Name - Shivam Pandey Class - Xith A Roll No. - 38 Subject - Chemistry Project On
Name - Shivam Pandey Class - Xith A Roll No. - 38 Subject - Chemistry Project On
Name - Shivam Pandey Class - Xith A Roll No. - 38 Subject - Chemistry Project On
PANDEY
CLASS – XIth A
ROLL NO. – 38
SUBJECT –
CHEMISTRY
PROJECT ON:-
Study of methods of water
purification
This is certified that Master
Shivam of class XIth section ‘A’ is
a bonafied student of Kendriya
Vidyalaya Ambikapur.
This is certified to be the bonafide
work of the student in the
Chemistry Subject during the
academic year 2019 – 2020.
He worked hard to complete this
project and this project is a result
of his great efforts and attention.
Date: 30/10/2020
ACKNOWLEGEMENT
CONTENTS 1.Sources
of water
2 Treatment
2.1 Pre-treatment
2.1.1 pH adjustment
2.2 Sedimentation
2.2.1 Sludge storage and removal
2.3 Dissolved air flotation
2.4 Filtration
2.4.1 Rapid sand filters
2.4.2 Slow sand filters
2.5 Membrane filtration
2.6 Removal of ions and other
dissolved substances
2.7 Disinfection
2.7.1 Chlorine disinfection
2.7.2 Chlorine dioxide disinfection
2.7.3 Ozone disinfection
2.8.4 Ultraviolet disinfection
2.8.5 Solar water disinfection
3 Other water purification techniques
4. Demineralised water
INTRODUCTION
Water purification is the process of removing undesirable
chemicals, biological contaminants, suspended solids and
gases from contaminated water. The goal is to produce water
fit for a specific purpose. Most water is purified for human
consumption (drinking water), but water purification may also
be designed for a variety of other purposes, including meeting
the requirements of medical, pharmacological, chemical and
industrial applications. In general the methods used include
physical processes such as filtration, sedimentation,
and distillation, biological processes such as filters
or biologically active carbon, chemical processes such
as flocculation and chlorination and the use of
electromagnetic radiation such as ultraviolet light.
The purification process of water may reduce the
concentration of particulate matter
including suspended particles, parasites, bacteria, algae, viruse
s,fungi; and a range of dissolved and particulate material
derived from the surfaces that water may have made contact
with after falling as rain.
The standards for drinking water quality are typically set by
governments or by international standards. These standards
will typically set minimum and maximum concentrations of
contaminants for the use that is to be made of the water.
It is not possible to tell whether water is of an appropriate
quality by visual examination. Simple procedures such
as boiling or the use of a household activated filter are not
sufficient for treating all the possible contaminants that may
be present in water from an unknown source. Even natural
spring – considered safe for all practical purposes in the 19th
century – must now be tested before determining what kind of
treatment, if any, is needed. Chemical and microbiological
analysis, while expensive, are the only way to obtain the
information necessary for deciding on the appropriate method
of purification.
According to a 2007 World Health Organization (WHO)
report, 1.1 billion people lack access to an improved drinking
water supply, 88 percent of the 4 billion annual cases
of diarrheal disease are attributed to unsafe water and
inadequate sanitation and hygiene, and 1.8 million people die
from diarrheal diseases each year. The WHO estimates that 94
percent of these diarrheal cases are preventable through
modifications to the environment, including access to safe
water. Simple techniques for treating water at home, such as
chlorination, filters, and solar disinfection, and storing it in
safe containers could save a huge number of lives each
year. Reducing deaths from waterborne diseases is a
major public health goal in developing countries.
PRESENTATION
Sources of water
Treatment
The processes below are the ones commonly used in water
purification plants. Some or most may not be used depending on the
scale of the plant and quality of the raw (source) water.
Pre-treatment
pH adjustment
Pure water has a pH close to 7 (neither alkaline nor acidic). Sea
water can have pH values that range from 7.5 to 8.4 (moderately
alkaline). Fresh water can have widely ranging pH values depending
on the geology of the drainage basin or aquifer and the influence of
contaminant inputs (acid rain). If the water is acidic (lower than
7), lime, soda ash, or sodium hydroxide can be added to raise the pH
during water purification processes. Lime addition increases the
calcium ion concentration, thus raising the water hardness. For highly
acidic waters, forced draft degasifierscan be an effective way to raise
the pH, by stripping dissolved carbon dioxide from the water. Making
the water alkaline helps coagulation and flocculation processes work
effectively and also helps to minimize the risk of lead being dissolved
from lead pipes and from lead solder in pipe fittings. Sufficient
alkalinity also reduces the corrosiveness of water to iron pipes. Acid
(carbonic acid, hydrochloric acid or sulphuric acid) may be added to
alkaline waters in some circumstances to lower the pH. Alkaline
water (above pH 7.0) does not necessarily mean that lead or copper
from the plumbing system will not be dissolved into the water. The
ability of water to precipitate calcium carbonate to protect metal
surfaces and reduce the likelihood of toxic metals being dissolved in
water is a function of pH, mineral content, temperature, alkalinity and
calcium concentration.
