This document contains information about Uzma Afrin Akhter, a 10th grade student studying science, and summaries of chapters on chemistry, physics, biology, and water recycling. The chemistry section discusses how hard water forms mineral deposits and how ion exchange and the lime-soda process are used to soften hard water. The physics section covers various water energy resources like hydropower, tidal power, and technologies using saline water. The biology section discusses treating wastewater through recycling to remove solids and reuse it for irrigation. The final section provides examples of communities that safely reuse treated wastewater.

1. NAME : UZMA AFRIN AKHTER
CLASS : X
SECTION :B
SUBJECT : SCIENCE
BOARD REGISTRATION NO. :B114084140109
ROLL NO. : 52

2. CHEMISTRY
HARDNESS
OF WATER

3. •
Perhaps you have on occassion noticed
mineral deposits on your cooking dishes,
or rings of insoluble soap scum in your
bathtub. These are not signs of poor
housekeeping, but are rather signs of
hard water from the municipal water
supply. Hard water is water that
contains cations with a charge of +2,
especially Ca2+ and Mg2+. These ions do
not pose any health threat, but they
can engage in reactions that leave
insoluble mineral deposits. These
deposits can make hard water
unsuitable for many uses, and so a
variety of means have been developed
to "soften" hard water; i.e.,remove the
calcium and magnesium ions.

4. •
Mineral deposits are formed by ionic reactions resulting in the
formation of an insoluble precipitate. For example, when hard
water is heated, Ca2+ ions react with bicarbonate (HCO3-)
ions to form insoluble calcium carbonate (CaCO3), as shown in
Equation 1
•
.This precipitate, known as scale, coats the vessels in which
the water is heated, producing the mineral deposits on your
cooking dishes. In small quantities, these deposits are not
harmful, but they may be frustrating to try to clean. As these
deposits build up, however, they reduce the efficiency of heat
transfer, so food may not cook as evenly or quickly in pans
with large scale deposits. More serious is the situation in
which industrial-sized water boilers become coated with
scale: the cost in heat-transfer efficiency can have a
dramatic effect on your power bill! Furthermore, scale can
accumulate on the inside of appliances, such as dishwashers,
and pipes. As scale builds up, water flow is impeded, and hence
appliance parts and pipes must be replaced more often than if
Ca2+ and Mg2+ ions were not present in the water.

5. •
For large-scale municipal operations, a process known as the "lime-soda process"
is used to remove Ca2+ and Mg2+ from the water supply. Ion-exchange
reactions, similar to those you performed in this experiment, which result in the
formation of an insoluble precipitate, are the basis of this process. The water is
treated with a combination of slaked lime, Ca(OH)2, and soda ash, Na2CO3.
Calcium precipitates as CaCO3, and magnesium precipitates as Mg(OH)2. These
solids can be collected, thus removing the scale-forming cations from the water
supply.

6. •
To see this process in more detail, let us consider the reaction for the precipitation of
Mg(OH)2. Consultation of the solubility guidelines in the experiment reveals that the Ca(OH)2
of slaked lime is moderately soluble in water. Hence, it can dissociate in water to give one Ca2+
ion and two OH- ions for each unit of Ca(OH)2 that dissolves. The OH- ions react with Mg2+
ions in the water to form the insoluble precipitate. The Ca2+ ions are unaffected by this
reaction, and so we do not include them in the net ionic reaction (Equation 2). They are
removed by the separate reaction with CO32- ions from the soda ash.
•
Household water softeners typically use a different process, known as ion exchange. Ionexchange devices consist of a bed of plastic (polymer) beads covalently bound to anion groups,
such as -COO-. The negative charge of these anions is balanced by Na+ cations attached to
them. When water containing Ca2+ and Mg2+ is passed through the ion exchanger, the Ca2+
and Mg2+ ions are more attracted to the anion groups than the Na+ ions. Hence, they replace
the Na+ ions on the beads, and so the Na+ ions (which do not form scale) go into the water in
their place.
•
When hard tapwater passes through the ion exchanger (left), the calcium ions from the
tapwater replace the sodium ions in the ion exchanger. The softened water, containing sodium
ions in place of calcium ions, can be collected for household use.

7. PHYSICS
WATER AS AN
ENERGY
RESOURCE

8. • Water energy
resources include
hydroelectric power
from lakes and rivers,
ocean energy in its
various forms, and
energy technologies
that take advantage
of saline water

9. •
Hydropower makes use of the kinetic energy
water gains when it drops in elevation.
Typically, water dammed in a lake or reservoir
is released through turbines and generators to
produce electricity, Hydropower has been a
staple of electricity since the beginnings of the
electric age. However, very little of this
potential is currently slated for development.
Significant legal and regulatory impediments,
such as land acquisition and environmental
protection, will be a part of any major hydro
project. Additionally, reservoirs are typically
built and managed as municipal water supply
and flood control systems and secondarily for
power production. This fact lowers the
potential impact of hydro development on the
energy picture.

