River/Hub Dam

Karachi water & sewerage board is one of the biggest water & waste water utility

in this region. Water is being supplied to Karachi from a considerably distant

located water source through bulk conveyance system comprising of a complex

network of canals, conduits, siphons, multi-stage pumping and filtration.

KARACHI WATER SUPPLY HISTORIC FACTS:

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The quota of 450 cusecs (242 MGD 1089ml/day for Ruby season) and 520 cusecs (280 MDG 1260ml/day for Kharif season) form Indus river was sanctioned on May 11, 1957.

In 1988, the same quota was increased to 1200 cusecs (2880 ml/day) by

Presidential decree, which has been exhausted in 2006 with implementation of K-

III Project.

WATER SUPPLY SCENARIO:

The present supply to Karachi from Indus and Hub source is approx.

650MGD (2925 ml/day).

115MG is being filtered at the KWSB Town Gulshan-e-Iqbal, having

maximum capacity of 119MG per day.

The per capita water demand @ 54 GPCD for population 20 Million is

estimated as 1080 MDG.

The current short fall is anticipated as 430 MGD.

First Phase of K-IV Project may take up to 5 years to complete i.e. by the

year 2015.

By the year 2015, projected population of Karachi will be 23 Million and @

54 gallons per capita per day, the demand of water shall be 1242 MGD.

By the year 2015 there will be a short fall of 600 MGD (2700 ml/day) water.

100 MGD (450 ml/day) additional water is required after every 5 years to

bridge the gap of demand and supply.

RAW WATER TRANSMISSION

Canals, conduits (3.3mx3.3m RCC)

Siphons/ Pipelines (2100-1800mm)

Bulk supply pumping stations (24-35 MGD)

FILTER WATER TRANSMISSION

Filter plants, Transmission mains (1600-900mm)

Secondary level pumping stations (5-15 MGD)

WATER DISTRIBUTION

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Area wise distribution mains (600-75mm) emerging from trunk mains, small

pumping stations.

BULK WATER SUPPLY SOURCE

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DISINFECTION

Water disinfection means the removal, deactivation or killing of pathogenic

microorganisms. Microorganisms are destroyed or deactivated, resulting in

termination of growth and reproduction. When microorganisms are not removed

from drinking water, drinking water usage will cause people to fall ill.

Water is disinfected before it enters the distribution system to ensure that any

disease-causing bacteria, viruses, and parasites are destroyed. Chlorine is used

because it is a very effective disinfectant, and residual concentrations can be

maintained to guard against possible biological contamination in the water

distribution system.

The disinfection of potable water and wastewater provides a degree of protection

from contact with pathogenic organisms including those causing cholera, polio,

typhoid, hepatitis and a number of other bacterial, viral and parasitic diseases.

Disinfection is a process where a significant percentage of pathogenic organisms

are killed or controlled. As an individual pathogenic organism can be difficult to

detect in a large volume of water or wastewater, disinfection efficacy is most

often measured using "indicator organisms" that coexist in high quantities where

pathogens are present. The most common indicator organism used in the

evaluation of drinking water is Total Coliform (TC), unless there is a reason to

focus on a specific pathogen. The most common indicator organism for

wastewater evaluation is fecal coliform but there has been discussion regarding

the use of Escherichia coli (E. coli) or Total Coliform. As domestic wastewater

contains approximately 1,000 times more indicator organisms than typical

surface water.

DISINFECTION MECHANISM

Disinfection commonly takes place because of cell wall

corrosion in the cells of microorganisms, or changes in

cell permeability, protoplasm or enzyme activity (because

of a structural change in enzymes). These disturbances in

cell activity cause microorganisms to no longer be able to

multiply. This will cause the microorganisms to die out. Oxidizing disinfectants

also demolish organic matter in the water, causing a lack of nutrients.

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TYPES OF DISINFECTION

Chemical disinfectants are defined by their mode of action and can be broadly

split into two groups, oxidizing and non-oxidizing.