Sedimentation
Waters exiting the flocculation basin may enter the sedimentation
basin, also called a clarifier or settling basin. It is a large tank with
low water velocities, allowing floc to settle to the bottom. The
sedimentation basin is best located close to the flocculation basin so
the transit between the two processes does not permit settlement or
floc break up. Sedimentation basins may be rectangular, where water
flows from end to end, or circular where flow is from the centre
outward. Sedimentation basin outflow is typically over a weir so only
a thin top layer of water—that furthest from the sludge—exits.
In 1904, Allen Hazen showed that the efficiency of a sedimentation
process was a function of the particle settling velocity, the flow
through the tank and the surface area of tank. Sedimentation tanks are
typically designed within a range of overflow rates of 0.5 to 1.0
gallons per minute per square foot (or 1.25 to 2.5 meters per hour). In
general, sedimentation basin efficiency is not a function of detention
time or depth of the basin. Although, basin depth must be sufficient so
that water currents do not disturb the sludge and settled particle
interactions are promoted. As particle concentrations in the settled
water increase near the sludge surface on the bottom of the tank,
settling velocities can increase due to collisions and agglomeration of
particles. Typical detention times for sedimentation vary from 1.5 to 4
hours and basin depths vary from 10 to 15 feet (3 to 4.5 meters).
Inclined flat plates or tubes can be added to traditional sedimentation
basins to improve particle removal performance. Inclined plates and
tubes drastically increase the surface area available for particles to be
removed in concert with Hazen’s original theory. The amount of
ground surface area occupied by a sedimentation basin with inclined
plates or tubes can be far smaller than a conventional sedimentation
basin.
The most common type of filter is a rapid sand filter. Water moves
vertically through sand which often has a layer of activated
carbon or anthracite coalabove the sand. The top layer removes
organic compounds, which contribute to taste and odour. The space
between sand particles is larger than the smallest suspended particles,
so simple filtration is not enough. Most particles pass through surface
layers but are trapped in pore spaces or adhere to sand particles.
Effective filtration extends into the depth of the filter. This property of
the filter is key to its operation: if the top layer of sand were to block
all the particles, the filter would quickly clog.
To clean the filter, water is passed quickly upward through the filter,
opposite the normal direction (called back flushing or backwashing)
to remove embedded particles. Prior to this step, compressed air may
be blown up through the bottom of the filter to break up the
compacted filter media to aid the backwashing process; this is known
as air scouring. This contaminated water can be disposed of, along
with the sludge from the sedimentation basin, or it can be recycled by
mixing with the raw water entering the plant although this is often
considered poor practice since it re-introduces an elevated
concentration of bacteria into the raw water
Some water treatment plants employ pressure filters. These works on
the same principle as rapid gravity filters, differing in that the filter
medium is enclosed in a steel vessel and the water is forced through it
under pressure.
Advantages:
● Filters out much smaller particles than paper and sand filters can.
● Filters out virtually all particles larger than their specified pore
sizes.
● They are quite thin and so liquids flow through them fairly rapidly.
● They are reasonably strong and so can withstand pressure
differences across them of typically 2–5 atmospheres.
● They can be cleaned (back flushed) and reused.
Membrane filtration
Membrane filters are widely used for filtering both drinking water
and sewage. For drinking water, membrane filters can remove
virtually all particles larger than 0.2 um—including giardia and
cryptosporidium. Membrane filters are an effective form of tertiary
treatment when it is desired to reuse the water for industry, for limited
domestic purposes, or before discharging the water into a river that is
used by towns further downstream. They are widely used in industry,
particularly for beverage preparation (including bottled water).
However no filtration can remove substances that are actually
dissolved in the water such as phosphorus, nitrates and heavy
metal ions.
Disinfection
Disinfection is accomplished both by filtering out harmful micro-
organisms and also by adding disinfectant chemicals. Water is
disinfected to kill any pathogens which pass through the filters and to
provide a residual dose of disinfectant to kill or inactivate potentially
harmful micro-organisms in the storage and distribution systems.
Possible pathogens include viruses, bacteria, including
Salmonella, Cholera, Campylobacter and Shigella, and protozoa,
including Giardia lamblia and other cryptosporidium. Following the
introduction of any chemical disinfecting agent, the water is usually
held in temporary storage – often called a contact tank or clear well to
allow the disinfecting action to complete.
Chlorine disinfection
The most common disinfection method involves some form
of chlorine or its compounds such as chloramines or chlorine dioxide.