10. •
Three distinct types of ocean resource are
commonly mentioned as possible energy
sources: tides, waves, and ocean
temperature differentials (ocean thermal
energy conversion, or OTEC). For example,
tidal energy schemes capture water at high
tide and release it at low tide. Wave energy
generation devices fall into two general
classifications, fixed and floating. In both
cases, the oscillating motion of an incoming
and outgoing wave is used to drive turbines
that generate electricuty. Tide energy
systems traps high tides in a reservoir.
When the tide drops, the water behind the
reservoir flows through a power turbine,
generating electricity. Ocean thermal
energy conversion uses the difference in
temperature between warm surface water
and cold deep ocean water to make
electricity.

11. •
Saline and brackish water is common normally it poses a problem for fresh water
supplies. Several technologies, however, can
take advantage of saline water for energy
production. These include solar ponds and
algae production. Solar ponds use the salt
water in such a manner that heat from
sunlight is effectively locked in the pool and
can be used for a number of process heat
applications or electricity production. The
ability of the pond to store solar thermal
energy is unique and overcomes the resource
variability that is a drawback of traditional
solar development. Salt water algaes grow
prolifically under cultivated conditions and
can be pressed to extract biodiesel
feedstocks or dried and burned for power
production. Although neither technology has
been demonstrated beyond pilot levels,
Texas is fortunate in that regions with saline
water resources also tend to be very sunny.
If coupled with ongoing fresh water chloride
control efforts, exploitation of the saline
water resource for energy production may be
possible for modest additional investment.

12. BIOLOGY
WATER
RECYCLING

13. •
•
Reclaimed water or recycled water, is former
wastewater (sewage) that is treated to
remove solids and certain impurities, and used
in sustainable landscaping irrigation or to
recharge groundwater aquifers. The purpose
of these processes is sustainability and water
conservation, rather than discharging the
treated water to surface waters such as
rivers and oceans. In some cases, recycled
water can be used for streamflow
augmentation to benefit ecosystems and
improve aesthetics One example of this is
along Calera Creek in the City of Pacifica, CA.
The definition of reclaimed water, as defined
by Levine and Asaneo, is "The end product of
wastewater reclamation that meets water
quality requirements for biodegradable
materials, suspended matter and pathogens."
In more recent conventional use, the term
refers to water that is not treated as highly
in order to offer a way to conserve drinking
water. This water is given to uses such as
agriculture and sundry industry uses.

14. •
•
•
Cycled repeatedly through the planetary hydrosphere, all
water on Earth is recycled water, but the terms "recycled
water" or "reclaimed water" typically mean wastewater sent
from a home or business through a pipeline system to a
treatment facility, where it is treated to a level consistent
with its intended use. The water is then routed directly to
a recycled water system for uses such as irrigation or
industrial cooling.
The recycling and recharging is often done by using the
treated wastewater for designated municipal sustainable
gardening irrigation applications. In most locations, it is
intended to only be used for nonpotable uses, such as
irrigation, dust control, and fire suppression.
There are examples of communities that have safely used
recycled water for many years. Los Angeles County's
sanitation districts have provided treated wastewater for
landscape irrigation in parks and golf courses since 1929.
The first reclaimed water facility in California was built at
San Francisco's Golden Gate Park in 1932. The Irvine Ranch
Water District (IRWD) was the first water district in
California to receive an unrestricted use permit from the
state for its recycled water; such a permit means that
water can be used for any purpose except drinking. IRWD
maintains one of the largest recycled water systems in the
nation with more than 400 miles serving more than 4,500
metered connections. The Irvine Ranch Water District and
Orange County Water District in Southern California are
established leaders in recycled water. Further, the Orange
County Water District, located in Orange County, and in
other locations throughout the world such as Singapore,
water is given more advanced treatments and is used
indirectly for drinking.

15. •
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•
•
1)Recycle water in your shower. Most people like to
run the water until it warms up before getting
into the shower. Get a bucket to put in your shower
and catch the water so that it's not wasted. You can
use this water for cooking.
2)Collect rainwater in order to recycle water. You
can collect it in buckets. Or, you can catch rainwater
from the downspout on your roof gutters. Attach a
water butt to the end of the gutter or use some
other kind of container that will catch the rainwater.
You can use this water to water your vegetable or
flower gardens. It's good to have in reserve also for
watering your shrubs.
3)Think before you toss the leftover water out of
water glasses. When you and your family drink water,
there's often some left in glasses sitting around the
house. Recycle that water by using it to water your
indoor plants.
4)Save the water in your sink after dishwashing. You
can use this water to pour into your toilet bowl tank
for flushing. Gather the water in a pitcher or pan to
transfer it to the bathroom. Of course, you may not
want to use the water if it has a lot of grease in it
from frying pans. You don't want greasy water
sitting in your toilet tanks.

16. Recycled water can be used for almost any use, as long as it
is treated to a level to make it fit for that intended purpose
(i.e. fit-for-purpose) from a health and environmental
perspective . However, the cost of treatment may make
reclamation uneconomical for some uses. Australia now has
more than 600 different recycled water schemes operating.
The bulk of these schemes involve:
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Urban and municipal environments
Households, golf courses and recreational parks.
Industry
Washing and cooling in power stations and mills.
Agriculture
Horticulture, forestry, pasture, flowers, viticulture and
sugar cane.
Other possible uses include:
•
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Fire fighting
Groundwater recharge
Municipal landscapes
‘Dual pipe’ urban uses
Environmental flows and wetland