Muhammad Fahad Ansari 12IEEM14

1. Water Treatment
Muhammad Fahad Ansari
12IEEM14
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2. Why do we treat water?
• The main objectives of the water treatment
processes are the reduction in
contamination or pollution levels present in
water.
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3. • 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 end-use.
• One such use is returning water that has been used
back into the natural environment without adverse
ecological impact.
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4. • It also may be necessary to remove
nutrients such as N and P, toxic
components, non-biologically degradable
compounds and dissolved solids.
• Removal of these materials are necessary
for the simple reason that discharge to the
environment will result in “damage”.
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5. • 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.
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6. • The damage is a function of the type of
pollutant discharged –
• Heavy metals = toxicity,
• Organic matter = oxygen depletion,
• N or P- eutrophication, etc.
• In the case of water treatment the objective is
to remove contaminants from the water which
can result in health or aesthetic problems.
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7. • Many pollutants fall into several
categories.
• For example, some biodegradable
organic matter is in the form of
suspended solids.
• So removal of SS sometimes results
in the removal of organic matter.
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8. • Each solids “type” may require a different
type of treatment process.
• Generally it is tried to remove large very
settleable or screenable particles first and
• Then proceed to the smallest and finally to
the soluble species.
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9. • Level needed to remove
contaminants.
• The degree to which drinking
water must be treated depends on
the raw water quality and the
desired quality of the finished
water.
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10. For example water treatment may
require "secondary treatment" as
shown here:
• BOD5 = 30 mg/L
• Suspended Solids = 30 mg/L
• pH (if industrial input) = 6 – 9
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11. • The" secondary" standards are just the
“basic” requirements.
• More stringent standards are placed on
effluents which are discharged to
potentially eutrophic lakes, etc. or
whenever there is a known toxic
contaminant in the wastewater (e.g.
industrial discharges).
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12. • For drinking water treatment the requirements are, of
course, much more stringent with many more
categories and lower contaminant limits.
Some examples are:
• Turbidity (a measure of suspended solids): less than 0.5
NTU in at least 95% of samples taken each month.
• Lead: 0.005 mg/L
• Copper: 1.3 mg/L
• Total Coliform: no coliform detection in more than 5%
of samples collected
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13. • The contaminants removal from water
Contaminant removal is accomplished by
a series of unit processes or unit
operations.
(The system of integrated unit processes or
unit processes used to treat a water or
wastewater is called a treatment train.
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14. • Treatment processes are usually divided into
two trains: liquid train, and the solids (sludge)
train.
• The reason for this is that we usually take a
rather dilute waste and through a series of
phase separation processes create a more
concentrated waste (sludge).
• The sludge then has to be treated accordingly.
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15. An example of a water treatment plant:
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16. Treatment
The processes below are commonly used in water purification
plants.
• Pumping and containment - The majority of water must be
pumped from its source or directed into pipes or holding tanks.
• To avoid adding contaminants to the water, this physical
infrastructure must be made from appropriate materials and
constructed so that accidental contamination does not occur.
• Screening - The first step in purifying surface water is to remove
large debris such as sticks, leaves, trash and other large particles
which may interfere with subsequent purification steps.
• Most deep groundwater does not need screening before other
purification steps.
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17. • Storage - Water from rivers may also be stored in bank
side reservoirs for periods between a few days and
many months to allow natural biological purification to
take place.
• This is especially important if treatment is by slow
sand filters.
• Storage reservoirs also provide a buffer against short
periods of drought or to allow water supply to be
maintained during transitory pollution incidents in the
source river.
• Pre-conditioning - Many waters rich in hardness salts
are treated with soda-ash to precipitate out.
• Pre-chlorination - In many plants the incoming water is
chlorinated to minimize the growth of fouling
organisms on the pipe-work and tanks.
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18. pH adjustment
• Distilled water has a pH of 7 (neither alkaline nor
acidic) and sea water has an average pH of 8.3
(slightly alkaline).
• If the water is acidic (lower than 7), lime, soda ash or
sodium hydroxide is added to raise the pH.
• For somewhat acidic, alkaline waters are the
cheapest way to lower the pH.