Oxidizing disinfectants such as Sodium Hypochlorite, Peracetic Acid and

Hydrogen Peroxide attack all cellular material and stop the micro-organism from

functioning. Unfortunately they will also attack any food soiling residues thereby

reducing the disinfectant efficacy.

Non-oxidizing disinfectants such as Quaternary Ammonium Compounds

(QAC’s) Biguanides and Amphoteric are more subtle in their operation, with a

different number of modes of action depending on the biocide and organism.

Disinfection can be attained by means of physical or chemical disinfectants. The

agents also remove organic contaminants from water, which serve as nutrients or

shelters for microorganisms. Disinfectants should not only kill microorganisms.

Disinfectants must also have a residual effect, which means that they remain

active in the water after disinfection. A disinfectant should prevent pathogenic

microorganisms from growing in the plumbing after disinfection, causing the

water to be re-contaminated.

For chemical disinfection of water the following disinfectants can be used:

Chlorine (Cl2)

Chlorine dioxide (ClO2)

Sodium Hypochlorite

Chlorine Dioxide

Hydrogen Peroxide

Peracetic Acid

Quaternary Ammonium Compounds (QAC’s)

Iodophors

Amphoteric

Biguanides

Hypo chlorite (OCl-)

Ozone (O3)

Halogens: bromine (Br2), iodine (I)

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Bromine chloride (BrCl)

Metals: copper (Cu2+), silver (Ag+)

Kaliumpermanganate (KMnO4)

Phenols

Alcohols

Soaps and detergents

Kwartair ammonium salts

Hydrogen peroxide

Several acids and bases

For physical disinfection of water the following disinfectants can be used:

Ultraviolet light (UV)

Electronic radiation

Gamma rays

Sounds

Heat

COD WATER TREATMENT PLANT

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Water from source Tunnels to transport water Rapid mixing

Settling tank Scrappers remove sludge Filtration Plant

Operating desk (FP) Filter Bed Model Sand filter bed

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Chlorine dissolved in water Track to move cylinders Nozzles use to refill

Storage Distribution

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Water inlet

Firstly raw water enters from Hub River through conduits and pipes which is

collected in a main chamber to proceed the treatment of water. The depth of

chamber is 30 feet.

Screening and rapid mixing

Screening is done prior to mixing to remove floatable material which can cause

damage to the machinery. Then pH is adjusted and water is rapidly mixed with

aluminum sulfate (alum), a coagulant that helps the impurities stick together to

form bigger particles called flocs. Foam is formed due to the escape of dissolved

chlorine and disturbance in water.

Rapid Mixing

Sedimentation

tank

Rapid

Sand Filter Chlorination

Storage Pump Distribution

Flow Chart

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Flocculation

After rapid mixing, the water flows into flocculation basins, where the flow of

water is slowed and the floc has time to grow bigger.

Sedimentation

Next, the water flows into sedimentation basins, where the heavy floc particles

sink to the bottom and are removed. These are also called Clarifiers. There were

3 Clarifiers at KWSB. Scrappers are moved once a day used to remove the

settled down sediments.

Filtration

The water travels through large filters made of sand, gravel, and anthracite.

Filtration removes any remaining microscopic particles and microorganisms.

Upper part of filter bed is Sand Filled/Fine Grained particles, and Lower part

comprises of Rock particles. They are used to filter impurities. At the base there

are receivers in which filtered water is collected.

Chlorination/ Disinfection

Finally, the water is disinfected to protect it against bacteria. Charleston Water

System uses chlorine dioxide and a combination of chlorine and ammonia called

chloramines to disinfect the water. Fluoride is also added support good dental

health.

In COD water treatment plant gaseous Chlorine is used. The cylinders contain

1/3-part infused pressure, and 2/3-part Liquid Chlorine. 500-600kg is the empty

weight and 1100kg is the cylinder weight when Chlorine is filled. The cylinders

are refilled and operated manually to mix Chlorine with impure water. Since

Chlorine will evaporate while mixing in water, hence it is already mixed with water

to reduce the loss of Chlorine while mixing.