Chlorine is a strong oxidant that rapidly kills many harmful micro-
organisms. Because chlorine is a toxic gas, there is a danger of a
release associated with its use. This problem is avoided by the use
of sodium hypochlorite, which is a relatively inexpensive solution that
releases free chlorine when dissolved in water. Chlorine solutions can
be generated on site by electrolyzing common salt solutions. A solid
form, calcium hypochlorite, releases chlorine on contact with water.
Handling the solid, however, requires greater routine human contact
through opening bags and pouring than the use of gas cylinders or
bleach which are more easily automated. The generation of liquid
sodium hypochlorite is both inexpensive and safer than the use of gas
or solid chlorine.
All forms of chlorine are widely used, despite their respective
drawbacks. One drawback is that chlorine from any source reacts with
natural organic compounds in the water to form potentially harmful
chemical by-products. These by-products, trihalomethanes (THMs)
and halo acetic acids (HAAs), are both carcinogenic in large
quantities and are regulated by the United States Environmental
Protection Agency (EPA) and the Drinking Water Inspectorate in the
UK. The formation of THMs and halo acetic acids may be minimized
by effective removal of as many organics from the water as possible
prior to chlorine addition. Although chlorine is effective in killing
bacteria, it has limited effectiveness against protozoa that form cysts
in water (Giardia lamblia and Cryptosporidium, both of which are
pathogenic).
Chlorine dioxide disinfection
Chlorine dioxide is a faster-acting disinfectant than elemental
chlorine. It is relatively rarely used, because in some circumstances it
may create excessive amounts of chlorite, which is a by-product
regulated to low allowable levels in the United States. Chlorine
dioxide is supplied as an aqueous solution and added to water to avoid
gas handling problems; chlorine dioxide gas accumulations may
spontaneously detonate.
Ozone disinfection
Ozone is an unstable molecule which readily gives up one atom of
oxygen providing a powerful oxidizing agent which is toxic to most
waterborne organisms. It is a very strong, broad spectrum disinfectant
that is widely used in Europe. It is an effective method to inactivate
harmful protozoa that form cysts. It also works well against almost all
other pathogens. Ozone is made by passing oxygen through
ultraviolet light or a "cold" electrical discharge. To use ozone as a
disinfectant, it must be created on-site and added to the water by
bubble contact. Some of the advantages of ozone include the
production of fewer dangerous by-products and the absence of taste
and odour problems (in comparison to chlorination) . Although fewer
by-products are formed by ozonation, it has been discovered that
ozone reacts with bromide ions in water to produce concentrations of
the suspected carcinogen bromated. Bromide can be found in fresh
water supplies in sufficient concentrations to produce (after
ozonation) more than 10 ppb of bromate — the maximum
contaminant level established by the USEPA. Another advantage of
ozone is that it leaves no residual disinfectant in the water. Ozone has
been used in drinking water plants since 1906 where the first
industrial ozonation plant was built in Nice, France. The U.S. Food
and Drug Administration has accepted ozone as being safe; and it is
applied as an anti-microbiological agent for the treatment, storage,
and processing of foods.
Ultraviolet disinfection
Ultraviolet light (UV) is very effective at inactivating cysts, in low
turbidity water. UV light's disinfection effectiveness decreases as
turbidity increases, a result of the absorption, scattering, and
shadowing caused by the suspended solids. The main disadvantage to
the use of UV radiation is that, like ozone treatment, it leaves no
residual disinfectant in the water; therefore, it is sometimes necessary
to add a residual disinfectant after the primary disinfection process.
This is often done through the addition of chloramines, discussed
above as a primary disinfectant. When used in this manner,
chloramines provide an effective residual disinfectant with very few
of the negative effects of chlorination.
Solar water disinfection
One low-cost method of disinfecting water that can often be
implemented with locally available materials is solar
disinfection (SODIS). Unlike methods that rely on firewood, it has
low impact on the environment.
One recent study has found that the wild Salmonella which would
reproduce quickly during subsequent dark storage of solar-disinfected
water could be controlled by the addition of just 10 parts per million
of hydrogen peroxide.
Other popular methods for purifying water, especially for local private supplies
are listed below. In some countries some of these methods are also used for
large scale municipal supplies. Particularly important are distillation (de-
salination of seawater) and reverse osmosis.
CONCLUSION
We can conclude from the project that there
are various methods of purification of water.
Today, we know that water is present
everywhere on earth in different forms but due
to human activities water is being polluted day
by day not only that about 97% of earths water
is in oceans which is not suitable for drinking
or any other purpose. So there is very small
volume of water is left, to utilise that humans
are using best ways to purify it. And in present
time humans are capable to purify water and
all the methods to purify it are mentioned in
the project.