• Lime is commonly used for pH adjustment for
municipal water, or at the start of a treatment plant
for process water.
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19. • Making the water slightly alkaline ensures
that coagulation and flocculation processes
work effectively.
• Also help to minimize the risk of lead being
dissolved from lead pipes.
• Acid (HCl or H2SO4) may be added to alkaline
waters in some circumstances to lower the pH.
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20. Flocculation
• Flocculation is a process which clarifies the water.
• Clarifying means removing any turbidity or colour so that
the water is clear and colourless.
• Clarification is done by causing a precipitate to form in the
water which can be removed using simple physical
methods.
• Initially the precipitate forms a very small particles but as
the water is gently stirred, these particles stick together to
form bigger particles - this process is called flocculation.
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21. • Many of the small particles that were originally
present in the raw water absorb onto the surface of
these small precipitate particles and so get
incorporated into the larger particles that
coagulation produces.
• In this way the coagulated precipitate takes most
of the suspended matter out of the water and is
then filtered off, generally by passing the mixture
through a coarse sand filter or sometimes through
a mixture of sand and granulated anthracite (high
carbon and low volatile coal).
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22. Coagulants / flocculating agents that may be used include:
• Iron Hydroxide: This is formed by adding a
solution of an iron (III) compound to pre-
treated water with a pH of 7 or greater.
• Iron (III) hydroxide is extremely insoluble
and forms even at a pH as low as 7.
• Aluminum Hydroxide is also widely used
as the flocculating precipitate although
there have been concerns about possible
health impacts and mis-handling led to a
severe poisoning incident
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23. Drinking water in U.S.
• The United States has one of the safest water
supplies in the world.
• In recent years, microbial contamination of the
water supply has led to highly publicized
outbreaks of disease, causing illness and even
death.
• How safe is our water?
• Where do these infectious microbes come from?
• How is water treated now and what’s being done
to make it even safer?
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24. Surface Water Treatment Plant
• Water treatment transforms raw surface
and groundwater into safe drinking water.
• Water treatment involves two major
processes:
• Physical removal of solids and
• Chemical disinfection.
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25. Water Disinfection
• Purpose of disinfection:
• To make Drinking water free of any disease causing
bacteria and microbes.
• Methods of disinfection:
• There are 3 mainly used disinfection methods at
large scale.
• CHLORINATION
• OZONATION
• ULTRAVIOLET RADIATION
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26. CHLORINATION
 Chlorine is the most common cost-effective means
of disinfecting water in the U.S.
 The addition of a small amount of chlorine is highly
effective against most bacteria, viruses, and
protozoa.
 But cysts (durable seed-like stages) formed by
parasitic protozoa such as Cryptosporidium and
Giardia can survive chlorine.
 Chlorine is applied to water in one of three forms:
elemental chlorine (chlorine gas), hypochlorite
solution (bleach), or dry calcium hypochlorite. All
three forms produce free chlorine in water
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28. OZONATION
OZONE is Strongest oxidant/disinfectant available.
More effective against microbes than chlorination.
But, costly and difficult to monitor and control under
different condition.
• Ozonation process:
• Ozone (o3) is generated on-site
at water treatment facilities by
passing dry oxygen or air
through a system of high voltage
electrodes.
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30. ULTRAVIOLET RADIATION
 When UV radiation penetrates the
cell wall of an organism, it
damages genetic material, and
prevents the cell from reproducing.
 Now a days emerging technology
made UV radiation to find a place
in both household and large scale
drinking water disinfection.
• How is UV light generated?
• Ultraviolet light is most typically generated
from a low pressure or a medium pressure lamp
generating UV light.
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31. ULTRAVIOLET RADIATION
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32. COMPLETE CYCLE
OF WATER TREATMENT: COAGULATION
STORAGE
SEDIMENTATION
DISINFECTION
FILTRATION

33. Design of a Chlorination Process
• Based on exposing a microorganism
for an amount of time with a minimum
amount of disinfectant
• Rough calculation of the amount of
time spent in a reactor is based on the
reactor volume and the flow rate:
• Time = volume/flow rate
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