Storage and distribution

After the water is treated, it is stored in an underground reservoir at the plant.

The clean water is then pumped into pipes that deliver it to more than 110,000

homes and businesses in Karachi City.

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RECOMMENDATION

Professionals from various educational institutions and government agencies have expressed dissatisfaction over the existing arrangement of potable water chlorination in mega cities of the country.

They have recommended civic agencies to replace chlorine with chlorine dioxide which, they said, was much safer and did not produce the by-products which threatened health.

The experts suggested the government to promote the use of solar radiation treatment system for water disinfection in rural areas, including desert of Tharparkar, Cholistan and other arid regions where the potable water was very little and that too contaminated most of the time.

Another recommendation urged the civic agencies like KWSB and Wasa and other water management bodies at district level to look into the possibility of total replacement of chlorine with much better disinfectant like Ozone, which, according to the scientists, had internationally been approved to be free from producing hazardous disinfection by-products (DBP) and also readily killed viruses. Also, develop appropriate technologies for water disinfection at the individual-house level.

In view of the frequency and importance of water borne diseases, relevant government organizations were urged to establish within their information systems epidemiological surveillance programs to help detect water borne disease outbreaks and epidemics.

Limitations

Cryptosporidium and other protozoan waterborne pathogens are highly resistant to chlorination.

Chlorination is less effective as a disinfectant at high pH value due to predominance of the hypochlorite ion over hypochlorous acid

When added to the water, free chlorine reacts with natural organic matter (NOM) and bromide in the water to form disinfection by-products. (primarily THMs and some halo acetic acids (HAAs)

Chlorine in either gaseous or hypochlorite solution form are hazardous and extremely corrosive , special storage and health and safety considerations regarding handling of these chemicals have to considered in the design of

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treatment plant and disinfection installation and in the framing of emergency response plans. Chlorine gas requires special leak containment measures and associated sensors and air scrubber facilities in the case of hypochlorite solutions, their separate containment is necessary to prevent cross containment with acid and the consequents release of chlorine gas.

Depending on water quality to be treated and the required dosage rates to be applied drinking water can have taste and odor problems, the precipitation of which can vary among consumers

Sodium hypochlorite degrades over time and with exposure to light resulting in the formation of chlorate as a by-product.

Sodium and Calcium hypochlorite are more expensive than chlorine gas,

Calcium hypochlorite as a solid must be stored in a cool dry place because of its reaction with moisture and heat. It also forms a precipitate following mixture with water due to additives mixed with the chemical.

WATER TREATMENT IN DIFFERENT PARTS OF THE WORLD

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BIBLIOGRAPHY

1. http://www.dawn.com/news/53653/karachi-experts-suggest-use-of-chlorine-dioxide-as-

disinfectant

2. http://www.kwsb.gos.pk/View.aspx?Page=25

3. https://www.norweco.com/html/lab/Disinfection.htm

4. http://www.hunterwater.com.au/Water-and-Sewer/Water-Supply/Water-Treatment-

Processes.aspx

5. https://en.wikipedia.org/wiki/Water_treatment

6. https://www.norweco.com/html/lab/Disinfection.htm

7. http://www.lenntech.com/processes/disinfection/what-is-water-disinfection.htm

8. https://www.ncbi.nlm.nih.gov/books/NBK218005/

9. http://www.oppinstitutions.org/Karachi%20Maps/Images/33-

Karachi%20maps_Karachi%20Water.jpg

10. http://c.tribune.com.pk/2011/05/map-SOURCE-KARACHI-WATER-AND-SEWERAGE-BOARD-

2006-DESIGN-NASIR-SHAHZAD-640x480.jpg

11. http://reliefweb.int/sites/reliefweb.int/files/resources/Karachi%20water%20demand%20supply%

20situation%20map_0.pdf

12. http://reliefweb.int/sites/reliefweb.int/files/resources/Karachi%20water%20demand%20supply%

20situation%20map_0.pdf

13. http://www.dawn.com/news/1096683